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I must take exception to Scott Hards’ Aug. 4 letter, “The irrational fears of radiation.” Hards is not an expert in radiation biology, or he would have drawn a distinction between external and internal radioactive emitters. There is not much of a case for any great danger from external emitters, except in very high dosages. This is the kind of radiation to which pilots and astronauts are subject, and even extended exposure to high background levels in places like Kerala, India, are no cause for concern.

However, once hot particles are ingested, it is entirely a different matter. An ingested particle will lodge in a particular tissue depending on its chemical affinity and, from there, will bombard the same area of tissue continuously, causing DNA breaks. Single-strand breaks are repairable, but double-strand breaks are not. As experts told us at a recent radiation safety seminar held by the German Army, if one is lucky with double-strand breaks, the affected cell will simply die, but if it doesn’t, a mutation will have occurred that is passed on by cell mitosis. Some of those mutations will lead to cancers, a fact well known and well documented in medical literature. This is especially true in young people, with high rates of cell division.

Particularly dangerous are alpha emitters such as the uranium and plutonium isotopes. They are completely harmless externally, yet pose a grave risk internally due to the very high energies released upon decay and their limited tissue penetration. In fact the equivalent body dose of alpha emitters is 20 times that of gamma or beta emitters. Four micrograms of plutonium ingested will give an equivalent body dose of 20 millisieverts/year, adding a body dose equivalent of more than 20 years of Tokyo background radiation (at the present elevated levels) per year.

Radiation workers go to great lengths to avoid internal contamination, which can happen through ingestion, inhalation, entry through skin wounds and the conjunctiva of the eyes. Hot particles are contained in contaminated food, contaminated water, and in the dust on the ground, which is stirred up by every breeze. Outside the body, these are no cause for concern, but get them inside and the story changes dramatically.

The opinions expressed in this letter to the editor are the writer’s own and do not necessarily reflect the policies of The Japan Times.

toby marshall

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