454 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 19 



be somewhat simpler for all activities at the microcurie level, or even at the 

 millicurie level for materials that emit only beta or alpha particles, the danger 

 of contamination should always be regarded as serious, particularly where 

 long-lived isotopes are involved. Radiochemistry and other processing 

 therefore should be confined strictly to those rooms prepared for these 

 processes so that the spread of contamination by possible exchange of instru- 

 ments, waste, clothes, etc., can be rigidly controlled. It is also clear that 

 entirely separate rooms placed as far as practicable from active materials 

 must always be maintained for radioassay and for experimentation with 

 prepared active materials. 



The most important feature is an adequately shielded and readily decon- 

 taminated hood. Concrete is probably the most economical material for this 

 kind of structure, and it enables easy fabrication. The thickness of all sides 

 including top and bottom should be great enough to attenuate the intensity 

 of all gamma radiation to considerably less than that which will deliver a 

 tolerance dose of 0.1 r per day at any accessible outside surface. The floor 

 of the hood should slope downward to localize the spread of contamination 

 caused by spillage, and it should be sufficiently large to enable nearly all 

 operations with active materials to be performed under the hood. If the 

 exhaust chimney passes through other portions of the building, particular 

 care must be taken to ensure against leakage of fumes due to corrosion and 

 also excessive accumulation of possible active condensates. Normally when 

 volatile or gaseous active materials are processed in the hood, some means is 

 provided for condensing and collecting the material. 



In addition to a hood, each radiochemistry laboratory should contain a 

 permanent vault or cove for storing all radioactive materials not in immediate 

 use. Concrete or lead structures are the most suitable for this purpose. 

 With properly designed compartments, each with its separate closure, access 

 to one compartment and its contents is possible without danger of excessive 

 radiation exposure from other materials stored in the vault. Wall thickness 

 should be sufficient to attenuate gamma radiation to negligible intensity in 

 all directions, and closures should be carefully checked with Geiger counters 

 to detect possible leakage of radiation scattered through cracks or poorly 

 fitting closures when high-intensity gamma emitters are stored. 



Improvised storage coves hastily assembled with lead bricks should be 

 avoided except in emergency since there is often a tendency to neglect bottom 

 and back shielding and to overlook radiation leakage. 



Additional permanent or semipermanent laboratory fixtures may include 

 large general shields of lead surrounding areas or apparatus handling high- 

 intensity gamma- and beta-active material. 



Surface finishing materials for table and bench tops and other working 

 areas may be expendable absorbing materials such as masonite or they may be 



