Showing papers by "R. Wadsworth published in 1990"

High-spin states in Ce 136 : Systematics of collective oblate rotation

Abstract: The level structure of the transitional even-even $^{136}\mathrm{Ce}$ nucleus has been investigated using the $^{122}\mathrm{Sn}$${(}^{18}$O, 4n\ensuremath{\gamma}) reaction. The prominent structure observed at high spin is a \ensuremath{\Delta}I=1 rotational band, populated with \ensuremath{\sim}25% intensity of the ${2}^{+}$\ensuremath{\rightarrow}${0}^{+}$ transition, which has a low dynamic moment of inertia 20${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$ for frequencies below \ensuremath{\Elzxh}\ensuremath{\omega}=0.45 MeV. This band is interpreted in terms of a two-quasiproton-two-quasineutron configuration with a shape close to the collectively rotating \ensuremath{\gamma}=-60\ifmmode^\circ\else\textdegree\fi{} oblate shape, and is related to the oblate \ensuremath{\pi}${\mathit{h}}_{11/2}$\ensuremath{\bigotimes}[\ensuremath{ u}${\mathit{h}}_{11/2}$${]}^{2}$ configuration seen in several nearby odd-Z nuclei. The systematics of such oblate rotational bands in this mass region are discussed. Other \ensuremath{\Delta}I=2 bands, built on states including ${\mathit{h}}_{11/2}$ quasineutron orbitals, are also associated with collective oblate rotation. In addition, tentative evidence is presented for a weak band (2% intensity), showing an enhanced dynamic moment of inertia \ensuremath{\sim}57${\mathrm{\ensuremath{\Elzxh}}}^{2}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}1}$, built on the highly deformed [\ensuremath{ u}${\mathit{i}}_{13/2}$${]}^{2}$ prolate configuration.

Quadrupole moment of the superdeformed band in 131Ce

Abstract: A mean lifetime measurement has been carried out on the states in the superdeformed band found in 131Ce using the Doppler shift attenuation method (DSAM). The measured intrinsic nuclear quadrupole moment is Q0 approximately=6 eb, assuming constant deformation, which corresponds to a quadrupole deformation beta 2 approximately=0.35. This is considerably smaller than the value deduced for 132Ce.

An i13/2 intruder band in 139Gd

Abstract: A rotational band of eleven gamma -rays has been observed in 139Gd showing an enhanced moment of inertia indicative of a band of higher quadrupole deformation than the low-lying states. This band is believed to be built on a single nu i13/2 intruder orbital, and extends the systematics of such bands, recently observed in several samarium nuclei (Z=62), to gadolinium (Z=64). An attempt is made to deduce the spins for levels within this band by fitting the extracted moment of inertia with a power expansion in terms of the rotational frequency. This method is also used to deduce the spins for other bands of enhanced deformation in this mass region; the method is shown to reproduce the known spins for the nu i13/2 intruder bands in the 135,137Sm isotopes.

Lifetime Measurements in Sm-135 - Large Deformation in the N = 6 Intruder Band and Evidence for Quenched Proton Pairing

Abstract: The quadrupole moment of the highly deformed band built upon the {ital i}{sub 13/2} neutron intruder orbital in {sup 135}Sm has been measured, using the Doppler shift attenuation method and Braune stopping powers, to be 70{plus minus}07 {ital e} b These data provide strong evidence that this high-{ital j}, {ital N}=6 intruder orbital is responsible for the highly deformed states seen in this region The result is compared to total Routhian surface calculations A possible explanation for the observed anomalous behavior of the {ital J}{sup (2)} moment of inertia in this nucleus is discussed in terms of quenched static proton pair correlations