[en] The reaction cross section of ⁵⁶Fe (γ, α₀) was measured from the electron energy of 15 to 25 MeV. The measured data were compared with the calculated ones based on statistic theory. Both agreed with each other. Therefore, affirmative result was obtained for the presumption that the reaction of (γ, α₀) of the nuclei around these energy levels can be explained by the statistical theory. The angular distribution of ⁵⁶Fe (γ, α₀) with 17 MeV electron energy was also measured, and E2/E1 ratio was obtained. In the measurement of ⁵⁶Fe ( Gamma , α₀) reaction cross section, a natural target of 2.69 mg/cm² was irradiated with the electron beam with energy from 15 MeV to 25 MeV at intervals of 0.5 MeV, and the emitted α particles were detected by a broad band magnetic distribution meter. The measured cross section of (γ, α₀) reaction agreed with the calculated one based on statistical theory. If this fact is recognized in many nuclei, the cross section of (γ, α₀) reaction of those nuclei has the following characteristics. When the increasing rate of the product of a complex nucleus formation cross section and α₀ penetration factor is larger than that of the sum of all penetration factors of possible channels, the cross section of (γ, α₀) reaction increases, and takes a peak value when above two increasing rates agree with each other. (Tai, I.)

[en] The angular distribution-measuring device for the protons released in the reaction (γ, p) was installed in a gamma channel. Its construction, performance and the results of test are described. In the Laboratory of Nuclear Science (Tohoku University), the giant resonance has been studied by (e, e'p) reaction, and the angular distribution of released protons provides a clue to the structure of the giant resonance, therefore the continuous measurement of the angular distribution as a function of gamma-ray energy is desirable. The angular distribution-measuring apparatus consists of semiconductor detectors arranged at angle intervals of 15⁰, pre-amplifiers, interchangeable targets, a scattering chamber, etc. (Mori, K.)

[en] Precise analysis was made on the cross section of ⁵⁶Fe (γ, α₀) reaction and the angular distribution at Esub(e) = 17 MeV, including the systematic error. The (γ, α₀) reaction cross section was compared with that by the calculation with compound nucleus model, utilizing the photon absorption cross section derived from the experimental values of ⁵⁶Fe (γ, n) and ⁵⁶Fe (γ, p) cross sections. From the (γ, α₀) reaction cross section data of various nuclei, an empirical formula was obtained for determining the position of a peak in the (γ, α₀) reaction cross section. The ⁵⁶Fe (γ, p₀) reaction cross section measured at excitation energy in the range of 14.6--25.0 MeV was compared with the calculated one with the compound nucleus model, but the form and size differ totally. (Mori, K.)

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[en] The (γ, p) reaction cross section of ⁵¹V and ⁵⁴Fe was measured for studying the iso-spin and the nuclear deformation effect. For the purpose, the (γ, n) and (γ, p) reaction cross sections are necessary, but the (γ, p) reaction data are little in the literature, accordingly the measurement was carried out. Some approximate method of the analysis of iso-spin effect is presented. The form and intensity of the (γ, p) and (γ, n) reaction cross sections in the giant resonance region of ⁵¹V and ⁵⁴Fe, can be explained with compound nucleus model though qualitative, and the assumption of a quantum number of good iso-spin. (Mori, K.)

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[en] Proton energy spectra have been measured at 90⁰ for the ¹⁹F(e,e'p)¹⁸O reaction in the giant resonance region. The (γ,p₀) and (γ,p₁) differential cross sections are extracted from the proton energy spectra by using virtual-photon spectra. The integrated differential cross section of the (γ,p₀) and (γ,p₁) reactions are 1.80+-0.27 and 0.50+-0.45 MeV-mb/sr, respectively. The results are discussed with the shell model theory by comparing with the (γ,p₀) cross section of the neighboring 4n-nucleus ²⁰Ne. A significant increase of the proton yield leaving the non-ground states is found at 25 MeV of the incident electron energy. This is discussed in terms of the core excitation effect. (auth.)

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