Kr369660 –Low- Z Boundary of the Island of Deforma

Abstract

Prompt γ-ray spectroscopy of the neutron-rich ^{96}Kr, produced in transfer- and fusion-induced fission reactions, has been performed using the combination of the Advanced Gamma Tracking Array and the VAMOS++ spectrometer. A second excited state, assigned to J^{π}=4^{+}, is observed for the first time, and a previously reported level energy of the first 2^{+} excited state is confirmed. The measured energy ratio R_{4/2}=E(4^{+})/E(2^{+})=2.12(1) indicates that this nucleus does not show a well-developed collectivity contrary to that seen in heavier N=60 isotones. This new measurement highlights an abrupt transition of the degree of collectivity as a function of the proton number at Z=36, of similar amplitude to that observed at N=60 at higher Z values. A possible reason for this abrupt transition could be related to the insufficient proton excitations in the g_{9/2}, d_{5/2}, and s_{1/2} orbitals to generate strong quadrupole correlations or to the coexistence of competing different shapes. An unexpected continuous decrease of R_{4/2} as a function of the neutron number up to N=60 is also evidenced. This measurement establishes the Kr isotopic chain as the low-Z boundary of the island of deformation for N=60 isotones. A comparison with available theoretical predictions using different beyond mean-field approaches shows that these models fail to reproduce the abrupt transitions at N=60 and Z=36.

Excitations of the magic N=50 neutron-core revealed in Ga81

“…More experimental details are given in Ref. [46]. Figure 1 shows the atomic charge and mass distributions for A = 81 and Z = 31 isotopes, observed in coincidence with γ rays in this experiment.…”

Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni78 Region: A Hint from Lifetime Measurements

“…The fission fragments were identified and their velocities were determined with the magnetic spectrometer VAMOS++ [17], placed at 28°with respect to the beam direction, using the procedure already described in Ref. [18]. A total of ≈1.5 × 10 7 fissionfragment events were identified out of which the 88 Kr, PHYSICAL REVIEW LETTERS 121, 192502 (2018) 192502-2 86 Se, and 84 Ge residues represented 3.0%, 1.7%, and 0.06%, respectively.…”

Lifetime Measurements Using RDDS Method in the Vicinity of $^{78}$Ni

“…Since the first indications from the trends in the first 2 + energies in Zr [2] and Sr [3] decades ago, studies of transition strengths and moments have most recently cemented a picture of a sudden increase in collectivity and shape changes for Sr [4], and a quantum phase transition in the shape of the Zr isotopes [5] at N = 60. In the Kr isotopic chain, just four and two protons below Zr and Sr, respectively, a rather gradual onset of collectivity towards N = 60 was concluded from mass measurements [6], Coulomb excitation [7], and fast-timing measurements [8], placing the N = 60 isotone 96 Kr at the low-Z boundary of the region of deformation described above [9]. Present information on the Se and Kr chain is limited to excitation energies out to 94 Se [10], the B(E2 ↑) strength of 86,88 Kr and 86 Se from Coulomb excitation [11], and lifetimes of excited states measured for 84,86 Se [12].…”