B. Crowell

The abrupt onset of collectivity in 87Mo

Abstract Excited states in the transitional N=45 nucleus 4287Mo were identified for the first time using the 58Ni(32S,2pn)87Mo reaction Low-lying states were found to be non-collective, but above 2 MeV an abrupt change in structure was observed. Two regularly spaced bands of states were found and the measurement of transitional quadrupole moments indicates a mean deformation of β2=0.17(3).

Crowell [ital et] [ital al]. reply

We assume that the s[minus]band configuration has K equal to zero on the average, but exhibits larger fluctuations in K than those present in the g band.

Observation of simultaneousg9/2proton and neutron alignment inKr74

High spin states in {sup 74}Kr were investigated in the reaction {sup 40}Ca({sup 40}Ca,{alpha},2{ital p}){sup 74}Kr at 125 and 140 MeV. A new decay scheme was established up to probable spin {ital I}=20. The rotational structure was found to be similar to {sup 76}Kr, showing a double alignment in the ground-state band and sidebands with constant moments of inertia. Measured lifetimes using the Doppler-shift attenuation method indicate very collective {ital E}2 transitions in the ground-state band.

Observation of simultaneous g sub 9/2 proton and neutron alignment in sup 74 Kr

High spin states in {sup 74}Kr were investigated in the reaction {sup 40}Ca({sup 40}Ca,{alpha},2{ital p}){sup 74}Kr at 125 and 140 MeV. A new decay scheme was established up to probable spin {ital I}=20. The rotational structure was found to be similar to {sup 76}Kr, showing a double alignment in the ground-state band and sidebands with constant moments of inertia. Measured lifetimes using the Doppler-shift attenuation method indicate very collective {ital E}2 transitions in the ground-state band.

Observation of simultaneous g9/2 proton and neutron alignment in 74Kr.

High spin states in {sup 74}Kr were investigated in the reaction {sup 40}Ca({sup 40}Ca,{alpha},2{ital p}){sup 74}Kr at 125 and 140 MeV. A new decay scheme was established up to probable spin {ital I}=20. The rotational structure was found to be similar to {sup 76}Kr, showing a double alignment in the ground-state band and sidebands with constant moments of inertia. Measured lifetimes using the Doppler-shift attenuation method indicate very collective {ital E}2 transitions in the ground-state band.

Spin-Stabilized Deformation in Transitional Nuclei

Nuclei that lie in the transition region between those that display pure single-particle and pure collective behavior at low spins tend to yield to the fictive forces generated by rotation and undergo structural changes. The role of angular momentum in stabilizing exotic shapes in nuclei has been dramatically demonstrated by observation of superdeformation at high spins in the A ≈130, 150, and 190 regions. Current theoretical predictions also point towards the lighter 80 < A < 100 region as likely terrain for such spin-stabilized deformations. This chapter centers around the high-spin spectroscopy of two transitional nuclei in this mass region, 86Zr and 10lAg, which were studied with the 8π spectrometer at Chalk River and the Gamma-Array at Yale. A status report on the assembly of a unique combination of detection devices for nuclear-structure studies at Yale will also be presented.