Homebrew neutron test sources

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Carl Willis
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Homebrew neutron test sources

Post by Carl Willis » Tue Jul 09, 2002 9:19 pm

A while back, Richard Hull mentioned his methodology for comparing neutron pulses from the Tom Dressel vs. Bicron scintillator units, including a brief statement and a caution, I believe, about the making of a simple RaBe source from radium paint and beryllium. (This source is not very hot in terms of neutron output but I gather it is hot enough to see an occasional pulse, and good for checking the gamma response as well.)

Richard, would you mind going into some more detail about that source? I have the materials (Be metal lumps and plenty of radium-faced meters) but have held off on messing with either of these particularly dangerous substances until I hear of a reasonably clean way to manipulate them into a source.

What advantages do you see in the paint (which has to be scraped loose from gauges in most instances) vs. smoke detector Am-241 sources (sealed 1 uCi) and Po-210 staticmaster brushes (500 uCi and sealed as well)? Do you have some order-of-magnitude suggestions about the activity of the paint on dials? How should it be scraped off the instruments without causing undue loose contamination or undue dilution or loss of material?

My other problem is with the beryllium, about which I have heard mostly horror stories. Thus far I have concluded that there is no reasonably safe way to turn chunks into fine powder with the stuff I have at home or college.

Please add your comments about this source if you don't mind. If others on this forum have experience with Ra paint or beryllium I'm interested in how you do things also.

Thanks,
Carl
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Re: Homebrew neutron test sources

Post by guest » Wed Jul 10, 2002 2:13 pm

We covered this stuff in the tread:
2002-02-08 18:20 Neutron Source (John Hendron.) [Latest: 2002-02-16 10:49] (11)
You can get the whole scope of the problem there.

Larry Leins
Physics Teacher

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Carl Willis
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Re: Homebrew neutron test sources

Post by Carl Willis » Wed Jul 10, 2002 6:15 pm

Larry,
You're right that this stuff has been covered (and better than I remembered it, so most of my questions have been answered)! Richard Hull's "Scintillator Test" post from April actually describes that the paint was not scraped off his instrument needles...and also there is an estimate of the total radium activity in those needles based on the observed neutron counts from the source.

I am curious how many gauge needles were packed into the cigar tube. I'll also point out that I am still confused about smoke detector Am-241 activity. Richard said in the post I refer to that 4 uCi is about 40 detectors worth, but the detectors I use state they contain "a maximum of 1.0 uCi," which should mean that 4, rather than 40, should do the job of all the radium hands in his source. It's certainly a picky thing to want to clear up, but I am trying to make an optimal, safe neutron test source for the little money I have.

-Carl
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Re: Homebrew neutron test sources

Post by Richard Hull » Wed Jul 10, 2002 7:30 pm

Gee, this is a gray zone. I will not post details on such construction, but will refer you to any one of the references regarding neutron physics in the ref forum. Paticularly good discriptions and methodolgies are given in the book by Beckertz and Wurtz on Neutron Physics.

I will mention that scraping the Ra paint is a near death sentence for any younger person. That stuff is mainly binder with the remainder old burned out ZnS:Ag. In an average watch hand of the late 40's there might be a micro gram of RaBr distributed on the entire hand. Making each one a 1 uC source, but not really. That's 4 pi. For a surface that halves to 2pi. With self absorption and measurement by a window it comes to about a measurable .2 X pi situation. 1 ugram of RaBr ingested and retained has about a 60% chance of inducing an internal related cancer within 20 years.......Well.. do you feel lucky?

DO NOT DISTURB A RADIUM DIAL.... MY only advice.

Po210 is totally out as it has far too short a half life. (couple of hundred days). How fresh is the static master refill in your wallet?

Am241-Be is the neutron source of choice and currently the only one licensable NEW in the US. Giving off no effective gamma or beta radiation it is much safer to handle and be around.

I have gone through the math in past posts on this subject and if memory serves me correct here it is 10-20k alphas of 5mev/sec/neutron per second in an intimate mixture of the Am241/Be dust. Thus, a 1uC source in absolute intimate mixture would give about .5n/s maybe. the Am241 sources in smoke alarms are vapor deposits you could never get even 1/4 of the .5n/s with the source covered with Be dust. Thus, realistically you are looking at say 10 little alarm buttons covered with Be dust or metal yeilding a grand total of 1.25 n/s @ 4pi isotropically. Assuming ideal pi distribution into a BC-720 fast neutron detector that mean a maximum of .3n/s in the scintillator. The system is about .6% efficient and that means you will see 1 count due to the intimate contact detector to source every 500 seconds or 1 count per 10 minute time period. Real hard to pick out of background noise fluctuations.

The beryllium is a non-issue compared to the Ra issue and doesn't even make the EPA score card in this discussion. wallowing in all your Be naked and washing good behind your ears with the stuff can't compare to the risks with the Ra material even if the Ra is well handled. If you are ready to roll the dice on the Ra gathering and condensing then forget even mentioning the Be problems for they are just icing on the biohazard cake.

Remember there is not a problem here at all! No immenent danger like instant death. However it might all come home to roost when 10, 15, 20 years down the road you are told sullenly by the doctor in a consultation that you have inoperable bone cancer, lukemia, etc.

Do you feel lucky?

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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