Study of Decay Modes from Nuclear Deep Hole States

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Nuclear hole states have provided direct evidence of the existence of inner orbital shell structure in nucleus. However, we did not have rich information on the decay modes of the highly excited deep-hole states whether the spreading width dominates or there exists the large escape width, until now. Nuclear deep hole states also have a close connection with the structure and decay of hypernuclei and are relevant to the nucleon decay measurement with the water Cerenkov Detector.After we developed the thin ィイD116ィエD10 target (a pair of SiOィイD22ィエD2 and Si of 2 mg/cmィイD12ィエD1) and a Peltier cooling system, we have measured the ィイD112ィエD1C(p,2p)ィイD111ィエD1BィイD1*ィエD1 and ィイD116ィエD1O(p,2p)ィイD115ィエD1NィイD1*ィエD1 reaction at EィイD2pィエD2 = 392 MeV together with decay charged particles (p,d,t and α) from s-hole states in ィイD111ィエD1B and ィイD115ィエD1N (A new experimental proposal on the neutron and γ decay has just approved as well.) The experiment has been performed at the Research Center for Nuclear Physics, Osaka University, using the double-arm spectrometer and ΔE-E SSD-ball telescope.α decay probabilities have been found to be suppressed in both s-hole states in spite of their large Q-values. Our results of decay branching ratios can not be reproduced by the statistical model calculation but are qualitatively consistent with the calculation of the microscopic cluster model assuming the decay from the doorway s-hole states. The excitation energy spectra around s-hole states show two or three bump structures, which suggests that the s-hole states split into some different components.