Target Material vs Fusion Yield for D-D, and D-T Reactions

This forum is for other possible methods for fusion such as Sonolumenescense, Cold Fusion, CANR/LENR or accelerator fusion. It should contain all theory, discussions and even construction and URLs related to "other than fusor, fusion".
lutzhoffman
Posts: 188
Joined: Tue Dec 08, 2009 1:59 am
Real name:

Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by lutzhoffman » Sun Mar 07, 2010 2:40 am

I have been pondering what the relationship is if any between the target metal, and the fusion yield, for these common reactions.

Mo was for example recently shown at Berkeley to produce 50% of the N yield, of a fresh D saturated Ti on copper target. Even an Aluminum blanking flange is sometimes used in the laboratory as a N source when bombarded by medium energy deuterons (100kev - 500kev)

What I would like to know is: If there is a relationship between the fusion yield. and the target metal used. One which goes beyond just the amount of D implanted into the metal, by the D+ beam?

To help answer this question I have been looking for a study where they bombarded a bunch of different metals with D+ beams, and recorded the N / fusion yield, under similar conditions.

I am wondering if there is a possibility that some metals, or even alloys of them, can hold the D in a way which lines up the D atoms to increases the hit probability as the D+ ion comes along from a specific direction?

In dense high A# metals the D+ ion may retain enough energy for example to still initiate a reaction with another implanted D atom, this is not however what I am looking for. I am looking for the "ducks in a row" at the shooting gallery so to speak. Under the chance that someone has such a study in their library, then I would love to see it. If Mo can do 50%, then what about Ta, U, or even the infamous Pd, with its ability to turn H2 & D2, into H+ and D+ while in its matrix? Thanks......

PS: Here is some work on the subject, but it is not exactly what I am looking for:
Attachments
Lowenmetalddreac..pdf
(309.14 KiB) Downloaded 130 times

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

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Carl Willis » Sun Mar 07, 2010 10:15 am

Hi Lutz,

I personally don't know of anything meeting the description of what you want, but I attached a paper about neutron generators that I think is a good overview of the design problems in general. These authors consider scandium as a target material, in addition to titanium.

An experimental comparison that aims to isolate effects other than "just the amount of D implanted in the metal" would seem to be enormously difficult to control, since this is the dominant issue and depends considerably on the metal in use. From the attachment:

>The neutron production efficiency of materials depends mainly on their capacity to retain deuterium and tritium and on their stopping power. The more deuterium and tritium they can retain, the more nuclear fusion reactions can occur between incoming ions and occluded gas. The lower the stopping power of the material, the less energy the ions will lose by interactions with it.

Provided for what it's worth.

-Carl
Attachments
Vujic_IRRMAFullPaperv2.pdf
(479.54 KiB) Downloaded 155 times
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Chris Bradley » Sun Mar 07, 2010 10:31 am

Just a 2¢ comment for your reflection: I would tend to think this is a job for a metallurgist with an interest in practical fusion!

Two chemically similar metals are not necessarily alike, and it may well not be due to the chemistry of the substance but rather the crystal structure phase and the interstitial characteristics therein.

Whether there is some phase of some doped or alloyed metal that is better than just that pure metal is a parameter space that you are on your own to experiment with, so I would suggest to approach this subject then you'd need a theoretical grounding in metallurgy to scope out the best candidates prior to experimentation.

Perhaps I might usefully suggest you begin by taking a look at the advances in those substances being developed to store hydrogen and understand why they are good at storing the stuff.

I cannot decide, thereafter, whether you would want to develop such a meta-material out of high Z elements (less nuclear energy transfer but more electrons) or low Z (more energy transfer to material, but fewer electrons). I'd hazard a guess you should want to aim for the highest [Z/density] value.

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Chris Bradley » Sun Mar 07, 2010 10:40 am

(EDIT: I posted these comments in error, without thinking it through. See below.)

So for a 120kW beam input, they are getting >2kW of neutrons out!

. >2% efficiency with just a beam into a hi-Z-target!

If ture, it rather makes the fusor's attempt to recirculate multiple-pass ions look silly, at 1E-6% efficiency, if you can do a one-pass beam at 2%!

OK, I've only read the abstract, but I find that to be a statement that needs to be teased apart for its veracity.

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

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Carl Willis » Sun Mar 07, 2010 7:19 pm

>I find that to be a statement that needs to be teased apart for its veracity.

I find that your math needs to be teased apart for its veracity.

The abstract claims a neutron yield of 1E+14 / s with either 1A or 2A of beam current through 120-150 kV, depending on design. Many other projects have arrived at similar numbers. This is not an outlying report in that regard.

The fusion energy output from the DT reaction:

1E+14 / s * 17.5 MeV * 1.602E-13 J / MeV = 280W

Of this, the neutron yield is ~225W, an order of magnitude lower than what you figured. Of course this is better than you get from a fusor...it's the DT reaction, for godssakes. Number yield from the DD branches at similar conditions is down by a factor of 100 or so...energy yield from DD is down by a factor of five...if this were a DD neutron tube you might expect about half a watt of fusion.

Neutron generator tubes do their job very well. It has never been a secret that they outpace amateur fusors by a long shot, and it's also easy to figure out why. The fusor's advantage as an energy reactor remains purely speculative despite all the sycophancy on its behalf. They are attractive to amateurs probably because they are simple. Neutron generator tubes are more complicated to realize.

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

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

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Carl Willis » Sun Mar 07, 2010 7:50 pm

Lutz,

I found another reference of potential interest to you by Fiebinger, although I cannot obtain it at my library. The excerpt below is from an article by Coon ("Targets for Production of Neutrons") in Marion and Fowler, Fast Neutron Physics Part I, that is a good read in its own right:

>Fiebinger [Z. Naturforsch. 11a, 607 (1956)] measured the yield of neutrons from 16 different elements bombarded with 50 uA of 300-keV deuterons. He found that after bombarding for a time sufficient to reach saturation as measured by neutron yield, gold and gray electroplated chromium gave the highest yields. In each case the yield was about half that obtained from D2O ice. Materials with high hydrogen solubility such as tantalum, zirconium, and titanium gave very low yields in these tests. Saturation yield for gold was obtained after bombarding with about 0.6 coulomb of beam through limiting aperatures of 1.2 cm diameter. Calculation of the maximum yield obtainable with this amount of deuterium to serve as target, indicates most of the beam must have been concentrated in a much smaller area of the order of 0.1 cm^2.

>[...] Fiebinger observed that in all his targets the yields dropped with increase in temperature of the target, the yield going nearly to zero at 800 C for all elements investigated.

>Attempts at Los Alamos to confirm the high D(d,n) yield from gold have failed. A near-saturation yield of only 0.12 that for D2O ice was observed after 0.75 coulomb on an area estimated to be 0.2 cm^2. This yield is only one-fourth that observed by Fiebinger, and the low value in this observation may have been the result of condensation of residual vapors on the surface of the gold. Fiebinger employed extreme vapor trapping near the target whereas Los Alamos experiments did not. To observe yields which are characteristic of the metal employed, the surface of the metal must be kept clean. [...]

>Absorbed gases in the surface of a metal have marked influence on further gas absorption. The performance observed by Fiebinger for tantalum, zirconium, and titanium probably would have been markedly improved if the metal had been outgassed prior to bombardment. Observations at Los Alamos gave much higher yields for zirconium outgassed by melting in vacuum than for untreated sheet stock.

>Many experimenters [references omitted, let me know if you want them] who have employed the beam loading technique as a convenient means for generating D(d,n) neutrons have obtained saturation yields only 0.05 that of D2O ice or even less. If gold were employed and if there were a feasible way of keeping the metal surface clean, these yields could probably be increased by a factor of 10.

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

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Chris Bradley » Sun Mar 07, 2010 8:06 pm


Fair play. I think I punched in "10>exp>14" into the calculator.

OK, so out by x10, and DD is usually presumed to have a yield 1/200th of DT. Still, that'd still be 1W which is 1E-3%, still 3 oom better than a fusor, or have I played butterfingers on the calculator again?

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

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Carl Willis » Sun Mar 07, 2010 8:33 pm

Chris,

That might be ballpark accurate for a lot of the amateur fusors that run at a few dozen kV.

But it may not be a fair comparison. I would expect closer competition for devices of similar scale. To be a fair comparison with this kind of neutron generator, you'd have to look for examples of fusors running 120-150 kV / 1-2A. There may be some that do this on a pulsed basis, such as at the University of Wisconsin.

I recall a comparison of actual devices sometime in the distant past on this board...a real experimental DD neutron generator, versus a fusor that used a similar amount of juice. I can't find it right now.

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

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by Chris Bradley » Sun Mar 07, 2010 8:49 pm

Carl Willis wrote:
> To be a fair comparison with this kind of neutron generator, you'd have to look for examples of fusors running 120-150 kV / 1-2A.
That's true also, theoretically another oom closer still. (..I'm not sticking by my earlier comment, incidentally, happy to withdraw it... I was incorrect to ignore the cumulative totting up of each of these differences.)

Were you thinking of the NSD devices?: http://www.nsd-fusion.com/2.5mev.php

lutzhoffman
Posts: 188
Joined: Tue Dec 08, 2009 1:59 am
Real name:

Re: Target Material vs Fusion Yield for D-D, and D-T Reactions

Post by lutzhoffman » Mon Mar 08, 2010 1:10 am

Thanks everyone, I have a lot to digest here now. I do realize that I am searching for something which may very well not exist. In this case I am looking for confirmation that it indeed does not exist, and that its all just a function of the amount of D trapped in the metal matrix.

What is interesting to me is that the crystal structure of metals can be influenced by so many things, and then it goes on and on when you get into alloys. Then there is also the posibility of bombarding with negative ions etc. My objective is not to make neutrons, rather it is to tweak the efficiency of the reaction for optimum yield. With D-D it just so happens that the neutrons produced provide a convenient way to measure the number of fusions occurring.

Maybe Doug's approach of using crystals is better, I just do not want to give up on metals just yet, because metals lend themselves to easy heat removal etc. and represent very durable targets.

I suppose the best approach would be to read as much as I can find on the subject, and then resort to good old experimentation. I like the idea of using low power uA level beams, at 50-500KV, this way the neutron hazard is kept down.

The discrepancy between the yield on Gold mentioned by Carl is also very interesting, it makes you wonder if there is some meta-stable products can be formed under bombardment conditions which boost the yield?

I agree with the point that to compare a fusor with a solid target, you have to be in the same ion energy range. I think that all approaches to fusion are equally valid when it comes to research. I mean if everyone only tried one approach, then the chances of a major breakthrough some day, would be much reduced. Either way it allows for so many potential experiments to be done, and that is after all the fun part, for many of us. We may not have multi million dollar labs, but we do have one advantage which is not having a board to consult for permission to try something : ) The hard part is in being scientific in the process, and in knowing when to move on, and when to try something else : )

Post Reply