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Depleted uranium weapons, metal particles and radiation dose
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C Busby,
03/11/2005
Green Audit, Castle Cottage, Sea View Place, Abersytwyth, SY23 1DZ, UK
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Abstract:
The biological effects of ionizing radiation are mainly mediated through the formation of ions and free radicals formed by interaction between secondary electrons and the genetic components of living tissue, mainly chromosomal DNA. Conventional risk models (eg. of the International Commission on Radiological Protection) concede the importance of ionization density at the target through a system of weighting of the quantity-absorbed dose to allow for high ionization density, eg. in the case of alpha particles, which carry a weighting of 20. These weightings are not yet extended to all other situations of high ionization density, eg. DNA-bound, Auger emitters, even though these are known to carry enhancement of risk relative to their averaged dose. However, an interesting radiological situation arises in the case of internal massive micron range particles of elements of high atomic number since the absorption of gamma radiation is proportional to the fourth power of the atomic number. Gamma absorption for photon energies below 250keV (eg. in natural background radiation) should be enhanced by such a factor and the enhanced absorbed energy in the particle is largely converted to short-range and highly ionizing photoelectrons.
I discuss the theoretical enhancement of ionization density in the region of massive particles of elements of high atomic number (uranium, gold) which arises through the enhanced absorption of natural background gamma photons and their conversion to photoelectrons and suggest that such a mechanism for radiation damage has been overlooked by current risk models but may contribute significantly to radiobiological effects. The idea is amenable to experimental investigation.
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Keywords:
Ionizing radiation, cancer risk, depleted uranium, photoelectron
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