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Measurement of the Energy Spectrum of Gamma-Emitting Radionuclides in Work Areas to Determine Rem per Roentgen Dose Conversion Factors for the Phosphate Industry



Gamma-ray energy spectra were measured at three phosphate mines, three processing plants, and other off-site areas using a germanium spectrometer. Conversion factors to determine actual exposure from survey meter readings (Ludlum models 12-S and 2401-P) were calculated using the measured energy spectra and the energy-dependent response curves. Dose conversion factors (Roentgen-to-rem) using the energy spectra and the energy-dependent data published by the International Committee on Radiological Protection (ICRP) for six orientations of external exposure were also calculated. Aluminum oxide carbide and lithium fluoride dosimeters were evaluated at the filtration areas and rock storage tunnels of the phosphate chemical processing plants.

Conversion factors of measured to actual exposure for the Ludlum 12-S and 2401-P (calibrated with a 137Cs source) are 0.55 ± 0.07 and 0.62 ± 0.06, respectively, averaged over the phosphate industry. The dose conversion factors of actual exposure to effective dose for the following orientations of external gamma irradiation to the body are 1.07 ± 0.04 antero-posterior, 0.89 ± 0.01 postero-anterior, 0.64 ± 0.01 right lateral, 0.69 ± 0.01 left lateral, 0.86 ± 0.02 rotational, and 0.73 ± 0.01 isotropic. Conversion factors of measured to actual dose (not including orientation of gamma radiation to the body) for the aluminum oxide dosimeter and the lithium fluoride dosimeter are 0.967 ± 0.012 and 0.918 ± 0.024, respectively, for the industry. The conversion factor to change the measured exposure of a survey meter to the effective dose is the product of the measured to actual exposure conversion factor and the dose conversion factor.