130 LOCKHART, PATTERSON, AND SAUNDERS S | GROSS BETA ACTIVITY, PC/M? 13 DEC. NOV. L JAN. | wml. FEB. MAR, 1962 APR. len MAY | JUNE 1963 Fig. 5-——Concentration of fission-product beta activity in the ground- level air at Washington, D. C., during 1963.