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.
User avatar
Chris Bradley
Posts: 2931
Joined: Fri May 02, 2008 11:05 am
Real name:

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

Post by Chris Bradley » Fri Jun 13, 2008 7:24 pm

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.

JohnCuthbert
Posts: 339
Joined: Mon Aug 19, 2002 8:30 pm
Real name:

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

Post by JohnCuthbert » Sat Jun 14, 2008 12:42 pm

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.

User avatar
Richard Hull
Moderator
Posts: 11368
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

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

Post by Richard Hull » Mon Jun 16, 2008 5:24 pm

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.

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.

User avatar
Chris Bradley
Posts: 2931
Joined: Fri May 02, 2008 11:05 am
Real name:

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

Post by Chris Bradley » Mon Jun 16, 2008 9:02 pm

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.

User avatar
Richard Hull
Moderator
Posts: 11368
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

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

Post by Richard Hull » Wed Jun 18, 2008 7:53 pm

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.

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.

User avatar
Frank Sanns
Site Admin
Posts: 1588
Joined: Fri Jun 14, 2002 6:26 pm
Real name: Frank Sanns
Location: Pittsburgh, PA USA

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

Post by Frank Sanns » Mon Jun 23, 2008 2:31 am

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) .

Frank Sanns

User avatar
Richard Hull
Moderator
Posts: 11368
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

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

Post by Richard Hull » Mon Jun 23, 2008 8:09 pm

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.
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.

DavidStewartZink
Posts: 10
Joined: Wed Jun 20, 2012 8:22 pm
Real name:

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

Post by DavidStewartZink » Wed Jun 20, 2012 9:59 pm

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.

User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 11:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

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

Post by Carl Willis » Wed Jun 20, 2012 10:29 pm

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.

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277

User avatar
Richard Hull
Moderator
Posts: 11368
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

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

Post by Richard Hull » Thu Jun 21, 2012 3:42 pm

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.

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.

Post Reply