Sec. 6.6] 



FISSION 



155 



further enhanced by the variation in initial energy, charge, and mass of the 

 fragments. Efforts to calculate a stopping formula and range-energy rela- 

 tion have been unsuccessful, mainly because the charge of the fragment is a 

 rapidly changing and, as yet, unknown function of velocity. The stopping 

 theory proposed by Bohr [25] is, however, confirmed in principle by results 

 of range and stopping-power measurements [33,34,35]. As is to be expected 

 from the mass and energy division of fission fragments, short- and long-range 

 groups are found which have been shown to correspond to the light and heavy 

 fragments, respectively. Ranges of the two groups in various gases are given 



1.2 1.6 2 2 4 



Range in cm air 



3.2 



Fig. 46. Velocity-range curves of light and heavy fission fragments in air [34]. 



in Table 21. Table 22 gives the stopping power of various solid absorbers 

 determined by Segre and Wiegand (37) from absorption measurements with 

 thin foils. More detailed ranges are given in Table 23. 



Table 21. Ranges of Fission Fragments in Gases [35] 



6.6. Radioactive Chains. The excitation energy of fission fragments 

 which still remains after evaporation of prompt neutrons is subsequently lost 

 by emission of delayed neutrons, beta particles, neutrinos, and gamma rays. 

 The remaining excess of neutrons is transformed to protons by successive 

 beta decay or, less frequently, lost by delayed neutron emission, until the 



