Bimodal fission

The other interesting feature in SF of very heavy actinides is bimodal fission. The existence of two distinctively different scission configurations for the same mass division was demonstrated in SF of the heavy actinides (Balagna et al. 1971 Hulet et al. 1986, 1989). The most... 

As typical data, the TKE and mass-yield distributions observed in SF of Md (Hulet et al. 1989) are depicted in Fig. 18.14a, b, respectively two components are clearly seen in the TKE distribution. The two-component analysis yielded the fact that the high-TKE events mostly constitute the sharp mass-yield curve around symmetry and the low-TKE ones a broad flat-topped distribution. Some theoretical calculations to understand bimodal fission of heavy actinides have been extensively performed (Warda et al. 2002 Asano et al. 2004 Bonneau 2006 Dubray et al. 2008 Ichikawa et al. 2009). 

There are, of course, many possible combinations of fragment pairs which may be formed by the disintegration of the compound nucleus. It is found that the preferred mode of break-up for fission caused by slow neutrons is a highly unsymmetrical one, where the most probable products are in the mass regions around 95 and 140. This is illustrated in Fig. 2.3, which shows the percentage yield of fission products from the fission of as a function of mass number. Similar bimodal distributions are obtained for the fission of the isotopes and Pu, which also undergo fission with slow neutrons. 

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