0000000000023494
AUTHOR
Robert Hoischen
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…
β−-delayed spectroscopy of neutron-rich tantalum nuclei: Shape evolution in neutron-rich tungsten isotopes
The low-lying structure of W-188,W-190,W-192 has been studied following beta decays of the neutron-rich mother nuclei Ta-188,Ta-190,Ta-192 produced following the projectile fragmentation of a 1-GeV-per-nucleon Pb-208 primary beam on a natural beryllium target at the GSI Fragment Separator. The beta-decay half-lives of Ta-188, Ta-190, and Ta-192 have been measured, with gamma-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion beta-gamma correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in W-188, W-190, and W-192, which highlight a change in nuclear shape at W-190 compared with that of …
Quantum-state-selective decay spectroscopy of Ra213
An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a $^{48}\mathrm{Ca}$ beam impinging on a thin $^{170}\mathrm{Er}$ target foil. Subsequent to velocity filtering of reaction products in the Separator for Heavy Ion reaction Products (SHIP), the nuclear ground state of the $5n$ evaporation channel $^{213}\mathrm{Ra}$ was mass-selected in SHIPTRAP, and the $^{213}\mathrm{Ra}$ ions were finally transferred into an array of silicon strip detectors surrounded by large composite germanium detectors. Based on comprehensive geant4 s…
Nuclear structure “southeast” ofPb208: Isomeric states inHg208andTl209
The nuclear structure of neutron-rich N>126 nuclei has been investigated following their production via relativistic projectile fragmentation of a E/A=1 GeV U-238 beam. Metastable states in the N=128 isotones Hg-208 and Tl-209 have been identified. Delayed gamma-ray transitions are interpreted as arising from the decay of I-pi=(8(+)) and (17/2(+)) isomers, respectively. The data allow for the so far most comprehensive verification of the shell-model approach in the region determined by magic numbers Z 126.
β-delayedγ-ray spectroscopy of203,204Au and200−202Pt
The beta decay of five heavy, neutron-rich nuclei, Pt-203,Pt-204 and Ir200-202, has been investigated following relativistic cold fragmentation reactions of lead projectiles using the FRS + RISING setup at GSI. This paper reports on the study of the low-lying states in the decay daughter nuclei Au-203,Au-204 and Pt200-202. The characteristic gamma rays for each nucleus have been determined using beta-delayed gamma-ray spectroscopy. Tentative level schemes, relative intensities, and apparent beta feedings are provided. These data are compared with shell-model calculations, which indicate a substantial contribution to the total beta strength from high-energy first-forbidden beta-decay transit…
'beta'-decay studies of neutron-rich 'TL', 'PB', and 'BI' isotopes
The fragmentation of relativistic uranium projectiles has been exploited at the Gesellschaft fur Schwerionenforschung laboratory to investigate the β decay of neutron-rich nuclei just beyond 208Pb. This paper reports on β-delayed γ decays of 211-213Tl, 215Pb, and 215-219Bi de-exciting states in the daughters 211-213Pb, 215Bi, and 215-219Po. The resulting partial level schemes, proposed with the help of systematics and shell-model calculations, are presented. The role of allowed Gamow-Teller and first-forbidden β transitions in this mass region is discussed. © 2014 American Physical Society.
Multipleβ−decaying states in194Re: Shape evolution in neutron-rich osmium isotopes
decays from heavy, neutron-rich nuclei with A∼190 have been investigated following their production via the relativistic projectile fragmentation of an E/A=1 GeV 208Pb primary beam on a ∼2.5 g/cm2 9Be target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. γ decays were observed and correlated with these secondary ions on an event-by-event basis such that γ-ray transitions following from both internal (isomeric) and β decays were recorded. A number of discrete, β-delayed γ-ray transitions associated with β decays from 194Re to excited states in 194Os have been observed, including previously reported decays …
Tz=−1→0βdecays ofNi54,Fe50,Cr46, andTi42and comparison with mirror(He3,t)measurements
We have studied the β decay of the Tz=−1, f7/2 shell nuclei Ni54, Fe50, Cr46, and Ti42 produced in fragmentation reactions. The proton separation energies in the daughter Tz=0 nuclei are relatively large (≈4–5 MeV) so studies of the γ rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision β-decay half-lives, excitation energies, and β branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these β decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths …
Isospin symmetry in thesdshell: Transition strengths in the neutron-deficientsdshell nucleusAr33
Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the ou…
FIRST RESULTS WITH THE RISING ACTIVE STOPPER
This paper outlines some of the physics opportunities available with the GSI RISING active stopper and presents preliminary results from an experiment aimed at performing beta-delayed gamma-ray spectroscopic studies in heavy-neutron-rich nuclei produced following the projectile fragmentation of a 1 GeV per nucleon 208 Pb primary beam. The energy response of the silicon active stopping detector for both heavy secondary fragments and beta-particles is demonstrated and preliminary results on the decays of neutron-rich Tantalum ( Ta ) to Tungsten ( W ) isotopes are presented as examples of the potential of this technique to allow new structural studies in hitherto experimentally unreachable he…
Half-Life Systematics across theN=126Shell Closure: Role of First-Forbidden Transitions in theβDecay of Heavy Neutron-Rich Nuclei
This Letter reports on a systematic study of β-decay half-lives of neutron-rich nuclei around doubly magic Pb208. The lifetimes of the 126-neutron shell isotone Pt204 and the neighboring Ir200-202, Pt203, Au204 are presented together with other 19 half-lives measured during the "stopped beam" campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of r-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden β strength reveal significant deviations for most of the nuclei with N<126. In contrast, theories including a fully microscopic treatment of allowed and first…
βdecay of102Y produced in projectile fission of238U
The population of 102Zr following the β decay of 102Y produced in the projectile fission of 238U at the GSI facility in Darmstadt, Germany has been studied. 102Y is known to ß decay into 102Zr via two states, one of high spin and the other low spin. These states preferentially populate different levels in the 102Zr daughter. In this paper the intensities of transitions in 102Zr observed are compared with those from the decay of the low-spin level studied at the TRISTAN facility at Brookhaven National Laboratory and of the high-spin level studied at the JOSEF separator at the Kernforschungsanlage Jülich.
Angular momentum population in fragmentation reactions
Neutron-deficient nuclei with N = 126 have been populated following projectile fragmentation of a 238U beam with energy 1 GeV/A. The decay of several previously reported isomers has been measured. This will allow us to calculate high-spin isomeric ratios and compare them with model calculations to allow a better understanding of the reaction mechanism. Algora, Alejandro, Alejandro.Algora@ific.uv.es ; Molina Palacios, Francisco Manuel, Francisco.Molina@ific.uv.es ; Rubio Barroso, Berta, Berta.Rubio@ific.uv.es
Superallowed Gamow-Teller decay of the doubly magic nucleus $^{100}$Sn
Expérience au GSI; The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During b1-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy fo…
Isomeric decay spectroscopy of theBi217isotope
The structure of the neutron-rich bismuth isotope 217Bi has been studied for the first time. The fragmentation of a primary 238U beam at the FRS-RISING setup at GSI was exploited to perform γ-decay spectroscopy, since μs isomeric states were expected in this nucleus. Gamma rays following the decay of a t1/2=3 μs isomer were observed, allowing one to establish the low-lying structure of 217Bi. The level energies and the reduced electric quadrupole transition probability B(E2) from the isomeric state are compared to large-scale shell-model calculations.
Relativistic Coulomb excitation of Kr 88
International audience; To investigate the systematics of mixed-symmetry states in N=52 isotones, a relativistic Coulomb excitation experiment was performed during the PreSPEC campaign at the GSI Helmholtzzentrum für Schwerionenforschung to determine E2 transition strengths to 2+ states of the radioactive nucleus $^{88}$Kr. Absolute transition rates could be measured towards the first and third 2+ states. For the latter a mixed-symmetry character is suggested on the basis of the indication for a strong M1 transition to the fully symmetric 21+ state, extending the knowledge of the N=52 isotones below Z=40. A comparison with the proton-neutron interacting boson model and shell-model predictio…
New μs Isomers in the Neutron-rich 210Hg Nucleus
Neutron-rich nuclei in the lead region, beyond N = 126, have been studied at the FRS-RISING setup at GSI, exploiting the fragmentation of a primary uranium beam. Two isomeric states have been identified in Hg-210: the 8(+) isomer expected from the seniority scheme in the vg(9/2) shell and a second one at low spin and low excitation energy. The decay strength of the 8(+) isomer confirms the need of effective three-body forces in the case of neutron-rich lead isotopes. The other unexpected low-lying isomer has been tentatively assigned as a 3(-) state, although this is in contrast with theoretical expectations. (C) 2013 Elsevier B.V. All rights reserved.
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…