0000000001289930
AUTHOR
A. Hübner
The identification and confirmation of isomeric states in 254Rf and 255Rf through conversion electron detection
Abstract The neutron-deficient isotopes 254,255Rf were produced in the fusion-evaporation reaction 50Ti + 206Pb at the gas-filled recoil separator TASCA. Decay properties of these nuclei were investigated by applying fast digital electronics. A search for isomeric states in both isotopes was performed by using the accompanying conversion electron emissions. Isomeric states with half-lives of 4(1) μs and >30 μs were measured for 254Rf and 255Rf, respectively, which confirm the findings at different separators. The present experimental results demonstrate the great potential of fast digital electronics for measurements of isomeric states in the heaviest nuclei, which are only producible in sm…
First Study on Nihonium (Nh, Element 113) Chemistry at TASCA
Frontiers in Chemistry 9, 753738 (2021). doi:10.3389/fchem.2021.753738
Backings and targets for chemical and nuclear studies of transactinides with TASCA
Abstract At GSI the gas-filled separator TASCA (TransActinide Separator and Chemistry Apparatus) was set up to investigate the chemical and physical properties of the heaviest elements making use of the highest beam intensities available [ www.gsi.de/tasca ; M. Schadel, D. Ackermann, A. Semchenkov, A. Turler, GSI Scientific Report 2005, GSI Report 2006-1, p. 262]. Appropriate backings and targets have to be developed. Conceivable backing materials are aluminium, titanium, and carbon. Aluminium backings and titanium backings in different thickness and from different companies are produced by cold rolling. Deposition by resistance heating is applied for carbon backings. For experiments in a c…
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…
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…
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…
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…
On the adsorption and reactivity of element 114, flerovium
Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its interaction with gold was investigated in two gas-solid chromatography experiments, which reported two different types of interaction, however, each based on the level of a few registered atoms only. Whereas noble-gas-like properties were suggested from the first experiment, the second one pointed at a volatile-metal-like character. Here, we present further experimental data on adsorption studies of Fl on silicon oxide and gold surfaces, accounting for the inhomogeneous nature of the surface, as it was used in the experiment and analyzed as part of the reported studies. We confirm that Fl is highly v…
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…
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…
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…
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
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…
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…
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.