Discovery of 68Br in secondary reactions of radioactive beams

Abstract

The proton-rich isotope 68 Br was discovered in secondary fragmentation reactions of fast radioactive beams. Proton-rich secondary beams of 70,71,72 Kr and 70 Br, produced at the RIKEN Nishina Center and identified by the BigRIPS fragment separator, impinged on a secondary 9 Be target. Unambiguous particle identification behind the secondary target was achieved with the ZeroDegree spectrometer. Based on the expected direct production cross sections from neighboring isotopes, the lifetime of the ground or long-lived isomeric state of 68 Br was estimated. The results suggest that secondary fragmentation reactions, where relatively few nucleons are removed from the projectile, offer an alternative way to search for new isotopes, as these reactions populate preferentially low-lying states.

Shape Changes in the Mirror Nuclei Kr70 and Se70Wimmer1, Körten2, Doornenbal3 et al. 2021Phys. Rev. Lett.Self Cite242170View full textAdd to dashboardCite

“…The A = 70 nuclei have been chosen for this because previous experimental investigations of the Coulomb energy differences of 70 Se and 70 Br found an anomalous behavior [11], which could be interpreted as a shape change between the isobars [12]. Spectroscopy of 70 Kr at T z = −1 was only achieved recently [13,14], but did not allow to probe the nuclear shape and test for a proposed shape change in the mirror pair 70 Se and 70 Kr [15]. Electromagnetic transition matrix elements, on the other hand, also allow for the determination of the shape or deformation of a nucleus.…”

“…Reaction products were identified in the ZeroDegree spectrometer [17] using the same technique as for BigRIPS. Further details of the experiment can be found in [14,19].…”

“…For the inelastic scattering off the Be target, the yield for states above the 2 + 1 state was subtracted to correct for indirect feeding as described in Ref. [14]. For the data taken with the Au target, the de-excitation from the 2 + 2 state at 1478 keV to the 2 + 1 state is not observed.…”

“…Theoretical calculations predict the 0 + 2 in 70 Kr at considerably higher energy than the 2 + 1 state [22,23] as well, so that its lifetime would be much shorter than the flight time to the BigRIPS focal plane. In the analysis of nucleon removal reactions from the same experiment no evidence for a low-lying 0 + state was found in either of the two nuclei [14]. Due to the low beam intensity, it was not possible to search for an isomeric state in 70 Kr as it was done for 72 Kr [19], where an isomeric ratio of 4(1)% was found.…”

Shell-model study on properties of proton dripline nuclides with Z, N = 30-50 including uncertainty analysis

“…In 2017, the proton emission from the ground-state of 72 Rb was measured for the first time [69]. Here, it is predicted to be proton unbound but two protons bound in this work.…”