Showing papers by "R. F. Casten published in 1998"

The first excited 0 + state in 152 Sm

Abstract: The properties of ${K=0}^{+}$ excitations in deformed and transitional nuclei have recently been of intense interest. We present results of a study of the deexcitations of the lowest excited ${0}^{+}$ state in ${}^{152}$Sm from the $\ensuremath{\epsilon}$-decay of ${}^{152}$Eu, yielding one of the few precisely known values of the branching ratio ${R}_{0g}^{\ensuremath{\gamma}}{=B(E2;2}_{\ensuremath{\gamma}}^{+}\ensuremath{\rightarrow}{0}_{2}^{+}{)/B(E2;2}_{\ensuremath{\gamma}}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ =0.048(4), which is extraordinarily small. From ${T}_{1/2}{(2}_{\ensuremath{\gamma}}^{+})$ we also obtain ${B(E2;2}_{\ensuremath{\gamma}}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})$=0.17 W.u. Values of ${R}_{0g}^{\ensuremath{\gamma}}$ calculated in the interacting boson model (IBA) go to zero extremely rapidly, changing by orders of magnitude for a narrow range of parameter values. ${}^{152}$Sm is a rare case of a transitional nucleus that lands almost at the minimum. ${}^{152}$Sm and ${}^{154}$Gd are the only nuclei from $90l~Nl~114$ where the $B(E2)$ values for all four transitions ${2}_{\ensuremath{\gamma}}^{+}\ensuremath{\rightarrow}{0}_{2}^{+}$, ${2}_{\ensuremath{\gamma}}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}$, ${0}_{2}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$, and ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}$ are now known. In ${}^{152}$Sm these $B(E2)$ values span three orders of magnitude, from 144 to 0.17 W.u. and are reproduced to within a factor of 2--3 by the IBA. The rather strong ${B(E2;0}_{2}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ value of 33 W.u. suggest that the ${0}_{2}^{+}$ level is an example of a good low energy $\ensuremath{\beta}$-vibration.

Evolution of nuclear structure in O(6)-like nuclei

Abstract: The evolution of nuclear structure along the Xe and Ba isotopes with N{lt}82 is studied in comparison with that in the Pt-Os isotopes and with interacting boson approximation calculations. As is well known, the Pt isotopes from {sup 188{minus}196}Pt exhibit a stable structure very close to O(6), the lighter Pt isotopes and the Os nuclei evolve towards a rotor, and the heaviest Pt nuclei, {sup 198,200}Pt, show a tendency towards vibrational character. In contrast, we show that the Ba nuclei are best described by a trajectory from U(5) towards SU(3) that passes through an intermediate structure that resembles O(6) for N{approximately}72{endash}76. The Xe appears to evolve from U(5) to O(6)-like. {copyright} {ital 1998} {ital The American Physical Society}

Experimental study of the deformed nucleus 153 Sm 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.