Alpha decay studies of very neutron deficient isotopes of Hf, Ta, W, and Re

Abstract

Very neutron deficient isotopes in the Hf-Re region were produced by bombarding targets of 1~176 nat'l~176 and l~ with 5SNi accelerated by the linear accelerator UNILAC at GSI. After separation from the projectile beam by the velocity filter SHIP, the fusion products were implanted with their full recoil energy into a silicon surface barrier detector. The subsequent alpha decay of the implanted ions was measured with the same detector. In some of the experiments the evaporation residues were implanted into a position sensitive silicon surface barrier detector. With a newly developed position and time correlation technique parent daughter relationships, half lives, and ~ branching ratios of a large number of isotopes could be determined. In the investigated reactions the eleven new isotopes 161-164Re, 16~157-161Ta, and 156Hf could be identified. The measured Q~ values, half lives, and ~ branching ratios are discussed. Two new high energy c~ transitions of (7,408+10) keV and (7,804_+ 15) keV were also found with half lives of 2.7 ms and 0.52 ms, respectively. A tentative mass and atomic number assignment gives A = 153-156 and Z =70-72. The energies of the excited isomeric states are between 2 MeV and 3 MeV. From the systematics of alpha ground state transitions in even nuclei a hindrance of l0 s can be deduced for both transitions, possibly indicating orbital angular momenta on the order of 10h for the alpha emitting states. The isomers are proposed to belong to shell model isomers beyond la6Gd.

Decay of201–203Raand200–202Fr

“…[17] for more details on the correlation method). The position difference between an ER implantation and its α decay (ER-α1 correlations) and between two subsequent α decays (α1-α2 correlations) was required to be within ±0.5 mm.…”

αdecay ofAu176

“…After separation by SHIP, the evaporation residues (ERs) were implanted into a 300 μm thick, 35 × 80 mm 2 16-strip position-sensitive silicon strip detector (PSSD), where their subsequent α decays were measured by using standard implantation and correlation techniques [12]. For the PSSD energy calibration we used known α-decay lines of the isotopes 176-182 Hg (and their daughters), produced in the 40 Ca + 144 Sm → 184 Pb * reaction, which was studied in the same experiment prior to the irradiation of the 141 Pr target.…”

Synthesis of superheavy elements by cold fusion

“…Since higher overall yields result in increased background The velocity filter SHIP (Separator for Heavy Ion reaction Products) and its detection system [13][14][15]. The drawing is approximately to scale; however, the target wheel and the detectors are enlarged by a factor of two.…”

“…This is the case because the recoil effects are small compared with the range of implanted nuclei, emitted α particles or fission products, and detector resolution. Recording the data event by event allows for the analysis of delayed coincidences with variable position and time windows for the identification of the decay chains [14].…”

“…However, as soon as relevant experiments could be performed, it turned out that the most successful methods for the laboratory synthesis of heavy elements are fusion-evaporation reactions using heavy-element targets, recoil-separation techniques, and the identification of the nuclei by generic ties to known daughter decays after implantation into position-sensitive detectors [13][14][15].…”