In relation to the relative abundances of heavy nuclei in primary cosmic rays discussed in the preceding paper, the rapid thermonuclear reactions that may occur in the supernova envelope are investigated. The reaction rates of important process, mostly resonance reactions at about 109 °K, are tabulated in Table I. This table is used for the following discussions dealing with those reactions which have lifetimes shorter than about 102 sec. The neutron production through 21Ne(α, n) 24Mg and 25Mg(α, n) 26Si reactions is examined and is found to be possible, if 21Ne and 25Mg are formed in the hydrogen burning zone by the Ne-Na and the Mg-Al cycles at temperatures slightly below 109 °K and densities around 1 g/cm3 and then α-particles thus formed by the cycles induce the (α, n) reactions. The neutron thus produced can trigger the rapid CNO cycle. As temperature decreases with times, neutrons are lost so that the cycle goes through β+-decays in place of (n, p) reactions. Then the abundances of β+-unstable nuclei increase, but many of them are eventually converted into carbon through the last frozen reaction 15N(p, α) 12C. 4N nuclei heavier than neon are produced by rapid α-capturing reactions with the supply of α-particles by the photo-dissociation of 20Ne as well as by the pre-existing ones. The rapid proton capture reactions are shown to account for the iron peak. The above results are favourable to account for the characteristic features of the relative abundances of cosmic ray nuclei, especially the over-abundances of C and Mg and the under-abundance of Ne, relative to the average galactic abundances. The rapid reactions are regarded as to take place in the burning front associated with the shock wave produced by the supernova explosion.
URL :
http://ptp.ipap.jp/link?PTPS/16/169/
DOI : 10.1143/PTPS.16.169