The $\gamma$-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

Abstract : Nuclei around doubly-closed shells play a crucial role in studying both a) the couplings between valence nucleons which provide information on the effective nucleon-nucleon interaction and, b) couplings of the valence nucleons with core excitations, which may be used as a unique test of various effective interactions used in mean-field based models, like Skyrme, Gogny etc. From a broader perspective, understanding the coupling of a single particle to vibrational motion in nuclei is of primary importance, as this coupling is responsible for the quenching of spectroscopic factors [1]; it is also the key process at the origin of the damping of giant resonances [2]. The vibrational phonons are best known from the spectroscopic studies of doubly-magic nuclei in which they appear, in general, as the lowest excited states. For example, in 208Pb, the lowest excitation (at 2615 keV) is the 3– octupole vibration with a large E3 transition strength of 34 W.u. We investigated the low-spin structures of 210Bi and 206Tl up to their neutroncapture states at 4.6 and 6.5 MeV, respectively, by using 209Bi(n,)210Bi and 205Tl(n,)206Tl reactions induced by cold neutrons at ILL Grenoble. The 210Bi nucleus (one proton and one neutron above the 208Pb core) was populated in the experiment performed at the PF1B and cold-neutron facility in which - coincidences were measured with the EXILL array consisting of 16 Ge detectors. It is the first time when such large array was employed for 209Bi(n,)210Bi reactions studies so the decay scheme could be revised and significantly extended. The analysis of the angular correlations of  rays provided information about transitions multipolarities and helped with the spin-parity assignments. The structure arising from the excitations of valence proton and neutron was compared to the shell-model calculations. Some of the observed states must come from the coupling of the valence particles excitations with the first excited state in 208Pb, that is 3– octupole vibration. The 206Tl nucleus was populated in the first (commissioning) experiment of FIPPS facility at ILL Grenoble. The  rays from the capture state at 6.5 MeV were measured by the array of 8 Ge clovers. We want to present the preliminary results of the -coincidence analysis which will allow to significantly extend the experimental information on the energy levels in 206Tl. The 206Tl nucleus, having just one proton-hole and one neutron-hole with respect to the best known doubly magic core 208Pb, is an ideal system for testing old and developing new shell model interactions in the south-west quadrant of the nuclear chart with respect to 208Pb.
Type de document :
Communication dans un congrès
6th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei (FISSION 2017), Mar 2017, Chamrousse, France. 〈https://indico.ill.fr/indico/event/64/〉

http://hal.in2p3.fr/in2p3-01503622
Contributeur : Emmanuelle Vernay <>
Soumis le : vendredi 7 avril 2017 - 12:57:27
Dernière modification le : mardi 22 mai 2018 - 21:48:11

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• HAL Id : in2p3-01503622, version 1

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N. Cieplicka-Oryńczak, S. Leoni, B. Fornal, D. Bazzacco, A. Blanc, et al.. The $\gamma$-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions . 6th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei (FISSION 2017), Mar 2017, Chamrousse, France. 〈https://indico.ill.fr/indico/event/64/〉. 〈in2p3-01503622〉

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