The Absolute Number of Quanta from the Bombardment of Fluorine with Protons

Abstract

From recent experiments it seems very probable that the 6.2-Mev quanta from the proton bombardment of fluorine are associated in one-to-one correspondence with the short range alpha-particles. This correspondence makes possible the establishment of the gamma-ray intensity by measuring the alpha-particle yield. With a specially designed variable pressure absorption-cell ionization-chamber to facilitate clear distinction between the short range alpha-particles and the scattered protons, the angular distribution and total yield of the alpha-particles at the lowest resonance (330 kv) have been determined. The determinations were based on plateaus appearing in curves of counting rate as a function of (1) cell pressure, (2) counter bias, and (3) bombarding voltage at angles of 60°, 90°, 120°, and 150° with respect to the proton beam. The results show that: ($a$) To within two percent the angular distribution of the alpha-particles is spherically symmetric; and ($b$) the yield over $4\pi$ steradians is 8.9±0.5×${10}^4$ alpha-particles per microcoulomb of 360-kv protons bombarding a thick crystal of Ca${\mathrm{F}}_2$. The absolute number of quanta from the reaction is presumably the same to the same accuracy. With both a heavily shielded counter and a similarly protected electroscope the ratio of the gamma-ray intensity at 1050 kv to that at 370 kv was found to be 42.0±0.8. Thus the gamma-ray intensity at 1050-kv bombarding voltage is ${3.7}_4$±0.2×${10}^6$ quanta per microcoulomb of protons on Ca${\mathrm{F}}_2$. The angular distribution of the gamma-radiation was found to be spherically symmetric to within the experimental error of five percent. Knowledge of the absolute intensity of the fluorine source greatly enhances its value in photo-nuclear and other experiments.