Lifetime measurements of excited states in ¹⁶³W and the implications for the anomalous B(E2) ratios in transitional nuclei

This letter reports lifetime measurements of excited states in the odd-N nucleus 163W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2⁺ → 17/2⁺)/B(E2:17/2⁺ → 13/2⁺) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed

Collectivity in N=Z mass 70 nuclei

There has been intense physics interest in the structure of self-conjugate medium mass nuclei in recent years [1-3]. Specific effort has been undertaken to map out the development of collectivity above mass 60, with emphasis on the influence of the deformation-driving g9/2 orbital. A number of even-even nuclei in this area have been studied, with B(E2) values deduced for 64Ge, 68Se, 72Kr and 76Sr (see ref. [4] and references therein). However no published measurements exist for the intervening odd-odd N=Z nuclei. An experiment was thus conducted to continue the mapping of deformation in the A=70 region by measuring the lifetime of the first excited 2+ state in the odd-odd N=Z nucleus 70Br. Excited states in 70Br were populated via one-nucleon-knockout at the NSCL facility at Michigan State University. De-excitation gamma rays were detected using the SeGA array, recorded in coincidence with recoils identified in the S800 spectrograph. The lifetime was deduced using the recoil distance Doppler shift technique, made possible through the use of a new differential plunger apparatus (TRIPLEX). The lifetime of the 2+ state in neighbouring 70Se was also measured for comparison, due to recent controversy over the shapes of the two nuclei. Lifetimes of low-lying states in 70Br, 70Se and other neighbouring nuclei will be presented and discussed

Isospin symmetry in the sd shell: Transition strengths in the neutron-deficient sd shell nucleus 33Ar^{33}Ar

Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been determined. With these first results the Tz = −3/2 nucleus 33Ar is now, together with 21Na (Tz = −1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent wa

Isospin symmetry in the sd shell: Transition strengths in the neutron-deficient sd shell nucleus Ar-33

Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been determined. With these first results the Tz = −3/2 nucleus 33Ar is now, together with 21Na (Tz = −1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent wa