l.NJLRV AM) l<l.t:c)\i:RV l.N M:L I R( )N-IRRAI)IAT1:D ammai.s 



dose of fission neutrons produces a hit^di percentai^e of irreparable chromo- 

 some breaks and leads to a prolonged delay in cell division (at least 22 hours)*. 

 A comparison of duodenal damage and recovery rate suggests a relative 

 biological effectiveness (R.B.E.) of greater than six when comparing the 

 efiects of neutrons and y-rays on intestinal sensitivity. 



A section of duodenum from a mouse irradiated with fission neutrons is 

 illustrated in Figure 1. The intestine was removed four days after the single 



Figure 1. Cross-section of mouse chujclcnum 94 hours alter 350 rad fission 

 neutrons (single whole-body irradiation) . 100. (Reduced by one-half when 



reproduced.) 



neutron exposure (350 rad). This photograph shows the results of typical 

 destruction of the crypts and the extensive loss of the epithelial covering of 

 the duodenal villi at this time. Note the reduced size of the villi, the enlarged 

 cells, chromatin masses, and severe damage and denuding of the mucosa. 

 This mouse would undoubtedly have died from bactcraemia and septicaemia 

 within a day or two. 



222 



