Synthesis and detection of a seaborgium carbonyl complex

A carbonyl compound that tips the scales Life is short for the heaviest elements. They emerge from high-energy nuclear collisions with scant time for detection before they break up into lighter atoms. Even et al. report that even a few seconds is long enough for carbon to bond to the 106th element, seaborgium (see the Perspective by Loveland). The authors used a custom apparatus to direct the freshly made atoms out of the hot collision environment and through a stream of carbon monoxide and helium. They compared the detected products with theoretical modeling results and conclude that hexacarbonyl Sg(CO) 6 was the most likely structural formula. Science , this issue p. 1491 ; see also p. 14…

Cubic boron nitride: A new prospective material for ultracold neutron application

Abstract At the ultracold neutron (UCN) source of the TRIGA research reactor in Mainz, we have measured for the first time the material optical wall-potential of cubic boron nitride. The measurements were performed with a time-of-flight (TOF) spectrometer. The samples investigated had a wall-potential of ( 305 ± 15 ) neV . This value is in good agreement with the result extracted from neutron reflectometry data and theoretical expectations. Because of its high critical velocity for UCN and its good dielectric characteristics, cubic boron nitride coatings (isotopically enriched) will be useful for a number of applications in UCN experiments.

Spectroscopy along flerovium decay chains. II : Fine structure in odd-A289Fl

Fifteen correlated α-decay chains starting from the odd-A superheavy nucleus 289Fl were observed following the fusion-evaporation reaction 48Ca+244Pu. The results call for at least two parallel α-decay sequences starting from at least two different states of 289Fl. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α-electron and α-photon coincidences, as well as the α-decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between 285Cn and 281Ds. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing groun…

Fast determination of impurities in metallurgical grade silicon for photovoltaics by instrumental neutron activation analysis

Standard wafer solar cells are made of near-semiconductor quality silicon. This high quality material makes up a significant part of the total costs of a solar module. Therefore, new concepts with less expensive so called solar grade silicon directly based on physiochemically upgraded metallurgical grade silicon are investigated. Metallurgical grade silicon contains large amounts of impurities, mainly transition metals like Fe, Cr, Mn, and Co, which degrade the minority carrier lifetime and thus the solar cell efficiency. A major reduction of the transition metal content occurs during the unidirectional crystallization due to the low segregation coefficient between the solid and liquid phas…

Editorial: 150 years of the Periodic Table of Chemical Elements

Spectroscopic Tools Applied to Flerovium Decay Chains

Abstract An upgraded TASISpec setup, with the addition of a veto DSSD and the new Compex detector-germanium array, has been employed with the gas-filled recoil separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, to study flerovium (element 114) decay chains. The detector upgrades along with development of new analytical techniques have improved the sensitivity of the TASISpec setup for measuring α-photon coincidences. These improvements have been assessed with test reactions. The reaction 48Ca+206,207Pb was used for verification of experimental parameters such as transmission to implantation DSSD and target-segment to α-decay correlations. The reaction 48Ca+ nat …

Delayed-Neutron Spectra Following Decay ofAs85andSb135

Nuclear Forensics: A methodology applicable to Nuclear Security and to Non-Proliferation

Nuclear Security aims at the prevention and detection of and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material". Nuclear Forensics is a key element of nuclear security. Nuclear Forensics is defined as a methodology that aims at re-establishing the history of nuclear material of unknown origin. It is based on indicators that arise from known relationships between material characteristics and process history. Thus, nuclear forensics analysis includes the characterization of the material and correlation with production history. To this end, we can make use of parameters such as the isotopic composition of the nuclear material…

Three-body correlations in electromagnetic dissociation of Borromean nuclei: The 6He case

20 pages, 2 tables, 9 figures, 1 appendix.-- PACS nrs.: 25.60.-t; 27.20.+n; 25.70.De; 25.75.Gz.-- Printed version published Sep 5, 2005.

The new nuclide225U

In the bombardment of a 270μg/cm 2 180Hf target with48 Ca projectiles at a primary beam energy of E/A=4.24 MeV/u the new nuclide225U was produced. The experiment was performed at the velocity filter SHIP. 225U was found to decay by α emission with Eα=(7880 ±20) keV (≈90%), (7830±20) keV (≈10%) and has a half-life ofT 1/2=(80 −20 +40 ms).

TASISpec—A highly efficient multi-coincidence spectrometer for nuclear structure investigations of the heaviest nuclei

TASISpec (TASCA in Small Image mode Spectroscopy) combines composite Ge- and Si-detectors for a new detector setup aimed towards multi-coincidence gamma -ray, X-ray, conversion electron, fission fragment, and a-particle spectroscopy of the heaviest nuclei. It exploits the TASCA separator's unique small image focal mode, i.e. the fact that evaporation residues produced in fusion-evaporation reactions can be focused into an area of less than 3 cm in diameter. This provides the possibility to pack detectors in very close geometry, resulting in an unprecedented detection efficiency of radioactive decays in prompt and delayed coincidence with implanted nuclei. Crown Copyright (C) 2010 Publis…

An EC-branch in the decay of 27-s 263Db: Evidence for the isotope 263Rf

Summary 27-s 263Db was produced in the 249Bk ( 18O, 4n) reaction at 93 MeV. The activity was transported by a He/KCl-jet to the laboratory where it was collected for 15 min and then subjected to a chemical separation specific for group-4 elements. The activity was dissolved in 0.5 M unbuffered α-HiB and eluted from a cation-exchange column. The effluent was made 9 M in HCl and group-4 tetrachlorides were extracted into TBP/Cyclohexane which was evaporated to dryness on a Ta disc. The Ta discs were assayed for α and SF activity. A SF activity with a half life on the order of 20 min was observed and assigned to the nuclide 263Rf. It is formed by electron-capture decay of 263Db with a decay br…

Exclusive measurements of nuclear breakup reactions of 17Ne

F. Wamers et al.; 4 pags.; 2 figs. Open Access funded by Creative Commons Atribution Licence 2.0

The recoil transfer chamber—An interface to connect the physical preseparator TASCA with chemistry and counting setups

Performing experiments with transactinide elements demands highly sensitive detection methods due to the extremely low production rates (one-atom-at-a-time conditions). Preseparation with a physical recoil separator is a powerful method to significantly reduce the background in experiments with sufficiently long-lived isotopes (t1/2≥0.5 s). In the last years, the new gas-filled TransActinide Separator and Chemistry Apparatus (TASCA) was installed and successfully commissioned at GSI. Here, we report on the design and performance of a Recoil Transfer Chamber (RTC) for TASCA—an interface to connect various chemistry and counting setups with the separator. Nuclear reaction products recoiling o…

Resonance ionization mass spectrometry for ultratrace analysis of plutonium with a new solid state laser system

Abstract Resonance ionization mass spectrometry (RIMS) is well-suited for isotope selective ultratrace analysis of long-lived radioactive isotopes due to its high element and isotope selectivity and good sensitivity. For the analysis of plutonium with a pulsed RIMS apparatus, a powerful, reliable and easy to handle Nd:YAG pumped titanium–sapphire laser system has been developed and combined with a time-of-flight mass spectrometer. Spectroscopic measurements led to an efficient three step excitation and ionization scheme for plutonium with λ1 = 420.76 nm, λ2 = 847.28 nm, and λ3 = 767.53 nm. The isotope shifts in this scheme for the plutonium isotopes 238 Pu through 244 Pu have been determine…

Comparison of electromagnetic and nuclear dissociation of Ne-17

8 pags., 10 figs., 3 tabs.

Alpha-Photon Coincidence Spectroscopy Along Element 115 Decay Chains

Produced in the reaction 48Ca+243Am, thirty correlated α-decay chains were observed in an experiment conducted at the GSI Helmholzzentrum fur Schwerionenforschung, Darmstadt, Germany. The decay chains are basically consistent with previous findings and are considered to originate from isotopes of element 115 with mass numbers 287, 288, and 289. A set-up aiming specifically for high-resolution charged particle and photon coincidence spectroscopy was placed behind the gas-filled separator TASCA. For the first time, γ rays as well as X-ray candidates were observed in prompt coincidence with the α-decay chains of element 115.

Invariant mass spectrum and α-n correlation function studied in the fragmentation of 6He on a carbon target

13 pags, 5 figures.-- PACS nrs.: 24.60.−t; 25.70.Ef; 27.20.+n.

Measurements of the dipole response with radioactive beams

First Aqueous Chemistry with Seaborgium (Element 106)

Systematic investigation of the drip-line nuclei 11Li and 14Be and their unbound subsystems 10Li and 13Be

Fragmentation reactions in a carbon target with beams of 11Li and 14Be at relativistic energies have been studied in a kinematically complete experiment at the ALADIN-LAND setup at GSI. Excited states in 11Li and 14Be were obtained from the data in the inelastic channel. The measured cross sections with the core nucleus in the final state show that in the 14Be case core polarization plays an important role. In the one-neutron knockout channels the measured angular correlations between fragment and neutron are asymmetric, which demonstrates the presence of states with different parities in the 11Li and 14Be ground states. For 10Li a low-lying virtual s-state, a p-state and evidence for a d-s…

Thermonuclear reactionS30(p,γ)Cl31studied via Coulomb breakup ofCl31

Coulomb breakup at high energy in inverse kinematics of proton-rich Cl-31 was used to constrain the thermonuclear S-30(p,gamma)Cl-31 capture reaction rate under typical Type I x-ray burst conditions. This reaction is a bottleneck during rapid proton-capture nucleosynthesis (rp process), where its rate depends predominantly on the nuclear structure of Cl-31. Two low-lying states just above the proton-separation threshold of S-p = 296( 50) keV in Cl-31 have been identified experimentally using the (RB)-B-3-LAND setup at the GSI Helmholtzzentrum fur Schwerionenforschung GmbH. Both states are considered to play a key role in the thermonuclear S-30( p,gamma)Cl-31 capture reaction. Excitation ene…

Recoil-α-fission and recoil-α–α-fission events observed in the reaction 48Ca + 243Am

Products of the fusion-evaporation reaction 48Ca + 243Am were studied with the TASISpec set-up at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. Amongst the detected thirty correlated α-decay chains associated with the production of element Z=115, two recoil-α-fission and five recoil-α-α-fission events were observed. The latter five chains are similar to four such events reported from experiments performed at the Dubna gas-filled separator, and three such events reported from an experiment at the Berkeley gas-filled separator. The four chains observed at the Dubna gas-filled separator were assigned to start from the 2n-evaporation ch…

Determination of the content in uranium oxide particles by fission track analysis

Abstract One of the most important tasks of nuclear safeguards is to control the activities in nuclear facilities worldwide. These activities include the enrichment of 235 U . To identify enrichments above the maximum authorised level in commercial enrichment plants (usually 5% 235 U ) swipe tests are performed and the 235 U enrichment is determined in the sampled uranium oxide particles. A method is described that allows to measure the 235 U content in small particles (around 1 μm in diameter) by the use of fission tracks. It is based on the fact that in uranium fuel, only 235 U atoms are fissile with thermal neutrons and contribute to the amount of fission tracks counted for individual pa…

Extraction of the fluoride-, chloride- and bromide complexes of the elements Nb, Ta, Pa, and 105 into aliphatic amines

Abstract Previous studies of the halide complex formation of element 105 in HCl–HF mixtures and extractions into triisooctyl amine (TIOA) have been performed with the Automated Rapid Chemistry Apparatus, ARCA II. Element 105 was shown to be absorbed on the column from 12 M HCl–0.02 M HF together with its lighter homologues Nb, Ta and the pseudohomologue Pa. In elutions with 10 M HCl–0.025 M HF, 4 M HCl–0.02 M HF, and 0.5 M HCl–0.01 M HF, the extraction sequence Ta>Nb>105>Pa was observed and element 105 behaved very differently from its closest homologue Ta. As it is not possible within reasonable effort to model the many presumably mixed fluoride–chloride complexes involved in these studies…

Energy Dependence of Collective Flow of Neutrons and Charged Particles in 197AU + 197AU Collisions

Collective flow of nuclear matter is one important aspect of the research performed at heavy ion accelerator laboratories. The phenomenon was predicted on the basis of hydrodynamical calculations [1], and experimental evidence was first presented for the systems 93 Nb + 93 Nb and 197 Au + 197 Au in the projectile energy range between 150 and 1050 MeV/u [2]. The comparison to microscopic calculations shows that nuclear matter is compressed to about two to three times the ground state density and that a substantial fraction of the kinetic energy in the entrance channel is converted into compressional energy [3]. In these calculations, the relation between density and compressional energy depe…

Production and Decay of Element 114: High Cross Sections and the New NucleusHs277

The fusion-evaporation reaction Pu-244(Ca-48, 3-4n)(288,289)114 was studied at the new gas-filled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of (288, 289)114. At a compound nucleus excitation energy of E* = 39.8-43.9 MeV, the 4n evaporation channel cross section was 9.8(-3.1)(+3.9) pb. At E* = 36.1-39.5 MeV, that of the 3n evaporation channel was 8.0-(+7.4)(4.5) pb. In one of the 3n evaporation channel decay chains, a previously unobserved alpha branch in (281)Ds was observed ( probability to be of random origin from background: 0.1%). This alpha decay populated the new nucleus (277)Hs, which decayed by spontaneous fission…

Measurement of the Dipole Polarizability of the Unstable Neutron-Rich NucleusNi68

The E1 strength distribution in Ni68 has been investigated using Coulomb excitation in inverse kinematics at the RB3-LAND setup and by measuring the invariant mass in the one- and two-neutron decay channels. The giant dipole resonance and a low-lying peak (pygmy dipole resonance) have been observed at 17.1(2) and 9.55(17) MeV, respectively. The measured dipole polarizability is compared to relativistic random phase approximation calculations yielding a neutron-skin thickness of 0.17(2) fm. A method and analysis applicable to neutron-rich nuclei has been developed, allowing for a precise determination of neutron skins in nuclei as a function of neutron excess.

Search for Superheavy Elements in theU238+U238Reaction

A search was made for spontaneously fissioning superheavy elements in damped collisions of two uranium nuclei. Different techniques were applied covering the elements 108 to 118 and approx. =126, and a half-life range from 1 ms to more than 1 yr. No evidence for superheavy elements was found at upper cross-section limits of 10/sup -32/, 10/sup -33/, and 10/sup -35/ cm/sup 2/ for half-lives from 1 to 100 ms, 100 ms to 1 d, and 1 d to 1 yr, respectively.

Production Cross Sections of 261Rf and 262Db in Bombardments of 248Cm with 18O and 19F Ions

Isotope Distributions in the Reaction ofU238withU238

Radiochemically determined cross sections $\ensuremath{\sigma}(Z, A)$ were used to construct charge and mass distributions for the reaction of 1785-MeV $^{238}\mathrm{U}$ ions with thick $^{238}\mathrm{U}$ targets. Fission of the colliding nuclei is found to dominate. For the surviving uraniumlike fragments an enhancement of yields compared to the Kr + U and Xe + U reactions is observed. The formation of heavy actinides is shown to be associated with the low-energy tails of the broad excitation energy distributions in damped collisions.

Exclusive measurement of breakup reactions with the one-neutron halo nucleus11Be

Electromagnetic and nuclear inelastic scattering of the halo nucleus ${}^{11}\mathrm{Be}$ have been investigated by a measurement of the one-neutron removal channel, utilizing a secondary ${}^{11}\mathrm{Be}$ beam with an energy of 520 MeV/nucleon impinging on lead and carbon targets. All decay products, i.e., ${}^{10}\mathrm{Be}$ fragments, neutrons, and $\ensuremath{\gamma}$ rays have been detected in coincidence. Partial cross sections for the population of ground and excited states in ${}^{10}\mathrm{Be}$ were determined for nuclear diffractive breakup as well as for electromagnetically induced breakup. The partial cross sections for ground-state transitions have been differentiated fur…

Low-lying states in Ra219 and Rn215 : Sampling microsecond α -decaying nuclei

Short-lived α-decaying nuclei "northeast" of 208Pb in the chart of nuclides were studied using the reaction 48Ca+243Am with the decay station TASISpec at TASCA, GSI Darmstadt. Decay energies and times from pile-up events were extracted with a tailor-made pulse-shape analysis routine and specific α-decay chains were identified in a correlation analysis. Decay chains starting with the even-even 220Ra and its odd-A neighbors, 219Fr, and 219,221Ra, with a focus on the 219Ra→215Rn decay, were studied by means of α-γ spectroscopy. A revised α-decay scheme of 219Ra is proposed, including a new decay branch from a previously not considered isomeric state at 17 keV excitation energy. Conclusions on …

Energy dependence of collective flow of neutrons and protons in197Au+197Au collisions

We investigate the beam energy dependence of neutron and proton squeeze-out in collisions of197Au+197Au atE/A=400—800 MeV. The azimuthal anisotropy that describes the enhanced emission of mid-rapidity neutrons perpendicular to the reaction plane rises strongly with the transverse momentum of the neutrons. This dependence of the azimuthal anisotropy follows a universal curve — independent of beam energy — if the neutron momenta are measured in fractions of the projectile momentum per mass unit. Analogously, the kinetic energy spectra of mid-rapidity neutrons exhibit a universal behaviour as a function of the kinetic energy of the projectile.

Development of quadrupole collectivity in the neutron-rich Ni, Zn, Ge, and Se isotopes

An experiment was performed to study the collective properties of neutron-rich Ni, Zn, Ge, and Se isotopes. Of particular interest is the vicinity of the N = 50 and Z = 28 shell closures. For most neutron-rich nuclei in this region of the chart of nuclei the B(E2) values of the transitions from the ground to the first excited 2+ states are unknown. This information would give valuable insight into the changes in nuclear structure when going to more neutron-rich nuclei.

Nuclear reactions in collisions of very heavy ions at energies below and near the barrier

Cross sections for nuclear reactions in collisions of238U+238U and238U +197Au near and below the coulomb barrier

Cross sections for nuclear reactions at beam energies near and below the spherical Coulomb barrier V c were measured in the very heavy collision systems238U +238U and238U +197Au. The most probable reaction channel with mass transfer is the one-neutron transfer. Its excitation function is understood in terms of Rutherford trajectories together with the quantal process of neutron tunnelling over large distances. In addition, the exchange of up to 15 nucleons is observed down to 0.90 V c . The excitation functions for the multi-nucleon transfer products have much steeper slopes than that for one-neutron transfer, and are steeper for238U +197Au than for238U +238U, suggesting that nuclear contac…

Decomposition studies of group 6 hexacarbonyl complexes. Part 1: Production and decomposition of Mo(CO)6 and W(CO)6

Abstract Chemical studies of superheavy elements require fast and efficient techniques, due to short half-lives and low production rates of the investigated nuclides. Here, we advocate for using a tubular flow reactor for assessing the thermal stability of the Sg carbonyl complex – Sg(CO)6. The experimental setup was tested with Mo and W carbonyl complexes, as their properties are established and supported by theoretical predictions. The suggested approach proved to be effective in discriminating between the thermal stabilities of Mo(CO)6 and W(CO)6. Therefore, an experimental verification of the predicted Sg–CO bond dissociation energy seems to be feasible by applying this technique. By in…

Two- and three-body correlations: breakup of halo nuclei

4 pages, 2 figures.

Lithium isotopes beyond the drip line

The unbound isotopes 10Li, 12Li and 13Li have been observed after nucleon-knockout reactions at relativistic energies with 11Li and 14Be beams impinging on a liquid hydrogen target. The channels , and were analysed in the ALADIN-LAND setup at GSI. The 10Li data confirm earlier findings, while the 12Li and 13Li nuclei were observed for the first time. The relative-energy spectrum shows that the ground state of 12Li can be described as a virtual s-state with a scattering length of -13.7(1.6) fm. A broad energy spectrum was found for the channel. Based on the assumption that the relative-energy spectrum is dominated by a correlated background presumably stemming from initial correlations in th…

Superheavy element flerovium (element 114) is a volatile metal.

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Expe…

New nuclides: Neptunium-243 and neptunium-244

We have observedγ-rays following the β−-decay of243Np and244Np after chemical isolation of neptunium isotopes from the products of the reaction of 835 MeV136Xe with244Pu. The ground-state of 1.85-min243Np hasJ=5/2. The decay of 2.29-min244Np (probableJπ=7−) populates high-spin members of the ground state rotational band in244Pu.

Evidence for Pygmy and Giant Dipole Resonances inSn130andSn132

The dipole strength distribution above the one-neutron separation energy was measured in the unstable $^{130}\mathrm{Sn}$ and the double-magic $^{132}\mathrm{Sn}$ isotopes. The results were deduced from Coulomb dissociation of secondary Sn beams with energies around $500\text{ }\text{ }\mathrm{MeV}/\mathrm{\text{nucleon}}$, produced by in-flight fission of a primary $^{238}\mathrm{U}$ beam. In addition to the giant dipole resonance, a resonancelike structure (``pygmy resonance'') is observed at a lower excitation energy around 10 MeV exhausting a few percent of the isovector $E1$ energy-weighted sum rule. The results are discussed in the context of a predicted new dipole mode of excess neut…

Speciation and interactions of plutonium with humic substances and kaolinite in aquifer systems

Abstract The speciation of plutonium (Pu) in contact with humic substances (HS) and kaolinite has been performed in aquifer systems. Mainly the redox behavior, complexation, and sorption of plutonium are discussed here. The redox behavior of Pu(VI) in contact with HS was studied and it was found that Pu(VI) is reduced to Pu(III) and Pu(IV) within a couple of weeks. The complexation constants (log  β LC ) of Pu(III) and Pu(IV) with HS have been determined by means of the ultrafiltration method. Furthermore, the sorption of Pu(III) and Pu(IV) onto kaolinite has been investigated as a function of pH by batch experiments under aerobic and anaerobic conditions.

Actinide Production in Collisions ofU238withCm248

Cross sections for the production of heavy actinides in damped collisions of $^{238}\mathrm{U}$ ions with $^{248}\mathrm{Cm}$ targets are reported and compared with similar data for other projectiles. The relatively small differences in the formation rates of a given isotope made by different projectiles indicate a balance between increased mass transfer probability with increasing projectile mass and a concurrent decrease in survivability because of an increase in excitation energy.

Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier

Fission-fragment angular distributions were measured in the reaction of40Ar with208Pb near the fusion barrier. For nearly symmetric mass-/charge splits we find angular distributions symmetric around θ=90 degrees, however, with unusually large anisotropies. These develop gradually into forward-backward asymmetric distributions as one moves away from mass-/charge symmetry. This indicates that non-compound fission (‘quasi-fission’) competes with true fusion-fission. The relative contribution of quasi-fission to the total fission cross section is somewhere between 51 and 85%. In the framework of the extra-push model this is equivalent to an extra-extra push energy for compound-nucleus formation…

Preparation of targets for the gas-filled recoil separator TASCA by electrochemical deposition and design of the TASCA target wheel assembly

Abstract The Transactinide Separator and Chemistry Apparatus (TASCA) is a recoil separator with maximized transmission designed for performing advanced chemical studies as well as nuclear reaction and structure investigations of the transactinide elements ( Z >103) on a one-atom-at-a-time basis. TASCA will provide a very clean transactinide fraction with negligible contamination of lighter elements from nuclear side reactions in the target. For TASCA a new target chamber was designed and built at GSI including the rotating target wheel assembly ARTESIA for beam intensities up to 2 μA (particle). For the production of longer-lived isotopes of neutron-rich heavier actinide and transactinide e…

Uran aus deutschen Nuklearprojekten der 1940er Jahre – eine nuklearforensische Untersuchung

Wir berichten hier uber eine nuklearforensische Analyse verschiedener Uranmaterialien aus deutschen Nuklearprojekten der 1940er Jahre, bei denen Uranmetall in verschiedenen Geometrien verwendet wurde. Mithilfe des 230Th/234U-Isotopenverhaltnisses konnte fur das Metall ein Produktionszeitraum von 1940 bis 1943 bestimmt werden. Die geographische Herkunft des Urans wurde anhand des Spurengehalts an Seltenerdelementen und der Strontium-Isotopenverhaltnisse bestimmt. Die Ergebnisse zeigen, dass das bei den deutschen Nuklearprojekten verwendete Uran aus Minen in der Tschechischen Republik stammt. 236U und 239Pu wurden in Spuren nachgewiesen. Diese entsprechen in etwa der Haufigkeit dieser Isotope…

Response of BGO detectors to photons of 3–50 MeV energy

Abstract The response of an array of 7 hexagonal BGO detectors each 7.5 cm long (6.7 radiation lengths) with 3.6 cm side-to-side distance was measured using monochromatic photons from the tagged-photon facility at the electron accelerator MAMI A at Mainz. The experimental spectra of the deposited energy for a single detector and for the array of seven modules compare very well with the predictions of Monte Carlo shower simulations using the code GEANT3. Significant improvement of the energy resolution is observed for the summed energy spectra compared to the resolution of a single module. This improvement deteriorates at higher photon energies because the length of the detector is not suffi…

Dipole response of neutron-rich Sn isotopes

The neutron-rich isotopes 129–133Sn were studied in a Coulomb excitation experiment at about 500 AMeV using the FRS-LAND setup at GSI. From the exclusive measurement of all projectile-like particles following the excitation and decay of the projectile in a high-Z target, the energy differential cross section can be extracted. At these beam energies dipole transitions are dominating, and within the semi-classical approach the Coulomb excitation cross sections can be transformed into photoabsorption cross sections. In contrast to stable Sn nuclei, a substantial fraction of dipole strength is observed at energies below the giant dipole resonance (GDR). For 130Sn and 132Sn this strength is loca…

A new assessment of the alleged link between element 115 and element 117 decay chains

Physics letters 760, 293-296(2016). doi:10.1016/j.physletb.2016.07.008

A large-area scintillating fibre detector for relativistic heavy ions

Abstract A scintillating fibre detector for relativistic heavy ions with an active area of 50 × 50 cm 2 has been developed and was tested with various ion beams (1 ≤ Z ≤ 92). At count rates of up to 10 5 particles/s, the position resolution was found to be determined by the fibre width of 1 mm; depending on the nuclear charge of the beam, efficiencies between 89% and 100% and time resolutions between 800 and 200 ps (FWHM) were obtained.

Fission in the landscape of heaviest elements: Some recent examples

The fission process still remains a main factor that determines the stability of the atomic nucleus of heaviest elements. Fission half-lives vary over a wide range, 10^−19 to 10^24 s. Present experimental techniques for the synthesis of the superheavy elements that usually measure α-decay chains are sensitive only in a limited range of half-lives, often 10^5 to 10^3 s. In the past years, measurement techniques for very short-lived and very long-lived nuclei were significantly improved at the gas-filled recoil separator TASCA at GSI Darmstadt. Recently, several experimental studies of fission-related phenomena have successfully been performed. In this paper, results on 254−256Rf and 266Lr ar…

Application of fast solvent extraction processes to studies of exotic nuclides

Fast solvent extraction is a chemical separation method, which can be applied to study exotic nuclides. Since about 1970 the SISAK technique, which is an on-line method based on multi-stage solvent extraction separations, has been successfully used to investigate the nuclear properties of β-decaying nuclides with half-lives down to about one second. During the last decade it has become possible to produce transactinide elements in high enough yields to investigate their chemical properties on a one-atom-at-a-time scale. For this purpose it was necessary to improve and change the detection part of the SISAK system in order to be capable to detect spontaneously fissioning and α-decaying nucli…

Unusual excitation-energy division in quasi-fission reactions between50Ti,54Cr and58Fe with207,208Pb at the barrier

Angular distributions in quasi-fission reactions

Abstract Angular distributions for fission-like fragments were measured in the systems 50Ti, 56Fe + 208Pb by applying an off-line K X-ray activation technique. The distributions d2σ/dθdZ exhibit forward-backward asymmetries that are strongly Z-dependent. They result from a process (quasi-fission) which yields nearly symmetric masses in times comparable to the rotational period of the composite system. A method for obtaining the variance of the tilting angular momentum, K02, from these skewed, differential angular distributions is described. The results indicate that the tilting mode is not fully excited in quasi-fission reactions. The results are compared to the sum of the variances of all …

Measurement of the92,93,94,100Mo(γ,n) reactions by Coulomb Dissociation

6th Nuclear Physics in Astrophysics Conference (NPA), Lisbon, Portugal, 19 May 2013 - 24 May 2013; Journal of physics / Conference Series 665, 012034 (2016). doi:10.1088/1742-6596/665/1/012034

Fission in238U+238U collisions below the Coulomb barrier

Integral fission cross sections in the system238U+238U were measured at beam energies below the interaction barrierVC. Scattering angle dependent probabilities and integral cross sections for Coulomb fission were calculated. It is concluded that earlier observed discrepancies between measured and calculated angular distributions for the one-neutron transfer product239U cannot be explained by sequential fission. Multi-nucleon transfer induced fission is observed down to energies (0.90±0.02)×VC.

Coulomb breakup of psd-shell neutron-rich nuclei

Inelastic scattering of loosely bound nuclei by Coulomb interaction at intermediate energies (400?600 MeV/nucleon) has been utilized as a spectroscopic tool for exotic nuclei. The observed electromagnetic dipole (E1) strength above the one neutron threshold of neutron-rich C, Be, B and O isotopes can be explained by a non-resonant transition of a neutron into the continuum. The shape of these strength distributions reflects properties of the wavefunction of the released neutron in the nucleus and hence ground-state properties of these isotopes. Neutron capture cross-sections such as for the 14C(n,?) 15C reaction which are of astrophysical relevance can be deduced indirectly.

Continuum excitations in6He

T. Aumann et al. ; 11 pags.; 6 figs.; 2 tabs. ; PACS number(s): 27.20.1n, 25.60.Gc, 25.70.De, 29.30.Hs

Coulomb breakup of 23O

Abstract The ground-state structure of the near-drip-line nucleus 23O has been investigated in a one-neutron Coulomb breakup reaction. Differential cross sections d σ / d E * for electromagnetic excitation of 23O projectiles (422 MeV/nucleon) incident on a lead target have been obtained from the measurement of the momenta of all breakup products including γ rays. The analysis of the deduced dipole-transition probability into the continuum infers a 2 s 1 / 2 ⊗ O 22 ( 0 + ) ground state configuration with a spectroscopic factor of 0.77(10) and thus a ground-state spin I π ( O 23 ) = 1 / 2 + , resolving earlier conflicting experimental findings. Final-state interaction is of significant influe…

Chemical studies on rutherfordium (Rf) at JAERI

SummaryChemical studies on element 104, rutherfordium (Rf), at JAERI (Japan Atomic Energy Research Institute) are reviewed. The transactinide nuclide261Rf has been produced in the reaction248Cm(18O, 5n) at the JAERI tandem accelerator with the production cross section of about 13 nb. On-line anion-exchange experiments on Rf together with the lighter homologues, group-4 elements Zr and Hf, in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCl and HNO3solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of …

A large area detector for high-energy neutrons

Abstract We present design studies, results of test measurements, and Monte Carlo simulations which served as a basis for the realization of a large area neutron detector (LAND). It has a front area of 2m×2m and a depth of 1 m, and features a multilayer structure of passive converter and active scintillator material. The detector is subdivided in independently operating paddles which allow time-of-flight and position measurement. An energy resolution of ΔT n / T n =5.3% for a flight path of 15 m and an overall detection efficiency of ϵ ≈ 1 is anticipated for neutrons with T n ≈ 1 GeV. The operation of LAND at the SIS facility of GSI is described.

Continuous separation and identification of neutronrich neptunium isotopes from heavy-ion reactions by means of the centrifuge system “sisak”

Abstract Neutron-rich neptunium isotopes formed in direct transfer reactions between 136 Xe projectiles and targets of 244 Pu have been separated from other reaction products with the on-line liquid-liquid extraction system SISAK. A four-detector delay method was used to determine the half-lives of the previously unknown isotopes 243 Np and 244 Np. From the decay of the 287.4 keV γ-line a half-life of 1.8 ± 0.3 min was determined for 243 Np. From the decay curves of the γ-lines at 162.7 and 216.7 keV, which fit into the known level scheme of 244 Pu, a half-life of 2.5 ± 0.3 min results for 244 Np.

Ca48+Bk249Fusion Reaction Leading to ElementZ=117: Long-Livedα-DecayingDb270and Discovery ofLr266

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the 48Ca+249Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294-117 and its decay products. A hitherto unknown α-decay branch in 270Db (Z=105) was observed, which populated the new isotope 266Lr (Z=103). The identification of the long-liv…

Syntheses of transuranium isotopes with atomic numbers Z≤ 103 in multi-nucleon transfer reactions

Abstract In Section 1 we will discuss multi-nucleon transfer reactions with light heavy ions, which can be thought of as competing with complete fusion at higher impact parameters. Quasi-elastic and multi-nucleon transfer reactions with the heaviest projectiles will be discussed in Section 2 . In Section 3 we will cover recent developments focusing on theoretical predictions of cross sections of superheavy nuclei, cover some new possibilities and look into the existing experimental challenges.

Giant resonances in unstable oxygen isotopes

Abstract Electromagnetic and nuclear breakup of the neutron-rich Oxygen isotopes ranging from A = 17 to A = 22 is studied experimentally in reactions at energies around 600 MeV/u. The beams were produced in fragmentation reactions and separated by the GSI Fragment Separator FRS. By measuring the four-momenta of all decay products after inelastic scattering and neutron decay of the projectile, the excitation energy is determined. From the differential cross sections dσ dE ∗ for electromagnetic excitation, the E1-strength distributions can be deduced. For 18,20,22O, low-lying dipole strength is observed, exhausting about 5% of the Thomas Reiche Kuhn sumrule for energies up to 5 MeV above the …

Anion-exchange Behavior of Rf in HCl and HNO3 Solutions

H. Haba,∗,a K. Tsukada,a M. Asai,a S. Goto,a,b A. Toyoshima,a,c I. Nishinaka,a K. Akiyama,a M. Hirata,a S. Ichikawa,a Y. Nagame,a Y. Shoji,c M. Shigekawa,c T. Koike,c M. Iwasaki,c A. Shinohara,c T. Kaneko,b T. Maruyama,b S. Ono,b H. Kudo,b Y. Oura,d K. Sueki,d H. Nakahara,a,d M. Sakama,e A. Yokoyama,f J. V. Kratz,g M. Schadel,h and W. Bruchleh Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 3191195, Japan Department of Chemistry, Faculty of Science, Niigata University, Niigata-shi, Niigata 950-2181, Japan Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka-shi, Osaka 5600043, Japan Department of Chemistry, Graduate Sc…

Searching for the 5H resonance in the t+n+n system

19 pages, 7 figures, 2 tables, 2 appendices.-- PACS nrs.: 27.10.+h; 25.60.Gc.-- Printed version published Jul 28, 2003.

Trace analysis of plutonium in environmental samples by resonance ionization mass spectroscopy (RIMS)

Resonance ionization mass spectroscopy (RIMS) is well suited for trace analysis of long-lived radioisotopes in environmental, biological and technical samples. By multiple resonant laser excitation and ionization of the elemental atoms under investigation, an extremely high element selectivity can be achieved. In addition, isotope selectivity is obtained by subsequent mass analysis. The excellent sensitivity results from the large atomic cross-sections in the excitation–ionization process and the good detection efficiency for ions. The element selectivity of RIMS allows a simplified procedure for the chemical preparation of the samples compared to the requirements of thin sources for α-spec…

Study of the $^{15}$O(2p, γ )$^{17}$Ne cross section by Coulomb dissociation of $^{17}$Ne for the rp process of nucleosynthesis

Acta physica Polonica / B 45(2), 229 - 234 (2014). doi:10.5506/APhysPolB.45.229

Search for superheavy elements in damped collisions betweenU238andCm248

Negative results for the production of superheavy elements in damped collisions between $^{238}\mathrm{U}$ projectiles and $^{248}\mathrm{Cm}$ targets are reported. This reaction was believed to permit a closer and more widespread approach to the predicted island of stability near Z=114 and N=184 than any practical fusion reaction. Aqueous and gas phase chemistry techniques were used to isolate superheavy element fractions. The fractions were counted for spontaneous fission activity, fragment kinetic energies, and neutron multiplicities. Cross-section limits for half-lives from hours to several years are g4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{…

Electromagnetic excitation of the two-phonon giant dipole resonance

Abstract The nuclear response of 136 Xe and 208 Pb to electromagnetic excitation was studied in peripheral, near-relativistic heavy-ion collisions. Large cross sections were observed for the one-phonon and two-phonon isovector giant dipole resonance. The results, in particular the unexpectedly large strength found for the double giant dipole resonance, are discussed and compared to that of other recent measurements.

Development of nuclear chemistry at Mainz and Darmstadt

Abstract This review describes some key accomplishments of Günter Herrmann such as the establishment of the TRIGA Mark II research reactor at Mainz University, the identification of a large number of very neutron-rich fission products by fast, automated chemical separations, the study of their nuclear structure by spectroscopy with modern detection techniques, and the measurement of fission yields. After getting the nuclear chemistry group, the target laboratory, and the mass separator group established at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, a number of large international collaborations were organized exploring the mechanism of deeply inelastic multi-nucleon trans…

Excitation functions for production of heavy actinides from interactions ofCa40andCa48ions withCm248

Excitation functions have been measured for production of isotopes of Bk through Fm in bombardments of /sup 248/Cm with 234- to 294-MeV /sup 40/Ca ions and with 239- to 318-MeV /sup 48/Ca ions. The maxima of the isotopic distributions for these elements occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions. The shapes of the distributions and the half-widths of about 2.5 mass numbers are quite similar to those observed previously for reactions of /sup 16/O, /sup 18/O, /sup 20/Ne, and /sup 22/Ne with /sup 248/Cm. In general, the excitation functions for /sup 40/Ca show maxima near the Coulomb barrier while those for /sup 48/Ca are about 20 MeV above the barrie…

Fission fragment angular distributions in the capture reactions 50Ti, 56Fe + 208Pb

The analysis of %-ray mult ip l ic i t ies measured I in coincidence with capture fission events in reactions of 26Mg through 54Cr, 58Fe, and 64Ni with 208pb in terms of Ko and~eff revealed1 that the resulting values of ~ /~e f f were rather independent of for a given system and, in a compound nucleus picture, were more in agreement with the 'shape of the non-rotating saddle than with the actually expected rotating saddle I f non-compound systenmhave to be considered these values of ~/J~ff__ shapes. suggested at least that the captured systems near the turning point from the inward radial motion to symmetric fragmentation had reached a remarkable compactness.

Resonance ionization mass spectroscopy for trace determination of plutonium in environmental samples

Resonance ionization mass spectroscopy (RIMS) is a sensitive and isotope selective method and well suited for trace analysis of plutonium in the environment. After the chemical isolation of plutonium from soil, air filters or urine, e.g., it is electrolytically deposited as hydroxide on a tantalum backing and covered with a thin titanium layer. By heating such a sandwich filament in the RIMS-apparatus under vacuum an atomic beam of plutonium is produced. The atoms are ionized by a three-step resonant excitation using pulsed dye lasers, and the ions are mass-selectively detected with a time-of-flight (TOF) spectrometer and a multi channel plate detector. RIMS yields a low detection limit of …

HCl gas gettering for crystalline silicon thin film solar cells

Crystalline silicon thin film (cSiTF) solar cells could be an attractive alternative for standard silicon solar cells. Only a small amount of the expensive high purity silicon is needed for the epitaxial deposition on a low-cost silicon substrate made from e.g. metallurgical grade (MG) or upgraded metallurgical grade (UMG) silicon. The resulting product is called epitaxial wafer equivalent (EpiWE) because it can be processed in a standard wafer cell production. MG-Si and UMG-Si still contain a huge amount of metallic impurities. These impurities have to be removed by gettering methods in order to prevent diffusion into the highly pure active silicon layer during the high-temperature deposit…

Spectroscopy along flerovium decay chains. III : Details on experiment, analysis, 282Cn, and spontaneous fission branches

Flerovium isotopes (element Z=114) were produced in the fusion-evaporation reactions 48Ca+242,244Pu and studied with an upgraded TASISpec decay station placed in the focal plane of the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Twenty-nine flerovium decay chains were identified by means of correlated implantation, α decay, and spontaneous fission events. Data analysis aspects and statistical assessments, primarily based on measured rates of various events, which laid the foundation for the comprehensive spectroscopic information on the flerovium decay chains, are presented in detail. Various decay scenarios of an excited state obse…

Target dependence in the study of collective modes in stable and exotic Ni nuclei

The appearance of the pygmy-dipole-resonance is a recently observed phenomenon that can be related to neutron-matter properties. Its study can be a tool to determine the nuclear symmetry-energy parameters and thus can contribute constraining neutron star models. We present the ( γ,n ) cross sections for different Ni isotopes obtained from a measurement in inverse kinematics at about 500 MeV/u in the LAND reaction setup at GSI. The question of the disentanglement of the Coulomb and nuclear contributions is addressed.

Determination of boron concentration in blood and tissue samples from patients with liver metastases of colorectal carcinoma using Prompt Gamma Ray Activation Analysis (PGAA).

As part of the studies on Boron Neutron Capture Therapy at the University of Mainz, Germany, a clinical trial has been started, in which our patients suffering from liver metastases of colorectal carcinoma, have been enrolled. Specimens of blood and healthy tissue samples taken from the patients were measured at the PGAA facilities at the HFR in Petten, The Netherlands, and at the FRM II in Munich, Germany. From the measured boron concentrations, pharmacokinetic curves and blood-to-tissue concentration ratios were produced.

Correlation between transfer and fusion in heavy ion reactions at the Coulomb barrier

Photoneutron cross sections for unstable neutron-rich oxygen isotopes.

The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A = 17 to A = 22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections d sigma/dE were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.

Measurement of the first ionization potential of lawrencium (element 103)

Lawrencium, with atomic number 103, has an isotope with a half-life of 27 seconds; even so, its first ionization potential has now been measured on an atom-at-a-time scale and agrees well with state-of-the-art theoretical calculations that include relativistic effects. The most dramatic modern revision of Mendeleev's periodic table of elements came in 1944 when Glenn T. Seaborg placed a new series of elements, the actinides (atomic numbers 89–103), below the lanthanides. In this issue of Nature, Yuichiro Nagame and colleagues report the first measurement of one of the basic atomic properties of element 103 (lawrencium), namely its first ionization potential. Lawrencium is only accessible vi…

Invariant-mass spectroscopy of $^{10}$Li and $^{11}$Li

Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb targets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing different reaction mechanisms. Invariant-mass spectroscopy for Li-11 and Li-10 is performed. The E1 strength distribution, deduced from electromagnetic excitation of Li-11 up to an excitation energy of 4 MeV comprises similar to 8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li-10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carrying 26(10)% of the strength and likely to be associated with an s-wa…

First superheavy element experiments at the GSI recoil separator TASCA: The production and decay of element 114 in thePu244(Ca48,3-4n) reaction

Experiments with the new recoil separator, Transactinide Separator and Chemistry Apparatus (TASCA), at the GSI were performed by using beams of Ca-48 to irradiate targets of Pb206-208, which led to the production of No252-254 isotopes. These studies allowed for evaluation of the performance of TASCA when coupled to a new detector and electronics system. By following these studies, the isotopes of element 114 ((288-291)114) were produced in irradiations of Pu-244 targets with Ca-48 beams at compound nucleus excitation energies around 41.7 and 37.5 MeV, demonstrating TASCA's ability to perform experiments with picobarn-level cross sections. A total of 15 decay chains were observed and were as…

Neutron momentum distributions from "core break-up" reactions of halo nuclei

Neutron angular distributions from violent break-up reactions of Li-11 and Be-11 have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to the momentum distribution of the loosely bound halo neutron(s) in the projectiles.

Attempts to chemically investigate element 112

Summary Two experiments aiming at the chemical investigation of element 112 produced in the heavy ion induced nuclear fusion reaction of 48Ca with 238U were performed at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. Both experiments were designed to determine the adsorption enthalpy of element 112 on a gold surface using a thermochromatography setup. The temperature range covered in the thermochromatography experiments allowed the adsorption of Hg at about 35 °C and of Rn at about -180 °C. Reports from the Flerov Laboratory for Nuclear Reactions (FLNR), Dubna, Russia claim production of a 5-min spontaneous fission (SF) activity assigned to 283112 for the 238U(48Ca,3n)…

Experimental study of the 15O(2p, γ)17Ne cross section by Coulomb Dissociation for the rp process

6th Nuclear Physics in Astrophysics Conference (NPA), Lisbon, Portugal, 19 May 2013 - 24 May 2013; Journal of physics / Conference Series 665, 012046 (2016). doi:10.1088/1742-6596/665/1/012046

Angular distributions in quasi-fission reactions: Evidence for incomplete relaxation of the tilting mode

Angular distributions of fission-like fragments have been measured for50Ti+208Pb and56Fe+208Pb collisions. Z-dependent asymmetries around Θincm= 90° preclude their interpretation in terms of compound nucleus fission with the transition state theory. Fits of the data with a simple ansatz for statistical angular momentum fluctuations (tilting) give evidence for an incomplete relaxation of the tilting mode in quasi fission reactions.

Fusion-fission in the reaction76Ge+170Er

Radiochemical yield measurements were performed to study mass- and charge distributions in the reaction of76Ge ions with170Er in the c.m. energy range from 222 MeV through 272 MeV. The magnitude of the resulting cross-section for fusion-fission is significantly lower than expected and is explained within the framework of Swiatecki's Extra-Push model.

Cover Picture: Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation (Angew. Chem. Int. Ed. 45/2015)

Measurement of the dipole response of neutron-rich nuclei in the A∼20 region

Abstract Coulomb break up of the neutron-rich 15,17 C and 17–22 O isotopes has been studied experimentally using secondary beams at energies of 500–600 MeV/u. A comparison between differential cross sections, d σ/ d E ∗ , with that obtained from a binary model shows that the main ground-state configuration of 15 C is 14 C(0 + )⊗ ν S 1/2 as expected. For 17 C, our preliminary data analysis reveals that the predominant (∼64%) configuration of the ground state is 16 C(2 + )⊗ ν s , d . For 17–22 O, the low-lying E1 strength amounts up to about 12% of the energy weighted sum rule strength depending on neutron number. The energy weighted E1 strength (integrated up to 15 MeV excitation energy) inc…

Excitation and decay of two-phonon giant dipole resonances

Abstract In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states.

Adsorption of Db and its homologues Nb and Ta, and the pseudo-homologue Pa on anion-exchange resin in HF solution

Anion-exchange chromatography of element 105, dubnim (Db), produced in the 206 Cm( 19 F, 5n) 262 Db reaction is investigated together with the homologues Nb and Ta, and the pseudo-homologue Pa in 13.9 M hydrofluoric acid (HF) solution. The distribution coefficient (K d ) of Db on an anion-exchange resin is successfully determined by running cycles of 1702 chromatographic column separations. The result clearly indicates that the adsorption of Db on the resin is significantly different from that of the homologues and that the adsorption of anionic fluoro complexes of these elements decreases in the sequence of Ta ≈ Nb > Db > Pa.

Dissociation of 8He into 6He + n + X at 240 MeV/u

4 pages, 3 figures, 2 tables.

Fragmentation of exotic oxygen isotopes

Abrasion-ablation models and the empirical EPAX parametrization of projectile fragmentation are described. Their cross section predictions are compared to recent data of the fragmentation of secondary beams of neutron-rich, unstable 19,20,21O isotopes at beam energies near 600 MeV/nucleon as well as data for stable 17,18O beams.

Reactions of40Ar with233U,235U, and238U at the barrier

Production cross sections for target-like transfer products in reactions of40Ar with233,235,238U at the barrier were determined using radiochemical techniques. The heaviest products detected are isotopes of californium (Z=98). In addition to the quasi-elastic component of the isotopic distributions observed in the vicinity of uranium, there are also relaxed contributions throughout the entire region. The peak positions of the isotope distributions of this component for fixed atomic number, after the transfer of > 3 charges, approach closely the minimum of the potential energy surfaces (PES). The experimental results thus indicate the cold formation of the reaction products. A search for lon…

Search for long-lived superheavy elements in the reaction of136Xe with238U

A search with radiochemical methods for long-lived superheavy elements in 238U targets bombarded with intense beams of136Xe ions produced negative results. A formation cross section of ≤1×10−35 cm2 is deduced at 95% confidence level for nuclides with half-lives between 1 and 200 d.

New nuclideHa263

A new nuclide $^{263}\mathrm{Ha}$ was produced in the bombardment of a $^{249}\mathrm{Bk}$ target with 93-MeV $^{18}\mathrm{O}$ ions. It was detected via spontaneous fission counting and was shown to have a half-life of about 0.5 min. This activity was also separated from the reaction products by automated rapid chemical separations using cation-exchange chromatography in 0.05M \ensuremath{\alpha}-hydroxyisobutyric acid. After chemical separation, $^{263}\mathrm{Ha}$ was found to decay by spontaneous fission (${57}_{\mathrm{\ensuremath{-}}15}^{+13}$%) and by \ensuremath{\alpha} emission (${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=8.35 MeV, 43%) with a half-life of ${27}_{\mathrm{\ensurem…

Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy

Abstract Resonance ionization mass spectroscopy (RIMS) in the presence of an external static electric field has been used for the determination of photoionization thresholds. Extrapolation of the thresholds obtained with different electric field strengths to zero field strength directly leads to the first ionization potential (IP). The ionization potentials of the transplutonium elements americium, curium, berkelium and californium could be measured for the first time. Due to the high sensitivity of RIMS, samples of only 1012 atoms have been used. The results are: IPAm = 5.9738(2)eV, IPCm = 5.9915(2)eV, IPBk = 6.1979(2)eV and IPCf = 6.2817(2)eV. The same technique was applied to thorium, ne…

Search for elements 119 and 120

A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab=281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical pr…

Proton Inelastic Scattering onNi56in Inverse Kinematics

Inelastic proton scattering to the first excited ${2}^{+}$ state of the doubly magic $^{56}\mathrm{Ni}$ nucleus was investigated in inverse kinematics, using a secondary beam of radioactive $^{56}\mathrm{Ni}$ nuclei. At an incident energy of 101 MeV/nucleon, a value $B(E2,{0}^{+}\ensuremath{\rightarrow}{2}^{+})=600\ifmmode\pm\else\textpm\fi{}120 {e}^{2}$ ${\mathrm{fm}}^{4}$ was measured. This result completes the set of experimental data for the first excited ${2}^{+}$ states in the $1f\ensuremath{-}2p$ shell with a closed shell of neutrons or protons. These data are compared to recent shell-model calculations.

Study of the Unstable NucleusL10iin Stripping Reactions of the Radioactive ProjectilesB11eandL11i

Reactions of the halo systems Be-11 and Li-11 (at 460 and 280 MeV/nucleon) with a carbon target demonstrate that (n + Li-9) has an (unbound) l = 0 ground state very close to the threshold. The neutron halo of Li-11 has appreciable (1s(1/2))(2) and (0p(1/2))(2) components.

Radiochemical study of the kinematics of multi-nucleon transfer reactions in 48Ca + 248Cm collisions 10% above the Coulomb barrier

Abstract The kinematics of multi-nucleon transfer reactions in 48Ca + 248Cm collisions at 262 MeV (center of target) was investigated by using a stacked-foil technique and radiochemical separations of trans-curium elements. Trans-curium isotopes were identified by α-particle spectroscopy. For Fm isotopes, by comparing the centroids of the measured post-neutron emission isotope distributions with the most probable primary mass number predicted by Volkov's generalized Q g g systematics, the missing mass (number of evaporated neutrons) is estimated. The latter is compared with that deduced from the measured centroid of the laboratory angular distribution peaked closely to the grazing angle and…

Search for Electron-Capture Delayed Fission in the New Isotope Md244

The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with $\ensuremath{\alpha}$-particle energies of 8.73--8.86 MeV and with a half-life of ${0.30}_{\ensuremath{-}0.09}^{+0.19}\text{ }\text{ }\mathrm{s}$ was assigned to $^{244}\mathrm{Md}$. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter $^{244}\mathrm{Fm}$ was observed, which results in an upper limit of 0.14 for the electron-capture branching of $^{244}\mathrm{Md}$. Two groups of fission events with half-lives of ${0.9}_{\ens…

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Mass and charge distributions for binary reaction channels have been measured for the reactions86Kr with76Ge,104Ru and130Te at the Coulomb barrier using chemical separations andγ-ray spectroscopy. These systems span the region where dynamical hindrance to complete fusion sets in. The binary reactions can be subdivided into two components associated withi) reflection from the outer potential barrier (quasielastic), andii) reseparation after passing the barrier (complex reactions). The sum of complex-reaction channels and evaporation residues from complete fusion can be reproduced by a barrier passing calculation. The fraction of the barrier passing flux leading to reseparation increases from…

Günter Herrmann (1925–2017): A tribute to his research and organizational achievements

Nuclear symmetry energy and neutron skins derived from pygmy dipole resonances

By exploiting Coulomb dissociation of high-energy radioactive beams of the neutron-rich nuclei $^{129\ensuremath{-}132}\mathrm{Sn}$ and $^{133,134}\mathrm{Sb}$, their dipole-strength distributions have been measured. A sizable fraction of ``pygmy'' dipole strength, energetically located below the giant dipole resonance, is observed in all of these nuclei. A comparison with available pygmy resonance data in stable nuclei ($^{208}\mathrm{Pb}$ and $N=82$ isotones) indicates a trend of strength increasing with the proton-to-neutron asymmetry. On theoretical grounds, employing the RQRPA approach, a one-to-one correlation is found between the pygmy strength and parameters describing the density d…

Hexafluoro complex of rutherfordium in mixed HF/HNO3 solutions

Formation of anionic fluoride-complexes of element 104, rutherfordium, produced in the 248 Cm( 18 O, 5n) 261 Rf reaction was studied by anion-exchange on an atom-at-a-time scale. It was found that the hexafluoro complex of Rf, [RfF 6 ] 2- , was formed in the studied fluoride ion concentrations of 0.0005-0.013 M. Formation of [RfF 6 ] 2- was significantly different from that of the homologues Zr and Hf, [ZrF 6 ] 2- and [HfF 6 ] 2- ; the evaluated formation constant of [RfF 6 ] 2- is at least one-order of magnitude smaller than those of [ZrF 6 ] 2- and [HfF 6 ] 2- .

New Short-Lived IsotopeU221and the Mass Surface NearN=126

Two short-lived isotopes ^{221}U and ^{222}U were produced as evaporation residues in the fusion reaction ^{50}Ti+^{176}Yb at the gas-filled recoil separator TASCA. An α decay with an energy of E_{α}=9.31(5)  MeV and half-life T_{1/2}=4.7(7)  μs was attributed to ^{222}U. The new isotope ^{221}U was identified in α-decay chains starting with E_{α}=9.71(5)  MeV and T_{1/2}=0.66(14)  μs leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the N=126 shell closure and its influence on the stability of uranium isotopes are discussed within the framework of α-decay reduced widt…

Halo excitations in fragmentation of He at 240 MeV/u on carbon and lead targets

Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while …

Recoil-alpha-fission and Recoil-alpha-alpha-fission Chains Stemming from Element 115

GSI Scientific Report 2014 - GSI Report 2015-1

Extraction Chromatographic Behavior of Rf, Zr, and Hf in HCl Solution with Styrenedivinylbenzene Copolymer Resin Modified by TOPO (trioctylphosphine oxide)

It is of great interest to study chemical properties of the transactinide elements with atomic numbers (Z) ≥ 104. One of the most important subjects is to establish the position of the elements at the extreme end of the periodic table. To this end we perform studies of chemical properties of these transactinides and compare them with those of their lighter homologues and with the ones expected from extrapolations in the periodic table. So far, chromatographic studies of the transactinides have provided experimental proof of placing rutherfordium (Rf, Z = 104) through hassium (Hs, Z = 108) into groups 4 to 8, respectively. 1-10 Quite recently, copernicium (Cn, Z = 112) has been shown to be a…

Radiochemical Studies of Complex Nuclear Reactions

Study of non-fusion products in the 50Ti + 249Cf reaction

Physics letters / B B 784, 199 - 205 (2018). doi:10.1016/j.physletb.2018.07.058

Titelbild: Uran aus deutschen Nuklearprojekten der 1940er Jahre – eine nuklearforensische Untersuchung (Angew. Chem. 45/2015)

The impact of the properties of the heaviest elements on the chemical and physical sciences

Abstract The unique role of the heaviest elements in chemical and physical sciences is discussed. With the actinide series (Z = 90-103) and the superactinide series (Z = 122-155), the heaviest elements have significantly shaped the architecture of the Periodic Table of the elements. Relativistic effects in the electron shells of the heaviest elements change the chemical properties in a given group in a non-linear fashion. Relativistically stabilized sub-shell closures give rise to a new category of elements in the Periodic Table: volatile metals. The prototype for this property is element 114 which, due to the relativistic stabilization of its 7s2 7p2 1/2 electron configuration, is volatile…

8He-6He: a comparative study of nuclear fragmentation reactions

19 pages, 3 tables, 6 figures.-- PACS nrs.: 27.20.+n; 24.70.+s; 25.06.-t.-- Available online Dec 4, 2000.

MicroSISAK: continuous liquid–liquid extractions of radionuclides at 0.2 mL/min

Abstract Continuous liquid–liquid extraction of short-lived radionuclides has traditionally been performed with the SISAK system consisting of static mixers and H-centrifuges for phase separation. SISAK operates at flow rates of typically 1 mL/s. Thus, it produces large volumes of radioactive liquid waste that is difficult to dispose of. Therefore, it has been aimed to develop and use a further miniaturised extraction unit based on microtechnology and precision engineering to reduce the flow rate by at least two orders of magnitude. The accordingly developed MicroSISAK device is a micro membrane extractor in which a micromixer element with 2 × 16 feed channels of 30 µm width followed by a 6…

Direct Experimental Verification of Neutron Acceleration by the Material Optical Potential of SolidH22

We have measured the acceleration of neutrons by the material optical potential of solid $^{2}\mathrm{H}_{2}$. Using a gravitational spectrometer, we find a minimal kinetic energy ${E}_{c}=(99\ifmmode\pm\else\textpm\fi{}7)\text{ }\text{ }\mathrm{neV}$ of neutrons from a superthermal ultracold neutron (UCN) source with solid $^{2}\mathrm{H}_{2}$ as an UCN converter. The result is in excellent agreement with theoretical predictions, ${E}_{c}=106\text{ }\text{ }\mathrm{neV}$.

First Observation of the Unbound NucleusNe15

We report on the first observation of the unbound proton-rich nucleus Ne-15. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u Ne-17. The Ne-15 ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to O-13 with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2(-) and 1(-) states in F-14 is observed. The Ne-15 ground state is shown to have a strong configuration with two protons in the (sd) shell around O-13 with a 63(5)% (1s(1/2))(2) component.

He-8 - He-6: a comparative study of electromagnetic fragmentation reactions

14 pages, 1 table, 2 figures.-- PACS nrs.:27.20.+n; 24.70.+.-- Available online Oct 8, 2001.

Erratum to "Determination of the irradiation field at the research reactor TRIGA Mainz for BNCT" [J. Appl. Radiat. Isot. 67 (2009) S242-S246].

Unveiling the two-proton halo character of 17Ne: Exclusive measurement of quasi-free proton-knockout reactions

7 pags., 5 figs.

The dipole response of nuclei with large neutron excess

The dipole response of neutron-rich nuclei in the mass range from A = 10 to A = 22 and with mass to charge ratios of 2.5 to 2.8 has been invesitigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies around 600 MeV/u.

Gas phase synthesis of 4d transition metal carbonyl complexes with thermalized fission fragments in single-atom reactions

Abstract The formation of carbonyl complexes using atom-at-a-time quantities of short-lived transition metals from fusion and fission reactions was reported in 2012. Numerous studies focussing on this chemical system, which is also applicable for the superheavy elements followed. We report on a novel two-chamber approach for the synthesis of such complexes that allows spatial decoupling of thermalization and gas-phase carbonyl complex synthesis. Neutron induced fission on 235U and spontaneous fission of 248Cm were employed for the production of the fission products. These were stopped inside a gas volume behind the target and flushed with an inert-gas flow into a second chamber. This was fl…

Fluoride complexation of rutherfordium (Rf, element 104)

The fluoride complexation of the group-4 elements Zr, Hf and Rf, and of the pseudo-homolog Th, has been investigated in mixed HNO3/HF solutions by studying Kd values on both cation exchange resins (CIX) and anion exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the four elements are strongly retained as cations below 10-3M HF. For Zr and Hf, the decrease of the Kd values due to the formation of fluoride complexes occurs between 10-3M HF and 10-2M HF. For Rf and Th, this decrease is observed at one order of magnitude higher HF concentrations. On the AIX, for Zr and Hf, a rise of the Kd values due to the formation of anionic fluoride complexes is observed …

Synthesis and Characterization of the Hybrid Clay-Based Material Montmorillonite-Melanoidin: A Potential Soil Model

The study of the interactions among metals, minerals, and humic substances is essential in understanding the migration of inorganic pollutants in the geosphere. A considerable amount of organic matter in the environment is associated with clay minerals. To understand the role of organic matter in the environment and its association with clay minerals, a hybrid clay-based material (HCM), montmorillonite (STx-1)-melanoidin, was prepared from L-tyrosine and L-glutamic acid by the Maillard reaction. The HCM was characterized by elemental analysis, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), scanning transmission x-ray microscopy (STXM), and thermal analysis. The presence…

Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence.

Towards a new measurement of the neutron electric dipole moment

International audience; The effort towards a new measurement of the neutron electric dipole moment (nEDM) at the Paul Scherrer Institut's (PSI) new high intensity source of ultracold neutrons (UCN) is described. The experimental technique relies on Ramsey's method of separated oscillatory fields, using UCN in vacuum with the apparatus at ambient temperature. In the first phase, R&D towards the upgrade of the RAL/Sussex/ILL apparatus is being performed at the Institut Laue-Langevin (ILL). In the second phase the apparatus, moved from ILL to PSI, will allow an improvement in experimental sensitivity by a factor of 5. In the third phase, a new spectrometer should gain another order of magnitud…

Chemical Properties of Element 105 in Aqueous Solution: Halide Complex Formation and Anion Exchange into Triisoctyl Amine

Studies of the halide complexation of element 105 in aqueous solution were performed on 34-s 262Ha produced in the 249Bk(18-O,5n) reaction. The 262Ha was detected by measuring the fission and alpha activities associated with its decay and the alpha decays of its daughter, 4.3-s 258Lr. Time-correlated pairs of parent and daughter alpha particles provided a unique identification of the presence of 262Ha. About 1600 anion exchange separations of 262Ha from HCl and mixed HC1/HF solutions were performed on a one-minute time scale. Reversed-phase micro-chromatographic columns incorporating triisooctyl amine (TIOA) on an inert support were used in the computer-controlled liquid chromatography appa…

Fusion reaction Ca48+Bk249 leading to formation of the element Ts ( Z=117 )

The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48Ca with the radioactive target 249Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293Ts. The present experimental results confi…

Determination of the first ionization potential of einsteinium by resonance ionization mass spectroscopy (RIMS)

Abstract The first ionization potential of einsteinium (IP Es ) was determined by resonance ionization mass spectroscopy (RIMS) using samples with ≤10 12 atoms of 254 Es ( T 1/2 =276 days). This method is based on the measurement of photoionization thresholds as a function of applied electric field strength, followed by extrapolation to zero field strength to yield IP Es . An atomic beam of Es was created by heating a filament on which einsteinium was electrodeposited from an aqueous solution onto a tantalum backing and covered with titanium metal. Es atoms were ionized via a three-step excitation scheme, and the ions mass-selectively detected in a time-of-flight (TOF) mass spectrometer. Th…

The application of neutron activation analysis, scanning electron microscope, and radiographic imaging for the characterization of electrochemically deposited layers of lanthanide and actinide elements

Lanthanide and actinide targets are prepared at the University of Mainz by molecular plating, an electrochemical deposition from an organic solvent, for heavy-ion reaction studies at GSI. To acquire information about deposition yield, target thickness, and target homogeneity, the following analysis methods are applied. With neutron activation analysis (NAA) the deposition yield and the average thickness of the deposited material is determined. We report on the analytical procedure of NAA performed subsequent to the molecular plating process. Scanning electron microscope (SEM) is used to determine the morphology of the target surfaces. In combination with energy dispersive X-ray spectrometer…

Study of non-fusion products in the Ti50+Cf249 reaction

The isotopic distribution of nuclei produced in the 50Ti + 249Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not ex…

Charge-Asymmetry Equilibration in the Reaction ofXe129,132,136withAu197near the Interaction Barrier

Neutron-proton population ratios for quasielastic and inelastic processes in the reactions of 761-MeV $^{129}\mathrm{Xe}$, 769-MeV $^{132}\mathrm{Xe}$, and 795-MeV $^{136}\mathrm{Xe}$ ions with thick $^{197}\mathrm{Au}$ targets were determined radiochemically. Completely relaxed $\frac{N}{Z}$ ratios are observed for damped collisions involving the transfer of $\ensuremath{\Delta}Zg~1$ charge units. The limiting condition $\ensuremath{\Delta}Z\ensuremath{\approx}1$ corresponds to a characteristic time of the order of ${10}^{\ensuremath{-}22}$ sec which indicates the absence of dissipative forces in the equilibration of the charge-asymmetry mode.

Spectroscopy along Flerovium Decay Chains: Discovery ofDs280and an Excited State inCn282

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made eleme…

Production of monodisperse uranium oxide particles and their characterization by scanning electron microscopy and secondary ion mass spectrometry

Abstract Secondary ion mass spectrometry (SIMS) can be confidently used to measure uranium isotopic ratios in single particles. Dense particles of known isotopic composition and size allow the precision and the accuracy of the applied procedure to be estimated. These particles can be obtained by dissolving standard reference uranium materials, nebulizing the solution in droplets of proper diameter and collecting the particles after the desolvation and calcination of the droplets. A new instrumental set up, based on a commercial vibrating orifice aerosol generator to generate monodisperse droplets of the solutions from four uranium oxide reference materials, is described. The droplets were d…

Investigation of the (d, p)-reaction on136, 132Xe in inverse kinematics

The one-neutron transfer reactions d(132,136 Xe, p)133,137 Xe have been investigated in inverse kinematics with xenon beams incident on deuterium loaded titanium targets. The angular distributions of the protons, measured with a detector array of 100 PIN-photodiodes, have been analyzed using standard DWBA. Generally, good agreement is obtained with results previously obtained in reactions induced by light-ion beams.

Coulomb and nuclear excitations of narrow resonances in 17Ne

Physics letters / B 759, 200 - 205 (2016). doi:10.1016/j.physletb.2016.05.073

To identify the atomic number of superheavy nuclei produced in Ca-48-induced fusion-evaporation reactions, an experiment aiming at measuring characteristic X-rays is being prepared at GSI, Darmstadt, Germany. The gas-filled separator TASCA will be employed, sending the residues towards the multi-coincidence detector setup TASISpec. Two ion-optical modes relying on differing magnetic polarities of the quadrupole magnets can be used at TASCA. New simulations and experimental tests of transmission and background suppression for these two focusing modes into TASISpec are presented.

Recent developments in and applications of resonance ionization mass spectrometry

Resonance Ionization Mass Spectrometry (RIMS) has nowadays reached the status of a routine method for sensitive and selective ultratrace determination of long-lived radioactive isotopes in environmental, biomedical and technical samples. It provides high isobaric suppression, high to ultra-high isotopic selectivity and good overall efficiency. Experimental detection limits are as low as 106 atoms per sample and permit the fast and sensitive determination of ultratrace amounts of radiotoxic contaminations. Experimental arrangements for the detection of different radiotoxic isotopes, e.g. 236–244Pu, 89,90Sr and 99Tc in environmental samples are described, and the application of RIMS to the ul…

Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS)

The high sensitivity of RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of ≤1012 atoms. By multiple resonant laser excitation, the actinide atoms under investigation are ionized in the presence of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold Wth—indicated by a sudden increase of the ion count rate—at various electric field strengths. Extrapolation of Wth to electric field strength zero leads directly to the first ionization potent…

Study of the average charge states of 188Pb and 252,254No ions at the gas-filled separator TASCA

The average charge states of Pb-188 and No-252,No-254 ions in dilute helium gas were measured at the gas-filled recoil separator TASCA. Hydrogen gas was also used as a filling gas for measurements of the average charge state of No-254. Helium and hydrogen gases at pressures from 0.2 mbar to 2.0 mbar were used. A strong dependence of the average charge state on the pressure of the filling gases was observed for both, helium and hydrogen. The influence of this dependence, classically attributed to the so-called "density effect", on the performance of TASCA was investigated. The average charge states of No-254 ions were also measured in mixtures of helium and hydrogen gases at low ga…

Absence of delayed fission in the? ?-decay of 2.3 min238Pa

We have searched for beta-delayed fission in the decay of 2.3 min238Pa produced in the238U(n,p) reaction with 14.7 MeV neutrons. Through microprocessor-controlled chemical separations of protactinium about 109 atoms of238Pa were isolated and exposed to fission track detectors. From the absence of fission tracks an upper limit for the betadelayed fission probability of238Pa, i.e.Pβf<2.6 10−8, is obtained at 95% confidence level. This rules out positive evidence for this decay mode of238Pa reported elsewhere. Simple theoretical estimates ofPβf range from 10−7 to 10−9.

Additional results from the first dedicated search for neutron–mirror neutron oscillations

International audience; The existence of a mirror world holding a copy of our ordinary particle spectrum could lead to oscillations between the neutron (n) and its mirror partner (n′). Such oscillations could manifest themselves in storage experiments with ultracold neutrons whose storage lifetime would depend on the applied magnetic field. Here, extended details and measurements from the first dedicated experimental search for nn′ oscillations published in [G. Ban, K. Bodek, M. Daum, R. Henneck, S. Heule, M. Kasprzak, N. Khomutov, K. Kirch, S. Kistryn, A. Knecht, P. Knowles, M. Kuźniak, T. Lefort, A. Mtchedlishvili, O. Naviliat-Cuncic, C. Plonka, G. Quéméner, M. Rebetez, D. Rebreyend, S. R…

Longitudinal and transverse momentum distributions of 9Li fragments from break-up of 11Li

7 pages, 3 figures, 1 table.

117番元素Ts合成のための48Ca+249Bk融合反応

We have performed an experiment to synthesize the element 117 (Ts) with the $^{48}$Ca+$^{249}$Bk fusion reaction. Four $\alpha$-decay chains attributed to the element 117 were observed. Two of them were long decay chains which can be assigned to the one originating from the $\alpha$ decay of $^{294}$Ts. The other two were short decay chains which are consistent with the one originating from the $\alpha$ decay of $^{293}$Ts. We have compared the present results with the literature data, and found that our present results mostly confirmed the literature data, leading to the firm confirmation of the synthesis of the element 117.

Electromagnetic and nuclear fission of238U in the reaction of 100, 500, and 1000 A�MeV208Pb with238U

The folding- and azimuthal-angle and velocity distributions for the238U fission fragments have been measured in reactions with 100, 500, and 1000 A·MeV208Pb. These distributions were used to decompose the fission cross section into its electromagnetic and nuclear components. The fraction of electromagnetic fission was found to be 0.16±0.07, 0.48±0.08, and 0.60±0.04, respectively. The electromagnetic fission cross section as a function of the208Pb nucleus energy is compared with theoretical predictions. The measured fission cross section from nuclear reactions (≈1.5 b) is approximately constant between 100 and 1000 A·MeV.

A rotating wheel system for the detection of spontaneously fissioning nuclides from heavy ion reactions

Abstract A rotating wheel system for the detection of spontaneously fissioning reaction products from heavy ion reactions was developed. In this system products recoiling from a rotating target wheel are stopped in a catcher foil stack which can be rotated at various velocities up to 80 rotations per second. All products emitted within a wide emission cone are stopped in the catcher foils and are rotated into shielded positions with stationary fission-track detectors positioned on both sides of each rotating foil. This technique allows a sensitive detection of spontaneously fissioning nuclides over a broad range of half-lives from 1 ms to about 1 d. By post-bombardment exposure of the catch…