Sec. 19.6] THE SAFE HANDLING OF RADIOACTIVE MATERIALS 461 



*16. Rubber gloves must be worn when directly handling receptacles 

 containing active solutions. 



*17. Masks must be worn when working with gaseous or volatile active 

 materials. 



*18. Pipetting solutions by mouth is strictly forbidden. 



*19. Smoking, eating, storing, or preparing food in the laboratory is forbidden. 



*20. Hands must be washed with soap and water before smoking and eating. 

 19.6. Radiation Shields. Shields and barriers intended for high-energy 

 neutrons and gamma and beta radiation should be designed with three factors 

 in mind: attenuation of direct radiation; emission of secondary radiation, 

 including both x-rays and electrons; and scattered radiation. Adequate 

 thickness of shielding material eliminates the first two factors. Insufficient 

 thickness, it should be noted, can be worse under certain conditions than no 

 shielding at all since the intensity of secondary radiation produced in the 

 shield may be many times greater than the primary and its secondary radia- 

 tion in air alone. The extreme case in point is encountered when the shield 

 thickness just equals the transition depth for thcgamma rays or fast neutrons. 

 Scattered radiation is sometimes difficult to predict but can be eliminated 

 by adequate coverage and by avoiding cracks and poor joints in shields. In 

 all cases when shields are assembled, the shield surface and working area 

 should be monitored before personnel are permitted to work. 



Concrete, because it is comparatively inexpensive and structures are 

 easily fabricated, is the most useful material for large shield structures such 

 as hoods and storage vaults. But because of the large variety of shields 

 needed in diverse procedures, lead is more convenient for most other shielding 

 purposes. It is usually made available in some convenient standard sizes of 

 plates and blocks small enough to be handled easily. For example, the lead 

 shield stock may include plates measuring 12 by 6 by 3^2 m - an d blocks 3 in. 

 square or 6 by 3 by 2 in. With these bricks and plates, shields of any size and 

 shape can be quickly erected for a specific operation. 



Estimates of shield thickness are easily obtained when the maximum energy 

 of the radiation and the absorption coefficient or half-value thickness are 

 known. If I is the intensity or dosage rate at the inside surface of the 

 shield, the intensity / of the primary radiation at the outside surface is 



/ = I e~^ 



where y. = absorption coefficient 



x = thickness 



or in terms of half-value thickness T the transmitted intensity through n half- 

 value la vers is ^T7»l &"■ 



J-M- ^S1H^> 



/•a 



'USSKARYI 





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