Determination of photon conversion factors relating exposure and dose for several extremity phantom designs.

Dosimetric measurements were performed to determine the exposure-to-dose conversion factors (Cx) for simple extremity phantoms suitable for extremity dosimeter performance testing. The phantoms studied represented the forearm or lower leg and the finger. Measurements were performed for solid plastic phantoms and for phantoms containing simulated bone material to determine the effect of backscattered radiations from the simulated bone to the phantom surface. Photon beam energies used for the measurements ranged from 16 keV to 1.25 MeV (average). The Cx factors for the finger phantoms did not vary significantly with phantom composition. The Cx factors in the arm/leg phantoms with the bone simulant material differed significantly from those for the solid plastic phantom over the energy range of 40-100 keV. This effect was attributed to the preferential absorption of the lower energy backscattered photons by the higher atomic number material that was contained in the bone-simulant insert. The position of the bone-simulating material below the surface of the phantom was more important than its size or level of bone equivalency. For calibrations and dosimeter testing, Al was found adequate as a bone-simulating material.

Toxicology of 85Kr: chronic exposure studies.

Male and female Wistar rats were exposed chronically to graded doses of 85Kr to determine long-term biological effects of simulated environmental exposure. Rats were exposed in 4 groups, including room air-exposed controls and 3 groups exposed to 85Kr concentrations equivalent to 10(2), 10(3) and 10(4) times the maximum permissible concentration (MPC) for the general population (3 X 10(-7) microCi/ml). Exposures continued 24 hr/day, 7 days/week for 808 days, until only approximately 10% of the original 400 rats were alive. No effect of 85Kr exposure was observed on weight gain or tumor incidence, including leukemias. The results support the adequacy of established 85Kr exposure limits for the general population in light of the absence of evidence of build-up in tissues after chronic exposure and the lack of exposure-related biological effects in rats after near-lifespan exposure to concentrations equivalent to 10,000 times the MPC.