Excited states in neutron-deficient iridium nuclei populated in radioactive decays ofPt177–181

Abstract

The radioactivity of neutron-deficient platinum isotopes Pt was studied after the production in Nd( Ar, zn) andNd( Ar, zn) reactions. The P-decay branches were identified by the detection of p transitions in the iridium daughter nuclei. We report p rays, pp coincidences, and halflives. Ground and excited states are discussed in terms of the single-particle structure in deformed nuclei and new results are presented for the systematics of the intruder h9/2 band and d3/2 states in iridium.PACS number(s): 27.70. +q, 23.20.Lv Neutron-deficient isotopes below the magic Z = 82 nuclei are particularly interesting for nuclear structure studies. They are located in a transitional region where the nuclear shape changes from well deformed to the shell-model lead nuclei. Assignments of deformed singleparticle Nilsson states had been derived from the identification of unhindered n decays [1,2] or from the iiivestigation of rotational bands observed in nuclear reactions in beam [3 -6]. P-decay studies may also give structure information since the transition probabilities to states in the daughter nuclei are closely related to the intrinsic level structure.In our systematic decay studies of hafnium-toplatinum isotopes, two interesting aspects are noted.First, the prolate-deformed lisy2 2 [541] proton orbital intrudes from beyond the Z =82 shell gap. It has been well established in neutron-deficient lutetium (Z =71) to gold (Z =79) nuclei [7 -10] and plays an important role in the rhenium (Z =75) and iridium (Z =77) isotopes [ll -13], where the actual knowledge on level structure is very scarce. Second, the vicinity of deformed states originating from the major d3y2 and hzig2 shells and the hgy2[541] orbital gives rise to a new island of long-lived isomers which has recently been discovered in decay studies of rhenium and iridium nuclei [12, 13].The earlier identification of these isotopes in the very neutron-deficient region was favored due to the strong o.-decay branches and the appealing features of o. spectroscopy such as low background, high detection eKciency, and good energy resolution. Today, using highly efficient detection and coincidence techniques, the Pdecay branches are also experimentally accessible.We report here on the P decays of neutron-deficient platinum isotopes Pt, which were identified by spectroscopy of p rays depopulating levels in the iridium daughter nuclei. The platinum isotopes were produced in fusion-evaporation reactions of highly enriched, 2.3 mg/cm thick sNd and Nd targets and a beam of Ar ions, provided by the VICKSI accelerator facility of the Hahn-Meitner-Institut in Berlin. The initial beam energy of 240 MeV was reduced in the entrance window of the reaction chamber and could further be reduced stepwise by additional tantalum degraders in front of the target. The mean energy in the middle of the target was thereby varied in the range 173 -201 MeV.The recoiling evaporation residues were thermalized and swept out of the reaction chamber with a He/NaC1 gas-jet flow. The samples were periodical...

α -decay branching ratio of Pt180

“…3 is the δ 2 α = 156(10)-keV value for 178 Pt (N = 100) which is ≈30% larger than those of other platinum isotopes in the saturation region. The T 1/2 ( 178 Pt) [30][31][32] and b α ( 178 Pt) [33,34] values from different studies are consistent with one another, which suggests that the experimental δ 2 α ( 178 Pt) value is reliable. Therefore the jump in δ 2 α could possibly be related to the change in deformation when going from 178 Pt to 180 Pt [35], and related to the possible change in the configuration mixing in the corresponding ground states [20,36,37].…”

Nuclear structure of $$^{181}$$Au studied via $$\upbeta ^+$$/EC decay of $$^{181}$$Hg at ISOLDE

“…The α decay of the 181,183,185 Au isotopes was studied at the UNISOR facility [53]. While the 183,185 Au isotopes have a similar decay pattern with dominant 5/2 − ground-state-to-ground-state unhindered α decay, the unhindered α decay of 181 Au dominantly feeds the 3/2 − excited state [54]. This suggests a 3/2 − assignment for the ground state of 181 Au.…”