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Stopping Radiation

by bassplayer142
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bassplayer142
#1
Oct9-07, 11:11 PM
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Is there any method of delaying radioactive materials? Could you put some kind of liquid or gas on a radioactive material or at some temperature or electrical current that would stop the object from being radioactive?
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malawi_glenn
#2
Oct10-07, 12:13 AM
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No I dont think there is a way to stop the nucleis from deacying (never heard of it). Altough you might bombard them with other nucleis and nuclear reactions might create stable nucleis in the end. But I think that shielding the radiation with lead is more efficent;)
cesiumfrog
#3
Oct10-07, 02:10 AM
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I suppose, by drilling holes in a bulk of material and inserting control rods or moderator, you could increase or decrease the rate of decay. In some sense this means you can freely choose the rate of stimulated decay, but there remains an apparently unavoidable* base rate of spontaneous decay, so indeed you'll still be wanting shielding.

*This suggests an alternative: rather than delaying the decay, you could just speed it up for a while beforehand (and take the energy as a bonus), since the base rate of spontaneous decay will drop as the radioactive ingredient within the material is depleted.

pallidin
#4
Oct10-07, 05:42 AM
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Stopping Radiation

Not sure, but I would guess that extreme supercooling would have a negative effect on radioactive expression.
Astronuc
#5
Oct10-07, 08:02 AM
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Radioactivity is a nuclear property, and as such is unaffected by any process imposed from outside the atom. Alchemists thought that they could 'chemically' treat matter to change lead into gold or generally change something of no value to something of high value, but chemistry simply involves rearraging atoms (matter) - not changing one element to another.

The nuclei of atoms can be transmuted via interaction with other nuclei or high energy photons, but that means producing radioactivity in the process. Phototransmutation requires gamma-rays. Transmutation by charged nuclei or particles like protons, deuterons, . . . . requires energies in the MeV range, and as charged particle pass through matter (atoms) they ionize atoms and produce brehmsstrahlung and X-ray radiation. Free neutrons can be absorbed by nuclear, but usually a gamma ray is given off spontaneously after the capture, and then the nucleus would be radioactive, unless the initial nucleus happens to be 1 amu below a stable nuclide.
vanesch
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Oct10-07, 08:12 AM
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Quote Quote by cesiumfrog View Post
I suppose, by drilling holes in a bulk of material and inserting control rods or moderator, you could increase or decrease the rate of decay. In some sense this means you can freely choose the rate of stimulated decay, but there remains an apparently unavoidable* base rate of spontaneous decay, so indeed you'll still be wanting shielding.
There's some potential terminology confusion here. "Decay" usually stands for natural radioactive decay: the kind of reaction which has only "one incoming particle", namely the nucleus itself. There's not much you can do about that, as others said: it is a property of the nucleus to decay.

However, nuclear REACTIONS (not decay) can be influenced, simply by changing the probability of collision or the energy of collision. Nuclear reactions are TWO-particle interactions. THIS is what you can influence, by inserting a control rod, switching off the accelerator, or adding a moderator: you're changing the incoming radiation.

However, for identical collisions, you cannot influence in any way the cross sections not more than you can change the half lives and decay paths of radioactive nucleae.
vanesch
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Oct10-07, 08:16 AM
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Quote Quote by pallidin View Post
Not sure, but I would guess that extreme supercooling would have a negative effect on radioactive expression.
Not at all, in fact. Only VERY high temperatures might influence it, but I'm talking about crazily high temperatures of several tens of billions of degrees where there is thermal equilibrium with a positron/electron plasma, which might influence beta decay for instance.
Count Iblis
#8
Oct10-07, 09:04 AM
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There can be a small effect if you put the radioactive material in degenerated matter. E.g. in a metal the electrons occupy all the energy levels up to the Fermi energy. A beta particle emitted as a result of the decay has to have an energy larger than the Fermi energy, so less hase space is available for the beta particle and therefore the probability ewill be a bit smaller.

An extreme example are neutrons in neutron stars. The neutrons are stable because all the electron states up till the maximum energy the beta particle could have are filled (if you imagine a situation where they are not filled, then the neutrons will decay until all available states are occupied, then the decay will stop).
vanesch
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Oct10-07, 10:16 AM
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I also thought of strong magnetic fields, which may play a minuscule role in the energy levels of nucleae and hence on the decay. But I guess that no realistic macroscopic magnetic field reaches in any way a level where this tiny effect might be measurable.
Astronuc
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Oct10-07, 05:55 PM
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Quote Quote by vanesch View Post
Not at all, in fact. Only VERY high temperatures might influence it, but I'm talking about crazily high temperatures of several tens of billions of degrees where there is thermal equilibrium with a positron/electron plasma, which might influence beta decay for instance.
With 11605 K /ev, the 10's of billions of K would be in the MeV range, and charged particles in the MeV range would be considered radiation.

Quote Quote by Count Iblis
E.g. in a metal the electrons occupy all the energy levels up to the Fermi energy. A beta particle emitted as a result of the decay has to have an energy larger than the Fermi energy, so less hase space is available for the beta particle and therefore the probability ewill be a bit smaller.
No. Atomic electrons have no influence on beta decay. Take any beta emitting element and heat it, compress it or cool it, and one will get the same half-life or decay constant.

Quote Quote by Count Iblis
An extreme example are neutrons in neutron stars. The neutrons are stable because all the electron states up till the maximum energy the beta particle could have are filled (if you imagine a situation where they are not filled, then the neutrons will decay until all available states are occupied, then the decay will stop).
Stellar interiors and atmospheres are somewhat full of radiation.

Vanesch raised an interesting point about intense magnetic fields, but the maximum stable B is about 10-12T, and I don't think that is sufficient to influence (delay) beta decay. I am not sure why it would.
sparkywowo
#11
Oct10-07, 08:25 PM
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Quote Quote by Astronuc View Post
The nuclei of atoms can be transmuted via interaction with other nuclei or high energy photons, but that means producing radioactivity in the process. Phototransmutation requires gamma-rays. Transmutation by charged nuclei or particles like protons, deuterons, . . . . requires energies in the MeV range, and as charged particle pass through matter (atoms) they ionize atoms and produce brehmsstrahlung and X-ray radiation. Free neutrons can be absorbed by nuclear matter, but usually a gamma ray is given off spontaneously after the capture, and then the nucleus would be radioactive, unless the initial nucleus happens to be 1 amu below a stable nuclide [or results in fission to rapidly decaying products].
This is correct.
If you wanted to make a block of radioactive waste less radioactive (or shorten the half life so it spontaneously decays to background in less time) the only remotely feasible way is transmutation. I use all terms here very loosely.
Annie Mathews
#12
Oct10-07, 09:56 PM
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In an experiment with a radioactive source, different stopping materials are used. With paper, detected count increased above the value with no absorber.How do you explain this?
vanesch
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Oct11-07, 01:32 AM
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Quote Quote by Annie Mathews View Post
In an experiment with a radioactive source, different stopping materials are used. With paper, detected count increased above the value with no absorber.How do you explain this?
Secondary radiation! The ionising radiation sets in motion high energy electrons, which ionise further on. If the material is not very thick, this secondary radiation (electrons) can escape and be detected with a sensitive enough detector. In fact, this is an issue in radiation protection: the dose at a certain depth under the skin can in fact be higher than at the surface, when exposed to certain radiation fields. This is why it is important to wear one's dosimeter in the prescribed way (for instance, on the chest) because it takes into account these effects, but that depends on how one wears it (mmm, read what I write but don't look what I do: usually I put my dosimeter on my belt, which I'm not supposed to do, but is the only practical way...)
vanesch
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Oct11-07, 01:36 AM
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Quote Quote by Astronuc View Post
With 11605 K /ev, the 10's of billions of K would be in the MeV range, and charged particles in the MeV range would be considered radiation.
Yes, right. It was a different way to talk about "radiation", namely "hot vacuum".

Vanesch raised an interesting point about intense magnetic fields, but the maximum stable B is about 10-12T, and I don't think that is sufficient to influence (delay) beta decay. I am not sure why it would.
It was purely theoretical because I also think that if the effect exists, it would be totally unobservable with practical fields. But I could think that if you put a nucleus in, say, a Megatesla field, you might cause some kind of hyperfine splitting of some sorts which might influence the decay (be it by simply changing the transition energy a little bit).
JeffKoch
#15
Oct11-07, 01:50 AM
P: 400
Quote Quote by bassplayer142 View Post
Is there any method of delaying radioactive materials? Could you put some kind of liquid or gas on a radioactive material or at some temperature or electrical current that would stop the object from being radioactive?
Strictly answering the OP's question, you can certainly "stop the object from being radioactive" by shielding it. But atomic spontaneous decay rates depend on the energy differences between initial and final states, state coupling factors (like dipole moments), and a bunch of constants - radioactive decay rates should depend on the same kinds of factors, suggesting that there isn't much you can do to "delay" radioactive decay unless you can somehow significantly perturb the nuclear states.
Count Iblis
#16
Oct11-07, 08:37 AM
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No. Atomic electrons have no influence on beta decay. Take any beta emitting element and heat it, compress it or cool it, and one will get the same half-life or decay constant.
There is an effect, but it is very small. Just compute the beta decay rate from first principles while taking into account the effect of the medium. Clearly you have less final states available for the beta particle after decay because electrons are fermions and some electron states are already occupied, so the summation over all final states will yield a smaller result than in case of a decay in vacuum. This is just the opposite effect than in case of stimulated emission. It is only important in degenerate matter.
Count Iblis
#17
Oct11-07, 08:46 AM
P: 2,157
The effect in strong magnetic fields would be interesting to calculate. Some important effects are described in the article: Physics in Ultra-strong Magnetic Fields


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