Calibration of were placed over an array of dosimeters ion chamber against a point 22625 at three sites on Bikini Island. source, A the pressurized 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. 906 90y 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, 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 on the basis of these results, pressurized ion chamber. chamber results and the LiF gammaray exposure rates is presented in Fig. 3. A linear regression of the two data sets gives agreement of about 13% between the two methods. One also finds that the correlation of points in Fig. as that in Fig. 2. 3 is not as good This difference is most likely due to the beta contribution to the LiF results, which may vary throughout the islands, lon chamber response — uR/h whe, thicknesses of aluminum absorbers causing spread in the data. 0 wu Departure from the 1:1 relationship in Fig. 0 3 may be due to an over- correction of the TLD data for beta response or to insufficient consideration of the ion chamber data for energy dependence. 10 [Pot 20 30 40 50 60 70 80 LiF response — uR/h Fig. 3. Comparison of responses of the pressurized ion chamber with LiF TLD's. The contri- bution due to cosmic radiation has been subtracted.