468 1S0T0PIC TRACERS AND NUCLEAR RADIATIONS [Chap. 19 



for beta and gamma radiation, air ionization chambers, and counters. Air 

 ionization chambers are particularly useful for detecting alpha particles and 

 very soft beta particles since there is no intervening absorber between the 

 surface to be measured and the sensitive volume of the chamber. Geiger 

 counters with thin windows may serve the same purpose and are more sensi- 

 tive in some cases, but generally they are more useful for energetic beta 

 particles and gamma rays. Either the bell or cylindrical types can be 

 mounted in appropriate holders to enable the operators to scan areas by 

 moving the counter with the window immediately adjacent to the surface. 

 Both ionization chambers and counter tubes are sometimes fitted with sliding 

 niters which can be moved over the window. With no filter in place, alpha 

 and beta particles are registered; with aluminum foil, only beta and gamma 

 radiation are admitted; and with sufficient thickness of bakelite, lucite, or 

 other plastic, alpha and most beta particles are stopped and only gamma 

 radiation is registered. 



19.8. Shipping Regulations. On the basis of investigations and sugges- 

 tions submitted by the subcommittee on shipment of Radioactive Substances 

 of the committee on Nuclear Sciences of the National Research Council, 



HANDLE CAREFULLY 



RADIOACTIVE MATERIAL 

 CLASS D POISON Group I or II 



NO PERSON SHALL REMAIN WITHIN THREE FEET OF THIS CONTAINER UNNECESSARILY 

 DO NOT PLACE UNDEVELOPED FILM WITHIN IS FEET OF THIS CONTAINER 



Principal radioactive content — , , — ..- 



Activity of contents... 



Radiation units from package No. _ - 



Not more than 40 units shall be loaded in one 

 car or one motor vehicle or held at one location. 



Thl» la to certify that the contents of this package 

 are properly described by name and are packed 

 and marked and are In proper condition for 

 transportation according to the Regula- 

 tion* prescribed by the Interstate 

 Commerce Commission. 



Shipper's name required 



hereon for ship. 



mente by 



EXPRESS 



Fig. 121. Label required for outside shipping container of Groups I and II radioactive 

 materials. Red printing on white paper measuring 4 by 4 in. square. 



