Can proton decay cause tranmutation?

May 18, 2009 12:35 PM

Could proton decay combined with matter/antimatter annihilation and radioactive decay cause transmutation?

Assuming proton decay exists, if you were to witness a very heavy atom like lead losing protons in super fast motion, is there a possibility that via some combination of proton decay / subsequent electron-positron annihilation / other types of radioactive decay you could see it "flicker" from one element to the next? Or would something like electron shell configuration absolutely prevent this?

Please forgive a question which is Google-able... I'm approaching this from an art perspective and I simply don't have a base level of education necessary to understand the results I get when I try.

posted by nathancaswell to science & nature (12 comments total)

If you have proton decay in heavy atoms, by definition you have transmutation; the number of protons is what defines an atom's element. Add/lose electrons and you have a charge; add/lose neutrons and you have an isotope of the same element. If you somehow lost a proton out of an atom of Oxygen, what you'd suddenly have is a positively-charged isotope of Nitrogen. If you had a magic positron-deletion wand, you could wave it and transmute any atom(s) into atoms lower on the periodic table (eg, with lower atomic numbers.) What this would actually imply, I happily leave to people who know physics. But if you're looking for a one-line response, number of protons equals element.
posted by Tomorrowful at 12:47 PM on May 18

Radioactive decay by itself causes an atom of one element to change to an atom of another element, in a sense. Alpha decay means that the atomic number of the atom goes down by 2 as an alpha particle (two protons and two neutrons) is emitted from the nucleus. The wikipedia article on alpha decay has some basic information on this phenomenon.

I don't see why, if a proton were to spontaneously decay and the products to leave the atom, you couldn't see that as a change of element as well.
posted by demiurge at 12:49 PM on May 18

Atoms regularly change from one element to another; this is the nature of nuclear radioactive processes. Decay chains are used to describe the transformation of an atom from one element to another.
posted by mr_roboto at 12:51 PM on May 18

You don't need (bare) proton decay to have transmutation. Radio-active decays come in essentially three types which can be described in a simplified manner as follows:
1. alpha decay, which changes the nature of the nucleus by removing two protons and two neutrons (and, subsequently, two electrons are shed from the atom);
2. beta decay, which changes the nature of the nucleus by changing one neutron into a proton (or vice-versa);
3. gamma decay, which does not change the nature of the nucleus (simply its energy state).

All three types of decays can be thought of as a lowering of the energy of an initial nucleus into a final nucleus, with the excess energy emitted in the form of particle (with kinetic energy) - again, this is a simplified description.

When you read about "proton decay", it is almost always meant to describe the decay of a isolated proton, not the decay of a proton inside a nucleus.

So, you don't need bare proton decay to have transmutation...
posted by aroberge at 12:52 PM on May 18 [1 favorite]

I don't think proton decay, if it exists, would be fast enough to flicker, like say the flavors of neutrinos on the way from the sun. I would guess it would be a quick event that leaves the atom changed. The wiki article notes that the timescale is 10^32 years. Since it's so rare, you could portray it as a single flame, illuminating the darkness? Especially since one of the mechanisms has a pion -> 2 photon decay.
posted by gensubuser at 12:52 PM on May 18

aroberge has it. Proton decay doesn't mean that, without it, protons can't change into other particles. Broadly speaking, any particle can change into any other particle(s) provide a set of conservation laws are observed.

Proton decay as it is usually discussed as a rare event is the violation of one of those conservation laws as well - the conservation of baryon number.

Otherwise, what you are talking about: protons changing into neutrons and vice versa happens already. Its called beta decay.
posted by vacapinta at 1:02 PM on May 18

Thanks for the replies so far I think this thread is going to be really illuminating (PROTON JOKE!). Anyway...

I guess I was under the impression that alpha, beta and gamma decay occur in unstable elements, and that as they decay they eventually settle into an element that is radioactively stable and that's where the phenomenon ends.

Now it's entirely possible that I'm totally misunderstanding this process, but what intrigued me so much about proton decay is that it might allow one stable element to decay into another, or a stable element to become unstable, and then alpha, beta or gamma decay into something stable... which is a little more interesting than watching radium decay into radon, which happens all the time.

aroberge: if proton decay exists, there's nothing preventing a proton decaying inside a nucleus is there?
posted by nathancaswell at 1:05 PM on May 18

(and by proton joke I mean proton > pion > gamma ray photons as gensubuser mentioned... which I do plan on exploring btw)
posted by nathancaswell at 1:09 PM on May 18

Now it's entirely possible that I'm totally misunderstanding this process, but what intrigued me so much about proton decay is that it might allow one stable element to decay into another, or a stable element to become unstable, and then alpha, beta or gamma decay into something stable... which is a little more interesting than watching radium decay into radon, which happens all the time.

True. You'd be subtracting a proton and subtracting a nucleon as well - so you might get some new pathways. On this chart, you'd be moving immediately from one square to the square that is diagonally to the upper right.
posted by vacapinta at 1:11 PM on May 18

You should know (perhaps you already do) that according to wikipedia, "recent experiments at the Super-Kamiokande water Cherenkov radiation detector in Japan give a lower limit of the proton half-life of 6.6 x 10^33 years".

(on preview, gensubuser already pointed that out.)

That's 5 x 10^23 times the current age of the universe. More pertinently it's about 10 billion times Avogadro's number, which means you'd need 10^10 * 207 / 82 grams of pure lead to have a 50% chance of observing one decay in one year of observation. That's 15,000 metric tons.
posted by mqk at 1:15 PM on May 18

In addition to alpha, beta, and gamma decay, there is also electron capture (and several more); in electron capture, the nucleus of an atom grabs an electron from one of the orbitals of the atom.

EC is interesting because it is the only mode of nuclear decay I've heard of in which the rate of decay can be changed by chemical processes:

Chemical bonds can also affect the rate of electron capture to a small degree (generally less than 1%) depending on the proximity of electrons to the nucleus.[1]
posted by jamjam at 2:03 PM on May 18

You know that the free neutron decays, but neutrons bound in nuclei usually don't. Similarly if the free proton could decay, protons bound in nuclei generally wouldn't.

In order to figure out whether a "parent" nucleus can decay, you have to know something about how the "daughter" nucleus behaves when it's excited. Usually a decay doesn't go directly to the ground state of the daughter but to some excited state where the nucleus is spinning or vibrating or misshapen or all three. The daughter then has to cool off and slow down by emitting some extra photons. If there's no acceptable final state in the daughter, however, the decay just doesn't happen.

For this reason, decays tend to go towards more tightly bound nuclei. If there is a nucleus that could decay by proton disappearance (or by neutron disappearance, which would also be allowed), it would probably be a transition from one stable nucleus to another. Certainly if proton disappearance could happen in an unstable nucleus, like a positron emitter, it'd be hard to find against the background of less interesting decays.

It would be pretty straightforward to go through the table of isotopes and list all the nuclei that could proton decay, as a function of the available energy. Probably someone did this before the free proton decay experiments started.
posted by fantabulous timewaster at 10:11 PM on May 18