sparrow: cytogenetic effects of ionizing radiations 



67 



B. Gamma Sources 



The availability of large amounts of long-lived isotopes emitting 

 gamma radiation has given plant radiobiology an unequalled oppor- 

 tunity for exposure of plants or plant parts to large amounts of ioniz- 

 ing radiation and created new opportunities for comparing chronic 

 exposure with the more usual acute methods of treatment. A list of 

 common gamma-emitting isotopes and the intensity of gamma radi- 

 ation per curie per hour at one meter is given in Table 3. The general 

 relationship between the energy of gamma photons and their dose 

 rate at 1 meter is given in Figure 4. 



10.0 



5.0 



2.0 



0.5 



0.2 



o 

 o 



0.1 



0.05 



0.02 



0.01 



DOSE RATE IN AIR AT ONE METER FROM ONE MILLICURIE POINT SOURCE 



0.001 0.002 0.005 0.01 0.02 0.05 0.1 0.2 0.5 



PHOTON ENERGY (Mev) 



1.0 2.0 



5.0 10.0 



Figure 4. — Dose rate in milliroentgens per millicurie per hour at 1 

 meter in air (without absorption) from a point source. After Slack and 

 Way (150). 



A large number of gamma ray sources (mostly Co 60 ) are now 

 available for biological use. These vary from sources of less than a 

 curie used for treatment of small samples in shielded containers up 

 to those of many kilocuries. Some of these are located in large but 



