Mass-yield distributions of fission products from photo-fission of Pb-nat induced by 50-70 MeV bremsstrahlung

Abstract

The mass-yield distributions of various fission products have been determined in the 50-, 60- and 70-MeV end point bremsstrahlung induced fission of Pb-nat using off-line gamma-ray spectrometric technique in the electron linac at Pohang Accelerator Laboratory, Korea. The mass-yield distributions are symmetric with average mass of 102.34, 102.25 and 102.03 and FWHM of 21, 22 and 23 mass unit, respectively. From the present data and literature data in the 50-85 MeV bremsstrahlung induced fission of Bi-209 the following observations were obtained: (i) The average masses of the yield distributions in the 50-85 MeV bremsstrahlung induced fission of Pb-nat and Bi-209 are around 102.25 +/- A 0.25 and 103 +/- A 0.5, respectively. (ii) The FWHM of the mass-yield distributions increases from about 21 mass units at 50 MeV to 23 mass units at 70-85 MeV, which is explained from the point of increase in multi-chance fission probability with increasing excitation energy. (iii) Within the bremsstrahlung energy range of 50-85 MeV, the role of nuclear structure effect in the mass-yield distribution was observed in the photo-fission of Bi-209, whereas it was not seen in case of Pb-nat. This may be due to the presence of so many isotopes in Pb-nat unlike mono-isotopic Bi-209.