The magnetic moments of the first excited 2(+) state in even-even nuclei Sn102-130 and the low-lying yrast states in odd-mass nuclei Sn-101-109,Sn-123-131 are calculated within the framework of the nucleon-pair approximation (NPA) of the shell model, by using the standard multipole-multipole interaction. Our calculations agree reasonably well with available experimental data. The g(2(1)(+)) values, as well as the contributions from their spin and orbital angular momentum components, are evaluated in terms of the small NPA subspace spanned by S and D nucleon pairs. The magnetic moment is suggested to be a sensitive probe of the nuclear wave function in this region.

The low-lying level schemes and electromagnetic transitions of Te-109, I-109, and the neighboring even-even nucleus Te-108 are calculated within the framework of the SD-pair approximation of the nuclear shell model. Good agreement is obtained between the calculated results and experimental data. The favored components of low-lying bands are discussed in the collective nucleon-pair subspace. The weak-coupling picture shown in these nuclei and its relationship with residual quadrupole-quadrupole interaction between valence protons and neutrons are analyzed.

In this paper we derive the analytical formulas of the number of spin-I states (denoted as D-I) for three identical particles, in a unified form for both fermions and bosons. This is done by using (n) over bar virtual bosons with spin 3/2, where (n) over bar equals 2j - 2 if one studies fermions in a single-j shell or 2l if one studies bosons with spin l. We first obtain a reduction rule from U(4) to O(3) for such virtual bosons and thereby derive the formulas of D-I. The formulas thus obtained are proved to be consistent with previous empirical formulas.