More on beta decay.

First post on the subject was here.

Will try to present these in more bite-sized portions.

crosspatch was looking for gamma emitters among the list of isotopes released at Fukushima. For each, wolframalpha answered “mode of decay: beta emission”. It never returned a hit of “gamma emission”.

So here’s the thing: gamma rays aren’t a mode of decay. The “mode of decay” is how a nucleus changes its proton/neutron ratio in seeking stability. Gamma rays aren’t a necessity, they’re a (common) by-product. Wolframalpha didn’t address whether beta-emitters also gave off gammas. Which is pitiful, really.

There are pure beta emitters: tritium, P-32, even Cs-137 (which I’d forgotten). But most beta emitters do emit gammas. Not necessarily with every decay, though.

And one beta emitter, mighty Cobalt-60, “Eater of Men’s Dose”, emits 2 gammas with every single decay. These, at 1.17 MeV and 1.33 MeV (mega electron-volts), are very powerful for decay gammas. In the commercial nuke field Co-60 is the largest single contributor to personnel dose–by far.

Are there pure “gamma” emitters, then? Not in decay. Again, radioactive decay is about the nucleus balancing protons and neutrons. Firing off a photon doesn’t change a thing in that regard.

But a nucleus can be in a “metastable” state. Which means…? Call it a state of excitation. Think of the entire nucleus “vibrating” with excess energy. Eventually, sooner or later, it will cast off that excess energy the way a plucked guitar string gives off a note.

(Which is a terrible analogy if extended any further, so just…don’t).

The most useful thing about the metastables comes in radiopharmacy. Since they emit only penetrating radiation, when taken into the body for diagnostic purposes you don’t hammer the patient’s insides with betas and alphas, which means….

Whoops, gotta run. Questions are always welcome!

About wormme

I've accepted that all of you are socially superior to me. But no pretending that any of you are rational.
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23 Responses to More on beta decay.

  1. crosspatch says:

    You can think of it sort of like heat. When you apply heat to something the atoms become more energetic. At some point they will begin to glow. Then as you make it hotter, it begins to emit light in increasingly higher frequencies of light until it is emitting all of them (white hot). Then imagine you take the atoms and get them even hotter. At this point the matter is probably plasma if you continue applying heat. The frequency will continue to go up and you will begin to get ultraviolet radiation, then x-rays, and then gamma rays. Gamma rays are just another color of light … way beyond what we can see … and can penetrate, like x-rays, deep into tissue.

    They can penetrate because their wavelength is so small that it can fit through the gaps between atoms. Longer wavelengths can’t. But if one of these photons hits an atom, it can mess it up, maybe cause an electron to fly off (ionize it). Once an atom has lost an electron, it REALLY wants it back … bad! It will go around looking for another atom to share an electron with, if it can. In other words, an ionized atom is more reactive … it bonds easier to other atoms than an atom of the same element that is in balance. These ions that are running around looking to bond with something are called “free radicals” and can be quite damaging. For example, an ionized oxygen molecule will become even more oxidizing that it already is. Maybe the ion will be lucky enough to capture a beta particle but most likely it will react with another atom of something and share an electron (gimmie that electron!), maybe even something that it wouldn’t normally react with. Radical little bugger, isn’t he?

    So gamma rays are just sort of like light … really, really, high frequency light that hurts you if you get enough of them hitting atoms in your body.

    • wormme says:

      I started to compare the process to heat, then paused. Thermally energetic atoms or molecules can pass on energy kinetically, or also by emitting it.

      But I’m not aware of any other way for a “metastable” nuclei to rid itself of that excitation energy. Had never thought about it before. But how else could it?

      The energy’s in the nucleus, not the atom as a whole, so no “bumping” other atoms or molecules to transfer it. Direct contact with another nucleus? Fusion? Nobody even cares about the “metastable” energy then.

      About all I got is a neutron bouncing off and taking the excess energy with it. Neutrino lasers seem more plausible than that.

      • poul says:

        termal analogy works, but up to the point.

        atom’s excessive energy is emitted as a photon. gamma photon, in this case. each atom has certain levels of energy it can occupy – it is not continuous – so when it falls from energy level 1 to level 2, it emits a gamma photon of exactly that energy, you can see it on the spectrum; when you have many atoms, you can identify each isotope by the lines on the spectrum it emits.

        now, if to achieve stability atom has to convert neutron into proton, it has to emit an electron, a.k.a. beta particle, to preserve the electric balance of the universe. the electron also takes away some energy with it in a form of its speed.

        • wormme says:

          There’s also “internal conversion”, a decay process not covered here yet. Maybe I’ll start tarting these things up:

          Atomic Cannibalism!

          Which results in cascade x-rays.

      • crosspatch says:

        Oh, yeah, it was *way* oversimplified on purpose. Not for your benefit, but for people who don’t know what gamma rays are, they are just another part of the electromagnetic spectrum such as microwaves, or light, or x-rays. Just a different wavelength.

        That was the major point I was trying to get across. And different elements have different energy levels so you get gamma rays at different frequencies … sort of like each one broadcasts on its own “channel” and if you do what amounts to a spectrum analysis (for the radio equivalent), you can tell what element(s) you are dealing with.

  2. crosspatch says:

    Oh, and it is also why they used film badges for dosimeters. Gama rays expose film just like regular light but you can enclose a piece of film in a light tight container and gamma rays will still reach it. Develop the film, check to see how much it has darkened, and you can tell how much exposure to ionizing radiation there has been.

    Gamma radiation will expose all that film in those little plastic film canisters so remember to shield your film when visiting a critical reactor core!

    • Sue says:

      My Father’s Master’s thesis (many years ago) was the development and calibration of the first film badges to measure exposure. Dosimeters have come a long way since then.

      • wormme says:

        Oh wow, yeah! And those were a great step forward. Folks like the Army once used “chemical” dosimeters…absorb enough radiation for your “badge” to change color, and…

        …and film badges were a godsend.

  3. Dmytry says:

    re: pure beta emitters – what’s about bremsstrahlung ? Electromagnetic radiation from betas being stopped. I was under impression that every beta emitter, even pure, is also making gammas by bremsstrahlung.

    • wormme says:

      More precisely, bremsstrahlung results from the paths of electrons (or potentially any charged particle) being “bent” by e.m. fields.

      Also, in my field we consider those photons “x-rays”, not “gammas”, which come from a nucleus. But I recently learned from Leopold that definitions differ.

      You are certainly right that they shed photons as they travel. But in the radiation protection field (my area), we’ve found they don’t produce appreciable ionizing photons when absorbed by materials with low Z numbers.

      I’ve surveyed P-32 (pure beta) many times through plastic bottles and never detected gammas/x-rays. But once I found x-rays coming off the outside of a shipping box. Puzzled, I opened it…to find the bottle wrapped in a very thin sheet of lead.

  4. oldHP says:

    >now, if to achieve stability atom has to convert neutron into proton, it has to emit an electron, a.k.a. beta particle, to preserve the electric balance of the universe. the electron also takes away some energy with it in a form of its speed.

    Don’t forget the neutrino…

    • wormme says:

      Nope, hadn’t forgotten. Dang betas, refusing to submit to spectrography. Pick an energy and stick with it like the self-respecting radiations!

      You too, positrons…

      • Well, positrons are just time-reversed electrons, it’s no surprise they’re a bit confused. First they don’t know where they are, or how fast they’re going (pick one). Then they don’t even know if their pocketwatch is running the right direction.

        Assuming they have pockets.

        • wormme says:

          Upon being taught that time pecularity, I had an epiphany. Since the positron goes backward and the electron forward, and we shouldn’t multiply entities needlessly, what’s the minimum number of electrons need to run the whole show?

          One. I postulate there is one electron in the entire universe.

          It’s just very, very busy.

      • You should give yourself a gold star, I heard Dick Feynmann make the same inference.

    • poul says:

      well yeah. actually, neutron emits a boson, which, being abhorent to nature, immediately decays into an electron and a neutrino. the reason boson is abhorent to nature is that not only it is disgustingly fat, but also that a fact of an observation of its cousin, higgs boson, is rumored to may cause the death of the universe.

      ok, ok, so i had a few…

  5. By the way, I did a bot of fun cipherin’ for a comment by Poul over at PJM. Consider that 0.54 Bq of Pu-238:

    There is detectable Pu in the soil any time, and pretty much everywhere, because of above-ground testing in the old days. Plus, someone set off both a uranium and a plutonium bomb in Japan not quite a half-life ago. The amounts of activity shown are truly minuscule — as I said 0.004 times a kilo of bananas.

    Pu-238 has a specific activity of around 634 GBq/g according to Wolfram Alpha — which means they’re detecting about 9×10^-13 grams, or only about something like 1 billion atoms of Pu per kilogram of soil.

    • wormme says:

      I’ve been putting so much thought into Cold War H-bomb testing lately, my assumption was that this discovery is due to that.

      So I sort of forgot the ones Japan saw that went off a lot closer to home. That’s…remarkable, in a way. Not good, but remarkable.

      • Well, Hiroshima and Nagasaki are at the south end of Honshu, and on Shikoku, respectively — so basically Fukushima is upwind. On the other hand, Novaya Zemlya is pretty well upwind of Japan, and that’s where they set off the 50 megatonne Tsar Bomba, which in a spectacular oopise, was rather greater yield than expected and turned from an air burst into a ground burst.

        I remember people worrying about the Strontium 90 from that when I was a child.

        • wormme says:

          What’s “funny”, not ha-ha, is that Sr-90 has made no grand appearance. If it doesn’t appear…aren’t we good? How can all the other hounds of hell appear without Strontium-90?

          If there’s a bogeyman…

  6. oldHP says:

    Night night. I’m gonna go search for some bare bottom…

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