Protective Methods in Radiology 273 



of expired air. Assuming that the tidal respiratory volume per 

 minute is 5 liters, it can be calculated that, if all the radon formed 

 from 0.1 [ig of radium in the body appeared in the breath, the 

 radon concentration of the expired air would be 2.5 X 10"^^ curie 

 per liter. The American figure of 10"^^ curie per liter thus as- 

 sumes that 40% of the radon is liberated. On the same basis, 

 the British figure of 10"^^ curie per liter corresponds to 1 [ig of 

 radium in the body. 



It must be mentioned, however, that the ratio of the liberated 

 to the trapped radon varies considerably, not wholly in relation 

 to the length of time during which the radium has been deposited. 

 In examining luminizers, the National Physical Laboratory, there- 

 fore, measures not only the exhaled radon but the gamma radia- 

 tion from the disintegration products of the trapped radon, as 

 this is the only way in which to assess accurately the total amount 

 of radium in the body. 



There is much conflicting evidence regarding radium poison- 

 ing: 



1. Evans ''^ reported that 7 persons carrying between 0.02 |.ig 

 and 0.5 \ig for 7 to 25 years revealed no clinical symptoms 

 of chronic radium poisoning. Similar examples can be 

 quoted from the results of tests made at the National 

 Physical Laboratory on workers who have been engaged 

 in luminizing for periods up to 30 years. In one case, a 

 person who worked full time on actual luminizing for 

 30 years was found to have 0.7 \ig radium in her body, and 

 there were no apparent ill effects. 



2. Opposed to the above is the evidence that fatalities have 

 occurred when the radium burden was above 1.2 \ig. 



3. The "normal" amount of radium in the body is between 

 0.01 and 0.015 ug. Expressing this in another way, , 

 Jones and Day ^- calculate that the normal radium content 

 of the body produces 0.025 X 10^ ions per cubic centimeter 

 of tissue per second. For comparison purposes, they show 

 that the radiation tolerance dose of 1 r per week produces 

 2.69 X 10^ ions per cubic centimeter per second, while a. 



