Counting Methods Used in Los Alamos Air Sampling
1. Gamma Background
External gamma background determinations are made daily using a portable
GM survey meter with the shield closed (Victoreen 2638 beta-gasma survey
meter). In addition a recording gemma meter is cperated, the shielded
probe being located three feet above the Administration Building reof,
2. Beta Activity of Particulate Matter in Air
Twenty-four hour air samples are collected seven days a week. The sampler
was fabricated at Los Alamos; the particulate matter is collected on a
MSA all dust filter, Cat. No. CR17651, approval No. 2133. Approxinately
1,00 cubic meters of air is sampled daily. Five to eight days after
collection the filters are counted for beta activity in a thinewindgy gas
(methane) flow counter having an overall efficiency of LX for Sr-¥7¥,
Results are reported in terms of microcuries per cubic meter of air,
equivalent to Sr-¥”’™
beta activity. The results indicate only the beta
activity resulting from relatively long half-elived emitters.
3. Beta Activity in Rain Water
One hundred cubic centimeters of rain water was evaporated after adding
dilute nitric acid. The residue was dissolved in distilled water and
transferred to a four inch by nine inch aluminum foil dish and svaporated
to dryness with an infra-red lamp. The foil was counted in the same
thin-window gas flow counter used for filter paper counting.