Explosive Stellar Hydrogen Burning in the Mass a = 30-40 Region

Explosive burning of hydrogen occurs in a variety of stellar sites, e.g. nova outbursts and supernova explosions. Energy production and nucleosynthesis for these objects are determined by the nuclear reactions involved. The present work describes the experimental investigation of hydrogen burning reactions on target nuclei in the mass A = 30-40 region. The (p,gamma) reactions on target nuclei ^{32}S and ^{36}Ar have been measured for bombarding energies important for explosive hydrogen burning. The corresponding stellar reaction rates were calculated and large deviations compared to previous values have been found. Furthermore, a resonance at E _{rm R} = 1.4 MeV in the reaction ^{36}Ar(p, gamma)^{37}K has been observed. The implications of the corresponding ^{37 }K state at E_{rm x} = 3.4 MeV for the Gamow-Teller strength -distribution in the mass A = 37 system are discussed. The (p,alpha) reactions on ^{31}P and ^{35}Cl, which return material to ligther mass regions, have been investigated together with the competing (p,gamma) reactions. Strong (p,alpha) reactions could lead to reaction cycles in the SiPS and SClAr mass regions, respectively, and might explain recent observations of heavy element enrichments in nova ejecta. In many cases, very weak cross sections of astrophysical importance cannot be measured directly using present available experimental techniques. In order to deduce spectroscopic information for the levels of interest in the compound nuclei ^{32 }S and ^{36}Ar, the reactions ^{28}Si( alpha,gamma)^{32}S, ^{35}Cl(^3He,d)^{36 }Ar, ^{32}S(^6Li,d)^ {36}Ar and ^{32 }S(alpha,gamma)^{36}Ar have been investigated. Stellar rates for the hydrogen burning reactions on ^{31 }P and ^{35}Cl have been calculated and are presented.