Nucleosynthesis in Explosive Hydrogen Burning

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(1) Investigation of the property of the crucial state, the 4.033 MeV 3/2^+ state in ^<19>Ne, which dominates the reaction rate of ^<15>O(α,γ)^<19>Ne that determines the onset of novae. This state was studied by the charge-symmetry reactions ^<20>Ne(d,t) and (d,^3He), resulting in J^π=3/2^+ and S=0.033. The α-decay property was also studied by exciting the state by the ^<20>Ne(^3He,t) reaction, and measuring the α decay with Si detectors. However, no significant events were observed above the background level, suggesting the upper limit of the α-width to be 100μeV. (2) The structure of ^<14>O which is crucial for the trigger reaction of the high-T rp-process, ^<14>O(α,p)^<17>F, was also investigated by a high-precision measurement of the ^<20>Ne(p,t) ^<18>Ne reaction with a magnetic spectrograph. Excitation energy determination with high precision and spin assignments were made for the states near the α threshold in ^<18>Ne. (3) Similarly, the structure of ^<22>Mg was studied by the (p … More ,t) reaction, resulting in a discovery of some new resonances near the proton threshold. The new resonances will have significant influences as they are in the range of the Gamow window of novae. (4) The asymptotic normalization (ANC) method was successfully tested with using a direct transfer reaction of ^<12>C(d,p)^<13>C at 11.8 MeV. It provided us a very low-energy direct neutron capture cross sections with an uncertainty of about 8 %. This proves that the ANC method is useful for applying to the direct neutron capture reactions within an uncertainty of about ±10 %. (5) A focal plane detector was developed which has a high ability in particle identification using a large-area Si detectors. (6) A new RI-beam separator and the experimental detectors were developed to study the nuclear reactions under explosive conditions in the Universe. (7) Nova model calculations, including the reaction rates obtained here, were performed to deduce the elemental abundance productions and also to identify crucial reactions to be investigated for the nova problem. Less