Radiochemical Study on Photonuclear Reactions of Complex Nuclei at Intermediate Energies

Abstract

A review is given on radiochemical study on photonuclear reactions on target nuclei ranging from ⁷Li to ²⁰⁹Bi at intermediate energies, i.e. bremsstrahlung end-point energies of 30-1200 MeV, by the author's group since 1980s. The study covers the yield measurements of photopion reactions, spallation, fragmentation and fission of preactinides, ¹⁹⁷Au and ²⁰⁹Bi, systematically performed with respect to photon energy, target mass (A_t) and/or target composition (N/Z) _t, and product mass (A) and product composition (N/Z). Such a thorough study has not existed in this field. Thouusands of the yield data were compiled and found to be smoothly varying functions of these parameters. And the relevant empirical expressions for the reaction yields were derived. The data for the four reaction channels above 140 MeV indicate clear shapes of Δ (1232) -resonance and strong effects of the nuclear medium on the cascade-evaporation process in nuclei with A_t higher than 110-130 or (N/Z) _t larger than 1.3-1.4. All of the results have been updatedly used to test Monte Carlo calculations based on the photoninduced intranuclear cascade and evaporation analysis (PICA) code and its improved versions, and the degrees of the validity of the codes have been demonstrated. New implications for nuclear structure and reaction mechanism have been discussed by referring to the nuclear models, on which the calculations are based. Kinematic information from additional experiments performed on several targets at the Δ-resonance region has supported the findings from the yield measurements. The results of the yield measurements and the characteristic features of the four channels are explained separately, though these channels are competitive. Important consequences and perspectives of the accounted works are pointed out relevantly.