Experimental study of the deformed nucleus 153Sm via (d→,t) and average resonance capture as a test case for the multiorbit interacting boson fermion model

Abstract

The ${}^{154}\mathrm{Sm}(\stackrel{\ensuremath{\rightarrow}}{d},t)$ reaction at high energy resolution $(n,\ensuremath{\gamma}),$ average resonance capture (ARC), and coincidence measurements were performed to study the deformed nucleus ${}^{153}\mathrm{Sm}.$ Strength distributions from $(\stackrel{\ensuremath{\rightarrow}}{d},t)$ and completeness for ${I}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}}$ and ${\frac{3}{2}}^{\ensuremath{-}}$ states up to 1500 keV from ARC provide one of the first detailed tests of the interacting boson fermion model (IBFM) in a deformed nucleus in a multiorbit environment. For negative parity states the model accounts for the large number of low spin (${\frac{1}{2}}^{\ensuremath{-}}$, ${\frac{3}{2}}^{\ensuremath{-}}$) states much better than the Nilsson model since the even-even core in the IBFM calculations automatically includes excited vibrational states. The IBFM calculations also predict $(d,t)$ spectroscopic factors better than the Nilsson model with pairing and Coriolis mixing. Neither the IBFM nor the Nilsson approach can explain the low lying positive parity states. The IBFM calculations show that for certain combinations of parameters, the monopole term in the boson-fermion Hamiltonian has more than a scaling effect: it can attenuate the Coriolis mixing (energy staggering). Finally suggested improvements in the treatment of pairing in the IBFM are made.