thicknesses of aluminum absorbers Calibration of the pressurized were placed over an array of dosimeters ion chamber against a point 226), at three sites on Bikini Island. source, A the method used with the feather analysis of the beta attenua- instrument in this study, leads to tion curves gave a maximum beta about a 3% overestimate in the energy between 1.5 and 2.2 MeV. measurement of "typical" environmen~ Given the known predominance of tal fields in this country.” 90.99, beta activities in the soil, similar correction were made to this energy range is consistent with these data, the 2.27 MeV 90, beta radiation. independent exposure-rate The analysis also revealed that the determinations (ion chamber and LiF average beta contribution to the TLD) would be within 10%. total LiF exposure rates was 27% -- considered to be satisfactory a rather significant contribution. agreement between the two reference Therefore, it was necessary to reduce techniques used in this work. the LiF results by this amount to Hence, on the basis of these results, obtain the free-air gamma-ray the NaI scintillation readings were exposure rates. normalized to the output of the The comparison between the ion If a the agreement of the two This is pressurized ion chamber. chamber results and the LiF gamma- of points in Fig. 3 is not as good as that in Fig. 2. This difference is most likely due to the beta con- tribution to the LiF results, which May vary throughout the islands, causing spread in the data. Departure from the 1:1 relationship ain S Oo oO 6 5&5 One also finds that the correlation Nn w 58 about 13% between the two methods. —_ two data sets gives agreement of oO A linear regression of the lon chamber response — uR/h Fig. 3. eo Oo ray exposure rates is presented in a 0 response or to insufficient 30 i 40 50 tt 60 70 8 LiF response — uR/h in Fig. 3 may be due to an overcorrection of the TLD data for beta 10 20 ! Fig. 3. Comparison of responses of the pressurized ion chamber The contri- consideration of the ion chamber with LiF TLD's. data for energy dependence. has been subtracted. bution due to cosmic radiation