Photodisintegration of Helium

Helium gas at atmospheric pressure was irradiated with 26-, 29-, 32-, and 40-Mev bremsstrahlung spectra. The energy and angular distributions of the protons produced by the photodisintegration of He⁴ were studied using nuclear emulsions to detect the charged particles. Angular distributions of the protons are fitted to a differential cross section of the form ${σ}({{θ}}c.m.){~}(a/b)+{{sin}²{θ}}c.m.[1+({{γ}}{b}){cos{θ}}c.m.]$. Over the energy range studied, the interference term may increase slowly with energy but is approximately constant (${{γ}}{b}=0.2±{}0.1); the isotropic term increases rapidly with energy from 0 to 0.33±0.2 at a mean photon energy of 32.5 Mev. The ({γ}, p$) cross section reaches a peak value of about 1.8 mb at about 26 Mev. ${∫}{20}⁴⁰{σ}dE=0.016±{}0.005$ Mev barns.