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The conversion of a small laboratory into a low background room suitable for counting whole body radiation

Department of Physics Applied to Medicine, Middlesex Hospital Medical School, London, W.1

This excerpt was created in the absence of an abstract.

The room placed at our disposal was a basement laboratory approximately 12x13x11 ft. It was required to reduce the background to a level low enough to enable whole body counting in the nanocurie range to be performed. The room was stripped to the bare walls, thoroughly washed down and then monitored for and activity. There was no detectable a activity but the number of -ray emissions detected by a 2x4 in. diameter NaI (TI) crystal above an energy level of 200 keV was about 220 per second. This compares with a value of around 120 disintegrations per second obtained in a normal brick laboratory at ground level. The discrepancy between these two figures is due to the presence of some relatively large sources of ⁶⁰Co and ²²⁶Ra in the nearby radiotherapy department. The aim was to reduce this background to about 1/25th of its original value by the use of suitable shielding materials.

The amount and type of shielding material were determined by the following factors:

(i) the size of the final room;

(ii) the difficulties of manipulating large or heavy loads in a small room with limited access;

(iii) amount of radiation attenuation required;

(iv) cost.