PNNL

Abstract

Inference of intakes and doses from inhalation of metal tritide particles has come under scrutiny because of decommissioning and decontamination of U.S. Department of Energy facilities. Since self-absorption of radiation is very significant for larger particles, interpretation of counting results of metal tritide particles by liquid scintillation requires information about emission spectra. Similarly, inference of dose requires knowledge of charged particle and photon spectra. Using the PENELOPE Monte Carlo radiation transport computer code, we calculated various dosimetric, microdosimetric and spectral emissions from tritides of Sc, Ti, Zr, Er, and Hf. For metal tritide particles with physical diameters in the range from about 0.01 mm to 25 mm, we present energy emission fractions, distributions of microdosimetric quantities, and the emitted spectra of electrons and bremsstrahlung photons. Results characterizing the effects of uncertainties associated with the composition and density of the tritides are also presented. Emission spectra are used to illustrate trends in the relationship between "apparent" and "observed" activity as a function of particle type and size. Emissions from metal tritide particles are weakly penetrating, and the emission spectra tend to "harden" as the particle size increases. Microdosimetric considerations suggest that the radiation emitted by metal tritides can be classified as a low Linear Energy Transfer (LET) radiation source. For cells less than about 7 mm away from the surface of a metal tritide, the primary dose component is due to electrons. However, bremsstrahlung radiation may deposit some energy tens, hundreds or even thousands of micrometers away from the surface of a tritide particle.