Analysis of $^4$He($\gamma,p)$T and $^4$He($\gamma,n)$$^3$He Reactions with Linearly Polarized Photons in the Energy Range up to 100\,MeV

• Main Author: Lyakhno, Yu. P
• Format: Journal Article
• Language: English
• Published: 26-12-2019
• Subjects: Physics - Nuclear Experiment; Physics - Nuclear Theory
• DOI: 10.48550/arxiv.1912.11865

In a number of investigations, one can find the data on the
$^4$He($\gamma$,p)T and $^4$He($\gamma$,n)$^3$He reaction cross sections in the
collinear geometry, which are due to spin {\it S}=1 transitions of the
final-state particles. The ratio of the differential cross section in the
collinear geometry to the differential reaction cross section at the nucleon
emission angle $\theta_N$=90$^\circ$, and specified by the {\it S}=0 electric
dipole transition at photon energies in the range 20$\le
E_{\gamma}\le$100\,MeV, is independent of the photon energy, within the
experimental error. In the meantime, experiments were made to measure the
asymmetry of the cross section $\Sigma(\theta_N)$, for the mentioned reactions
with linearly polarized photons. It has been found that in the energy range
between 20 and 90\,MeV, the $\Sigma(\theta_N)$ value is also independent of the
photon energy, within the experimental error. These data are in agreement with
the assumption that transitions with spin {\it S}=1 can be due to the
contribution of $^3P_0$ states of the $^4$He nucleus, and are inconsistent with
the assumption that the spin-flip of the particle system occurred during the
reaction as a result of the meson exchange current contribution. The available
measured data on the collinear geometry reaction cross sections and the ones on
the cross-section asymmetry of the reaction with linearly polarized photons do
not agree between themselves. The above mentioned reactions seem to be more
convenient for measuring the degree of photon beams linear polarization than
the deuteron photodisintegration reactions.