[news] Extreme DIY: Building a homemade nuclear reactor in NYC

[Chris Bradley]

[The video appears to show...]

Carl Willis wrote:
> It is not possible to infer the neutron source rate based on the provided information, for the simple reason that the source-to-detector distance is unknown.
He appears to be leaving it on top of the chamber (6" tee?). I assumed 'within 30cm', so my estimate will be high. There appears to be no dedicated holder for it around.

> The sensitivity of the BTI detector is also unknown
24b/mrem

Also, if he has a turbo but starts backfilling at 10^-4 torr, is there a question to be raised about his lowest achievable vaccum (in reference to leaks)?

[Carl Willis]

Where's the video located?

[Chris Bradley]

..err... it is the link in the top thread, Carl.....

You can also see photos of the setup on his blog...also linked to in the Perfesser's posts in this thread.

[honickmonster]

On the topic of the news and media snowballing this has created. I received a call yesterday from a reporter from the AP who had found the article that my local paper ran back in January. She wanted to ask a few questions about this "guy in Brooklyn" (I had not yet seen the article so I was a little oblivious). I gave her the usual run down on the fusor, my (conservative) feelings on fusion power, and how it is completely safe and poses no public health hazard etc. etc. etc. She seemed to have a pretty good grasp on things, though I do wish the would put the science reporters on these stories sometimes, I know they have them.

Matthew

[Carl Willis]

Thanks Chris. I have not been following this project closely.

The BBC video in the top post does show an experiment (evidently not the same one that produced the 4 bubs pictured on the Perfesser's link) from which you can kind of make out the likely position of the BTI at 3:37. The blog http://prometheusfusionperfection.com/2 ... w-chamber/ says that the chamber has 8" CF flanges, which are typically bored for a 6" OD, so that would put the source-to-detector distance on the order of 3" and the emission rate at about 400 +/- 200 neutrons per second. Of course all of this could be complete nonsense because of bad inferences from a low-res video of a different experiment...the best plan for anyone sufficiently interested in the neutron source rate from this fusor would be to ask the guy directly.


-Carl

[Chris Bradley]

I was also going on the photos of his blog. There is, certainly, no critique of lack of information on his experiment. Well documented. I might have concluded that the news was a bit thin at the moment, but the press attention is well-deserved for the effort and seemingly what he was after.

Not sure what the 'next steps' are, and it would be nice if some of the attention was from 'real' science correspondents, rather than the 'human angle' types. However, fusors do seem reasonably well known [by knowlegable science types, and increasingly so] so they might well have noted the low neutron rate and concluded there was little science news in it.

So the photos of note, wrt neutron count, are;
http://prometheusfusionperfection.files ... =450&h=337

which you can compare with, and see it is sitting on top of;
http://prometheusfusionperfection.files ... =450&h=337

and the bti cal can be seen here;
http://lh3.ggpht.com/_eZmKGTaqgB0/TCATr ... G_9436.JPG
_____________________________________________________________________________________

[Mike Beauford]

I think he wants to create a amateur built polywell device and is looking for funding.

[Richard Hull]

I fielded a call from the same AP reporter yesterday. We chatted for a few minutes about both possibilities and impossibilities. She noted she had already talked with Matthew, but seem fixated on the NYC famulus story, noting that AP was a bit behind the curve on this viral fusion thingy.

It has certainly heralded and increase in posting newbs. How many lurkers must there be?!

Related to the post, You might expect to measure between one half to one millirem of neutrons in 10-15 minutes of running at 30kv - 10ma.

Richard Hull

[famulus]

Hey guys, here are my neutron / second calculations:

http://prometheusfusionperfection.com/2 ... ns-second/

Please Note: I have not yet incorporated error rates or the background reading (although I've done a background reading). Could use a hand on these points.

Thanks!

-Mark

[Tyler Christensen]

Do you have any guesses as to why you're getting orders of magnitude lower than typical neutron rates at the power level you're putting in? Is your vacuum system leaky reducing the deuterium gas quality perhaps? Just wondering if there's some physical explanation or some experiment you're performing that would address this.

[Carl Willis]

Hi Mark,

Your calculation looks good. I'm glad you got help from Rob Noulty; he is certainly a good source of information.

Statistical uncertainty is what Rob means when he says you have a 50% error (or equivalently, the example I made in a post upthread of 400 +/- 200 n/s). There are two ways to derive the uncertainty--experimentally, by making many trials of the same experiment and calculating the variance, which is impractical under the circumstances; or by application of the appropriate statistical model to calculate the "standard deviation". Because the bubble detector is binary--when a neutron interacts you either get a count (bubble) or you get no counts--the appropriate statistical model is the binomial distribution, whose standard deviation is

sigma = SQRT(x * [1 - p])

where x is the experimentally-measured value, e.g. 4 bubs, and p is the probability of detecting a neutron incident on the BTI. Upon the further simplification that p is small, which it is since on the order of one in a million neutrons incident will form a bubble, the standard deviation simplifies to

sigma = SQRT(x) = SQRT(4 bubs) = 2 bubs

This practically means if you were to repeat this same experiment many times, you would expect various results (as calculated from the Poisson CDF, see Wikipedia's Poisson distribution article):

0 bubs: once per 56 experiments
1 bubs: once per 14 experiments
2 bubs: once per 7 experiments
3 bubs: once per 5 experiments
4 bubs: once per 5 experiments
5 bubs: once per 6 experiments
6 bubs: once per 10 experiments
[etc.]

Quantities that are derived from the measurement, e.g. neutron source rate, total fusion rate, carry uncertainty propagated through the calculation from all the constituent experimental values. If there is a lot of uncertainty in the detector's effective position (and there will be, because it is close to the source and has considerable geometric extent), that will enter the calculation too. Calculating the total number of fusions by multiplying the neutron source rate by two (to account for the aneutronic H-2(d,p) reaction) is only a very coarse approximation.

Convention is to report values rounded to the nearest statistically-significant figure. If the neutron source rate is 364.2 n/s and the uncertainty is 182 n/s, the reported value is "400 +/- 200 n / s."

-Carl

[Steven Sesselmann]

Mark,

I agree with Tyler, you should be able to get a higher fusion rate with 30 Kv/10ma.

You need to double check the main elements of your system.

Final vacuum pressure - is the gauge working?
Vacuum leaks - how long does the chamber hold vacuum ?
Deuterium gas purity - Did you get this from a trusted supplier?
Power supply - Is the polarity right, and is the output actually 30 kv.?

Using a neutron counter with audio output can really help you hone in on the sweet spot.


Steven