Energy and absorption of the gamma-radiation from Li7 + H1

Abstract

It is shown that a study of the pairs ejected from foils in a Wilson cloud chamber gives more reliable and useful information regarding gamma-radiation of very high energy than can be obtained from the recoil electrons. By this method the gamma-radiation from Li7 + H1 is found to consist of a line at 17.1±0.5 Mev of relative intensity 0.75 and probably one or more lines at about 14 Mev of relative intensity 0.25. No radiation is found between 2 and 10 Mev. The spectrum below 2 Mev has not been investigated. The distribution of recoil electrons is consistent with this and with the Klein-Nishina formula. The division of energy between members of pairs is in agreement with the predictions of Bethe and Heitler. It is shown that the usual method of measuring absorption coefficients leads to erroneous results for radiation much above 3 Mev and a method is described which depends on counting the number of high energy pairs observed in cloud chamber pictures taken alternately with and without 1 cm of lead in the beam. The results agree with theory within the experimental errors. The origin of the radiation is discussed and it is shown that the data can be accounted for if we assume that the proton is captured by the Li7 nucleus producing a Be8 nucleus in an odd state. According to Breit this should be a P state and the nucleus may drop to the ground state (1S) with emission of 17 Mev radiation or to an even state at 3 Mev (1D) and subsequently break up into two alpha-particles.

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