A computer code has been developed to simulate the production of heavy element compound nucleus recoils and their trajectories through gas-filled magnetic separators. The simulation is carried out in ...three steps: positions and trajectories of heavy element recoils in the target layer, propagation through remaining target material, and trajectories through the gas-filled separator. Separators with quite different magnetic configurations are modeled: the Berkeley gas-filled separator (BGS) and two magnetic configurations for the TransActinide separator and chemistry apparatus (TASCA). While computing trajectories through the gas-filled separator, special attention is paid to the charge exchange/equilibration and scattering in the gas. New features of these simulations include mixed He/H2/N2 gas operation and a gas density (pressure) effect. Numerical procedures used in the simulations are explained in detail. Results of the simulations are presented, showing the gas mixtures/pressures that result in the highest efficiency for collecting compound nucleus recoils at the focal plane of the gas-filled separator. Comparison between simulation and experimental results are presented for average recoil ion charge in various gases, focal plane image size, and magnetic rigidity dispersion.
An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two ...α-decay chains, produced via the ^{243}Am(^{48}Ca,xn)^{291-x}Mc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to ^{284}Nh (Z=113), the α-decay daughter of ^{288}Mc (Z=115), while the second occurred at A/q=288 and was assigned to ^{288}Mc. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.
The heaviest elements are synthesized in heavy-ion induced hot fusion reactions with various actinide targets. Because the actinide material is often available only in very limited amounts, a ...deposition method with high yields (~90 %) is needed. We report on the production of
244
Pu,
243
Am,
248
Cm,
249
Bk, and
249
Cf targets on thin Ti backings by molecular plating. Different chemical purification steps using ion chromatographic techniques were applied for the purification of
249
Cf and
244
Pu. The deposition procedure applied for the production of ~0.4–0.8 mg/cm
2
thick targets is described. The deposition yield was determined either by α-particle or γ-ray spectroscopy. Furthermore, neutron activation analysis has been applied in the case of
244
Pu,
243
Am, and
248
Cm. Information about the spatial distribution and homogeneity of the target layer was obtained by radiographic imaging.
Search for elements 119 and 120 Khuyagbaatar, J.; Yakushev, A.; Düllmann, Ch. E. ...
Physical review. C,
12/2020, Letnik:
102, Številka:
6
Journal Article
Recenzirano
Odprti dostop
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 predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.
Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made ...possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}624,9/2^{-}734) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}624,9/2^{-}734)⊗8^{-}π^{2}(7/2^{-}514,9/2^{+}624) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.
Recent discussions about the origin of the so-called gallium anomaly have motivated a remeasurement of the half-life of 71Ge. Here, we have conducted three separate measurements using dedicated ...planar Ge detectors—one with 55Fe as a standard, one with 57Co as a standard, and one standalone 71Ge measurement. Our results yield a half-life of 11.468±0.008 days, which is consistent with, but significantly more precise than, the currently accepted value. With this experiment, the potential explanation of the gallium anomaly being due to an unexpectedly long 71Ge half-life has been ruled out, leaving the anomaly's origin as an open question.
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