Does radiation make things radioactive?

The short answer is “no” but the devil is always in the detail.

Firstly, “radiation” here applies specifically to ionising radiation; alpha particles, beta particles and gamma photons. In particular, we are excluding non-ionising nuclear radiation in the form of neutrons, which definitely can turn previously stable nuclei into radioactive materials. This effect is a significant contributor to the clean-up involved when decommissioning a nuclear power plant, where the neutrons that are essential to the reactor’s operation also generate radioactive isotopes in the graphite rods and steel housing of the structure. (For more information, see https://world-nuclear.org/information-library/nuclear-fuel-cycle/introduction/physics-of-nuclear-energy.)

Secondly, “radiation” is taken to mean irradiation: that is to say, exposure where there is no physical contact between the radioactive source and the object. Clearly, if there were contact then contamination could occur and the object would then appear to be radioactive – but this would be due to presence of particles from the radioactive source on the object’s surface, not any radioactivity that has been induced within the object itself.

So why doesn’t irradiation by radioactive sources make objects radioactive? To answer this we must first remember that nuclear radiation is emitted when a nucleus becomes more stable and it would be necessary to push energy into a stable nucleus to transform it into an unstable state. This is an unlikely process, not least because the nucleus is a very small “target” that constitutes only a tiny fraction of an atom’s cross-sectional area.  

That said, let’s consider, in a bit of detail, each of the three types of ionising radiation in turn.

If an alpha particle were projected towards the nucleus it would encounter electrostatic repulsion. This is the basis of Rutherford’s famous gold-foil scattering experiment, which has been discussed in a previous post (https://physbang.com/2020/10/04/rutherfords-gold-foil-experiment/). In short, alpha particles with energies produced during radioactive decay cannot even get close to a nucleus, let alone enter it, so they cannot “create” (induce) radioactivity.

Beta particles of an appropriate energy can exhibit diffraction due to encounters with the nucleus but otherwise they are simply absorbed by materials and their kinetic energy is transferred as heat. Although it is possible for a nucleus to capture an electron, this can only happen when the electron is close to the nucleus. Those energy levels are already filled by atomic electrons and, thanks to the Pauli exclusion principle, the population cannot be increased by adding an additional beta-particle electron. So beta radiation cannot induce radioactivity either. (There is more about electron capture in a previous post, at https://physbang.com/2025/11/14/electron-capture-and-internal-conversion/.)

Gamma photons generally pass right through materials but a direct hit on a nucleus can result in brief excitation and re-emission of a gamma photon. That sounds like induced radioactivity but the process is very brief and there is no “retained” radioactivity in the sense of there being a half-life for decay over a humanly-meaningful timescale.

In short, none of these interactions can turn a previously stable nucleus into a radioactive source.

A final way of thinking about this question would be to turn it on its head. Suppose that irradiation did make things radioactive: how then could a GM tube work? The purpose of a GM tube is to detect radioactive decay events but if the proximity of many such events resulted in an object becoming radioactive then a GM tube would cease to be useful as a detection device, which is not the case. (It is true that GM tubes suffer from saturation and dead times that can cause measurements to be under-recorded but this is due to a completely different effect.)

Given that irradiation doesn’t make objects radioactive but has the ability to damage (or even kill) living cells, this technology can safely be used to sterilise medical instruments. It can also be used to extend the shelf-life of foods. Gamma radiation is the only type of ionising radiation that has sufficient penetrating power to pass through metal parts and food packaging to reach enclosed spaces that would be hard to sterilise by other means.

That is about the limit of coverage for this topic in school curricula but it is not the full story.

A nice explanation of gamma radiation in food and agricultural applications, complete with a couple of self-test questions, is given in Biology Dictionary, at https://biologydictionary.net/irradiation/. Efficient though it is, there is significant public resistance to the use of irradiation in food handling. All irradiated foods, in the UK, EU and the US must be labelled as being irradiated and this sets alarm bells ringing due to a high degree of suspicion and ignorance amongst the general public about all things nuclear.

Milk can be sterilised by heating (pasteurisation) and other foods can sometimes be preserved by treatment with microbicidal gases but these, unlike gamma radiation, cannot penetrate frozen foods. Irradiation is also more versatile as it not only reduces the risk of potential food poisoning but also can delay fruit ripening and help stop vegetables from sprouting. Proponents of food irradiation also cite favourable environmental and energy considerations. On the other hand, irradiation can affect the nutritional value of foods by degrading vitamins.

Clearly there are two sides to this coin. A particularly informative discussion of this subject was published by the UK Food Commission in July 2002. It quoted a survey by the UK Food Standards Agency in January 2001, finding that “24% of people questioned expressed concern with regard to irradiated food” and noting that UK supermarkets “continue to maintain their position against stocking of irradiated foods on the grounds that they perceive a lack of consumer demand for such products”. The full document is available at http://www.foodcomm.org.uk/campaigns/europe_and_the_uk/.

In the case of medical instruments, routine sterilisation can be conducted using autoclaves, which can be thought of as large pressure cookers containing superheated water and steam. But for items that cannot withstand these conditions, or are in sealed packaging, gamma radiation is likely to be the best option. Even here, however, there are limitations. Things can get particularly tricky when handling surgical grafts as it is necessary to achieve a sterilised condition without causing tissue damage and irradiation can be problematic in such situations. For more information, see https://pmc.ncbi.nlm.nih.gov/articles/PMC5820857/.

Further Reading

For more information about irradiated food, see https://www.fda.gov/food/buy-store-serve-safe-food/food-irradiation-what-you-need-know (US), and https://www.food.gov.uk/safety-hygiene/irradiated-food (UK).

Although the full text is behind a paywall, substantial extracts from Irradiation as a Method for Decontaminating Food: A Review (published in International Journal of Food Microbiology, Volume 44, Issue 3, November 1998) can be read at https://www.sciencedirect.com/science/article/abs/pii/S0168160598001329.

There is also a wider discussion about sterilisation of medical instruments, published by the US Food and Drug Administration, available at https://www.fda.gov/medical-devices/general-hospital-devices-and-supplies/sterilization-medical-devices.