Speaker
Description
C. Sotty on behalf of IS650/IS665 IDS, IFIN-HH, Univ. York, IKS Leuven collaborations
The $^{232}Ra$ $\beta^{-}$decay chain was investigated through $\beta$ and $\gamma$-ray spectroscopy at CERN-ISOLDE. A radioactive beam of $^{232}Fr$ and $^{232}Ra$ was implanted on the ISOLDE Decay Station tape, where the $\gamma$-rays originating from the $\beta^{-}$decay chains $^{232}Fr$-$^{232}Ra$-$^{232}Ac$-$^{232}Th$ were registered using a mixed array consisting of (4 HPGe- 2 LaBr$_{3}$(Ce)–1 Beta) detectors arranged in close geometry. The production yields were measured for different experimental conditions of $UC_{x}$ targets, also involving the formation of $^{213}RaF$ molecular beam inducing a substantial contamination.
Prior to our study, K.-L. Gippert et al. used the multinucleon transfer reaction to produce the $^{232}Ra$ precursor. Due to low statistics and the absence of $\gamma$-$\gamma$ coincidences, only a few $\gamma$-ray transitions were associated with $^{232}Ac$. In the present work, we report on revised and considerably extended level schemes for $^{232}Ac$ (24 new $\gamma$-rays, 19 new levels) and $^{232}Th$ (67 new $\gamma$-rays, 36 new levels), revealing the existence of new structures lying at higher energy and a different $\beta$-strength distribution. Thanks to our low $\gamma$-ray/X-ray energy capabilities, few $K$-$shell$ internal conversion coefficients have been newly extracted for $^{232}Ac$, providing clues to assign multi-polarities to the related transitions. An isomeric state at $E_{x}=97.7$ keV, on top of which a newly discovered structure is build, was identified and measured in $^{232}Ac$ with HPGe detector array using the standard electronic timing technique.
The experimental results will be discussed and confronted to the systematics present neighbouring nuclei, where similar structures/mechanisms are observed.
