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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 thecollinear geometry, which are due to spin {\it S}=1 transitions of thefinal-state particles. The ratio of the differential cross section in thecollinear geometry to the differential reaction cross section at the nucleonemission angle $\theta_N$=90$^\circ$, and specified by the {\it S}=0 electricdipole transition at photon energies in the range 20$\leE_{\gamma}\le$100\,MeV, is independent of the photon energy, within theexperimental error. In the meantime, experiments were made to measure theasymmetry of the cross section $\Sigma(\theta_N)$, for the mentioned reactionswith linearly polarized photons. It has been found that in the energy rangebetween 20 and 90\,MeV, the $\Sigma(\theta_N)$ value is also independent of thephoton energy, within the experimental error. These data are in agreement withthe assumption that transitions with spin {\it S}=1 can be due to thecontribution of $^3P_0$ states of the $^4$He nucleus, and are inconsistent withthe assumption that the spin-flip of the particle system occurred during thereaction as a result of the meson exchange current contribution. The availablemeasured data on the collinear geometry reaction cross sections and the ones onthe cross-section asymmetry of the reaction with linearly polarized photons donot agree between themselves. The above mentioned reactions seem to be moreconvenient for measuring the degree of photon beams linear polarization thanthe deuteron photodisintegration reactions.

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