Two-frequency shell model for hypernuclei and meson-exchange hyperon-nucleon potentials

A two-frequency shell model is proposed for investigating the structure of hypernuclei starting with a hyperon-nucleon potential in free space. In a calculation using the folded-diagram method for Λ¹⁶O, the Λ single particle energy is found to have a saturation minimum at an oscillator frequency ħωΛ≈10MeV, for the Λ orbit, which is considerably smaller than ħωN=14MeV for the nucleon orbit. The spin-dependence parameters derived from the Nijmegen NSC89 and NSC97f potentials are similar, but both are rather different from those obtained with the Jülich-B potential. The ΛNN three-body interactions induced by ΛN-ΣN transitions are important for the spin parameters, but relatively unimportant for the low-lying states of Λ¹⁶O.Yiharn Tzeng, S. Y. Tsay Tzeng, T. T. S. Kuo, T.-S.H. Lee, and V. G. D. Stok

Angular correlation and coincidence studies of excited 0/sup +/ and other levels in the transitional Ce nuclides /sup 142/Ce, /sup 144/Ce, /sup 146/Ce, and /sup 148/Ce

The decays of the neutron-rich nuclides /sup 142/La, /sup 144/La, /sup 146/La and /sup 148/La to the levels of the transitional nuclides /sup 142/Ce, /sup 114/Ce, /sup 146/Ce and /sup 148/Ce, respectively, have been studied using mass-separated sources. Angular correlation studies have been employed to identify new excited 0/sup +/ levels in /sup 146 /Ce and support spin and parity assignments for 1/sup -/, 3/sup -/, 2 /sup +/, 3/sup +/, 4/sup +/ and 6/sup +/ levels in /sup 144/Ce and /sup 146/Ce. An excited 0/sup +/ level in /sup 148/Ce is indicated by coincidence ratios and electron studies, while no clear evidence can be found for the location of an excited 0/sup +/ level below 2 MeV in /sup 144/Ce. The resulting isotonic and isotopic systematics are discussed in terms of the transition from the closed shells at N=82 and Z=50 to the region of deformed nuclides. (13 refs)