Product yields for the photo-fission of 209Bi with 2.5 GeV bremsstrahlung

Abstract

The mass-yield distribution of fission products in the 2.5GeV bremsstrahlung-induced fission of 209Bi have been determined by using the recoil catcher and the off-line γ-spectrometry technique in the high energy electron linac at the Pohang Accelerator Laboratory. The mass-yield determination involves the measurements of cumulative yields for 32 fission products and independent yields of 17 fission products in the photo-fission of 209Bi nuclei. It was found that the mass-yield distribution of fission products in 209Bi is symmetric with an average mass of 95±0.5 and a FWHM of 51±2.0 mass units. Present data at 2.5GeV along with the literature data at 1GeV, 700–600MeV, and 85–28MeV were interpreted from the point of increase of multi-chance fission and multi-nucleon emission probabilities with an increase in excitation energy. It was found that the average mass of the mass-yield distribution of the fission products decreases from 103±0.5 at 28–85MeV to 95±0.5 at 2.5GeV. On the other hand, the FWHM of the mass-yield distribution increases from 19 mass units at 28–40MeV to 51 mass units at 2.5GeV. It was also found that the nuclear structure effect observed at the photo-fission of 209Bi with 28–85MeV bremsstrahlung is washed out at higher energy.