Photofission of ¹⁹⁷Au at Intermediate Energies

Abstract

The reaction yields of 58 radionuclides with the mass number A = 42-131 produced in the photofission of ¹⁹⁷Au by bremsstrahlung of end-point energies (E0) from 300 to 1100 MeV have been measured using the catcher foil technique. The reaction yields increase steeply with an increase of E0 up to 600 MeV and increase gradually above 600 MeV, indicating the resonance-type excitation function attributed to the (3, 3) resonance. The charge distribution was found to be well reproduced by a Gaussian function with the most probable charge (Zp) expressed by a linear function of A, i. e., Zp = RA + S, and with the A-independent full width at half maximum (FWHM_CD). The charge distribution parameters R, S, and FWHM_CD were found to be independent of Eο above 600 MeV, reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values at E0≥600 MeV were R = 0.424 ± 0.001, S = 0.7 ± 0.1, and FWHM_CD = 2.2 ± 0.1 charge unit (c.u.). Based on these parameters, the symmetric mass yield distributions with the most probable mass Ap of 92 ± 1 mass unit (m.u.) and the width FWHM_MD of 39 ± 1 m.u. were obtained. The characteristics of the charge and mass yield distributions were discussed by referring to the literature data including those of proton-induced reactions.