407836 YY HASL SURFACE ATR SAMPLING PROGRAM Gamma Activity Measurements for March 1970 Attached are the results of the gamma activity analyses of filters from the HASL Surface Air Sampling Program for the month of March 1970. The weekly samples are composited on a monthly basis and counted on an 8" x 4" sodium iodide (Tl) crystal. The integrated response between 100 Kev and 3.0 Mev is corrected by the average detection efficiency (35%) of the gamma photons present in fallout. The results are reported in units of photons per minute per 1000 standard cubic meters (sea level conditions of the ICAO Atmosphere). 1 - Gamma concentrations in surface air for 1970 Figure 1 - Gamma Activity as a function of latitude, March 1970 Figure 2 - Average monthly hemispheric gamma concentrations f ae aa oe Table