Energy efficient proton production?

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Quantum
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Energy efficient proton production?

Post by Quantum »

Firstly, I hope I've managed to post this question in the correct forum now.

Secondly, It would seem that ALL the big synchrocyclotrons use RF/magnetron sources for proton beams, but even they only achieve about 13% efficiency producing protons from hydrogen.

Thirdly, while I appreciate that the energy of the protons produced (in electron volts) is relative to the energy used to produce them, their energies can be increased (accelerated) using magnetic/electrostatic fields.

Now, assuming the purpose of the exercise is to produce protons for proton/boron 11 fusion, the first criteria is to produce as many protons as possible using the least amount of energy possible.

Producing unwanted ions, and then 'filtering' them out wastes energy, but is probably unavoidable.

So the most energy efficient way to produce protons would appear to be to produce ions of low energy (electron volts), filter out the unwanted ions, and then accelarate the remaining protons to the required velocities.

Or, would producing low energy ions produce more H2 ions and less protons?

Would producing high energy ions result in more proton production?

I hope this question is 'specific enough'....Any suggestions will be appreciated.
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Chris Bradley
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Re: Energy efficient proton production?

Post by Chris Bradley »

By electrostatic means, you can't just produce high energy protons straight-off. First you stick in ~13eV's worth of energy to get a proton, then it gets accelerated by whatever field or process you've devised to accelerate it. For p11-B, you really need to be talking 161keV to get it up to enough energy to hit the point where there is a little resonant peak for fusion.

So if you get only 1% 'yield' of H+ out of your process, as compared with 100%, then providing you 'filter' it with magnetic means before you accelerate it significantly the different between the average energy for each proton you've 'wasted' by having just a 1% ionisation efficiency is 13eV x 99, which is <1% increase in power input into the overall acceleration of the beam protons. Corollary; not worth worrying about. Just get a mixed-up bag of low energy ions by the cheapest and most abundant means you choose, but after that make sure it's only the protons you actually accelerate.
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Re: Energy efficient proton production?

Post by Quantum »

So I then presumably have to use a Penning trap to 'store' the H2 ions?

Or can I trap them with a cathode?

I imagine I can't trap them by 'sputtering', in the usual sense, due to the fact that the H2 ions would combine with electrons from the cathode, and I'd end up with hydrogen gas again, which would just contaminate the whole system.

And I can't re-circulate them back to behind the ionizer, where they could possibly be re-combined with electrons, and re-cycled as fuel, because his would create a path for un-ionized hudrogen molecules to leak into the system after the ionizer, again contaminating it.

Or have I missed something somewhere?
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Re: Energy efficient proton production?

Post by Quantum »

Unless, of course, I have three ionizers......arranged so that any hydrogen molecules that try to leak past get ionized and 'pulled back' to where they can be filtered. If I can design this system, it should (eventually) convert all hydrogen fed into it into protons.
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Chris Bradley
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Re: Energy efficient proton production?

Post by Chris Bradley »

Ash Small wrote:
> So I then presumably have to use a Penning trap to 'store' the H2 ions?
>
> Or can I trap them with a cathode?
>
> I imagine I can't trap them by 'sputtering', in the usual sense, due to the fact that the H2 ions would combine with electrons from the cathode, and I'd end up with hydrogen gas again, which would just contaminate the whole system.
>
> And I can't re-circulate them back to behind the ionizer, where they could possibly be re-combined with electrons, and re-cycled as fuel, because his would create a path for un-ionized hudrogen molecules to leak into the system after the ionizer, again contaminating it.
>
> Or have I missed something somewhere?

hmmm.... you're kinda missing a question, I think?!

*If* your objective is to ensure that you only generate protons AND you want to keep those without allowing them any chance to recombine, then, I guess, yeah you need an ion trap like a Penning trap. I'd have to ask "why" though - overall you'll not get the efficiency of just generating a stack of ions and picking out the ones you want.

If you're expecting to be accelerating protons to 100's keV then your losses in generating the actual slow, pre-accelerated ions in a discharge, whatever that is, are going to be trivial. Like I say, if you *want* to have THE most efficient way of generating protons PRIOR to their acceleration, well, I'd suggest it's not exactly a well-research area as there's not much point. If you want to do that *for the challenge* then I'll look forward to the results of your experiments, but I don't see why anyone would really [want to] know.
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Chris Bradley
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Re: Energy efficient proton production?

Post by Chris Bradley »

What, exactly, is the end result you're aiming at? If you're serious about trying some beam-target p-11B then you do realise that worrying about efficiencies at the proton-generating end is like trying to work out what colour to paint your home-build rocket to add the least weight so that you'll get as high as possible? (If you're anywhere near of dreaming that you'll get energy pay-back, then your target for your home-build rocket is no less than a Moon landing.)
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Re: Energy efficient proton production?

Post by John Futter »

Ash
We use cold cathode penning type ion sources at work these run at around 2kV at 2mA giving up to 1.8mA in a faraday cup inserted downstream. By adjusting the axial magnetic field and voltage on the ion source a sweet spot is found for the gas species in use.
Hydrogen is neat as it only gives one +state of charge. Neutrals tend to stay within the ion source and only the +charge state ones are drawn out through the extraction electrode which is at a negative potential as compared to the cathodes of the ion source.

plenty of info on the web on ion sources
check out hot and cold cathode penninig ion source
also duoplasmatron ion source

and of course Andrews anode layer source and the Sesselman- Hendron ion source here on this site
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Re: Energy efficient proton production?

Post by Quantum »

I may be missing the point here, but, Chris, what happens to the ions that are filtered out...Where do they go, and what do they do if you don't 'trap' them. They would need o be removed somehow, surely? ...I appreciate that 're-cycling' them could prove to be less efficient than just removing them., but 'storing' an 'ever increasing number in a Penning trap will use up more and more energy, surely?

John, Will a 'cold cathode' trap hydrogen?...I can see how it would trap heavier ions, but won't the H2 ions just become gaseous hydrogen molecules again?....and eventually build up in concentration until they contaminate the whole system?

Or do I just run the vacuum pumps in overdrive?

While I don't wish to get ahead of myself yet (I'm dealing with the proton production here, not the problems associated with a Boron 11 target, and any alpha particles produced, but I do have experience of installing the Tungsten target at RAL, along with it's beryllium neutron moderators, I could post some photos I took if any-one is interested) I'm dealing with the problems associated with operating a 'sustained' proton beam here, as opposed to a system that can only be run for short periods of time, before it has to be shut down for maintenance..
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Re: Energy efficient proton production?

Post by Carl Willis »

Hi Ash,

This is a well-written line of inquiry and is in the right place.

The key to good efficiency in proton or deuteron ion sources is to prevent recombination of ions that have been made. Huge losses in the proton fraction occur when metal surfaces are exposed to the plasma and when high-vapor-pressure materials outgas into the plasma. The company I work for lines parts of the copper discharge waveguide with HIPped boron nitride sheets, and that turns out to be quite important. Historically, the RF types of ion sources that are electrodeless and carried out in glass tubes have been pretty efficient, but they don't produce much current.

Another thing to think about is how much plasma volume is being excited. Except for the region of plasma that feels the extraction fields, you might as well be heating meatloaf. So one possible line of experimentation concerns how to keep the discharge appropriately restricted in size.

I have to disclose some prejudices. Every time p-B11 gets mentioned on this site I get ready for a lot of silliness. Absolutely, identically, NO amateur effort has taken place in which this reaction has been done. Lots of people hemm and haw about it, but it has been exclusively an armchair topic. Anyway, enough about my prejudices.

-Carl
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Quantum
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Re: Energy efficient proton production?

Post by Quantum »

Thankyou for your comments, Carl.

Surely if the hydrogen is introduced into the region that feels the extraction fields, and ionized upon entry, all will be extracted?

I've not yet done the maths, as there is no point until you can estimate proposed losses, but , if my memory serves me correctly, 6x(10^23) protons at 161keV=161kW (or something of that order). And 6x(10^23) Alpha particles at 3.76MeV+12x(10^23) Alpha paricles at 2.46MeV= 8.68MegaWatts, more than 50 times the original power, so break-even is 2% efficiency.

So, Working on the fact that fission reactors are only 40% efficient at converting energy to electricity, Any proposed fusion reaction has to be at least 5% efficient to reach break-even (as far as the fusion reaction itself is concerned)

Due to the limitations of RF ion sources, certainly the ones I've come across so far, I'm forming the opinion that only some form of high efficiency plasma torch will be up to the job. I built a prototype in 2002. (well, a fore-runner of a prototype, to be exact).

Even the plasma torch they've constructed to test proposed materials for ITER is only 5% efficient when burning 100% hydrogen, but I'm pretty certain I can improve on this. Also, plasma can be introduced directly into the region that feels the extraction field.

It looks like I could now be looking for some suitable ceramic electrodes.

Maybe a combined plasma torch/RF ion gun would be more efficient that either on it's own?.
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Carl Willis
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Re: Energy efficient proton production?

Post by Carl Willis »


>6x(10^23) protons at 161keV=161kW

The energy needed to accelerate one such proton is 161 keV or equivalently 2.6E-14 joules. The energy needed to accelerate 6E+23 of them would be 6E+23*2.6E-14 = 15.6 GJ. If you define the proton current then you can calculate the beam power. Otherwise, units of power do not come out of your calculation.

Let's try the other one:

>6x(10^23) Alpha particles at 3.76MeV+12x(10^23) Alpha paricles at 2.46MeV= 8.68MegaWatts

The first particle has 3.76 MeV of kinetic energy or equivalently 6E-13 J. The second and third particle each have 2.46 MeV (4E-13 J). All three collectively have 6E-13 + 4E-13 + 4E-13 = 1.4 pJ. 6E+23 of a set of these three particles has 840 GJ. The calculated quantity as before has units of energy, not power. It also tells you nothing about where breakeven is. It tells you that N times the kinetic energy of one particle is the total kinetic energy of N particles. In other words...not much.

>Working on the fact that fission reactors are only 40% efficient at converting energy to electricity, Any proposed fusion reaction has to be at least 5% efficient to reach break-even

This makes no sense to me. A power plant of any kind has a thermal efficiency that is less than unity and that's about the only generalization that can be made. It need not be limited to 40%. High-temperature gas cycles can be more efficient; Rankine steam cycles tend to be much less efficient unless superheat is added to the steam. Point is, the heat source could have Q(out)/Q(in) be arbitrarily larger than 1 (e.g. 1.000000001) and still work, as long as the heat source is at a high enough temperature and the cold sink at a low enough temperature. Carnot's theorem and all.

P-B11 is a classic, hashish PIPEDREAM as we know it on this site. No member has built SQUAT that accomplishes it, or even tried. And yet, we keep rehashing basic thermo and Bert-and-Ernie math in the discussions. I'm not trying to get personal or display an unwelcoming attitude. (Maybe I am displaying an unwelcoming attitude?) The minute someone does their background research and makes a hardware commitment on a worthy p-B11 project I may stop looking down my nose every time I hear its name.

-Carl
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Re: Energy efficient proton production?

Post by Quantum »

I think you've missed the point, Carl....Either that or I have the wrong font.
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Re: Energy efficient proton production?

Post by David D Speck MD »

I was just reading the ORNL web page about their neutron spallation source. They dump 500 kW of protons into a target of liquid mercury to make a whole lotta neutrons in a hurry.

Of interest is the description of their proton source -- they negatively charge Hydrogen ions and accelerate them through a thin metal foil, which strips off the two electrons and leaves bare protons behind.

I wonder if this would be possible on an amateur scale.

Dave
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Re: Energy efficient proton production?

Post by Chris Bradley »

Negative ions through a foil is, I thought, normally the way to make a neutral beam, not a charged particle beam? I wonder why it'd help to strip 2?

Ash, if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is.
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Re: Energy efficient proton production?

Post by Carl Willis »

Sorry, that happened when I tried to type Roman characters on a public Internet cafe computer here in Kobe, Japan. I thought I had it figured out because it looked right on my screen. Evidently not. I am going back to edit it now...

*Earlier post fixed. Small-to-medium-sized rant appended to it.*
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Re: Energy efficient proton production?

Post by John Futter »

Chris / Ash
Yes we use a negative ion source on our EN tandem
You have to to get the atoms De jour to go through it. A previous post from me on the activation of iron for wear coupons is a case in point for protons.
our unit uses an extremely thin carbon foil at the terminal in the middle of the machine to strip the electrons of the atoms selected, other machines use a recirculating gas stripper to do the same. The terminal is positive at 6MV so the ions get attracted towards it, on loosing their electrons going through the foil they want to get away from the positive terminal as they are now positively charged so the tandem gives a second 6MV push, the ions now have 12MV of push (for hydrogen) other elements of greater mass like silver we can strip more electrons off say up to 11 so the total acceleration is now 12, 1 going to the foil + 11 after the foil so you end up with a 72MeV silver beam.
Now back to your enquiry
If your ion source is working right the H2 will have been dissasociated into H+ ions. Neutral H2 if remaining will leak slowly out of the ion source and not be accelerated towards the H+ target area and will be pumped away and or mass selected by a Wein filter or mass selection magnet to make sure that only H+ ions get to the target.

Ash back to your previous answer/ question to my last post.
cold cathode or hot the ion source if working right keeps the ions bottled up in the centre via the external electromagnet so they do not touch the inner surfaces (anode) of the ion source. If the magnet is not strong enough the ion source interior would get sputtered by the active ions hitting it ( although the sputtering yield for H+ is lousy) For the back cathode and the front cathode (the one with the hole in it to extract the ions we use a material with high work function) we use Aluminium or Tantalum.
The cathodes have to be replaced every 100 hours of running but the anode surfaces only need a clean and this is when using Argon not hydrogen.

Our other accelerator the KN (single ended machine) uses H2, He, He3, D2 in an Rf excited ion source this ion source runs for about 18 months continuously before it needs service.

Remember the more + ions you produce the more they push against each other (repulsion) which means an ion source producing more needs a greater mag field to keep them compressed to the middle section. Also extracted beams of higher ion current will defocus further due to the same repulsive forces.
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Chris Bradley
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Re: Energy efficient proton production?

Post by Chris Bradley »

John Futter wrote:
> Remember the more + ions you produce the more they push against each other (repulsion) which means an ion source producing more needs a greater mag field to keep them compressed to the middle section.
Do you get involved in the actual calculations looking at ion denisties? Various reading suggests the Brillouin limit is the one applicable to anaylsis of such situations - I believe - but I've also read academic treatments and experiments that say it can be a few orders of mag better than Brillouin suggests - and other that say the precise opposite!! What is your feeling for 'n' for a given B? Is Brillouin generally right, in practice?
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Re: Energy efficient proton production?

Post by Quantum »

"I was just reading the ORNL web page about their neutron spallation source. They dump 500 kW of protons into a target of liquid mercury to make a whole lotta neutrons in a hurry."

RAL use a similar system, but they use a Tungsten target....I have photos of it that I took while installing it, (the most recent ones were taken a few days before they first fired the proton beam to target) but I'm still trying to work out how to upload pics here.
(I also have photos of the beryllium neutron moderators, and the rest of their target system)

"they negatively charge Hydrogen ions and accelerate them through a thin metal foil, which strips off the two electrons and leaves bare protons behind. "

Thanks for that advice, I though something like that would be possible.
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Re: Energy efficient proton production?

Post by Quantum »

"if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is. "

I did rather suspect that may be the case, but wondered if the energy levels of the protons were high enough (Giga-Watts?), that maybe the impact ebergy would be sufficient. While I respect your reasoning and advice, Do we know this for certain until it has been tried?

RAL use a solid Tungsten target for their beam, (I can look up the energies involved if you are interested), this produces 'a lot' of neutrons, which, after moderation, are then used to create pions, which, in turn, create muons. One of the things they are doing (RIKEN-RAL) is 'muon catalyzed fusion', which, although it is not what this site is about, may be of interest to some here.

http://riken.nd.rl.ac.uk/ral.html
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Re: Energy efficient proton production?

Post by Chris Bradley »

Ash Small wrote:
> "if you pile MW of protons at a piece of 11B, statistically speaking you'll end up with no fusion at all. Almost all, bar a trillionth, will just scatter around and generate heat [destructive to the boron]. You need to come to understand this. beam protons into a lump of something isn't a fusion reactor - it is merely the way you learn how unreactive that really is. "
> Do we know this for certain until it has been tried?

Yes. Definitely. It was the first approach ever tried, by Oliphant, and, fortunately for him I guess, the rate of fusion reactions did not produce enough energy to provide an excess of energy to keep the reaction going. This is just what a fusor does, and does it with a 1E-9 inefficiency.

The way physicists refer to it is simply to say "cross-section[scattering]>>cross-section[fusion]" meaning a nucleus will scatter of another waaaaaay more often than it will fuse, so all that almost all the scattered energy just ends up as heat rather than powering a fusion reaction. So if you see "sigma[scattering]>>sigma[fusion]" in anything you read on the subject, then it's their shorthand for saying "beam-target fusion? you gotta be kidding".

....and that's not even counting the electrons that soak up the particles energy from ionisation.....
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Re: Energy efficient proton production?

Post by Quantum »

Carl, firstly, I don't claim to fully understand he maths involved, however your reply does not give figures for input energy versus output energy (theoretical) for this reaction.I'm curious to know what the theoretical figures are, and was hoping some-one would 'correct me', or at least start a debate on the subject.

My figures were based (loosely) on what has been published by Tom Ligon and Robert W Bussard, who, would appear to have convinced the US govt. that It will work (although I am dubious about their proposal to convert the energy directly to electricity)

I would have assumed, from the 'hype' of the British Govt in the past, that the theoretical 'payback' of a fusion reactor would be considerably higher than fifty-fold, although this will obviously depend on the reaction concerned. I assume those involving large amounts of neutrons have a higher theoretical payback, but I'm only guessing here.

There seems to be a consensus, particularly on this site, that ITER and DEMO will be destroyed by neutron bombardment from the inside out, so proton-boron 11 has to be considered, along with others, if the claims of Bussard and others are true, even if neutrons give more theoretical energy.

While I'm aware that some power stations have run at over 60% efficiency, they have all 'broken' as a result. I was being conservative with my estimates.

Finaly, it wouldn't be much of a 'forum for debate' if we all agreed all the time. I respect your right to your opinions, and I also respect your opinions in their own right.
If we are not 'collectively' working towards a solution, then all we are really doing is contributing to global warming, etc..
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Re: Energy efficient proton production?

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"the rate of fusion reactions did not produce enough energy to provide an excess of energy to keep the reaction going."


You may have mis-inderstood. I'm not suggesting that this would trigger a 'chain reaction'.....just a sort of 'energy amplifier. It needs a constant supply of protons to initiate 'reactions'....Alhough I can accept that, no mater how high the energy of the proton, inless ot is a 'head on' collision, the proton will 'glance off'.....however, if the energy level was sufficiently high, ot could still have enough energy for fusion even after 'several' glancing blows. The 'success rate' needn't be a very high percentage to reach 'break even'.

Can you explain what happens with the proton beam to target at RA? I installed this target station last year. (target station 2). The target is Tungsten, and it gives off neutrons, I'm assuming that the neutrons are 'knocked off' the nucleus, rather than being expelled due to a fusion event, but what happens to the protons?...Where do they end up?
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Re: Energy efficient proton production?

Post by Quantum »

John, Thanks...That's a very informative post.
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Re: Energy efficient proton production?

Post by Quantum »

Would this not also depend on how quickly they are accelerated away from the source?...The slower they are accelerated away, the greater the concentraion, and vice versa.
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Re: Energy efficient proton production?

Post by Chris Bradley »

Ash Small wrote:
> "the rate of fusion reactions did not produce enough energy to provide an excess of energy to keep the reaction going."
> You may have mis-inderstood. I'm not suggesting that this would trigger a 'chain reaction'.....just a sort of 'energy amplifier.
No, I understood, just a comment to reflect the total lack of efficiency of the process.


> It needs a constant supply of protons to initiate 'reactions'....Alhough I can accept that, no mater how high the energy of the proton, inless ot is a 'head on' collision, the proton will 'glance off'.....however, if the energy level was sufficiently high, ot could still have enough energy for fusion even after 'several' glancing blows. The 'success rate' needn't be a very high percentage to reach 'break even'.
I didn't say "cross-section[scattering]>>cross-section[fusion]" meant there was no future for considering alternatives, just that it's a tough nut to crack and there is currently no substantiated, viable way forward with it. I've done my best with my own discussions on breaking through this issue;

viewtopic.php?f=15&t=7183#p49055

but it is still unsubstantiated and the calcs. show you're only gonna get to a max of something like Q=3 anyway, even if there is a way to do what I suggest.

So what you're saying is right, protons will scatter and get a few 'stabs' at fusion, but the probability is a billion billionths and they get a hundred scatters before they've lost all their energy (these numbers are indicative of what can happen... you can do the calcs for yourself if you think they're not very accurate, but they're about right for, e.g. a fusor at a few 10's keV).

>
> Can you explain what happens with the proton beam to target at RA? I installed this target station last year. (target station 2). The target is Tungsten, and it gives off neutrons, I'm assuming that the neutrons are 'knocked off' the nucleus, rather than being expelled due to a fusion event, but what happens to the protons?...Where do they end up?
They'll loose their energy and take up an electron. Hydrogen embrittlement will result. Some might stay stuck in the target nucleii - all manner of things, I can imagine, but there are others far more able to say, mine are only guesses as I don't really need to know much more detail than that.
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