Examining measuring the degree of linear photon-beam polarization in the energy range up to 100 MeV with the use of He4(γ⃗,p)H3 and He4(γ⃗,n)He3 reactions

Abstract

The paper gives physical justification of a new method for measuring the degree of linear photon-beam polarization, which relies on the experimental data for the total cross section of spin $S$ = 1 transitions in the $^{4}\mathrm{He}(\ensuremath{\gamma},p)^{3}\mathrm{H}$ and $^{4}\mathrm{He}(\ensuremath{\gamma},n)^{3}\mathrm{He}$ reactions. The experimental information on the cross section was obtained from both the mentioned reactions and the reactions of radiative capture of protons by tritium nuclei. The total cross section for transitions with spin $S$ = 1 is $\ensuremath{\approx}1%$ of the total cross section for the reaction. The ratio of the differential cross section in the collinear geometry, specified by the $S$ = 1 transitions, to the differential reaction cross section at the nucleon emission angle ${\ensuremath{\theta}}_{N}={90}^{\ensuremath{\circ}}$ in the energy range 20 $\ensuremath{\le}{E}_{\ensuremath{\gamma}}\ensuremath{\le}$ 100 MeV is independent of the photon energy within the experimental error. The total cross section for the $S$ = 1 transitions can be also determined from the experimental data on the cross-section asymmetry of the reaction with linearly polarized photons $\mathrm{\ensuremath{\Sigma}}({\ensuremath{\theta}}_{N})$. However, the total cross section for transitions with spin $S$ = 1, calculated from the asymmetry of the cross section $\mathrm{\ensuremath{\Sigma}}({\ensuremath{\theta}}_{N})$, is several times greater than that calculated from the differential cross section. This inconsistency of the experimental data may be due, in particular, to the overestimate of the degree of linear photon-beam polarization. The above-mentioned reactions seem to be more convenient for measuring the degree of linear photon-beam polarization than the deuteron photodisintegration reactions.