Evaluation for photonuclear production cross sections, (1)

Nuclear data evaluation about radioactive production cross sections of photonuclear reactions, which are used in planning on maintenance work of electron accelerators, has been required in Japanese Nuclear Data Committee. This report represents a result of the first evaluation work about the photonuclear production cross sections which was performed in response to that requirement. The production cross sections of the following reactions were evaluated: 23Na(γ,n)22Na, 25Mg(γ,p)24Na, 48Ca(γ,n)47Ca, 46Ti(γ,n)45Ti, 52Cr(γ,n)51Cr, 55Mn(γ,n)54Mn, 59Co(γ,n)58Co, 58Ni(γ,n)57Ni, 65Cu(γ,n)64Cu, 90Zr(γ,n)89Zr, 100Mo(γ,n)90Mo. The main reasons why these reactions were selected are that the target nuclides are largely included in structural materials of the accelerators and the reactions have relatively large reaction cross sections. Range of incident gamma-ray energies is from the threshold energy to 140 MeV. Photonuclear absorption cross sections were evaluated first. Second, branching ratios of (γ,n) and (γ,p) reactions were calculated using the MCPHOTO code. Finally, the evaluated values of the production cross sections were obtained by making the product of the absorption cross sections and the branching ratins. On evaluating the absorption cross sections, measured cross sections were mainly referred in the giant E1 resonance region, and the other hand, theoretical cross sections were only used in the quasi-deuteron absorption region. The calculated photoneutron cross sections show reasonable accordance with the measured data in the giant E1 resonance region. On the other hand, those in the quasi-deuteron absorption region cannot be compared with experimental data because of no measured cross sections. Hence, it is still not clear to what degree of accuracy the evaluated cross sections have in the latter region. (author)