FAQ - Why no neutrons exit atoms in natural decay processes

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FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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.

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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull »

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.

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

Post by Chris Bradley »

Sorry, it's just occurred to me what you're getting at. You're saying that as radioactive products are formed by, say, an alpha emitting process of uranium why do NONE of those products themselves then have odd, dominantly neutron emitting behaviour.

I would speculate that the answer is as follows - whether a nucleus emits a neutron or an alpha particle, both are mediated by the strong force and that if the particles bound within the nucleus achieve a quantum jump over that binding force, or otherwise is in a sufficiently excited state, then it would be thermodynamically more favourable to that nucleus to drop off an alpha than anything else. It's a bit like asking why petrol/gasoline burns into H2O/CO2 - why would it ever do a half-job and burn half the molecule off into ethanol?

For nuclear reactions, an alpha (4He) is the H2O/CO2 equivalent of the lowest energy product.

You might get a smattering of 'CO' and the equivalent is a smattering of neutrons (stretching the analogy!), but you have to deliberately do something to interfere with the natural 'burn' to get that. In the nuclear case, you have to jam in an extra neutron, for example, like in a uranium chain reaction.

As for the product that comes out of any decay, the same principle applies - if there is enough exitation energy to prompt another strong-nuclear decay then it would, again, prefer to drop off an alpha given half the chance.

If there is not enough energy to drive a strong decay, then the exitation energy will likely be released as a photon. The weak beta decay is a different beast altogether - a bit like the gasoline evaporating instead of getting to the stage of burning (gee - really pushing that analogy!!)

The reason why there are no 'imbalanced' nucleii already knocking around so as to emit a neutron in the first place is simply because, if you think of where it must've come from, the same applies. Whatever mechanism created that natural nucleus it would've shed that neutron already at that moment of the mechanism taking place, if it were going to imbalance the nucleus and leave it in a higher energy state.

Is this closer to a suitable answer?

best regards,

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

Post by JohnCuthbert »

Apart from fission (which as has been pointed out is so rare as to be nearly non existent), does any decay process produce any particle that is unstable?

If not then this validates Chris's point about neutron emission being the equivalent of only partially burning things.
The whole point of decay is to get to the lowest energy state and an unstable particle isn't the lowest state.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull »

I would question the statement that a neutron can't be emitted from an unstable nuclear state since any excited item to fall to a lesser or lower excitation would not emit another unstable particle.

Neutron emission is only seen to occur when just such an effort is desired by some unstable nuclear states. (drop to a lower energy state.)

The real reason is that no natural, continuing decay process here on earth is so over excited as to be able to emit a neutron. Neutrons are pretty locked into all matter on earth even naturally decaying radionuclides.

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

Post by Chris Bradley »

There is a question still on the table here - we humans, along with supernovae and other 'unnatural' events, can create isotopes that release neutrons.

But of all those neutron emitting nucleii, are there any daughter products from those, after those neutron emissions, that also go on to emit neutrons?

My thinking is that there aren't any. Once they've bumped down the potential energy curve just once then they've done all their neutron emitting. The neutron emission is like 'settling up' the odd nucleons in the nucleus, and that only needs to be done once.

The point being that all materials we now find lying around on and in the earth have already done that 'settling up' and no longer have any inclination to emit neutrons - they may go on to do a thermodynamically favourable full alpha emission, but they have no further need to emit a neutron when they can do that alpha emission instead.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Richard Hull »

Spontaneous fission is an example of a natural neutron emission process where daughter products also later emit neutrons. (prompt versus delayed neutrons)

Alpha emission is never seen to have energies where neutrons could be emitted.
The strongest alpha's are the 1 usec alpha emiters such as the radium daughter Po214 (Ra C') where the alpha energy max's out at around 7 mev, a near neutron emitting level!

Alpha emission, itself, is a mystery that may have clues. Why would an atom blow out such a monsterous particle (2 protons and 2 neutrons) as a unit item when the excitation energy is so far below that of a lone neutron emission level? Alphas range between about 2.5 to 6 mev in most natural emitters. The evidence has inspired a few to think in the direction of a nuclear shell model as a composition of Alpha particles.

So far as settling up all the odd neutrons in the nucleus............ Beta emission is also settling up all the odd neutrons in the nucleus as well. They are going bye-bye, but not being emitted.

It just goes back to how excited is the nucleus? All Beta emitters, (lots of them nautral), are also very neutron overburdened, they just don't spit them out.

Neutrons are atom builders and the nucleus hoards them unless excited to over 7mev.
There are no 7 mev+ unstable atoms on earth save for the occasional fission. Internally, neutrons can be assembled due to intense nuclear densities , electron capture, or dismantled via internal decay, Beta emission.

By theory the only places neutrons can be assembled are in stars or in the nuclei of atoms. A most interesting dichotomy of scale.

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

Post by Frank Sanns »

I believe in the beginning there were only neutrons.

Protons and electrons are the decay products of neturons and this would explain entirely why the universe is neutral. Neutrality is not by chance but it is as it was in the begining (or shortly thereafter).

It takes protons to tend the neutrons and prevent their decay. The incestuous exchange that goes on between the substance of neutrons and protons (notice I did not say quarks) is in equilibrium. No more neutrons can, without external stimulation, be released from the exchange family group because there are just the right amount of proton tenders around. Neutrons can now have a bad day and not fission (etimology biological as well as nuclear) .

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

Post by Richard Hull »

Interesting thoughts.

I believe in the particulate evolution based on universal temperatures. Currently, charged matter dominates to a net neutral. I know there was an age of mesons, and other stuff prior to that each age lasting longer in time.

Save for isolated pockets of high temperature densities and random high energy collisional events, the remnants of age of the mesons is rarely seen today. The universe of the super subatomics is totally gone and they are all part of what we now know at the 3 kelvin point we abide in today.

Even in special events in regions of tremenedous energy densities found at the cores of man's mightiest machines, such existences, even stretched out in time by relativity, are in the sub microsecond class and much less for the pre-mesonic materials. They are not part of today's matter nor are they constituents, but entities that just can no long exist in space or in matter. They are what became, as we know it.

I imagine that the familiar forces we know, quite possibly, evolved or devolved, (your choice), right along with that which occupied each such age.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by DavidStewartZink »

Just wanted to mention that most earthly free neutrons are produced by lightning strikes (1000s / m^3), however that is probably not emission but electron capture by hydrogen.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Carl Willis »

David, what is your source of information?

Numerous reliable references you can easily find with a Google search (as well as texts like Glenn Knoll's "Radiation Detection and Measurement") inform that the main source of neutrons at the Earth's surface is secondary cosmic radiation. This has been well-established for decades and in fact some cosmic activity monitors use neutron detection as a surrogate.

The origin of the cosmic secondary neutrons is not explained by electron capture on hydrogen (I strongly suspect your source of that tidbit is not a mainstream scientific one), but by spallation and a slew of other high-energy reactions, the other byproducts of which are also detectable (a variety of light radionuclides, muons, pions, etc.)

Regardless of whether some neutrons accompany lightning, the main sources of terrestrial neutrons and the means of production of those neutrons are pretty well established at this point and a quick trip to Google or your library will be usefully informative.

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

Post by Richard Hull »

As Carl notes, most terrestrial, (within the atmosphere), neutrons are of cosmic origin and are the result of Bev and Tev nuclear events as cosmic rays that have wandered the universe for God knows how many millions of years, slam into dense matter, like air, after exisitng in a hyper vacuum at near lightspeed velocities for a long, long time.

Neutrons are cherished and useful chunks of matter. But once outside the nucleus they were in, they are doomed to return to the hydrogen gas from which they were originally formed via beta decay, unless they join with another nucleus of matter before their death moment arrives.

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

Post by Dennis P Brown »

Correct me if I am wrong but does not natural uranium (mix of the isotopes) undergo (rarely) spontaneous fission and release neutrons? As such, uranium ore should provide a low level emmision of neutrons. Of course, background cosmic ray effects would be an issue.
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Re: FAQ - Why no neutrons exit atoms in natural decay processes

Post by Carl Willis »

U-238 is a source of spontaneous fission neutrons, about 0.011 n/s per gram. This is readily detected with sensitive equipment and appropriately long count times. I have an experiment in the Detection forum back in 2005 demonstrating SF as a probable source of neutrons from uranium. It is likely the most important source of neutrons in natural uranium under most conditions, but other effects can contribute significantly, such as

-(a,n) reactions on light matrix nuclei, typically those of oxygen in oxide minerals or compounds, which can be expected to be much more important if the high-energy / short-lived alpha daughters in the decay chain are present near equilibrium concentrations

-spallation induced by muons and other secondary cosmic particles of high energy (this effect is detectable if dense material like lead is placed around a sensitive neutron counter, and uranium could be expected to have a similar contribution)

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

Post by Richard Hull »

Spontaneous fission was noted in several replies above.

Carl has put a fine point on it. A kilogram (~2.3 pounds) of pure, freshly refined U will have about 11 neutrons produced in each second. Most all will be lost (absorbed) and are undetectable within the mass, itself. Some microscopic few will slow (thermalize) and might induce reactions in the U235 contained (very rare). Fast neutrons from fissioning can also induce fission in the U238, also rare. However, a natural uranium reactor relies on these rarer processes to work! You just need many tons of refined U to trap and use those internally accumulating neutrons. (note: it can't be depleted U though).

Both fissile and fertile elements have natural decay rates as alpha only emiters. fission is not a major decay process compared to their normal particle emitting decay rates. (noted in above postings by me.)

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

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

Post by DavidStewartZink »

Of course cosmic rays don't produce neutrons through electron capture, that's a silly idea, and also: yours.

And say what you will about "science establishing this or that", but strangely enough science merely asserts, and very often when dealing with natural rather than theoretical phenomena most of the assertions are just so much hot air. To be replaced next week by different hot air. Nature is complicated.

Most cosmic ray neutrons don't reach the surface of the earth. Lightning neutrons—which have been reported for decades but no one bothered to test for them until recently—form very near the surface and are very dense.

I'm a bit surprised people so willing to assert authority do so little to keep up. I'm also saddened that no one googled "lightning neutrons" before responding.

Physics review letters good enough for you? "Strong Flux of Low-Energy Neutrons Produced by Thunderstorms"
http://prl.aps.org/abstract/PRL/v108/i12/e125001

Whether more lightning neutrons or cosmic ray neutrons reach the surface I think was speculation based on someone's back of the envelope calculation; similarly for whether neutrons are created by electron capture of temporarily overwhelmed hydrogen (most stable atoms will capture an electron if immersed in enough electrons, but will expel it again when the crisis is over; only hydrogen loses its atomic nature in this situation) or through D-D fusion. However already disproven are both spallation from lightning-created radiation, and lightning focussing of existing cosmic rays. Time and further research will tell.
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