DETERMINATION OF FISSION BARRIER HEIGHTS FROM BETA-DELAYED FISSION

Beta delayed fission (βDF) gives a possibility to investigate the fission barrier for nuclei far off beta stability. However, before any information on the fission barrier can be extracted, the effect of low-lying structures in the beta-strength function (Sβ) on the βDF branching ratio has to be considered. This is in general not done. In this paper the lowlying structures that occur in Sβ are discussed and microscopic calculations for the Gamow-Teller strength function are presented for232Th (β--decay) and232Pu,240Cm,244,248Cf and248Fm (β+-decay). Using the calculated strength functions β+DF branching ratios are calculated and compared with the experimental ones. The sensitivity of the results to different shapes of Sβ is investigated. It is concluded that, when the expected structures in Sβ are considered, there are at present no indications from β+ DF measurements that the errors in the fission barrier calculations are larger than the uncertainty given for those calculations. The difference in magnitude between the β- DF and the β+DF branching ratios is also explained by the occurrence of low-lying structures in Sβ. © 1979 Springer-Verlag.