G. N. Sylvan

Band Structure in 79Y and the Question of T=O Pairing

Gamma rays in the N=Z + 1 nucleus Y-79 were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental setup consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma rays were found to form a strongly coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N=Z and N=Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T=0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. [S0556-2813(98)50612-7].

Band Structure in 79Y and the Question of T=0 Pairing

Excited states in the N = Z+1 nucleus Y-79 Were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental set up consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma-rays were found to form a strongly-coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N = Z and N = Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T = 0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. (Less)

Angle-corrected doppler-shift attenuation analysis

If all nuclei from a reaction recoil from a thin target at essentially the same velocity, it is easy to correct for the variation of γ-ray energy with emission angle due to the Doppler shift to combine data from different detectors and improve the statistical accuracy. However, the situation is more complex with thick-target experiments in which γ emission occurs over a wide range of velocities. Now charged-particle detector arrays allow the determination of the exact recoil angle and velocity from fusion-evaporation reactions on an event-by-event basis. Corrections for the variations in the Doppler shift due to different angles between each detector and each recoil event and for the variations in the recoil velocities would provide better statistical accuracy and more accurate line shapes for analysis using the Doppler-shift attenuation method to infer mean lifetimes of excited states. A technique to make these corrections has been developed using simulated line shapes.

Nuclear structure of neutron-rich 78 As

Excited states in the neutron-rich doubly-odd nucleus78As have been identified for the first time by proton-γ and γ-γ coincidence measurements via the76Ge(α, pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5(+) to (10+) states are ascribed to the (πg9/2⊗νg9/2) intruder two-quasiparticle configuration with some collective components in the 9(+) and (10+) states.