Number-projected three-quasiparticle description of the odd Sn isotopes

Abstract

An account is given of the description of the low-energy properties of the odd Sn nuclei in terms of number projected one-(1 q.p.) and three-quasiparticle (3 q.p.) states. The shell model space for the neutrons consists of one major shell. A simple Gaussian force is used as an effective interaction. Its strength and the single-particle energies, which are the only parameters, are derived in a consistent way from spectroscopic data on the onequasiparticle states. We find that the spectra can be well interpreted in terms of l q.p. and 3q.p. states. Branching ratios of gamma decay, one-nucleon transfer spectroscopic factors, electric and magnetic moments show generally good agreement with the experimental data. For halflives and mixing ratios, which are most sensitive to details of the 3 q.p. components, the agreement is less, but all have the correct order of magnitude.

Gyromagnetic ratio of the 159 keV 3/2+ state of117Sn

“…In the three-quasiparticle description of the odd tin isotopes by van Gusteren et al [11] the g-factor was calculated as g~or = + 0.47 again in excellent agreement with our experimental result. This model calculation reproduces also the ground state magnetic moment exactly, whereas the calculated half-life of the 159 keV state theor T1/2 (159 keV)=2.1 ns is about one order of magnitude too long.…”

A broken-pair description of89Y,91Nb and93Tc

“…One reason for this is that here also particle-hole excitations of the closed shell were included, which makes the nucleus sufficiently soft to lower collective excitations of the vibrational type. Another point is however that in Sn nuclei (Z=50) more complicated collective states have been observed in even nuclei [26] which possibly also play a role in the odd nuclei [22]. In the present investigation we do not find indications for a similar situation around the N = 50 closed shell.…”

“…one-broken-pair model to the odd N=50 isotones are considerably more convincing than earlier applications to odd Sn isotones [21,22]. One reason for this is that here also particle-hole excitations of the closed shell were included, which makes the nucleus sufficiently soft to lower collective excitations of the vibrational type.…”

“…In the present paper we report the application of the projected quasiparticle [15] or broken-pair [16] model to odd N = 50 isotones. So far this model has 0340-2193/79/0292/0159/$02.20 been applied to odd Sn nuclei only [21,22]. Since it is known [23] that in Sn nuclei certain deformed structures may appear at rather low excitation energy, the N = 50 isotones might be more suitable for the application of the model.…”