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Specialty Chemistry Forums => Nuclear Chemistry and Radiochemistry Forum => Topic started by: Enthalpy on July 09, 2017, 09:13:14 AM

Title: Tokamak produces radioisotopes
Post by: Enthalpy on July 09, 2017, 09:13:14 AM
Hello dear friends!

I'd like to propose to produce radioisotopes using the D-D reaction in miniature Tokamaks, especially for medicine.

Tokamaks (including stellarators) top the rate of permanent nuclear fusion reactions for a given size and input power
https://en.wikipedia.org/wiki/Tokamak
https://en.wikipedia.org/wiki/Stellarator
so big machines fed with D-T claim to produce net energy (present) at affordable cost (uncertain future)
https://en.wikipedia.org/wiki/ITER

As a neutron source instead, the machines would
Their activity or misuse would produce little plutonium, tritium and radioactive waste. From my estimates, the isotopes production would be naturally good - maybe at a lower cost than the other alternatives to fission reactors.

---------- Figures

Welcome to double-checkers, even more as usually, as a 3.7×1010 factor may well lack somewhere!

Iter is to produce 500MW heat (over 400s, let's forget that) from a 17.6MeV reaction, that's 1.8×1020/s. At the same induction, density and 150MK, the D-D reaction is 0.012× as frequent as D-T and the machine is 1000× smaller, for a reaction rate of 2.1×1015/s. Every second D+D reaction produces 3He+n, the other T+p, but T is consumed 80× faster in a D+T reaction that produces one neutron too: 4He+n. So 2.1×1015/s neutrons as well.

The target shall catch all neutrons (how?) and consist of pure 98Mo (that costs) in the example I choose. Something (Nitrogen behind graphite and molybdenum? Heavy methane?) shall thermalize the 4kW neutron flux to 77K=6.6meV:
http://www.nndc.bnl.gov/sigma/index.jsp thank you!
(n, total) 6.07b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=1&nsub=10
(n, elastic) 5.79b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=2&nsub=10
(n, γ) 0.26b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=102&nsub=10
I heavily overinterpretate curves made by models and don't integrate over the energy distribution. Then, the inelastic collisions section is 0.28b and (n, γ) make 90% of these or 1.9×1015/s. Still 60% at 300K so money shall decide.

Over a 5×24h week, the tokamak produces 8.3×1020 atoms of 99Mo. 2.75 days half-life = 343ks exponential decay mean 2.4×1015Bq = 65 000 Ci produced per week.

99Mo decays fully to 99mTc used for medical imaging. The worldwide demand is 12 000 Ci per week according to Aiea
https://www.iaea.org/About/Policy/GC/GC54/GC54InfDocuments/English/gc54inf-3-att7_en.pdf
satisfied by one mini-tokamak - rather several ones, since 99Mo must be transported swiftly. This allows for:
Produce and sell two mini-tokamaks per continent for redundancy.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: marquis on December 02, 2017, 08:39:35 PM
Ok, I'm totally outside of my specialty.  So forgive my ignorance.

The problem with the tokamak and other such devices is containing the plasma.  It takes powerful magnets and much electric force to do that.

But if I read correctly, that MAY have already been done by mother nature in the form of ball lightning.  Would a better approach be to further investigate ball lightning for possible easier ways to contain plasma?

Regards
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on December 03, 2017, 06:35:24 PM
Hi marquis, thanks for your interest!

Ball lightning has long been denied because it's difficult to observe, despite there were so many consistent testimonies, including from people of very different culture. About 3 years ago, a Chinese research team could measure a spectrum emitted by a lightning ball and found it consistent with the soil that had been hit by lightning. So the prevalent direction for theories is presently that lightning ejects a plasma from the struck object. No mention about confinement nor magnetic fields - but I didn't study the topic. My vague impression is that the plasma ball just dissipates freely.

Tokamaks begin to work presently. They do need strong magnetic fields, for which the oldish superconductors suffice, especially at the most recent attempt, ITER. Fusion is long achieved, fusion sustained for tens of seconds too, and the ancestors already produced more heat (...not electricity!) than the injected energy. The remaining problems are more
- How to produce tritium in proper amount?
- How to produce it cleany? [I do see a fundamental flaw here: to me, the operation is as dirty as uranium fission]
- What materials shall survive the neutron irradiation over years?
- How to stabilize the plasma safely for months?
And many more.

As compared with electricity production by D-T (deuterium-tritium) fusion, what I propose is much simpler in many aspects:
- I fuses D-D. No worry about T production.
- The tokamak is 10*10*10* smaller hence it's cheaper and easier. I suppose the magnetic field can decrease if the volume is less small.
- The reaction rate per volume unit is 80* slower, so the neutron flux is 80,000* smaller.

I have still to describe how to capture the neutrons efficiently by the target material, typically 98Mo to produce 99Mo and 99mTc. I see more or less how but must put figures on it and write it cleanly.
Title: Re: Tokamak produces radioisotopes
Post by: pcm81 on June 17, 2018, 08:58:57 PM
Neutron sources other than fission based nuclear reactors are usually spallation driven. A 1Gev energy protons are smashed into heavy metal target breaking up its atoms and releasing neutrons. Look up SNS at oak ridge. So far that is the cheapest way the world found to produce neutrons. What you ae suggesting is still allot more expansive per neutron if yo do the math.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 18, 2018, 09:21:05 AM
What you ae suggesting is still allot more expansive per neutron if yo do the math.

Can you show us your maths? The SNS has already cost 1.4G$, while the tokamak I suggest is 1000 times smaller than the existing ones.
Title: Re: Tokamak produces radioisotopes
Post by: pcm81 on June 26, 2018, 10:56:06 PM
What you ae suggesting is still allot more expansive per neutron if yo do the math.

Can you show us your maths? The SNS has already cost 1.4G$, while the tokamak I suggest is 1000 times smaller than the existing ones.

To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torrus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

MIT is trying to create a small tokamak, but it's still much bigger than what you are suggesting: https://www.computerworld.com/article/3028113/sustainable-it/mit-takes-a-page-from-tony-stark-edges-closer-to-an-arc-fusion-reactor.html

Here is another article talking about smaller tokomak: https://physicsworld.com/a/smaller-fusion-reactors-could-deliver-big-gains/

And once ain, the idea is not bad, it is possible to have stable fusion in a smaller reactor; but we have to invent a way to make much stronger magnetic fields.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 27, 2018, 04:54:28 AM
To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

Sorry to be so direct, pcm81, but you ignore the topic: about every of your sentences above contains a basic misunderstanding, which I won't comment individually. I'd suggest to you not to be affirmative on subjects you ignore.
Title: Re: Tokamak produces radioisotopes
Post by: P on June 27, 2018, 06:36:56 AM
I saw a youtube video a couple of years back about magnetic bottling and plasma containment in tokamaks using modern supermagnetic materials. It was presented by the Russians who were confident that their new materials would shield a tokamak and give it the fields it needed to contain a plasma on something of the kind of scale that would fit on a lab bench.  I can no longer find the vid - I do not know if was just boasting and fibs or propaganda or a serious breakthrough, but they seemed confident of cracking it soon.

It reminded me of the Mr Fusion, blender sized device, used at the end of Back To The Future.
Title: Re: Tokamak produces radioisotopes
Post by: pcm81 on June 27, 2018, 09:51:55 AM
To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

Sorry to be so direct, pcm81, but you ignore the topic: about every of your sentences above contains a basic misunderstanding, which I won't comment individually. I'd suggest to you not to be affirmative on subjects you ignore.
Don't be sorry about being direct. I got tough skin. I survived grad school in Russia... with lions and tigers and bears... and snow; oh my.

Back to the subject at hand. It all boils down to inventing a super conductor that can do the job. What I vaguely remember from my superconductivity course at moscow state (13 years ago) is that temperature as well as strong magnetic field have adverse effect on super conductivity.  In a tokomak you are trying to have something very hot, plasma, reasonably close to something very cold, super conducting magnet. Meanwhile by making the unit smaller you are increasing the magnetic field strength requirement. All this is putting a tall order on super conductor used to make a magnet. There are other issues like stability of plasma, leakage etc etc etc, most of which can probably be overcome if we can just invent the magic super conductor.

Oh, and as far as costs are concerned. Tokomak in europe is running north of $15bln so the $1.5bln for spallation source is chump change in comparison.

EDIT:
Don't get me wrong, i am all for fusion research and if you can design a working system, which actually does what you describe, that would be a great news for the world, because you would have also invented the technologies to power the world. I recall my undergraduate nuclear physics instructor doing a calculation on energy content of sea water. As i vaguely recall 1 gallon of sea water, if fusion was possible, has the same energy content as 400 gallons of gasoline used in combustion. So yeah, you would probably get Nobel prize in every category that year if you could invent the technologies required to make possible what you are proposing.
Title: Re: Tokamak produces radioisotopes
Post by: wildfyr on June 27, 2018, 03:09:26 PM
pcm,
I feel that I should remind you that Enthalpy's concept isnot for doing fusion for energy, but rather for element synthesis. Its an entirely different branch of fusion reactor technology.

Quote
As a neutron source instead, the machines would
Not try to produce any energy, even less net energy;
Receive only deuterium (2H or D) without the scarce 50% tritium (3H or T);
Be 10×10×10 times smaller than Iter with the same operating conditions:
Φ=1.2m and 50kW input and 20M€ (...err);
Emit neutrons to irradiate fertile material like 98Mo.
Title: Re: Tokamak produces radioisotopes
Post by: pcm81 on June 27, 2018, 05:42:24 PM
pcm,
I feel that I should remind you that Enthalpy's concept isnot for doing fusion for energy, but rather for element synthesis. Its an entirely different branch of fusion reactor technology.

Quote
As a neutron source instead, the machines would
Not try to produce any energy, even less net energy;
Receive only deuterium (2H or D) without the scarce 50% tritium (3H or T);
Be 10×10×10 times smaller than Iter with the same operating conditions:
Φ=1.2m and 50kW input and 20M€ (...err);
Emit neutrons to irradiate fertile material like 98Mo.

I understand that, however not producing power does not take away the requirement to be able to be build it (still need to invent the magic super conductor that can survive in those magnetic fields) and producing neutrons cheaper than competing sources like spallation per neutron. And I am not even mentioning that D-D reactions have much lower cross section than D-T reactions.  Don't get me wrong, i am all for fusion and in physics la-la-land this would work wonderfully, but in real world the technology does not exist to make this design possible or competitive with alternative means.

The baseline need in this concept is a cheap neutron source. The world has a good demand for neutron sources, ranging from medical needs like boron therapy to research needs like neutron scattering. When i did my grad research in russia, the nuclear reactor that was used there was producing 0.5 grams on neutrons per year with an operating budget on $1M/year. And that is when the lead engineer on that reactor was making $300/month (my science advisor). The point is, neutrons are in demand and they are expansive, even in the countries where labour is dirt cheap. Many people thought long and hard about how to make cheaper, more efficient neutron sources. Yes, small fusion reactors could do the job, if only someone can invent the technologies needed to make them work.
Title: Re: Tokamak produces radioisotopes
Post by: pcm81 on June 27, 2018, 05:55:04 PM
Also, something that is actually on topic of my masters thesis:
The target shall catch all neutrons (how?) and consist of pure 98Mo (that costs) in the example I choose. Something (Nitrogen behind graphite and molybdenum? Heavy methane?) shall thermalize the 4kW neutron flux to 77K=6.6meV:

Really to get to thermal range you just need water. Methane or heavy methane are needed to go to e-5 energy range. The advantage of methane is that it has a low excitation level, which means neutrons of low energies can still loose energy by hitting methane and sending it into spin, even though these neutrons already have too low of an energy to interact with hydrogen or deuterium as free gas.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 28, 2018, 04:52:16 AM
Better superconductors would make tokamaks more compact, everyone agrees, and at least one team in the US tries that direction.

The size of a tokamak doesn't result from centrifugal force and induction like in an accelerator. Tokamaks before ITER were smaller. The size results from the need to keep the heat in the plasma to achieve a net energy gain, which I don't want
https://en.wikipedia.org/wiki/Lawson_criterion

Because I don't seek energy production, the reaction can use D-D which is available in the Ocean. Tritium, for D-T that would produce energy, is not.

It is my hope that the size can scale down like the neutron production, if energy is provided from outside. 103 smaller than ITER, despite the D-D reaction rate is 0.012× as much as D-T at identical conditions.

I did not try to provide cost estimates... Dividing the cost by 103 like the volume was a joke, I hope everyone noticed my "...err". ITER, which runs out of financial control, is over 15G€. Other tokamaks are less expensive: Wendelstein 7-X cost 0.37G€ to build (it's a stellarator, or improved tokamak) for the same plasma temperature and density, using standard Nb-Ti superconductors for 3T rather than 5T
https://en.wikipedia.org/wiki/Wendelstein_7-X
and reducing the size a lot will make it cheaper - by how much remains to see.

It's been a year and I still haven't described how 98Mo shall catch the neutrons. Thermalize for sure. I have ideas in mind but must put more figures on them. Size / 103 supposes most neutrons serve; if this proves unrealistic, the size can shrink less.
Title: Re: Tokamak produces radioisotopes
Post by: P on June 28, 2018, 05:00:08 AM
This is from a couple of years back - Smaller tokamaks with high temp superconducting magnets:-  https://physicstoday.scitation.org/doi/full/10.1063/PT.3.2941

I still can't find any of the Russian stuff I saw a few years back.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 29, 2018, 06:02:05 AM
Thanks P!

A smaller tokamak thanks to stronger induction would also ease the capture by 98Mo of the emitted neutrons, one more advantage.

Whether having 5T, 10T or 20T, a tokamak to produce radionuclides rather than electricity is easier on several points, not just the size. For instance the neutron flux is much smaller, so the materials are reasonably stressed, and the heat production shrinks too. Both ease the design of the magnets. Not fully optimizing the energy efficiency relaxes many design constraints too. And the arguably highest hurdle for electricity production, the regeneration of tritium, is removed.

So it is my hope that the production of radionuclides is a much easier, useful, and economically sensible goal for small tokamaks. If I didn't put nonsense and if one or few teams get interested, it would be a first, nice and graspable goal for tokamak designers, including stellarators.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 24, 2022, 05:56:23 PM
Replacing 98Mo by a fissile material as a target for the tokamak's neutrons would seemingly ease the separation of the Mo produced then by fission. Just chemical separation of Mo would provide a big proportion of 99Mo, and the other isotopes disappear quickly or are stable. Alas, this attempt is impractical.

The mini-tokamak itself is nonproliferating. It would produce too little Pu or 3H to make bombs. Keeping this advantage excludes targets of 235U and Pu. Natural U or 238U or 232Th can make nonproliferating targets, but they need fast neutrons to fission, like 14MeV, and then only very thick target blankets intercept the neutrons, and very little 99Mo must be extracted from much fissile material.

A fission cross-section like 1b needs 4t/m2 of 238U to intercept 14MeV neutrons with fair probability. It also needs more neutrons, as the yield to 99Mo is like 5%.

Fission yields, cross-sections and more data is available there, thanks
  iaea.org (https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html) - bnl.gov (https://www.nndc.bnl.gov/sigma/index.jsp?as=238&lib=endfb7.1&nsub=10) , also iaea.org (https://www-nds.iaea.org/sgnucdat/safeg2008.pdf) - wikipedia (https://en.wikipedia.org/wiki/Fission_product_yield)
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on June 29, 2022, 05:56:00 PM
All data sources indicate the mean energy of thermalized neutrons as kT.
I believe it should be 1.5×kT, for instance 39meV at 300K.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 02, 2022, 11:57:17 AM
[...] So 2.1×1015/s neutrons as well. [...]
Wrong! Every second D+D reaction produces T+p, but T has 1MeV recoil energy while the magnets confine only mean 20keV hydrogen. Tritium escapes the reaction zone.

2.1×1015n/s need a machine 8×8×8× smaller than Iter rather. Or better magnets, as these progress.

And the neutrons have 2.45MeV as emitted by the D(D, n)T reaction, not 14.1MeV as in T(D, n)4He.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 03, 2022, 05:09:38 PM
Natural uranium blankets and thermal neutrons could produce 99Mo after all, but this takes a bigger tokamak, and the little molybdenum must be extracted from much uranium. At least, no isotopic separation is needed.

300K neutrons see 450b section for 235U fission, 67b for 235U absorption, 2.2b for 238U absorption. 0.72% and 99.28% abundances give natural uranium mean 5.9b with 55% chances to fission 235U. Natural C provides 4.9b for collisions (22mm mean free path) and 3.2mb for absorption. Accepting 1/3 neutrons lost in C, 923 moles C pass the neutrons many times through each mole U in a Brownian motion. Mean 510 collisions before absorption let a neutron spread by very roughly 0.5m rms. The uranium load is a bit over 1t.

Neutrons leaving a blanket inwards shall serve at opposite blankets. U absorbs too strongly between 1keV and 3eV so most neutrons must survive in well separated C. I didn't check deuterated polyolefins, light water nor the proliferating heavy water. Liquid oxygen could replace graphite, save a little bit uranium, and bring many drawbacks. Colder moderators bring little and liquid deuterium has big drawbacks. And the tokamak's coils must sit somewhere but will catch some neutrons.

Materials that absorb neutrons little: ethylene and propylene glycol carbonates and their eutectic, oxalates of alcohols or Be, including deuterated variants.

Some 30mg 99Mo made in a day must be extracted from >1t U. As the fission destroys the U molecule, maybe the chosen environment could build a new Mo molecule easy to separate.

6.1% of the fissions yield 99Mo. Maybe every second neutron misses the blankets or is absorbed elsewhere. 1/3 is lost in C. Among U events, 55% produce Mo. All this takes 100 neutrons per Mo atom, so the tokamak is only 1.7×1.7×1.7× smaller than ITER, alas. But producing no energy and needing no tritium, it's simpler. Adding U blankets at the top and if possible the bottom would reduce the size.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 05, 2022, 07:18:27 AM
I took initially an arbitrary size. So what tokamak size meets the demand for radioisotopes by fission of natural uranium by thermalized neutrons?
Plasma size: H=1.6m Di=1m Do=3m. The volume is Iter /77.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 07, 2022, 05:51:44 AM
Tritium escapes the reaction zone.

No it doesn't. "Welcome to double checkers", as I said. For instance at 5T, 1MeV tritium and 3.5MeV helium turn in few cm. Which keeps in the plasma this part of the produced energy.

So, back to 0.5+0.5 neutron per D+D fusion, with energies 2.45MeV and 14.1MeV.

The tokamak meeting the radioisotope demand has a volume 150× smaller than ITER, dimensions /5.33, plasma H=1.3m Di=0.8m Do=2.3m.
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 09, 2022, 09:40:49 AM
A beam of protons can fission uranium into 99Mo. But it isn't very convenient.

Protons above 20MeV fission 238U with 1.3b section. 235U is as sensitive, Pb and Bi less so, and I have no data for Th, so natural uranium is the target
  oecd-nea.org (https://www.oecd-nea.org/janis/book/book-proton.pdf) p784 (8MB)
I didn't check if deuterons or helions improve.

The section changes little up to 200MeV, a longer proton path in uranium improves fission chances. Braking from arbitrary 60MeV to 20MeV takes 3mm in metallic uranium
  physics.nist.gov (http://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html)
so mean 1.6b provide 2.4% fissions per proton. Starting from 30 or 40MeV needs much more beam power. 100 or 140MeV save some power but need a longer linear accelerator.

The cumulated yield of fission products resembles that of neutron fission
  escholarship.org (https://escholarship.org/uc/item/36n4s519) - www-nds.iaea.org (https://www-nds.iaea.org/sgnucdat/safeg2008.pdf)
so I take 6% 99Mo per fission. Producing 1.4×1014 atoms/s as in the 05 Jul 2022 message needs 16mA beam intensity.

60MeV need then 1MW beam power, ouch. Niobium cavities lose little power, oven magnetrons are affordable (synchronization?), electricity costs 1M€/year of which 1/3 is for 99Mo.

The target must evacuate 1MW heat. Sweeping a D=2mm spot at non-sine >100kHz isn't trivial and needs 10-100kVA; interrupting the beam can help. Maybe the beam can instead be defocussed to 1dm2 and the 2mm thin target be strongly tilted, say as a deep cone backed with flowing water. Then some 3kW/cm2 resemble the flux at the wall of a rocket engine. Multiple foils, wires, grains of uranium compound in water behind a thin wall would ease that.

Neutrons are produced by fission and spallation, possibly above 1MeV. Useless radionuclides too.

And now the good news: 0.2mg 99Mo must be separated from 1kg uranium only, and chemical separation suffices.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 10, 2022, 10:51:47 AM
First alternative using a proton beam:
  100Mo(p,np)99Mo (for chemists: 100Mo + p :rarrow: 99Mo + p + n)

100Mo makes 9.6% of natural Mo, the target is highly enriched. The swept or defocussed proton beam passes a window (thin Be, carbon-carbon, thinner Ni...) and brakes from 75MeV (more would save electricity) to 20MeV in 100Mo over 79kg/m2 range (7.7mm if metallic) where the sought reaction has 0.14b section, according to
  oecd-nea.org (https://www.oecd-nea.org/janis/book/book-proton.pdf) p482 (8MB)
so 0.66% of the protons make a 99Mo, and 1.4×1014 atoms/s need a 3.4mA 250kW beam. Bad, but less so than protons fissioning uranium.

The target can be immersed, for instance as biassed foils, wires, grains... in water, so cooling is reasonable. Maybe it's a concentrated solution.

I believe the Nb, Ru... byproducts must be eliminated before filling the "moly cow" with the mixture of 99Mo and 100Mo
  wikipedia (https://en.wikipedia.org/wiki/Technetium-99m_generator)
Whether 0.2mg/1kg suffice?  More compact cooling can reduce the target below 1dm2. Or if the nuclear reaction breaks the molecule, separation can ease. After use, the customer returns the 100Mo for reuse.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 10, 2022, 04:56:58 PM
Other alternative with a proton beam: convert to neutrons for absorption by 98Mo.

The table compares conversion nuclides. Data is from
  oecd-nea.org (https://www.oecd-nea.org/janis/book/book-proton.pdf) (8MB)
which lacks neutron data for W Re. I didn't check the more usual Pb Bi. I aim here 1.4*1014 neutrons/s as if the subsequent step were lossless. Deuterons may well outperform protons.

Nuclide  Page   MeV in   MeV out  kg/m2   Thick     Barn   Conv    mA      kW
==============================================================================
  2H       4      25       10      2.4     27m      0.15   1.1%     2.0    51
  7Li      6       6        2      0.52   0.94mm    0.3    0.13%   17     102
  9Be     11      18        3      4.1    0.22mm    0.1    0.27%    8.2   147
181Ta    673+     70       13     82      4.9mm     +++    6.0%     0.37   26
==============================================================================


I couldn't think of a good deuterium compound, so the target would be gaseous, under pressure for shortness, which needs a strong thin window: thin nickel, cold-drawn stainless, beryllium? For instance 1mm Be uses 3.4MeV above 25MeV. Deuterium seems the cleanest neutron source.

Lithium needs some vessel too, as I didn't find a good compound. It can have the natural composition. Beryllium instead could be a naked thin layer over the coolant, easier. It's monoisotopic naturally. The next light elements appear to need more and more power.

Heavier elements like lead expel more neutrons. Here refractory tantalum eases the design, like a naked thin layer over the coolant, or biassed foils in water. It's monoisotopic naturally. I cumulated the sections for 5, 4, 3, 2 neutrons over energy ranges.

The irradiated target produces many nuclides and particles, more so with heavy elements and high beam energy. But a neutron converter can at least be sealed.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 16, 2022, 07:54:36 AM
Finally I've read a bit about how other Sapiens produce neutrons without uranium fission.

========== Electrostatic accelerators

They provide a big beam current like 1A but a low energy, like 0.2MeV
  Verbeke (https://www.osti.gov/servlets/purl/775126)
so only D+D and D+T react. The beam smashes D and optionally T ions on a metal target that adsorbs them before new ions collide with them. The metal wastes much ion energy, and fusion reactions are rare at 0.2MeV. 1.4×1014 neutrons/s (if each one makes a 99Mo!) then need 0.5MW beam power. As the D+D reaction is 20× slower than D+T at this energy, this neutron flux demands tritium, proliferating and obtained from a uranium reactor. Not my goal.

The targets are of Ti or Nb as they adsorb up to 2 hydrogen atoms per metal atom and are lighter than Pd hence brake protons less.
========== Linear accelerators

Resonant cavities at 2K achieve a higher ion energy. 3MeV is reasonably short, 20MeV takes already a long building. This limits targets to Li, maybe Be and D.

========== Synchrotrons

High ion energy, optionally high beam current, focus, but look expensive. Small units are under development, interesting.

========== Cyclotrons

30MeV fits in a normal room, 90MeV is a bigger machine. Most cyclotrons work at room temperature, some use superconducting magnets.
  wikipedia (https://en.wikipedia.org/wiki/Cyclotron)
3mA is a record
  arxiv (https://arxiv.org/abs/1707.07970) - arxiv (https://arxiv.org/abs/1302.1001) - accelconf.web.cern.ch (https://accelconf.web.cern.ch/c81/papers/ei-03.pdf)

Cyclotrons produce already varied medical radioisotopes by proton impact. Some hospitals are equipped (with low beam intensity). Cyclotrons also make neutrons by spallation, usually of Pb or Bi at higher proton energy. This is a path to 99Mo.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 17, 2022, 10:44:05 AM
Reactions cross-sections exist for protons, deuterons and alphas, ranges too, many thanks
  oecd-nea.org (https://www.oecd-nea.org/janis/book/book-proton.pdf) - oecd-nea.org (https://www.oecd-nea.org/janis/book/book-deuteron.pdf) - oecd-nea.org (https://www.oecd-nea.org/janis/book/book-alpha.pdf) (8MB 3MB 5MB)
  physics.nist.gov (http://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html) - physics.nist.gov (https://physics.nist.gov/PhysRefData/Star/Text/ASTAR.html)
and cyclotrons accelerate them all, so which is better?

========== Alphas are bad

They're known to extract a neutron from Be, but at meaningful 18MeV, their 58µm range obtains only 0.014 neutron for 100 alphas, while protons obtain 0.27 neutron.

Entering Ta with reoptimized 120MeV and 2.8mm range, the cumulated sections for emitting 8 to 2 neutrons provide 0.015 neutron per alpha. A 70MeV proton achieves 0.06 neutron.

I checked 70MeV alphas, accessible to the same cyclotron as 70MeV protons, in favourable 97Mo. The beam power is 30× worse than for p hitting Ta.

========== Deuterons

To estimate deuterons range, I double the range of protons that have half the energy.

I suppose some D+D reactions make more neutrons than here fusion, but I have no data.

I limit the deuteron energy to 20MeV, more would improve much. The same cyclotron accelerates protons to 40MeV.

Nuclide  Page   MeV in   MeV end  kg/m2   Thick     Barn   Conv    mA      kW
==============================================================================
  2H    Absent    20        1      1.1   7m 1bar    0.1    0.33%    6.7   134  Only fusion!
  7Li      6      20        2      3.0    5.6mm     0.3    0.77%    2.9    58
 11B      19      20       12      3.2    1.4mm   2×0.045  0.16%   14     285
 51V      77      20       10      2.6    0.43mm  2×0.6    0.41%    5.5   109  Not so dirty?
 98Mo    195      13        6      2.0    0.19mm    0.2    0.024%  81    1200  99Mo directly
==============================================================================


========== Protons update

Limiting the cyclotron size to 40MeV protons.

69Ga makes 60% of the natural abundance, and the 40% 71Ga are decent too.

Nuclide  Page   MeV in   MeV end  kg/m2   Thick     Barn   Conv    mA      kW
==============================================================================
 69Ga    281...   28       15       9     1.5mm   2×0.4... 1.3%     1.7    47
 75As    324...   40       20      19    ~3.3mm   3×0.3... 1.2%     1.9    78
181Ta    673...   40       13      28     1.7mm   3×0.6... 2.1%     1.1    42
209Bi    738...   40       13      29     3.0mm   4×0.5... 2.2%     1.0    41  Looks dirty
==============================================================================


So both protons and deuterons are interesting, alphas are not, and 40MeV can suffice though suboptimum. I didn't check the paramount unwanted radioisotopes.

All these computations would need software.

The cyclotron draws power for its magnetic field, so less beam MeV buy many more kW. This also favours fewer production sites.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 24, 2022, 07:41:24 AM
Thoughts about cyclotrons, here the coil for DC field. I haven't read about beam focussing etc, which constraint much the design, so exert due mistrust.

========== Wind the coil

Many DC electromagnet coils seem to use thick rectangular conductors, difficult to wind, and flow the coolant parallel to the current on a long narrow path.

Thin band fills well the volume and is easily wound around the magnet's axis as a spiral. Or two couterrotating spirals in an other, fed where they meet, let return the current from the extreme turns to ease the insulation. Uninsulated OFHC copper band (or pure aluminium) is easily available. A thin insulating film can separate the turns.

The example sketch takes generous 1.4T in 0.22m gap so 40MeV protons orbit with R=634mm. This needs 2×123kA×turn in the coils. 428 turns per coil take 287A, 5.65m×428turns of (not displayed to scale) 0.6mm×0.5m lukewarm copper resist 0.16Ω per coil for safe 46Vdc. Consumption is 13.3kW per coil. 1.0T in 0.12m gap would take only 2.0kW per coil.

Commercial 0.1mm thin insulating film can zigzag between the metal turns: Petp, Pi... Metal fills 85% of the volume. Some mm film width spaced by few unsupported cm leave room for the coolant. Some films are adhesive, even at heat (polyimide). Heat-resistant epoxy seems possible, glassfibres too.

Cores of DC magnets are often of pure Fe, from Armco or other. Fe saturates at 2.1T, expensive FeCo at 2.3T. For instance four 45° pillars close the flux loop at 2.0T. I believe the faces near to the RF acceleration voltage must be plated with Au, or at least Cu or Al.

========== Cool the coil

I compute with liquid commercial diphenyl oxide/biphenyl (Dowtherm A, Terminol...), but farnesane, phytane... would outperform them and fatty esters (exist as transformer oil) be biodegradable.

From 40°C to 50°C, the fluid absorbs 16kJ/kg so 0.81dm3/s per coil suffice. 428 turns spaced by 0.1mm on mean R=0.9m offer almost 2×0.12m2 to the flow. The laminar speed parabola peaks at 10mm/s, its curvature over 50µm is 8.0Mm/s/m2, so 2.3mPa×s viscosity drops 18kPa/m or 0.18bar over 0.5+0.5m.

The temperature drop across the copper and fluid thicknesses is tiny, the drop in copper across a spacer half-width too.

A complete coil can be encased in glassfibre composite for instance. Epoxy at the spacer film would resist reasonable fluid pressure, sewing across the coil thickness resists more.

========== More uses

Eddy currents in the wide bands prevent quick changes of the induction. Split width improves that. A DC electromagnet doesn't care and benefits from superior cooling, other uses too.

Take a copper coil, R=0.2 to 0.4m, H=0.3m. An axial flow of 80dm3/s of deionized water can extract 10MW from 40°C to 70°C. Water in 10% of the section needs only mean 2m/s while 90% copper resists 0.7µΩ/turn2, so 10MW electricity provide 3.8MA×turn that create 30T in air. Counterrotating spirals can leave the duct at ground potential. The copper foil might be insulated. Forces must be addressed.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 24, 2022, 05:28:03 PM
Some metals conduct much better at cold without superconducting. This can save power despite the chilling effort, as I already suggested there
  chemicalforums (https://www.chemicalforums.com/index.php?topic=110699.msg391485#msg391485)

Copper resists only 20pΩ×m at 20K instead of 20nΩ×m when lukewarm
  nist (https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote365.pdf) [5MB] page 40

========== Cyclotron

Imagine the previous cyclotron electromagnet at 2.0T instead of 1.4T, with the current ×1.43. Neglecting iron saturation, which I shouldn't, the losses climb to 2×27kW if lukewarm, but at 20K it's only 2×27W.

Foam would leak too much heat, but multilayer superinsulation can leak 10W per coil. It must be enclosed in bags for vacuum. This is available commercially.

If each coil needs 40W cooling, the common chiller consumes 4.2kW if 30% as efficient as Carnot's limit. This saves 50kW.

Cyclotrons operate in radiation bunkers, so gaseous helium shall chill the coils, not hydrogen. From 19K to 21K at 1atm it absorbs 10.5kJ/kg so each coil needs 3.8g/s. Density 2.4kg/m3 takes 1.6dm3/s per coil.

As previously, flow through 0.12m2 means 19mm/s at the top of the laminar flow parabola. If the cooling channels are 25+25µm thin now, with curvature 62Mm/s/m2, 3.5µPa×s viscosity take 220Pa/m, dropping only 2mbar in the coils.

More than 2.0T is possible without superconductors, but iron can't help then.

Chilled metal would also reduce the losses at the accelerating cavities or equivalent.

========== 30T electromagnet

Instead of 10MW warm as previously, copper would consume 10kW at 20K. Beware I didn't check the magnetoresistance, so this may be very wrong.

Heat leaks are small here. If 30% as efficient as Carnot's limit, the chiller consumes 520kW instead of 10MW for the warm coil.

In both examples, the conductors are much cheaper and easier to process than superconductors, the cold is easier to achieve, and the remaining consumption doesn't justify superconductors.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 26, 2022, 12:41:26 PM
Transverse magnetoresistance of Cu and Al at cryogenic temperatures:
  lss.fnal.gov (https://lss.fnal.gov/conf/C720919/p539.pdf)
In the more favourable transverse effect, the induction is perpendicular to the current. It happens at electromagnets like here.

========== Cyclotron coil

For 2t in the gap, each coil provides 176kA that create up to 0.7T or 7kOe in the 0.3m wide slit hosting the coil. From fig.1 in the pdf, the magnetoresistance would add 1.4× the zero-field resistivity of Al.

The 0.7T appear only near the open end of the slit, so the 1.4× is reduced by /3 as a mean, or rather by /2 as the current redistributes.

The pillars carrying the return flux cover only half of 360°. Where they're absent, the induction is around /3 and the 1.4× drops even more. Almost a factor /2 gained over 360°.

The pillars can stand farther away to reduce the induction through the coils. Improve easily /2. They can also be thicker and narrower to improve the gain over 360°.

So the magnetoresistance adds rather 0.35× at the sketched cyclotron coil, and with minimal optimization 0.1×. Fine.

========== 30T electromagnet

The field reaches 30T or 300kOe at the coil's inner face and almost as much at the outer face. Fig.2 shows Cu up to 100kOe, so if Kohler's law holds, the magnetoresistance adds up to 170× to the cold resistivity, ouch. Fig.1 shows Al measured up to 40kOe: if daring to extrapolate linearly the curve of 2100 residual resistivity ratio (RRR) to 300kOe, the magnetoresistance adds up to 6.2× to the cold resistivity, provided that the current distribution is stable.

The field increases linearly from zero at the section's centre point but decreases beyond a half-thickness, so we can count 2/3 of the 6.2×, that is 4.1×.

Purer Al can rescue the chiller consumption. Increasing the RRR from 2100 to 28200 worsens by 2.8 the magnetoresistance but it's relative to the zero-field cold resistivity which drops by 4 to 5, providing a net 1.6 gain.

Together, magnetoresistance makes the ohmic loss and chiller power 3.6× worse than I estimated in the previous message: 1.9MW instead of 10MW lukewarm. Still interesting. Reooptimize the temperature?

========== Laminar flow

I supposed a laminar helium flow, but η=35µP=3.5µPa×s doesn't help the intuition. ν=η/ρ=1.4mm2/s and 13mm/s in 100µm channel width define Reynolds Re=u×h/ν ~1 <<2000 so the flow is laminar.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 28, 2022, 06:39:40 AM
Among the uses of strong magnets is magnetic resonance imaging MRI, and also NMR
  wikipedia (https://en.wikipedia.org/wiki/Magnetic_resonance_imaging) - wikipedia (https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance)
It goes without saying, but maybe better if I say it.

Most MRI machines have superconducting coils cooled by liquid helium to create 1.5T. Possibly aluminium coils around 20K can replace them for cheaper. I should throw a few figures at that some day.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on July 31, 2022, 11:34:34 AM
Figures about aluminium coils at 20K for MRI. 1.5T, the rest is arbitrary just to assess the feasibility.

A uniform induction needs more current density at the ends. I take two currents for simplicity. Solving for 1.5T at two points gives 1.81MA and 1.17MA, as illustrated.

Real cases refine that. Dividing more the current distributes the induction better. Choosing some reasonable axial induction distribution, outside the coils too, and deconvolving by the distribution of a current loop using a Kálmán filter would do it too. Surely dozens of methods exist.

Each of the four coils is L=1m Ri=0.87m Ro=1.13m big on the example. Aluminium fills only 70% because other coils need voids to vary the flux locally. So length=6.28m and S=0.182m2 for 1 turn.
  nvlpubs.nist.gov (https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote365.pdf) (5MB) page 20 - lss.fnal.gov (https://lss.fnal.gov/conf/C720919/p539.pdf)
the resistivity is 6.3pΩ×m at zero field, but magnetoresistivity adds 4.6× at 15kOe (1.5T in air). This extreme value happens at the inner face, so as a mean 2.3× for 21pΩ×m. 0.72nΩ/turn2 dissipate then 2.4+1.0+1.0+2.4=6.7kW at 20K. Heat leaks can be much smaller. 30% of the 6.2% Carnot limit towards +50°C=323K let evacuate 360kW in the air. If the machine operates for 4h/day and 250 days/year, the electricity bill is 300k€ in 4 years. I suspect superconducting coils cost more, and they need cooling power too, at 4K.

0.23kg/s = 0.10m3/s gaseous helium from 19K to 21K shall remove the 2.4kW from the outer coils thanks to 10.5kJ/kg and 2.4kg/m3. An axial flow through 10% of the coil section or 0.16m2 needs mean 0.6m/s helium speed, so easy.

That's a part of the picture. For instance the mechanical stability of the coils matters. Open MRI apparatus, more generally a vertical main field, saves power with shorter induction lines in air, while cold aluminium coils create a longer observation zone than permanent magnets do.

A thought for Sapo.
Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 06, 2022, 11:43:38 AM
Sources of γ rays sterilize objects, measure thicknesses without contact, display the contents of closed containers, etc. But radionuclides like 60Co are also a danger. A switchable γ source could be useful. As usual, I didn't check what is already done or abandoned. Nor am I reliable on the topic.

Bombardment by protons or deuterons lets some targets emit γ.
========== Example

Among these fourth-type reactions, in this message I consider
  19F(p,γ)20Ne. For chemists: 19F + proton :rarrow: 20Ne + γ
Data is gratefully taken from the Janis books
  protons (https://www.oecd-nea.org/janis/book/book-proton.pdf) (8MB) page 62 - deuterons (https://www.oecd-nea.org/janis/book/book-deuteron.pdf) (3MB)

Natural fluorine is pure 19F. 20Ne is stable. I understand the γ carries 12844keV reaction energy plus 19/20 of the incident proton contribution: an energy not available from radioactivity, twice as penetrating as 1.33MeV from 60Co, for instance to measure thicker red-hot steel plates when rolled.

The first competing reaction is on p63 in the Janis book, with similar sections over the energy range
  19F(p,α)16O
The product is stable and the α stops within the source. If emitting no additional γ, this reaction looks harmless and acceptable.

The next competing reaction is on p59
  19F(p,n)19Ne
which is 4MeV endothermal, so a smaller proton energy prevents it and the others.

The useful reaction has a measured section around 40mb from 1.4 to 0.3MeV. Target fluorine can be AlF3 since the Janis book lists no reaction of Al active at these energies. NaF and MgF2 seem clean too. 13N from (CF2)n would emit 1/1000 γ at 511keV with 10min half-life. Very pure 11B is less convenient. Li and Be emit other radiations.

32%wt Al and 68%wt F brake 1.4MeV protons over 44g/m2, that is 30g/m2 F, as deduced from
  physics.nist.gov (https://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html)
and then 40mb section let 3.8ppm of all protons create a γ, so a 1.4MeV 1.6mA 2.2kW proton beam emits 1Ci. Maybe protons up to 4MeV improve the yield but the Janis book lacks experimental data, and 1.4MeV accepts a small cyclotron, or maybe a linear accelerator with radiofrequency quadrupoles (RFQ).

Aluminium or other, possibly cooled by water, can support AlF3 of which 10-20µm stop the protons. The two transmutations deplete F in few years of continuous 1Ci operation, faster degradation processes are plausible.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 07, 2022, 09:55:33 AM
Some more proton-to-γ reactions. Reactions not indicated in the Janis book may ruin the attempts.

Target  Nature  Product  Janis    Q   Avoid  Section  From   To   Yield
           %              page   MeV   MeV      mb     MeV   MeV  Ci/mA
=========================================================================
  7Li    92.50     8Be    007  +17.3   1.64    7?      1.6   0.5  0.5?
  9Be   100       10B      13   +6.6   1.85    0.5?    1.8   1.0  0.02
 44Ca     2.09    45Sc    103   +6.9   4.43    1.8     4.0   2.0  0.2
 51V     99.75    52Cr    147  +10.5   1.53    0.2     1.5   1.2  0.02
 52Cr    83.79    53Mn    162   +6.6   5.49    0.6     4.0   2.0  0.06
 58Fe     0.28    59Co    194   +7.4   3.09    1.4     3.0   2.0  0.03
 59Co   100       60Ni    201   +9.5   1.86    0.6     1.8   1.6  0.002
 62Ni     3.63    63Cu    230   +6.1   4.73    2.4     4.3   3.0  0.06
 64Ni     0.93    65Cu    235   +7.5   2.45    1.1     2.4   1.2  0.02
 63Cu    69.17    64Zn    243   +7.7   4.15    1.8     4.1   2.8  0.1
 65Cu    30.83    66Zn    250   +8.9   2.13    0.6     2.1   1.8  0.004
 68Zn    18.80    69Ga    274   +6.6   3.70    7       3.6   2.8  0.1
 >Zn                     Lacks γ data
=========================================================================


  7Li: No data about 6Li. Does the data distinguish 8Be from α+α? How much energy in the photon vs α+α?
44Ca: Remove well 42Ca 48Ca.
51V : Leave 50V.
52Cr: Remove well 53Cr 54Cr. Produced 53Mn has 3.7My half-life.
58Fe: Remove well 54Fe 56Fe 57Fe.
59Co: No separation.
62Ni: Remove well 58Ni 60Ni 61Ni 64Ni. Can start below 4.3MeV.
64Ni: Remove 58Ni 60Ni 62Ni. Remove well 61Ni.
63Cu: Remove 65Cu and start below 2.13MeV, or remove well 65Cu.
65Cu: Remove 63Cu.
68Zn: Remove well 64Zn 66Zn. Remove 67Zn and start below 2.41MeV, or remove well 67Zn.

9Be, 51V, 59Co need no isotopic separation. 63Cu, 65Cu accept limited isotopic purity and emit lower energy γ. Insufficient data to tell about 7Li. The others need strong isotopic purity for cleanliness.

Energetic protons make more gammas but need a bigger cyclotron. All nuclides accept weaker protons.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 09, 2022, 02:17:55 PM
A 1.4MeV protons cyclotron for a switchable gamma source is D=0.8m H=0.6m small and can be added to a production facility or an imaging apparatus. Illustration appended. Please remember I didn't consider beam focussing.

0.89T give protons 13.56MHz cyclotron frequency, 6 sectors receive power at the 40.68MHz ISM frequency. If the energy must vary, move the extraction electrode radially?

The DC magnet coils provide 2×14.2kA×turn. 90% fill factor
  chemicalforums (https://www.chemicalforums.com/index.php?topic=92021.msg395201#msg395201)
gives them 2.4µΩ/turn2 so they consume 2×0.5kW.

1.36T and 2×20.34MHz would shrink the cyclotron to D=0.7m but need 2×1kW in the coils.

6 sectors all fed with slightly over 5kVpk provide 60keV/turn. Each sector has stray 50pF to the iron compensated by a 0.3µH coil each. These coils can consist approximately of 2.5 turns of 6mm gold-plated wire on D=37mm air. They dissipate roughly 6×65W, so oil and even blown air can isolate and cool them.

A linear accelerator for 1.4MeV using radiofrequency quadrupoles (RFQ) is shorter than 2m and sleek. Its beam can be bent, even by permanent magnets. Serious competitor.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 14, 2022, 03:37:41 AM
More reactions for a switchable γ source, as alternatives to proton capture.

Data is from the Janis book.

========== β+ and ε

Proton impact makes naturally proton-rich nuclides that decay by β+ emission or by electron capture ε. The impact often emits neutrons too, but surrounding boron can absorb them with little added radioactivity.

The β+ decay can emit a useful γ, but the e+e- annihilation emits also two 511keV γ. If the 511keV are usable, many radionuclides and reactions are possible and known. Removing undesired 511keV is difficult and wastes the other γ even at 2MeV. I didn't insist.

A few proton-rich nuclides decay by ε without β+, hence without 511keV γ. The emitted neutrino takes some energy, and at least a part of the γ spectrum is continuous, less valued for imagery. Maybe some nuclide exists with useful γ energies and credible production reactions, but I didn't find any in a limited time.

========== β-

No 511keV γ here, and some nuclides have a clean γ spectrum. Neutron-rich nuclides are harder to produce by impact. The reactions I found get a deuteron and emit a proton. I checked for unwanted reactions only in the Janis book, they exclude for instance 18O to 16N and 18O to 19O.

Target  Nature  Product  Janis  Avoid  Barn  From   To   t1/2  Gamma   %  Yield
           %              page   MeV          MeV   MeV         MeV       Ci/mA
================================================================================
  15N      0.37    16N      33     ?     0.7   2.6+  1.2  7.1s  6.13   67    19
  27Al   100       28Al     46    4.1    0.2   4.0   2.4  2.2mn 1.78  100    10
================================================================================


The β- emits few photons by braking, even in Al. At 1.5MeV it's around 2%.

The choice is again narrow and implies diverse drawbacks:
Maybe some applications prefer these drawbacks to a permanent radioactive source.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 18, 2022, 08:33:31 AM
I didn't find how to contain gaseous 15N as a target for 2.6MeV deuterons already stopped by 10µm nickel, so this gamma source needs a nonvolatile nitrogen compound.

The deuterons react with pretty much all light elements like B, C, O, Al, Si... to produce radionuclides that would still radiate after the useful 16N has decayed. My answer is to combine N with yttrium or heavier, as the 2.6MeV deuterons attain the nucleus rarely, a million times less often than nitrogen. Unless someone wants to shoot at HN3 or synthesize N8, of course.

The compounds I found are nitrides: YN, ZrN, NbN, TaxNy, WN, while HfN and others are less known, possibly nonexistant.

Among these, Ta3N5 provides the best nitrogen content and reaction probability for 15N: only /2.7 as compared with pure N. The yield drops from 19 to still excellent 7Ci/mA. It offers decent resistance to heat and water too. Some Nb in Ta is acceptable. The heavy Ta reacts extremely little with 2.6MeV deuterons.

The other compounds reduce the reaction probability by /4 roughly, so they can be considered if more stable for instance.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 20, 2022, 05:30:18 PM
How big is a cyclotron for 4MeV deuterons used in the reaction with aluminium I proposed here on 14 Aug 2022?

1.78T lets deuterons orbit at 13.56MHz, so the acceleration power can use the 27.12MHz or 40.68MHz ISM frequencies. At 4.0MeV, the path radius is 0.23m with a slightly reduced gap there. 2×28.3kA achieve 1.78T in 40mm gap.

The flux returns between R=0.41m and R=0.51m, where 1/3 of the area is open. The cyclotron takes D=1.02m H=0.7m as sketched and weighs 4.5t.

Smaller is possible. Less γ activity enables less energetic deuterons. Cold coils, optionally superconducting, can produce a stronger induction, but then iron doesn't help.

Lukewarm copper coils can fill 90% of R=0.26m to R=0.40m and H=0.18m each. 430 turns of 0.3mm foil plus 0.025mm spacing resist 165mΩ, so 10.9V and 66A dissipate 715W per coil. Two gamer PC power supplies suffice.

Or use D=1mm aluminium wire at 20K. I imagine yarn wound loosely on the wire so 0.04mm spacing leaves helium through, with a polymerizing resin that impregnates the yarn. At 0.25T=2.5kOe, the magnetoresistance adds 0.7× the zero-field resistivity, but this induction drops linearly with the height and drops also where the return path is removed, so ×0.23 as a mean. 170×131 turns resist 0.87Ω so 1.27A and 1.10V dissipate 1.40W at 20K. 50+ plies of multilayer insulation wrapped around a coil leak 0.3W. The atmosphere presses on the separators, which may need more plies. If 30% as efficient as Carnot's limit, the singe cooler consumes 180W. Square aluminium wire would save 30W.

========== 2.6MeV deuterons

For the reaction with nitrogen, the cyclotron can be 0.813× as big, or D=0.82m H=0.56m. Consider a linear accelerator with RFQ.

========== Switch on faster

When the γ activity needs less beam current, starting with the full current achieves the sought activity faster.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 21, 2022, 02:32:19 PM
[MRI apparatus use to be much shorter than depicted here on 31 July 2022. The conclusion remains.]

==========

Open Magnetic Resonance Imaging began with permanent magnets and 1/4T that blurrs the image. One present commercial success is Philips' Panorama High-Field Open that offers 1.6m opening between two pillars and 1.0T. The pillars seem too narrow for an iron return path, so the supposedly superconducting coils must create the induction unhelped. They look like horizontal Helmholtz coils
  wikipedia (https://en.wikipedia.org/wiki/Helmholtz_coil)
Smaller currents added nearer to the axis must even out the induction. More coils create induction gradients, produce and pick the RF fields.

20K aluminium coils seem globally cheaper than superconductors in that use. Cold sensor coils and preamplifiers are good for small signals too.

I compute with plain Helmholtz coils as the corrections need little current and power. R=1m and 1m spacing take 2×569kA×turn. Diagram appended. Data source as previously.

Aluminium wire is square 2mm×2mm here, finer can help varying fields. Band would limit the supply voltage. 15 900 turns fit in D=0.3m. A straight cable would create 0.76T at its surface, but I take 1.0T=10kOe, so the magnetoresistance would add 1.75× the 24pΩ×m zero-field resistivity with RRR=2100, and averaged over the radius it's 1.17×, leading to 52pΩ×m. Each 1.3Ω coil uses 35.8A and safe 46.5V, together 3.32kW at 20K.

Narrow (adhesive) tape or (resin impregnated) yarn wound around the wire insulates and defines the 100µm cooling channels. Interleaved 50µm windings guarantee the channel thickness. 0.13m3 helium at 1atm from 19K to 20K remove the heat. The mean speed is 1.5m/s in the channels, so 1.4mm2/s and 100µm define Re=150 < 2000 and the flow is laminar. Speed curvature 1.74Gm/s/m2 in the channels lets drop only 6kPa over 0.3m.

The heat insulation needs vacuum and reflective surfaces, multilayer insulation is optional. Polymer straps can hold the coils, but I didn't put figures. Forces are like 2MN while deformations are undesired, interesting.

The cooler consumes and dumps 180kW if 30% as efficient as Carnot's limit. This is much, but:
Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 25, 2022, 05:23:04 AM
Updates to my last message.

The magnetic forces are nearer to 1/2 MN rather.

0.13m3/s helium. The helium pressure drop over straight 0.3m would rather be 2kPa but the path zigzags. 4kPa wouldn't be pleasant, adding 520W heat to ohmic 1600W. A quadrupolar flow improves this. Or increase the 100µm spacing, it works cubed.

Helium data is from BNL, many thanks
  bnl.gov (https://www.bnl.gov/magnets/staff/gupta/cryogenic-data-handbook/Section2.pdf)
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on August 28, 2022, 09:35:22 AM
New update of the protons-to-neutrons conversion, starting from 40MeV.

98Mo is needed at the neutron target anyway. Y outperforms Ga and Ta. 100Mo(p,n+p)99Mo uses no intermediate neutrons. kg/m2 use the natural isotopic composition. d(d,n+p)d at 20MeV may be more efficient and convenient than p(d,n+p)p at 40MeV but I lack data.

Beam power is for 1.4×1014n/s as previously.

Nuclide  Page   kg/m2     Barn     Conv    mA      kW
======================================================
  2H      004     6.7      0.13    5.2%    0.43    17  <<< Cleaner!
 89Y    411-417  21      3×0.30... 2.7%    0.83    33
238U      784    26    2.3×1.4     2.1%    1.1     43  Fission
 98Mo     473    13      3×0.60... 1.5%    1.5     54
======================================================
100Mo     482    20        0.18    0.23%  10      400  99Mo directly
======================================================


2H needs a non-volatile compound or a container that waste few protons.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 04, 2022, 10:42:52 AM
If a switchable source provides intense γ, it needs an strong beam, and the design must cool the target. Examples and illustrations for the reactions of 14 Aug 2022, 14 Aug 2022, 06 Aug 2022, 07 Aug 2022 here.

========== Al target, 4MeV×3mA in 1cm2, 30Ci

Deuterons stop in 0.18mm Al, so boiling water cools the target easily. I've already cooled a thin copper tub from an oxygen-acetylene burner that provided >10kW over 1cm2, as measured from the water evaporation speed. Rocket engines jackets accept also 5kW/cm2 just with "kerosene".

Al creeps and corrodes at heat, so 50µm Ni is deposited on the inner face. 10bar water pressure in D=20mm create 200MPa in warm Ni.

12kW/cm2 drop about 200K in Ni and 200K in 0.3mm pure Al, bringing the surface around +500°C. The Al vapour pressure is negligible.

12kW evaporate 5g/s water. Or liquid water from 40 to 70°C would take 100g/s, D3mm suffice at +1bar, I didn't check the transfer.

AlMg5 (alloy AA5083) as the inner face seems less easy than Ni. The uncommon Mo would outperform Ni. Cermets are interesting. Rotating or liquid targets accept more power density, as for X-rays. At melting temperature, the vapour of Al has just 10-8torr equilibrium pressure, and it condenses locally.

========== 15N target, 2.6MeV×3mA in 40mm2, 21Ci

Supposing here that Ta3N5 can be processed, is stable at heat, reasonably resistant to occasional air, contact and moisture. It's a bit new and less known than TaN, which YN, ZrN, NbN may outperform. Heat conductivity matters.

Deuterons stop in <0.1mm Ta3N5. 0.3mm CuCr1Zr (>200MPa after 10000h at 350°C and 360W/m/K, wow) supports the layer and conducts the heat to the water with 160K drop. It can be hard-drawn for easier machining.

========== F target, 1.4MeV×3mA in 22mm2, 1.8Ci

20µm AlF3 seems perfect, but possible reactions of Al with 1.4MeV protons would let prefer heavier nuclei. CrF3 is one candidate, compounds with more F seem more volatile.

CuCr1Zr remains a good substrate. AlMg5 might help processing.

========== 7Li target, 1.6MeV×3mA, 1.5Ci

Oxygen seems unreactive to 1.6MeV protons, P Cl Br maybe too, but compounds like Li3PO4 waste many protons. More promising is metallic Li, cleaned and covered by semiconductor processes with thin Al, Si, Mo, Ta, W, Rh, Ir, Pt, Au... Something unreactive to 1.6MeV protons and impervious to warm Li. 0.5µm Ir wastes 0.05MeV above 1.6MeV.

Lithium can also be molten once in vacuum. At melting temperature, its vapour pressure is small.

========== Downsize

Not every use needs 30Ci, then the impact spot can shrink. A tilted target too accepts a finer beam, and the γ source seems smaller from some directions. A finer beam allows a bigger curvature for a sturdier or thinner target substrate.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 07, 2022, 09:43:59 AM
I expect very quick proton-to-γ reactions, so the proton beam can modulate the gamma emission.

The quickly modulated γ must have more uses than I imagine:
Modulated γ should inherit the uses of modulated X-rays, just at thicker items, including the soil.

Cavities modulate naturally the beam at a linear accelerator or a cyclotron or other. If cheap magnetrons for microwave ovens feed them at 2.45GHz, then 10mm depth make lambda/2pi phase shift on the direct-and-return path. Cyclotron sectors fed at 100MHz give rather 1/4m depth resolution, in that first estimate.

Known means can suppress chosen proton bunches, especially before the acceleration. This lets modulate the γ emission more slowly than the acceleration does, to avoid the uncertainty over an integer number of periods. Some pulse sequences with good autocorrelation combine range and resolution, for instance PN sequences. Ask your local signal processing specialist.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 13, 2022, 08:26:10 AM
Here's a concept of a target for a 250kW beam of 75MeV protons. Meant for the 100Mo(p,n+p)99Mo reaction of 10 Jul 2022 here, it can inspire less difficult designs, like neutron production from a Ta target.

All protons stop in the Mo target to confine the radioactivity, none in the coolant. 0.6mm Mo and tg=1/16 suppose parallel proton paths, keep an eye.

Do lighter Mo isotopes produce undesired nuclides? I didn't check enough. That would demand purer 100Mo than for yield. After irradiation, chemical separation keeps essentially Mo, of which 100 is the substrate, 99 the product, 98-94 and 92 are stable and natural, so a bit of 98-95 isotopes in the target seem acceptable.

This design targets only 31g Mo of which for instance 1/5000 becomes 99Mo. Not as concentrated as in uranium fission products, but better than by neutron irradiation. I hope the moly cow, which separates the desired 99mTc from Mo, accepts such a concentration.

The imagery offices send back the used but precious 100Mo to make a new target, for instance by electroforming at the cyclotron site. Some hot compaction may be needed. A D=30mm t=0.6mm cylinder would buckle under 30bar, a flanged cone improves. Conduction through 0.6mm/3 of compact Mo drops 70K.

250kW evaporate 0.11kg/s water. Squirting at the cone may be safer. 50ms without water pierce the target, so something stops the beam if a point of the target overheats. Before it gets too hot, Mo emits light, but so do the p reactions. Distinguish?

A secondary cooling circuit can confine potential radioactivity better. I'd have 1bar in the primary, possibly less in the secondary. Heat pipes?

The sought reaction emits one neutron per 99Mo, others contribute. After thermalization, neutrons can vanish in boron. Or they can produce useful radioisotopes, by 98Mo(n,g)99Mo or other. This would favour heavy water.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 18, 2022, 02:58:42 PM
Here's a concept for protons to neutrons using deuterium that seemed efficient and rather clean here on 28 Aug 2022.

The deuterium compounds I checked waste many protons and add much radioactivity, so the target is gas at +60 to +100°C and 300bar to stop the 40MeV protons in 0.37m=7kg/m2.

I found only beryllium for the proton window.
But what reactions are missing in the Janis book, what do the neutrons produce? Oxygen, carbon and more impurities in beryllium get activated too.

Page  Product   Decay     Emits keV
====================================
 11      9B    p2α 1as      Clean
12&16    7Be   ec 53d       γ 478
 13     10B    Stable
 14      8Be   2α 0.07fs    Clean
 17      6Li   Stable
====================================


18m/s axial wind evacuates the 18kW to the finned walls and to the water. Transverse 0.4m/s would cool the deuterium but not the window. At the sketched position, the blower is less exposed to the neutrons supposedly emitted forward. The pressure vessel's material should minimize the activation by neutrons and their absorption.

Best Cyclotron Systems, Inc. have a gaseous target to produce neutrons, no idea how similar it is. They boil with heavy water too, after all.

Maybe some part, possibly the vessel, should multiply the neutrons. I suppose the neutron source and the Mo, U or other are all in a big pool.

This converter uses 1.2GeV per neutron if the RF source is 70% efficient, and without neutron multiplication. I didn't compare with lead spallation. If D-T +Li fusion provides 25MeV converted to 10MeV electricity, then such a source can complement only 0.8% to the regeneration of tritium, that is, uninteresting.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 24, 2022, 07:46:01 AM
I seek 1.4×1014 neutrons/s for medical 99Mo, but cyclotrons can produce 1mol/year neutrons for instance, or 100× more. The one at PSI supposedly exceeds that.

If the incident particle has more energy, the target's electrons squander less of it, while fission and spallation are more frequent and produce more neutrons. I suppose spallation produces more than Janis' maximum 7 neutrons, and less stable elements like Ta might outperform Pb, but I have no data, so I consider the fission of 238U by 200MeV protons.

Protons brake from 200MeV to 30MeV in 510kg/m2 uranium (27mm metal, oxide a bit more)
  Nist (http://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html)
The fission section is 1.6b so 1 proton provokes 0.20 fission, each emitting mean 9 neutrons
  osti.gov (https://www.osti.gov/servlets/purl/6633244) p28/69 and p30/69
so 1mol/year neutrons needs 1.7mA beam current, 0.34MW beam power, 0.48MW electricity.

Just 2.5kW beam power would provide 1.4×1014 neutrons/s, while 40MeV protons hitting deuterium need 17kW
  chemicalforums (https://www.chemicalforums.com/index.php?topic=92021.msg395504#msg395504)
but saving 20kW over 10 years, or 0.35M€, intuitively doesn't buy the bigger machine.

A 500MeV cyclotron would triple the neutron flux using 2.5× more electricity, not quite original neither. Increasing the current is doubtful.

Marc Schaefer, aka Enthalpy
Title: Re: Tokamak produces radioisotopes
Post by: Enthalpy on September 26, 2022, 05:16:45 AM
A cyclotron for 500MeV protons isn't that big: D=6.6m H=2.9m on the appended sketch - unless beam focussing brings other constraints.

115kA per small lukewarm copper coil consume only 59kW together, while accelerating the protons for 1mol/year neutrons draw some 1.2MW at the plug. Bigger coils would reduce the 59kW or let increase the gap.

730t Fe cost ~1M€, as little as 100kW over 5 years.

A smaller cyclotron needs more than 1.8T, hence without iron, and the consumption jumps. 4T at the centre need 2×2.2MA. Pure Al at 20K and 60kOe resists 76pΩ×m, so each coil dissipates 52kW at 20K, and the cooler evacuates 5.6MW: as expensive in a month as iron costs once. The power is only proportional to the induction since the dimensions vary too. 6T at the rim limit the coils' size, which I didn't check as it won't improve much the consumption.

Maybe superconductors do that better, I can't tell. The unshielded field remains badly dangerous.

Marc Schaefer, aka Enthalpy