Low-lying 128I excited states from the (n, γ) reaction

Abstract

Gamma and conversion-electron spectra following the 127I(n, γ) 128I reaction have been studied with bent-crystal, magnetic, Ge(Li) and Si(Li) spectrometers in the range 20–600 keV. Gamma-gamma prompt and delayed coincidences in the range 25–600 keV have been investigated with the use of two Ge(Li) detectors. The 128I level scheme involving 40 levels in the energy range 0–1000 keV has been constructed. Parity is determined for all the levels introduced. Unique spin values are assigned to 30 levels. The half-lives of the 133.611, 137.851 and 167.367 keV levels have been measured to be 12 ± 3, 845 ± 20 and 175 ± 15 ns, respectively. The 127I(d, p) 128I reaction has been investigated with 22 MeV deuterons at an angle of 30°. The 129I(d, t) 128I reaction has been studied with 15 MeV deuterons at an angle of 30°. The (n, γ) levels are found to match well with those from the (d, p), (d, t), (n res, γ primary) and (p, n) reactions. A comparison of the (n, γ) levels with the (d, p) and (d, t) levels enabled the identification of the π g 7 2 ν S 1 2 , π g 7 2 ν d 3 2 , π g 7 2 ν h 11 2 , π d 5 2 ν S 1 2 , π d 5 2 ν d 3 2 and π d 5 2 ν h 11 2 two-quasiparticle multiplets. Energy splittings of these pn configurations by residual interactions taken as a combination of short-range Wigner, singlet and tensor forces have been calculated.