The level structure of 124Sb and residual p-n interactions

Abstract Gamma and conversion electron spectra following the 123 Sb(n, γ) 124 Sb reaction in the energy range 35–1030 keV and 16–600 keV, respectively, have been studied with bent crystal and magnetic spectrometers. Gamma-gamma coincidences in the energy range 40–500 keV have been investigated with a Ge(Li)-Ge(Li) arrangement. Gamma-gamma delayed coincidences have been taken with two Ge(Li) detectors in the range 0–10 μs and with a Ge(Li) detector and plastic scintillator in the range 0–300 ns. The 124 Sb level scheme involving 40 excited states up to 1060 keV has been constructed. Parity is determined for all the levels. Unique spin values are assigned to 30 levels. The half-lives of the 40.804, 80.764, 125.231 and 248.369 keV levels have been measured to be 3.2 ± 0.3 μ s, 4 ± 1 ns, 86 ± 2 ns and 380 ± 70 ps respectively. It is shown that the present level scheme energies differ from those previously found in the 123 Sb(d, p) 124 Sb reaction by a systematic shift of 40 keV. The (n, γ) levels are found to match up well with those from the (d, p), (n res , γ) and (n, γ primary ) reactions. A comparison of the 124 Sb level scheme from the (n, γ) reaction with that from the (d, p) reaction and with the 122 Sb level scheme enabled the identification of the p g 7 2 ns 1 2 , p g 7 2 n d 3 2 π g 7 2 ν h 11 2 and π d 5 2 ν h 11 2 two-quasiparticle multiplets. Energy splittings of these p-n configurations by residual interactions taken as a combination of short-range Wigner, singlet and tensor forces have been calculated. It is shown that in order to reproduce experimental branching ratios, configuration mixing should be taken into account, though the amplitudes needed for the admixed configurations are rather small and are, on the average, equal to 0.25. It is also shown that the parameters of residual interactions are about constant in the mass range A = 48 → 210, namely, the parameter of Wigner forces V 0 = −32 ± 6 MeV, the singlet force parameter V 1 = 14 ± 6 MeV and the range parameter r 0 = 1.9 ± 0.3 fm. The occupation numbers of neutrons in the 1 h 11 2 subshell in the range A = 110 → 134 and of protons in the 2 d 5 2 and 1 g 7 2 subshells in the range A = 122 → 142 are determined.