FAQ - Why no neutrons exit atoms in natural decay processes

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Richard Hull
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FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull » Thu Jun 12, 2008 4:11 pm

Neutrons are hoarded in the nucleus and are just not emitted in any natural process that we normally see.

A neutron heavy radioactive nuclide will beta decay to reduce nuclear neutron count. It iwll not let go of a neutron, per se.

All neutron releases from nuclei are artificial in nature or virtually always man induced.

A nucleus would need an internal energy of 7 mev or more to emit a neutron. Large nuclear energies, (2-6 mev), are handled by Alpha emission.

Neutrons are commonly emitted in fission processes, namely that of U235 and Plutonium. During fission "prompt neutrons" are seen. Nuclear fission ash is often so excited that it often decays over very short periods via a beta decay process. Among certain key fission products are the rather massive Br87 and I137 isotopes. These beta decay to Kr87 in 55 seconds and Xe137 in 22.5 seconds, respectively. Both of these duaghters are super excited and instantly, (10e-12sec), throw out a neutron. these late arriving neutrons after fission are referred to as "delayed neutrons".

Man can bombard any number of materials in accelerators and make such stepped neutron decaying isotopes or actually create rapid fissioning elements higher that naturally occuring uranium, such as californium that also neutron emits when it self-fissions.

So, we can make up any number of neturon isotopes in massive accelerators or assemeble fissionable materials and create neturon emitting fission products, but nature in our environment, here on earth, sees no extant neutron emitters in all of the natural radioactive decay products.

Cosmic rays and atmospheric gases can both spallate and create short lived neutron emitters, but that is like being in an accelerator, as well.

It all ends up that nature just doesn't decay to neutrons from long lived natural radioactive istopes here on earth. Neutron emission is a sign that an atom has been raised to a super excited state from some outside source of energy.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by JohnCuthbert » Thu Jun 12, 2008 4:50 pm

I thought nature did at least one neutron producing reaction- spontaneous fission.
Anyway, I think all the other neutron emitters have short half lives. If they ever had existed in nature they would have decayed by now.
Perhaps they were plentiful once, but we missed it.

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Frank Sanns » Thu Jun 12, 2008 6:12 pm

But Mr. Wizard how do we get neutrons from deuterium?

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Wilfried Heil » Thu Jun 12, 2008 7:32 pm

Spontaneous fission is a natural process which liberates neutrons, usually competing with alpha decay. Another natural process would be spallation, which creates most of the ambient background neutrons.

There are rare radioactive decays where fragments with weights of a multiple of an alpha particle are emitted.
I wouldn't be surprised if such a rare process exists for neutron emissions as well. As always, we usually can only find what we look for.

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by waltsphotos » Thu Jun 12, 2008 7:37 pm

Frank we are talking about "natural atomic decay" not fusion in this thread. Your question makes me question if your reading the threads and if you have any idea of what deuterium is. (I question it, I'm not convinced.... yet)

____
Richard, I agree with John natural spontainous fission can and does produce neutrons. Out of the different types of atomic decay (radiation) I would agree that Neutron emission is a rare form. More common is beta- and gamma or even alpha.

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull » Thu Jun 12, 2008 7:43 pm

Spontaneous fission was covered as a neutron source in my post under Californium a man made elemental item.

Spontaneous fission in say the richest natural source on earth, U238, is so slow that even in a 100 pound block the fission neutrons either don't make it out or are statistically unmeasurable at the amateur level.

Spontaneous fission half lives of U238 and Thorium are in the quintillions of years. Right up there with the decay rate of natural Bismuth.

D-D fusion is not a natural earthbound source of neutrons, of course.

Again, all decay neutrons are emitted instantaneously and the average half life by our time is determined by the progenitor's half life which, itself, is always measured in seconds.

There are just zero real, natural sources of experimentally usable neutrons on this planet. We have to make them up as good hunter gatherers. Nature keeps her neutrons to herself in quiescent environs where biota can thrive....and blessedly so.

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by waltsphotos » Thu Jun 12, 2008 8:18 pm

I see your point Richard, but rather then say there are no neutrons from natural decay. your saying there are no significant natural sources of neutrons, and no natural sources that could be used for experimental purposes.

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Chris Bradley » Thu Jun 12, 2008 9:00 pm

Richard, please forgive me if I misunderstand you exact angle on this, but the reason there are no natural neutron emitters with decay times less than billions of years is surely fundamentally simple - we live in a solar system that is scientifically estimated as >4 billion years old. Anything with a decay time less than this would've decayed by now!!

Reverse the question - if I came across a neutron emitter and its natural decay time was just a couple of years, for example, I would then say 'ah! this must have been recently formed because there can be no natural sources of it as it would all have decayed by now in our 4 billion year old rocks'.

I need not say that, for thermodynamic reasons, an unstable nucleus must change into something with less energy that itself - so it can never 'bounce' neutrons back and forth with another nucleus species endlessly. Instead it reverts to another nucleus species. maybe that is stable. Fine. But if not then that one goes through the same process until it ends up as a set of stable isotopes. Any sole neutrons that pop out of that process end up as protons -> hydrogen.

Another way to look at this - go live next to a fresh supernova and then say there are no natural neutron emitters.

So is it not a simple answer?; there used to be plenty of neutrons and neutron emitters as you describe, but they've all finished up their 'emitting' now and retired as smaller, stable, isotopes!!

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Frank Sanns » Fri Jun 13, 2008 2:57 am

I think it is very relevant but for the moment don't look at the left side of the equation that says deuterium because then it is f***** word that I am not allowed to mention since this is a fission thread. Instead, look at the right hand side at a time only a yocto second after the first f word happens.

d+d = He3 ( 0.8mev) + n ( 2.45mev)
d+d = T(1 mev) + p ( 3 mev)
d+d = He4 + gamma ray + 17MEV

In the last and the least likely, is an alpha particle and much energy. I find this simple neutron, proton or alpha emitting example to be an intriguing decay sequences. It is a man made excited state but it is a simplified version of what is seen in heavy fissioning atoms. Most interesting outcomes from the same input energy.

Frank Sanns

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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull » Fri Jun 13, 2008 3:49 pm

There are many, many naturally produced unstable, radioactive isotopes on earth right now as I type this and many of them have half lives of micro seconds, milliseconds, seconds, minutes and hours. None emit neutrons. None are man made.

Only man can make significant neutron emitting isotopes on earth.

In my original posting I limited the discussion to earth bound, naturally available sources.

In any 300mev omnipresent enegetic environment where we can establish no laboratory nor survive as experimenters, sure, matter could even cease to be anything but mesons and no primary particles. Anything can be imagined at any place in space and any energy level density might be found, but we are earth bound for the purposes of my post and there are no neutron sources we can use without hunter gathering and utilizing clever assemblies.

Neutrons are just not emitted on earth's surface in usable or easily measured form.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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