FAQ - Fusion reactions other than D-D

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Richard Hull
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FAQ - Fusion reactions other than D-D

Post by Richard Hull » Thu Feb 06, 2003 8:06 pm

We all seek to do fusion better. D-D reactions which are the bread and butter of amateur fusion work is not necessarily an ideal reaction depending on what you want to do.

In general, fusion is a low Z arena. That is, only the lightest elements can be made to fuse.

All hot fusion reactions are radioactive (throw off radiation). NONE are clean. Some are more clean than others. All fusion reactors, regardless of reaction chosen, produce copius quantities of X-rays. The danger of this ever present hazard are directly proportional to the acceleration voltage needed to make the reaction go.

All fusion reactions require seed energy.

Some fusion reactions are easier to achieve than others. That is, they require less seed energy. This may or may not make a particular reaction more efficient.

The various fusion reactions are a trade off. Reactions that are highly desireable from a safety or energy return standpoint might cost a lot to implement or require huge amounts of seed energy.

Other reactions that are really messy to implement might be ideal from every other standpoint.

Choices have to be made and these will reflect the costs of implementation, safety, seed energy and radioactive byproduct hazards.

Before leaping into a discussion of the various reactions we must consider whether we are talking theorectical (we can't build it and test it) or if we are talking hardware reality at our level.

If theorectical, any discussion in the forums will forever remain just so much wind over the deck.

If we are talking implimentation, then we are talking about how well heeled we are and complex reactions will demand a significant cash outlay and a long term effort. In some cases, a group effort might be demanded.

With all the above in mind I will lay out the most obvious reactions of generally accepted value and discuss the pro's and con's of each.

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D + D = T + 3He
D + D = P + N

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About the reaction

This is a two fer'!! Two reactions of equal probability occur. This is the only reaction ever done and reported at the amateur level. It is the classic reaction in our fusors.

Radiation

The only radiation capable of exiting the fusor would be neutrons of 2.45 mev energy. These are fast neutrons and as such, are considered very dangerous with an RBE of 10-20. Thus far in amateur circles the neutron output is low by any standard of the industry and the run times are abysmally short. Neutron activation of exterior items is possible if the neutrons are first deliberately thermalized. Again, at ridiculously low levels based on even the most potent of amateur fusor produced to date.

The omnipresent X-ray hazard is usually not a problem due to the low amateur energies. 40 kv x-rays just can't punch through most standard fusor shells.

Costs

This is the absolute cheapest way to do fusion! No reaction known to man can be implemented, scaled up and varied as cheaply, safely and easily as the D-D reaction. PERIOD!!!

Deuterium gas can be had from most of the better welding gas supply houses. A 25 liter bottle can be good for years of experiments if metered out well and costs under $200.00

The power supply for a system using D-D need not exceed 100kv and can be built or purchased surplus for under $300.00

Engineering

The parts and accesories needed for all fusion devices are similar, but deuterium is not corrosive or unduly hazardous if small amounts are accidentally released. It is ready to use right out of the lecture bottle. Therefore, no heroic enegineering effort is needed to implement a D-D system.

In larger really successful systems capable of operation over longer periods, tritium buildup can boost the reaction in an ostensibly D-D machine. But this is a double edged sword for Tritium is radioactive and insidious in its manner of entering the body as HTO. In small D-D machines of amateur construction this is a non-issue.

Cross Section

Here is where D-D falls on its face. The reaction is not a particularly active one even at it peak near 1.5 mev input energy. The reaction cross section never hits even the 1 barn level at 1.5 mev. In spite of a rather abysmal cross section, the reaction really drags itself out of a sub-millibarn mud hole at 10kv to an appreciable portion of its maximum at just over 100kev. This is well within the amateur level of experimentation. It is this last saving grace that makes D-D worth doing at all on a purely fusion basis.

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D + T = 4He + N

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About this reaction

The D-T reaction is an incredibly rich one and an incredibly dangerous one, not to mention, illegal. It is mentioned here only because it is/was used a lot by fusion community and it is a possible secondary reaction in a normally operated D-D machine.

Radiation

This reaction produces a rather incredibly fast 14 mev neutron and a 3.5 mev alpha particle (helium nucleus). Needless to say the neutron is a very dangerous particle from a biological standpoint. The alpha particle can never leave the chamber and will wind up as a neutral helium gas molecule within a closed fusion reactor vessel.

Cost

Sort of a non-issue for we amateurs, for there is no source of tritium available to the amateur as this highly, radioactive gas is tighly controled by the NRC. One must obtain a site radionuclide license to purchase even the smallest amount of tritium. This puts the amatuer out of this picture.

Engineering

Like deuterium, Tritium is ready to use out of the bottle. The radiation from tritium willnot even penetrate its container as it is a mere 13kev beta particle. Far more active electrons bombard the inside of your TV screen! However, in the body 13kev electrons are highly damaging. Engineering issues mainly focuses on the absolute necessity of avoiding any form of tritium leak into the environment for tritium gas is readily taken up in the body as HTO. Its 13 year half-life makes it biologically very dangerous. In spite of all this, blessedly, the body excretes tritium at a prodigious rate mainly via urine, perspiration and exhalation. Most all D-T fusion systems are now shut down due to insane safety and health standards imposed and regularly checked on by the NRC. The use of tritium is a political and litigeous football that virtually every employer and academic institution just as soon not run down the field with.

Vacuum systems pumping D-T reactor vessels will have to have their exhausts specially handled due to tritium being constantly pumped out of the system. Some sort of recycling arrangement must be made up. (very costly and complicated.)

Cross section

THE MOST FANTASTIC OF ALL FUSION CROSS SECTIONS!!!!!!

This superlative reaction is a fusion dream come true. D-T produces far more than 1000 times the fusions per unit input energy as D-D!!!! At 15 kilovolts D-T is dong what a DD machine is doing at 100kev!!!! As matter of fact, if you put more than 125 kev on a D-T machine you are coming back DOWN in cross section and doing less fusion than at 100 kev!!!

So, D-T peaks at about 110kev which is stunningly amazing, peaking at over 45 Barns! Absolutely no fusion reaction competes with D-T. NONE

Too bad we can't do it in its pure form and that it requires such a nastey, un-obtainable, radioactive component to go with the relatively safe deuterium.

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D + 3He = 4He + P

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About this reaction

Apparently, one of the modern "darling" reactions as it is relatively non-radioactive. Side reactions producing neutrons are possible, but so rare than it is not a real issue in the operation of a D-3He machine. The current reaction of choice at all of the academic institutions where fusors are running.

Radiation

This is an aneutronic reaction. A real plus for schools and industry where radiation concerns are paramount. The main radiation is composed of protons at 14.7 mev and alpha particles at 3.6 mev. Both are stopped in the first layers of the shell of the reactor wall. X-radiation and neutrons can be side reactions here as well as some activation of the body of the device internally. Add to this the x-radiation due to the required higher input acceleratroy energy and you can have a pretty nastey x-ray source in a D-3He machine.

Cost

Here is the snag that will keep most all amateurs out of this arena. 3He gas is a super specialty item and can only be ordered from out-of-state, specialty, scientific gas supply houses. A very samll lecture bottle of He3 can readily exceed $2000.00

*****Update 2010*****

Due to a worldwide shortage of 3He. Any though of using this gas is no longer possible. The need for 3He neutron detectors for use by homeland security in vast numbers, has burned off most of the available supply to the point that the government controls the distribution of this gas on a priority basis. It is such that the 10 or 20 liter bottle that might have cost $2000.00 in 2001 would now cost $25,000, if you could find someone willing to sell it to you!

Engineering

3He, like deuterium, is ready to use out of the bottle, is not radioactive or toxic. This allows the system's engineering costs to be as low as that of a D-D device. The hassle comes in the fact that the reaction is just not energetic until you supply over 60 kev! This means a more expensive and complex supply capable of about 700,000 volts is demanded if the most is to be obtained from the reaction.

Cross section

The D-3He cross section is such that the reaction doesn't really start to go until about 40 kev. At this point a simple D-D fusor is really moving out and out performing it. If, however, you can supply more voltage the reaction equals a D-D machines output at about 90kv applied and quickly surpasses D-D in output reaching a maximum at about 600kev. At this elevated level, D + He3 is producing about 30 times more fusion than D-D and approaches 8 barns in cross section here. This is really nice in spite of the huge voltage required to reach it. Needless to say that at this level you will need a pit to bury the device it to avoid x-raying you neighbors to death in minutes.

This is perhaps the only other reaction that a well heeled amateur might casually dabble in. (See cost/availability ammendment above - 2010) Its real attraction for most is the aneutronic nature of the principle reaction and high peak cross section. Ultimately, though, the D-He3 machine is not practical from an X-ray hazard standpoint anywhere near its peak of operation.

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P + B11 = 3 (4He) + (8.7mev)

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About this reaction

Another much touted reaction of an aneutronic nature that is the absolute best reaction for "direct conversion" processes. First it ain't totally a neutronic and secondly it is a poor performer demanding lots of seed energy and specially engineered devices to force the B11 into the device. For all this, the promise of hooking the wall outlet directly to the shell of the device is extremely attractive.... no boiling water losses, no carnot issues, no multiple handlings of energy. This "sirens song" of direct conversion comes about through the attempt to directly decelerate those lucious, multi-mev alphas against an electricity grabing series of grids in the fusion reactor.

This never accomplished dream is powerful enough to leave a hushed "PB11" on the lips of the fusion hopeful.

Radiation

There is no radiation, ostensibly, but a lot of side reactions producing neuts are possible. There are enough different ones that neuts will pour out of a P-B11 machine. (for the low down check out Scott Stephens NUKE FUELS post back on Jan 18th 1998 SONGS BBS list.) Scott was one of our first good guys.

Due to its demand for nearly 500 kev seed energy, the X-rays from a working device are very dangerous.

Cost

The use of Boron in a reactor means the admission of a borated gas or vapor. Normally, this would be the toxic and corrosive, Boron Trifloride. Costs for containing storage and exhausting the material would hurt the amateur pocket. The gas, itself, is not cheap. Some form of proton ion gun system is also demanded. The reaction demands a power supply of about 500kev making for a good deal of expense.

Engineering

This reaction might not lend itself to a fusor device readily. Complex beam targeting would be required to make a P-B11 reactor work. The multiple deceleration grids would be tricky to make and sustain in such an environment.

Cross section

The cross section diagram shows that virtually zero fusion happens until you supply about 150 kev, but the reaction peaks out shortly thereafter at about 500kev. The P-B11 peak occurs at about 0.4 barns, making it a bit more whimpy than simple D-D fusion at the same energy.

If it were not for the 3 alphas and dreams of direct conversion, I could not image how P-B11 ever got honorable mention in the grand scheme of fusion reactions worth considering.

Summary for this FAQ

There are a lot more possible fusion reactions. Most fall in the not worth considering category for either they take too much seed energy, use tritium or have poor or narrowly peaking cross sections.

I may, from time to time, update this posting with new reactions, therefore, I consider this a work in progress.

A couple of more reactions of note are

T + T = 4He + 2 N
D + Li6 = 2(4He) + 22.4 mev.

Others can, again, be found in Scott Steven's early SONGS posting, NUKE FUELS, mentioned above.

Finally all of the above discussion is slanted towards the 'doing' by amateurs. No attempt was made to reconcile or recommend the processes with the concept of doing power ready fusion. Instead, I have looked at what would be the better reactions for amateurs to actually investigate and have shown most of the benefits and shortcomings of the reactions. I hope this has helped out.



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

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Re: FAQ - Fusion reactions other than D-D

Post by 3l » Fri Feb 07, 2003 2:04 pm

Richard will have a field day with P-B tho.
P-B is very hard to do.

New****
Got your post most work is done with Bbr3 now with a heated
block made of fused tungsten powder.
Although B does make for a difficult reactor fuel it would make a good blanket for energy conversion tho.

Fusion is fun!

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Re: FAQ - Fusion reactions other than D-D

Post by Tom Dressel » Fri Feb 07, 2003 5:27 pm

Would anyone care to explain what is going on in the solid state or so called "cold" fusion?

Tom Dressel

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Re: FAQ - Fusion reactions other than D-D

Post by Richard Hull » Fri Feb 07, 2003 6:37 pm

The cold fusion/LENR (Low Energy Nuclear Reaction) field is still very much alive and well with good researchers in abundance. One of my favorites is ex Los Alamos reseacher, Ed Storms.(retired) and the Chubbs (Naval Research Labs)

You knew, i suppose, that George Miley of U of IL fusor fame was actually assigned a grant of a few million to study LENT reactions (Low Energy Nuclear Transformations) but once Robert Parks, (self appointed watch dog of "real science"), and others beefed, the grant was never actually awarded. So much for real, empirical investigations being set asside by dogmatic attitude and bluster.

Don't let anyone tell you that no real good instituions are studying this, for they are. The budgets are low and a lot of the work is done in the background, but it is being done.

Infinite Energy magazine is a great source for positive updates. Check out their site for pointers to Storms and many others. Click on the home page "cold fusion papers" button and then try the Ed Storms' "student guide to CF"

http://www.infinite-energy.com

I take the magazine along with several other pubs that follow what might best be termed 'alternative' science.

Naturally, all articles are read with the huge grain of salt as everyone has an axe to grind. Francis Bacon's commentary on "Studies" is well taken here.

Basically, and so far as I am concerned, there is definitely some interesting and perhaps new physics going on in the solid state. I also feel that it is most likely some form of proton exchange mechanism that is just flat out not understood at this time. I also feel that the energy output is somewhere between chemical and nuclear levels for each reaction and that the reactions are not directable enmass to the point of extracting large amounts of energy. This may change, but it isn't looking real hopeful.

There is just too much evidence of stable odd isotope production in CF cells and systems to ignore out of hand. This year's International Cold fusion conference is to be held just outside the gates of MIT.

Based on what I see in hot fusion, it is a crap shoot as to which camp is really moving forward. I look at hot fusion reports with about the same skepticism as I view cold fusion reports. Only results feeds the bull dog. It is just that hot fusion gets the money in spite of stepping on their dicks and pulling ours for the last 50 years. (pardon my french)

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

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