H3(p,γ)4He reaction and the (γ,p)/(γ,n) ratio inHe4

The absolute differential cross section for the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(p,γ${)}^4$He reaction has been measured at ${\mathrm{\theta }}_{\gamma }$=90° for ${\mathit{E}}_{\mathit{p}}$=2.0–15.0 MeV, corresponding to photon energies ${\mathit{E}}_{\gamma }$=21.3–31.1 MeV. The present results are 35% lower than previously measured (p,γ) cross sections and are in excellent agreement with recent (γ,p) data obtained with monoenergetic photons. Comparing our results to current photoneutron cross sections gives a ratio σ(γ,p)/σ(γ,n)=1.09±0.17 for ${\mathit{E}}_{\gamma }$=24–31 MeV. This ratio is consistent with conventional theoretical predictions, indicating that no charge-symmetry violation in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is required.