Help Me Clarify My Understanding of Ionizing Radiation

I have recently been reading about radiation exposure, from Marie Curie’s isolation and study of radium in the 1890’s to the horrible fate of the “Radium Girls”, Eben Byers, and the guy who developed the radium paint used for watch and instrument dials in the early part of the 20th Century, to the atomic bomb era, Cold War, various accidents… Not that it was all about death and destruction. Smoke detectors have saved many lives with little risk to the users and most depend on Americium, there’s all sorts of medical imaging, judicious use of radiation in medicine, in detecting weaknesses in aircraft parts before failure and death…

Anyhow - there’s all sorts of varieties of radiation. I just want to be sure I have a handle on some of it.

Mostly, I’m talking here about ionizing radiation, not things like light.

There are alpha-emitters, which, well, emit alpha particles. Alpha radiation is basically a bare helium nucleus. It can cause damage to living tissue but is easily blocked by minimal barriers, like the dead skin cells that form the surface of your skin. The biggest problem is if alpha-emitters get into your body where your living cells have no barrier between them and the bouncing alpha particle. Given their (relatively) high mass they can be extremely dangerous once in the body because their high mass means they can do a lot of damage compared to other radioactive particles. Then they can cause all sorts of havoc. To deal with alpha-emitters in your environment you don’t eat the local food, don’t drink the water, and don’t breathe the air. Yes, you wear a serious hazmat suit. A thorough shower of said suit followed by careful removal should be all the protection you need.

Beta-particles are basically rampaging electrons OR positrons (hey! anti-matter! How cool! How Star Trek!) They are more penetrating than alphas, less so than gammas. A thin metal plate can stop them, but they will get through your skin. This is where a “lead suit” type of hazmat gear could be useful even if pretty damn heavy. So… fantastic! We can protect again alpha and beta! (Albeit with come inconvenience and trouble). Betas are harder to shield from, but if they get inside the body may not be as damaging as alphas do to having almost no mass.

Something I only recently learned about betas is that when you shield against them and they go through the shielding material they slow down, and can emit gamma rays during the slow down. Also, the atomic weight of the material used as a shield also effects the energy level of those gamma rays. So it’s actually safer to use a shield of, say, aluminum or wood than of lead because the gamma that results from beta slow down would be less from the lighter shields than the lead. So maybe you don’t want a lead hazmat suit, you really do want a hat made of tinfoil (aluminum) in that situation!

Gamma rays are photons. Really, really energetic photons. They are also really, really penetrating. They have uses in industry as, essentially, x-rays on steroids for imaging purposes because they go through a lot of stuff. Shielding against these guys is challenging although, fortunately for squishy creatures like us, the Earth’s atmosphere does a pretty good job of filtering out a lot of gamma rays that would otherwise come to us from outer space.

What I’m still fuzzy on here, though, is the role that neutrons play in radiation. I know that shooting neutrons at atoms can cause changes in atomic number, which can cause all of the above sorts of radiation. The shooting neutrons come from atoms fissioning, right? Also from fusion? From matter/anti-matter interactions going >BOOM<?

In most cases, radiation doesn’t cause a person or items to become radioactive, that’s usually a case of people or things becoming contaminated with radioactive isotopes (hence, don’t eat the food, don’t drink the water, don’t breathe the air, and take a shower). Under what circumstances does radiation cause the formation of radioactive isotopes in people and things? Gamma rays? Wandering neutrons? Is there something else I’m missing here?

Your understanding of alpha, beta, and gamma radiation is broadly correct; there are a few statements in there that I’m not sure about, but they might be right and I would need to look into them to be sure. So for now, I’ll just focus on the questions you asked at the end.

Neutrons are usually bound up inside nuclei, and they’re not usually released unless a nucleus gets re-arranged. This happens in nuclear reactions, where one or more nuclei turn into one or more other nuclei. (Fission and fusion are two types of nuclear reactions.) During these reactions there can sometimes be neutrons “left over” with a substantial amount of energy, so they zip away and can play merry hob with other matter.

For a piece of matter to become radioactive, you have to have one of the above-mentioned nuclear reactions taking place. In other words, something like the following has to happen:

(stable nucleus + radiation) -> (radioactive nucleus) -> (stable nucleus + radiation)

Neutrons could definitely do the trick; this process is called neutron activation. Alpha particles can do this as well, though I think it’s less common.

Gamma rays, though, generally can’t do this. For a nuclear reaction to happen, it helps if the incoming radiation is made of nucleons (protons and neutrons); that way the incoming nucleons and the parent nucleons can rearrange themselves to form a new nucleus, possibly radioactive. But gamma rays are (as you note) photons on steroids, and so they don’t contain any new nucleons to help in the reaction. The nucleus can still briefly absorb the gamma rays, in principle; but it will then re-emit them pretty promptly, and we’re back where we started.

The one exception to this is if you get an incredibly high-energy gamma ray with enough energy to split a nucleus apart. This is called “photodisintegration”, and if it occurs, then the resulting fragments can be radioactive. But most gamma rays don’t have enough energy to do this.

In principle, any sort of radiation can transmute atoms (usually rendering them radioactive in the process), but it takes really, really high energies for anything but neutrons or maybe alphas.

To a large degree, the different danger level from different kinds of radiation is precisely because of how penetrating they are. Alpha particles will interact with almost anything they encounter. If they hit a bit of dead skin, they’ll interact with that bit of dead skin (which stops them). If they hit a DNA molecule, then they’ll interact with that DNA molecule. Which also stops them, but probably mutates in the process.

On the other end of the scale, gamma rays aren’t likely to interact with any matter they encounter. If a gamma ray hits a sheet of foil, it probably won’t interact with it, and just keep going on its way. If it hits a living cell, it still probably won’t interact with it, which means that the cell is unaffected. But it might interact with either, meaning on the one hand that it’s possible to shield against gamma rays if you have thick enough shielding (typically a few feet), and on the other hand that if you don’t have thick enough shielding, they can still mess you up.

Take it to the extreme, and you have neutrinos. Neutrinos have damned near no interaction at all with anything. On the one hand, this means that even the entire thickness of a neutron star is not effective as shielding. On the other hand, it means that nobody cares about shielding against neutrinos, because they’re as good as guaranteed to leave living tissue (or whatever else you care about) untouched.

An interesting question.

I too am interested in understanding the ‘big picture’ of how all this fits together.

Building on the original question, is this substantially correct?

Atoms are elements where the balance of electrons, protons are stable in respect to the electromagnetic force.

Knock off a few electrons or add them and you get an ion that is unbalanced in terms of its electromagnetic force and they acquire a positive or negative charge. The electromagnetic force can be balanced following a chemical reaction where stable molecules are formed by joining ions of elements that have too many or too few electrons.

The reactions between ions is the basis of much of Chemistry and it is pretty easy to turn a stable molecule into ions. A solvent like water will allow the atoms of salt to separate as ions in solution. Chemical reactions often result in surplus or deficit in the amount of energy and that is released as photons that is manifest as photons energise atoms and this is appears as heat. Powerful exothermic chemical reactions are the basis of explosives.
You can also ionise atoms using electricity and a vacuum tube. The electrons streaming from the cathode to anode will knock off the electrons from a small amount of any gas in the tube. It will be become ionised. Or the electrons in gas atoms can be excited into a higher state and then fall back, emitting a photon in the process. This is the basis of the fluorecent tube light. This streams of electrons coming from the negative side to the positive side of an electrical circuit passing through a vacuum tube was one of the first forms of radiation discovered and led to an understanding of the electromagnetic force in the atom by firing electrons at various elements to create ions. Electron beams in a vacuum tube can be controlled using magnets and coils and firing a beam at screen coated in phosphor is the basis of television. Electrons are beta radiation.

There are other forces at work in the atom besides electromagnetism. Within the nucleus, the protons and neutrons are bound by the weak nuclear force. This also tends towards stable configurations that can be altered by changing the number of neutrons in nucleus. These variations are isotopes of an element. When the weak nuclear force is unbalanced it can lead to the atom releasing alpha or beta radiation to restore the balance. The larger the atom, the more likely the weak nuclear force is unbalanced. Hence it occurs most often in very large elements like Radium. Some isotopes are highly unstable and radioactive, emitting helium nuclei (alpha), electrons (beta) radiation and high energy photons (gamma) radiation. That radioactivity can cause cell damage. Nuclear reactions created by bombardment with neutrons are often accompanied by a release of energy in the form of heat alpha or beta particles and more neutrons. Instead of firing electrons at an atom, neutrons are fired, hoping to hit the nucleus and dislodging the neutrons. Splitting the uranium at produced enough neutrons to create a runaway nuclear fission and a very big bang.

Fusion involves the another force, the strong nuclear force and typically occurs in the centre of stars. The surplus of energy resulting from the fusion reaction in the Sun is manifest as a stream of photons of various energies, and ions in the solar wind. Some of the high energy photons are absorbed by the gases in the atmosphere. The ions are deflected by the earths magnetic field and this can be seen in action in the Northern and Southern lights as they collide with the gasses in the rarified upper atmosphere that emit photos we can see.

Ions persist in a vacuum or in solution, but they don’t last long in air, they quickly combine the gases in the air to form stable molecules. It takes a lot of energy to ionise air, but it happens during electrical storms.

Radiation is a catch all term.

It can be

Alpha - Helium nuclei
Beta - Electrons
Radio/Microwaves/Infra Red/UV/XRays/Gamma Rays - increasingly energetic Photons

Then there are a wide range of subatomic particles radiating from space, some are very hard to detect.

Physicists use particle accelerators produce beams of


and fire them at targets in a vacuum. They try to detect the particles that created by high energy collisions in order to try to understand the sub atomic particles and forces that make up regular neutrons, electrons and protons.

Fusion reactors try to achieve extremely high temperatures required to reproduce the nuclear reactions taking place in a start by heating ionised gas (plasma) using high energy beams of Photons from lasers and confining the plasma using magnetic fields .

Have I made any conceptual mistakes here? I am looking for the big picture of how it all hangs together rather than detail and precise definitions.

AIUI, heavier elements like uranium and plutonium can undergo “spontaneous fission” and eject neutrons. Those neutrons can be “captured” by other U/Pu atoms, thereby rendering them unstable and causing them to split apart, releasing more neutrons. plus other forms of radiation and thermal energy.

it’s called activation product. One example I can think of is the boiling water reactor (BWR.) that kind of power reactor sends steam directly from the reactor pressure vessel into the turbines instead of using an intermediate heat exchanger like a PWR, so if the turbines have to be serviced they must be left alone for a while for the activation products in the water to decay. IIRC it’s mostly Nitrogen-16 which has a 7 second half life.