Environmental radiation background variations between residences.

Reports environmental background radiation exposure measurements made in approximately 100 residences in the vicinity of Livermore, California showing variations in annual exposure from 52 to 130 mr. Measurements were made with CaF2:Dy (tld-200) dosimeters at quarterly intervals for a period of 1 year. Dwellings were typically wood-frame structures with stucco exteriors. Interior exposure rates were, on average, about 25% lower than those outdoors. Dosimeters were used without energy filters, since it appears photons with energies less than 100 kev contribute little to the total dose from natural radiation sources. Elimination of energy filters materially simplifies packaging and handling requirements for these measurements.