PubMed · 15909009
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Olav Spigset, Lars Slørdal. 2005-05-19. [Basic pharmacokinetics--balance].. https://pubmed.ncbi.nlm.nih.gov/15909009/
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Tritium occurs from both natural and manufactured processes. In the environment, tritium can exist in the form of tritiated water (HTO) and in an organic form known as organically-bound tritium (OBT). Although, the concentrations of environmental OBT are relatively low, there is concern that current risk factors may underestimate the risk from OBT. Because tritium poses an internal hazard at cellular levels, microdosimetric techniques provide suitable tools for the study of radiation quality of tritium. In this study, microdosimetric simulations are performed for tritium uniformly distributed in a medium, and for tritium bound to biologically critical sites of dimensions from 10 nm to 2 microm. Results of local energy density are different for these two cases in microscopic regions. Based on the spatial distribution of energy deposition, dose mean lineal energies are calculated for tritium in forms of HTO and OBT. The dose mean lineal energies of OBT are about a factor of 1.7 higher than those of HTO in a wide range of target dimensions of biological interest. The results are consistent with radiobiological findings that OBT is about twice as effective as that of HTO.
In this contribution quantum/classical surface hopping methodology is applied to vibrational energy relaxation of a quantum oscillator in a classical heat bath. The model of a linearly damped (harmonic) oscillator is chosen which can be mapped onto the Brownian motion (Caldeira-Leggett) Hamiltonian. In the simulations Tully's fewest switches surface hopping scheme is adopted with inclusion of dephasing in the adiabatic basis using a simple decoherence algorithm. The results are compared to the predictions of a Redfield-type quantum master equation modeling using the classical heat bath force correlation function as input. Thereby a link is established between both types of quantum/classical approaches. Viewed from the latter perspective, surface hopping with dephasing may be interpreted as "on-the-fly" stochastic realization of a quantum/classical Pauli master equation.
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