Office of Radiation Protection BACKGROUND RADIATION ACCUMULATION AND LOWER LIMIT OF USED BY THE CENTRALIZED EXTERNAL DOSIMETRY SYSTEM DETECTION IN THERMOLUMINESCENT BETA-GAMMA DOSIMETERS

A value for "average background radiation" of 0.75 mR/week has been determined from a total of 1680 thermoluminescent dosimeters (TLD's) exposed in 70 houses for periods up to one year. The distribution of results indicates a rather large variation among houses, with a few locations exhibiting backgrounds double the general average. Some discrepancies in the short-term background accumulation of TLD's have been explained as being due to light leakage through the dosimeter cases. In addition the lower limit of detection (LD ) for deep and shallow dose equivilents has been determined for these dosimeters. The LD for occupational exposure depends strongly on the time a dosimeter is exposed to background radiation in the field. The LD can vary from a low of 2.4 mrem for high energy gamma rays when the background accumulation period is less than a few weeks to values as high as 66 mrem for uranium beta particles when background has been allowed to accumulate for more than 21 weeks.