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

Abstract

The mass-yield distribution of fission products in the 2.5 GeV bremsstrahlung-induced fission of Bi-209 have been determined by using the recoil catcher and the off-line gamma-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 Bi-209 nuclei. It was found that the mass-yield distribution of fission products in Bi-209 is symmetric with an average mass of 95 +/- 0.5 and a FWHM of 51 +/- 2.0 mass units. Present data at 2.5 GeV along with the literature data at 1 GeV, 700-600 MeV, and 85-28 MeV 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 28-85 MeV to 95 +/- 0.5 at 2.5 GeV. On the other hand, the FWHM of the mass-yield distribution increases from 19 mass units at 28-40 MeV to 51 mass units at 2.5 GeV. It was also found that the nuclear structure effect observed at the photo-fission of Bi-209 with 28-85 MeV bremsstrahlung is washed out at higher energy. (C) 2009 Elsevier B.V. All rights reserved.