6533b860fe1ef96bd12c2f60

RESEARCH PRODUCT

Study of the neutron-rich nuclei with $N$ = 21, $^{35}$Si and $^{33}$Mg, by beta decay of $^{35}$Al and $^{33}$Na

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Abstract The first information on the level structure of the N =21 nuclei, 35 Si and 33 Mg, has been obtained by the beta decay study of 35 Al and 33 Na, produced by fragmentation of an UC target with 1.4 GeV protons at CERN/ISOLDE. The experimental technique involved β – γ , β – γ – γ , and β –n– γ coincidences, neutron spectra being obtained by time of flight measurements. Gamma detection was made either using large Ge counters or small BaF 2 scintillators (for lifetime measurements). In the case of the 35 Al decay, ( T 1/2 =41.6(2.2) ms), a simple structure has been found for the level scheme of 35 Si ( Z =14, N =21) which has been interpreted with the level sequence : 7/2 − , 3/2 − and 3/2 + corresponding respectively to the ground state and the states at 910 and 974 keV. The life-time of the 974 keV [ T 1/2 =5.9(6) ns] is found consistent with the proposed level scheme and multipolarities. The investigation of the N =21, very neutron rich isotones, has been carried on with the study of 33 Mg resulting from the 33 Na decay, ( T 1/2 =8.0(6) ms). In this case also, a level scheme could be obtained for the first time, with 5 bound states in 32 Mg and 31 Mg levels, populated in the 1n and 2n channels. These results are compared with sd–fp shell model calculations which give a fair account of the Gamow–Teller distribution and a reasonable explanation of the lowest levels with predominant contribution of 1p–1h and 2p–2h excitations.