23 



INJURY AND RECOVERY IN 

 NEUTRON-IRRADIATED ANIMALS* 



Howard H. Vogel, Jr., Donn L. Jordan and Samuel Lesher 



Biological and Medical Research Division, Argonne National Laboratory, 



Lemont, Illinois, U.S.A. 



INTRODUCTION 



During the past several years a programme has been carried on at Argonne 

 National Laboratory, near Chicago, Illinois, in which the biological effects 

 of fission neutrons and of ^"Co y-rays have been studied and compared in a 

 wide variety of organisms^. All exposures have been carried out in a special 

 gamma-neutron radiation chamber'^. This exposure facility has been used 

 in various experiments over the past six years, first, at the heavy-water 

 reactor, CP-3', and, more recently, at Argonne's present research reactor, 

 CP-5. The fast neutron flux was obtained by Zirkle's method^ of using the 

 thermal column of a reactor in conjunction with a sheet of uranium to 

 convert the thermal flux to one of fission neutrons. Pure y radiation was 

 obtained from eighteen ""Co sources mounted on a turret as part of the 

 chamber. 



MORTALITY MODES: INTESTINAL AND HAEMATOLOGICAL SYNDROMES 



Evidence has been presented"* that exposure to these two radiations appears 

 to produce death in mice by different mechanisms. A characteristic early 

 mortality mode is observed after irradiation of mice with fission neutrons^. 

 Recent histological and cytological studies of the duodenum of neutron- 

 irradiated mice indicate that this early four to ten-day mortality is correlated 

 with severe damage and partial denudation of the intestinal mucosa". On 

 the other hand, mice in-adiated with "°Co y-rays, within the acute lethal 

 dose range, do not usually die from this intestinal syndrome. Although 

 their intestinal cells show damage following irradiation, recovery is rapid, 

 and the mucosal lining appears in good condition three to four days after 

 exposure to y-rays (up to 1000 rad, single, whole-body dose). Mice dying 

 after X or y irradiation, within the acute lethal dose range, usually show a 

 high mortality peak near the end of the second week after exposure, with 

 a characteristic haematological syndrome. 



The intestinal syndrome, in neutron-irradiated mice, seems to reach a 

 peak between three and a half and six days following exposure. The duo- 

 denum of mice exposed to a single dose (350 rad) of fission neutrons is 

 severely damaged with complete destruction of the crypts and the subsequent 

 extensive loss of the epithelial lining of the villi. Less than half of such 

 irradiated animals live beyond the six-day period. Irradiation with this 



* This work was performed under the auspices of the United States Atomic Energy 

 Commission. 



221 



