464 1SOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 19 



many possibilities that exist for otherwise undetected contamination and 

 radiation leakage, no preparations and procedures, however cautiously- 

 planned to guard against exposure, can be considered safe until every possible 

 type and source of radiation has been measured. This requires also that 

 careful monitoring be practiced as a part of normal laboratory operations. 

 Because of the insidious nature of radiation in that no immediate effects are 

 apparent and the fact that the time and effort spent in monitoring do not 

 contribute to the work at hand, there is sometimes a tendency toward 

 leniency or even disregard for adequate monitoring. This fact alone makes 

 it imperative to enforce strictly the monitoring regulations that are adopted 

 by a laboratory. 



The principal techniques and instruments used at the present time for 

 monitoring activities up to the 100-millicurie level are described below. For 

 the most part they are adapted from the methods employed in the labora- 

 tories of the Atomic Energy Commission. Although they are essential to all 

 levels of activity and adequate for levels of activity handled in most private 

 institutions, at very high levels, additional and more elaborate measures 

 must be taken and reference to the declassified project literature listed at 

 the end of this chapter is suggested. 



a. Film-badge Meter. Film badges have been widely adopted as personnel 

 exposure indicators wherever radiations are encountered. They should be 

 worn constantly by all personnel, including visitors, in areas likely to contain 

 contamination, active material, or radiation fields from high-energy accelera- 

 tors. When a permanent record of each person's film exposure is kept, it 

 provides a necessary history of his total exposure as well as legal protection 

 for the institution in suits over injuries claimed to have resulted from exces- 

 sive radiation exposure. 



Beta-particle and gamma-ray film meters usually consist of dental film 

 mounted in a metal holder designed to be clipped on outer clothing such as the 

 lapel or sleeve. Two films are sometimes inserted, one sensitive in the dose 

 range from 20 to 3,000 milliroentgens and the other in the range 0.5 to 20 r 

 [3]. The response of the emulsions is nearly proportional to the roentgen 

 dose and is practically independent of gamma-ray energy over a wide range. 

 There is, however, usually a marked increase in sensitivity for very soft 

 gamma rays in the energy range 0.05 to 0.3 mev where the sensitivity is 

 greater by a factor of ~ 20. Part of the film is covered by a cadmium mask 

 thin enough to pass gamma rays with energies greater than ~ 75 kev, and the 

 remainder of the film is left uncovered except for the paper wrapping to detect 

 beta particles. The darkening of the uncovered portion, however, is not 

 always a reliable measure of beta exposure if soft gamma-ray exposure has 

 been received as well. Also darkening behind the cadmium shield can be pro- 

 duced by the reaction Cd(n, 7)Cd on exposure to slow neutrons. After 



