The penetration into concrete of gamma radiation from fallout has been measured in an idealized geometry as a function of time after the detonation of a nuclear device. At the same time, the exposure dose rate in air at heights of 3 and 9 ft above the ground was measured with two detectors suspended from a tower and shielded from above with lead so as to be sensitive primarily to radiation from fallout on the ground. For this test a 'sandwich' made of seven concrete slabs, forming a mass of concrete with face dimensions large enough to reduce edge effects to a negligible amount, was buried with its top surface flush with the ground. Remote-reading detectors were placed between the concrete slabs, thus permitting measurements of dose rate as a function of depth in concrete. The concrete mass and the tower were located in the center of a cleared and leveled area approximately 200 yd in diameter. Thus the gamma radiation at the detectors originated from an essentially infinite-plane source of radiation. Results are presented both as a function of time after detonation and of depth of penetration of the radiation into concrete. A comparison of the results with theoretical calculations is made. (Author).