Sec. 19.7] THE SAFE HANDLING OF RADIOACTIVE MATERIALS 467 



contamination should be regarded as a hazard particularly if it is alpha active 

 since it becomes a potential source of radioactive dust which then may be 

 breathed or ingested. More often the principal objects of contamination are 

 equipment and apparatus used in handling and in radiochemistry. Shoes, 

 hands, and laboratory coats are also subject to contamination and should be 

 monitored when contamination is possible. 



Surface monitoring normally is the most important function of routine 

 surveys and should in part also be made a responsibility of the persons using 

 apparatus and work space. Periodic surveys should include measurements 

 of the alpha, beta, and gamma activity of all permanent surfaces such as 

 floors, workbenches, hoods, telephones, sinks, etc., where active material 



Table 43. Radioactive -contamination Tolerance Levels* 



Object Tolerance Level 



Hand 1 mr/hr of (3 and y 



Shoe : outside 14 mr/hr of (3 and y 



inside l^ mr/hr of (3 and y 



Clothing y z mr/hr of f3a.nd y 



1,500 disintegrations/min of a from area of 



150 cm 2 



Thyroid 1,000 mr/24 h in thyroid 



Table tops, floors, etc 0.1 mr/hr with counter at surface 



2,000 disintegrations/min of a from area of 



150 cm 2 



Smear tests on any surface : 



2 sq. in. filter paper smeared 200 cpm of /3 and 7; 



over 12 sq in. and counted disintegrations/min of a 



with a, 13, and 7 counters 



* These tolerance levels are based on values established for the Clinton Laboratories of the Atomic 

 Energy Commission, Oak Ridge, Tenn., and reported in references 1, 3, 4, and 7. 



could be spread. When a surface shows an activity higher than the tolerance 

 level, it should be posted with signs and necessary remedial steps taken as 

 soon as possible. 



Part of the responsibility for monitoring working surfaces and equipment 

 is placed with the person working with them. The suggested procedure as 

 practiced in some laboratories requires that such persons survey the work 

 surfaces and apparatus before work is begun and again when work is com- 

 pleted, or at the end of his shift. This also applies to glassware and other 

 equipment that has just been cleaned. After a spill, in hoods as well as on 

 benches and floors, the affected area should be carefully surveyed after it 

 has been cleaned, and it should not be considered decontaminated until a 

 survey shows that the activity is no greater than the tolerance level. 



A great variety of portable survey instruments have been developed which 

 are useful for surface-activity measurements, and some of these are now com- 

 mercially available. They include electroscopes with thin windows suitable 



