Decay ofCs128

Abstract

Samples of $^{128}\mathrm{Cs}$(3.9 min) in equilibrium with its parent $^{128}(2.4\phantom{\rule{0ex}{0ex}}\mathrm{d}\mathrm{a}\mathrm{y})$ have been produced by \ensuremath{\sim}800-MeV proton-induced spallation in praseodymium metal foils. Chemical purification and isotope separation have been performed to produce pure samples. Measurements of $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence spectra have been made. A total of 66 $\ensuremath{\gamma}$ rays between 442 and 3104 keV are assigned to the decay of $^{128}\mathrm{Cs}$, 57 of which have been placed in a proposed level scheme for $^{128}\mathrm{Xe}$ involving 22 established and 3 tentative excited states. Absolute $\ensuremath{\gamma}$-ray intensities have been computed based on the positron and x-ray intensities. Spin and parity assignments are proposed based on the $log\mathrm{ft}$ values and the existence of $\ensuremath{\gamma}$ rays depopulating the states. The first excited ${0}^{+}$ state is found to occur at 1582 keV. Evidence is presented which suggests that it is of predominantly "three-phonon" character, in agreement with some theoretical predictions for transitional nuclei in this mass region.RADIOACTIVITY $^{128}\mathrm{Cs}$ [from Pr (spallation) $^{128}\mathrm{Ba}$ decay]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$; $^{128}\mathrm{Xe}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. Isotope separation, Ge(Li) detectors.