The ionisation of atoms surrounding the trajectory of an alpha or beta particle in matter, or the interaction of a gamma ray with a nucleus or an electron, is a microscopic phenomenon. Any effects on the scales that we can see are the result of a very large number of these fundamental interactions.
By expelling electrons from the atoms they pass, the ionising particles cause a temporary instability in these atoms and molecules. The key role these electrons play in the molecular structure means that these expulsions cause disruptions. Free radicals (segments of molecules) are created in an extraordinarily brief lapse of time. Depending on the surrounding conditions, these highly active free radicals can either recombine or induce chemical transformations in the substance.
The macroscopics effects naturally depend on the dose given off and the area irradiated: living or inert, solid or liquid, organic material or not. The effects on humans have a special importance to us and deserve their own chapter. Our interest is only natural, as the alpha and beta particles have the ability to ionise our cells and potentially damage our precious DNA. Effects have been observed at doses in excess of one gray (Gy), and in radiotherapies cancerous tumours are exposed to doses of the order of 50 Gy for curative purposes. The possible effects of weak doses remain unclear despite the extensive investigations made.
Ignoring humans and living beings for the moment, the exposure of inert matter (such as food and drink) to radiation produces very little effect. There is, however, no reason not to expose such materials to very high doses.
The most extreme example is that of the nuclear fuel at the heart of a reactor, which receives the equivalent of several billion grays. Similar doses are also absorbed by those detectors placed at the heart of large experiments in nuclear or particle physics using high energy accelarators.
High levels of exposure can change the structure of matter, accelerate ageing processes or, in the case of crystalline structures, provoke structural deformation. It was the ignorance of these effects that led to the 1957 Windscale accident – the most severe nuclear accident in British history.
High doses, though nowhere near on the scales mentioned above, are often used in industry, agriculture and the food industry, as well as in hospitals and museums.
Beneficial changes to the molecular structure can be induced by carefully moderated exposure to radiation. These changes have been seen in a range of products that are in current use. Links in many polymers, for instance, have been altered by radiation to have specific characteristics – such as the ability to shrink under exposure to heat. These polymers are regularly used in the packing industry.