Neutron radiation is our next topic and it is probably the least publicized form of the four types of radiation I have discussed, and this is possibly because it is the rarest “common” kind. You will likely never encounter neutron radiation in your life as the only place that it regularly occurs is in the direct handling of nuclear fuels. This is because, outside of some very rare cases, neutron radiation only occurs when an atom undergoes fission either spontaneously or by design. A fission event releases one or more neutrons, which move very quickly and unlike alpha or beta radiation are uncharged and thus are not slowed down by simply passing nearby an atom, thus penetrate much farther into any given material. This means that sources of neutron radiation require specific shielding to protect people or delicate equipment from exposure. In nuclear reactors and other places that use neutron sources for scientific purposes, this shielding usually takes the form of thick walls of concrete and thick panes of special composition glass.
Contrary to popular belief, it is not large dense slabs of material that most effectively stop neutron radiation. Rather it is light atoms and molecules such as water, boron or liquid hydrogen that provide the best shielding for two reasons. Firstly it provides large numbers of atoms for the neutron to collide with and shed its energy, like a cue-ball bouncing around a billiards table and slowing down with every collision with another ball. The same metaphor also works for why using large atoms like lead is a bad idea because that works more like the break at the start of the game, where the neutron would slam into the racked balls and break apart the formation, leading to the multiplication of the number of neutrons that have been liberated and now must be captured and slowed down to prevent them from exposing any people.
This ability to multiply the amount of radiation is almost unique to neutron radiation and is actually the basis for creating power from nuclear reactors. By controlling how the neutrons break apart other specific atoms and the rate at which this happens, a specific amount of heat can be created and used to generate power. Unfortunately, a downside of this ability is that sometimes the neutrons get absorbed by materials that do not split and help create energy but instead turn into different elements that only decay via alpha or beta radiation. This is how low-level nuclear waste is created, materials that have been exposed to neutron radiation and have become slightly, but not harmfully radioactive themselves.
Now not everything that gets exposed to neutron radiation becomes radioactive and not even everything that Can become radioactive will turn out so. If you are interested in learning how this process happens and what can be done to minimize it I encourage you to look up “Neutron Absorption Cross-Section” by whatever method you find most enjoyable (read more about it here).
If you are a bit confused that I don’t seem to be downplaying the risks of neutron radiation like I did with alpha and beta radiation, it is because I am not. Neutron radiation is inherently dangerous, however, the dangers can be mitigated very simply. We must still respect it and the dangers it poses, the same way that we do for hazardous chemicals or other matters of workplace safety.
Without neutron radiation, however, nuclear power wouldn’t exist. It takes careful coordination to control how the billiard balls bounce around inside the reactor core to create useful energy. Neutron radiation also allows for a technique that could conceivably get rid of all nuclear “waste” safely and reliably. The process by which this happens is a word I haven’t mentioned before, transmutation, the process of turning one element into another. It’s not precisely lead into gold, but with careful control, it is possible to change and atom of nuclear waste material into another radioactive element that becomes stable much faster than the original atom.
The generally accepted figure is that proper waste transformation can reduce the danger period of nuclear waste material from 100,000+ years to approximately a mere 1000 (again another topic I hope to explore in more detail in the near future).
It might sound like I’m calling neutron radiation a high-risk, high-reward scenario, but nothing could be farther from the truth. The science and behaviour of neutron radiation is very well understood and thus the risks can and have been easily mitigated in modern usage. This is thanks to, ironically, the hyperbolic fears of radiation and people clamouring for more and more ridiculously stringent safety requirements. But like children who have burned themselves on a stove, we still keep learning how to use it safely and now we can really start cooking.