Abstract
The energy spectrum of has been investigated theoretically using the basis functions of the nuclear (harmonic-oscillator) shell model. Random-phase-approximation (RPA) techniques are used to decouple the core state from the excited configurations, thereby overcoming the problem of the exaggerated ground-state depression found in standard shell-model calculations. The general equations of the higher RPA are reduced to a more restricted but tractable form which contains both the Tamm-Dancoff approximation and the standard (first) RPA as special cases. For the even-parity states, it is found that the resulting secular equation reduces in good approximation to that of a shell-model calculation with the core state removed. Interaction matrices between all one-hole one-particle and two-hole two-particle states at and excitation were diagonalized to obtain the level structure of in the absence of spurious states of center-of-mass motion. A Gaussian central force with Rosenfeld exchange was employed, the strength being determined by a rough fit to the lowest , levels. Despite the restricted nature of this fit, a remarkably good agreement between the calculated and observed energy spectrum is obtained. The spectrum is well represented apart from two states (with ) which are calculated below the lowest corresponding observed levels. Moreover, the states of both parities fall correctly in relation to each other and to the fitted states, and the states are well reproduced.
- Received 1 August 1966
DOI:https://doi.org/10.1103/PhysRev.153.1039
©1967 American Physical Society