640 ADOLF F. VOIGT 



3600 X m, and W = energy required to produce one ion pair = 32.5 

 X lO"*' m.e.v. in air. 



The uncertainties in W and n make this equation only an approxi- 

 mation. As written it apphes only if each decay process gives one 

 and only one y I'ay. For a substance with a complex decay scheme it 

 is necessary to replace E in the above by YlPt^t "^ which pt is the frac- 



i 



tion of the total number of disintegrations in which a y ray of energy 

 Ei is given off. 



In order to calculate the amount of shielding necessary to bring 

 the radiation at a given distance down to the desired value, the half- 

 thickness of the radiation must be obtained from a curve such as 

 Figure 2. From this half-thickness the necessary shielding can be 

 calculated or one can determine the safe working distance with given 

 shielding (60). Calculation of dosage for /3 radiation is less certain. 

 jS rays do not have enough penetration to constitute a serious hazard 

 if shielding is provided in the walls of the containing vessel or in the 

 gloves and clothes of the worker. Only in the case of high energy /3- 

 ray emitters will additional protection be necessary and it is more 

 readily provided by heavy-walled apparatus than by a shield. 



The same principles apply if a worker, experimental animal, or 

 biological system is exposed to radiation from an internal source, 

 whether by accident or design. Again one assumes maximum toler- 

 ance to be 100 mr. per day for y radiation, but now the day is 24 

 hours long. Tolerances for other types of radiation have been set at 

 100 mr.e.p. for ^ rays and 10 mr.e.p. for a particles. Calculations 

 in this field involve a knowledge of the behavior of the particular 

 element in the body and its possible concentration in the various 

 organs, its biological elimination rate and other factors. For these 

 aspects of the problem, the reader is referred to the chapter by Gray 

 as well as to several recent articles {62,63) . 



2. Instruments and Methods 



Monitoring assumes several aspects. Personnel must be moni- 

 tored to see that they do not get overdoses while handling the active 

 material. Surfaces of working areas, apparatus, and glassware must 

 be surveyed after active materials have been handled and possibly 

 spilled to reduce the possibility of ingesting and inhaling radioactive 

 dust and, more serious, to eliminate the danger of contaminating one 

 experiment with the spilled activity from previous ones. Personnel 



