Cross-Section for the Disintegration of the Deuteron by 2·76 MeV. γ-Rays

Abstract

SINCE our recent communication¹, calibrated sources of radiosodium have become available. In view of the high value for the cross-section for photodisintegration of deuterium with radiothorium γ-rays, we decided to repeat our measurements with a radiosodium source. At the same time, several improvements in the apparatus were made ; a spherical electrode instead of a cylinder now defines the sensitive volume of the ionization chamber ; this avoids the error due to low field at the corners, and reduces the γ-ray background. This improvement, and a slight reduction in valve noise, enable higher counting-rates to be used, and enable pulses of 150-keV. energy to be counted before γ-ray and noise background becomes troublesome. The shielding due to positive ions does not reduce any pulses below this energy, and the correction for this effect is zero; the wall-effect correction is also reduced (4 per cent for radiothorium source, 6 per cent for radiosodium source).