β-delayed charged particle decays of neutron-deficient nuclei $^{20}$Mg and $^{22.23}$Si

Abstract : The neutron-deficient nuclei 20Mg, 23Si and 22Si were produced by fragmentation at NSCL, at MSU (USA), and implanted into an array of 3 double sided stripped Si detectors, surrounded by 16 high-purity Ge detectors. This novel arrangement allowed the detection of the charged particles emitted by the unbound excited states in coincidence with the γ rays emitted by the de-excitation of the daughter. The βp decay of 20Mg is very well-known and therefore was used to test and optimize the analysis programm. The β-delayed proton transitions to the first 3 excited states in 19Ne were identified and compared to previous measurements. The half-life, the branching ratio of the transitions and the excitation energies, including the IAS, were measured and are in good agreement with the adopted values. The study of the β+ decay of 23Si allowed the identification of 14 excited states in 23Al. The emission of 2 protons from the IAS was unambiguously identified. The measurement of the IAS energy allowed a better determination of the mass excess of 23Si, giving 23.27 (7) MeV. A possible β3p decay channel was also tentitavely identified. Most of the theoritical predictions are in favor of a 2-proton radioactive 22Si. The β2p decays to the first excited state and the ground state of 20Na were identified. The branching ratio of the decay to the IAS is 2.05 (44) %, and the IAS excitation energy was measured to be 9040 (54) keV. The additional measurement of the half-life gives T1/2 = 30.38 (45) ms, and allowed the determination of the partial half-life. In this study, we propose a parametrization of the statistical rate function f for the superallowed Fermi β decays. This allow the first indirect mass measurement of 22Si ground state, 31.49 (14) MeV. The two-proton threshold is then S2p = 645 (100) keV and does not allow 2p radioactivity.
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M. Babo. β-delayed charged particle decays of neutron-deficient nuclei $^{20}$Mg and $^{22.23}$Si. Nuclear Experiment [nucl-ex]. Université de Caen Normandie, 2016. English. ⟨tel-01461303⟩

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