FAQ - Neutron-detection videos

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Frank Sanns
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Re: FAQ - Neutron-detection videos

Post by Frank Sanns » Tue Nov 17, 2009 10:18 pm

Wax and HDPE should be essentially identical since compositionally they are the same.

PVC is baaaaaddd. Cross section of chlorine will suck up as much as 30% of the neutrons.

Frank

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Doug Coulter
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Re: FAQ - Neutron-detection videos

Post by Doug Coulter » Tue Nov 17, 2009 10:38 pm

Thanks, Frank,
I'd used some for my silver activation neutron oven, replaced it today with HDPE, betcha my silver gets hotter now, I'll test on the next run.
Why guess when you can know? Measure!

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Carl Willis
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Re: FAQ - Neutron-detection videos

Post by Carl Willis » Wed Nov 18, 2009 1:43 am

I appreciate the encouragement and am glad to hear that some people enjoyed these videos. I will make some more as time permits. Thanks, Richard, for bestowing the "FAQ" honors on this humble contribution.

Frank, to answer your question about moderators, the common moderators that will produce the highest fluxes of thermal and resonance neutrons are those with a high density of H-1: HDPE, water, wax. Other moderators like D2O, Be, graphite have superlative overall neutron economy because of low capture cross-section, but they can't counteract the geometric attenuation of the neutrons as quickly as H-1 because of the lower fractional energy loss in elastic scattering. For this kind of experiment, the light-hydrogen moderator materials are practically the best. Oxygen is lossy for fast neutrons, so the hydrocarbons fare better than water by a modest margin even if their density is lower. This is probably not so true for fusor neutrons at 2.4 MeV as it is for the fast flux from an AmBe source.

-Carl
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Richard Hull
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Re: FAQ - Neutron-detection videos

Post by Richard Hull » Wed Nov 18, 2009 4:10 pm

I should not have to bestow FAQ as an honor.

Anyone that creates a purely informational posting that explains in some detail an erudite point which seems to constantly ellict continuously asked questions, needs to place the FAQ prefix on their post.

Such an author should be prepared to be corrected in critique by anyone bringing up errors or who notes that an addition of an unmentioned point might improve the FAQ.

If the error is of a major nature, or the author realizes that an additional point so mentioned would enhance his original, he should edit the original to correct the error or add additional points brought up in replies that he feels are important.

Do not let errors or omissions in the original FAQ stand and just admit the error in the eighth reply down. Correct the original FAQ as that is what a newb will see and read in a future search. In short, get you original FAQ perfect or as near as possible based on helpful comments in replies.

The above are my rules for me and my FAQs. They might be good ground rules in future for anyone so bold as to use the FAQ in front of their major, contributional magnum opus on a topic.

Do not be afraid to use the FAQ prefix if you have condensed a key point in fusor work, radiation detection, etc. FAQ is not an honor to bestowed upon the poster, but a gift bestowed upon future curious fusioneers by its author with contributed corrections and ammendments by its replies from other knowledable contributors.

Richard Hull
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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 - Neutron-detection videos - another one

Post by Carl Willis » Sat Nov 21, 2009 9:23 am

http://www.youtube.com/watch?v=ng6NOH8S7Bk

This video illustrates an activation experiment in which Mn-56 is made in a sample of manganese dioxide, then detected by scintillation spectroscopy. The neutron source is my little AmBe source, but the principles apply to fusor-based neutron activation as well. Both the gamma energy spectrum and the time rate of decay are used to positively confirm the presence of significant Mn-56 in the irradiated sample. Brief mention is made of the importance of moderating fast neutrons for activation. A "neutron oven" is shown to effect this. The detector, NIM-based signal chain, MCA, and data acquisition on my computer are all described. The time and energy data are simultaneously collected into different parts of the MCA's memory bank, for both the irradiated and the background MnO2 samples. At the end of the video, processed data is discussed. That same data is in the figures below.

Pacing is fast (in order to keep within YouTube's 10-minute time limit), at the expense of detail. So I'm happy to address any details that were glossed over in the movie itself.

Bon appetit!

-Carl
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Steven Sesselmann
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Re: FAQ - Neutron-detection videos - another one

Post by Steven Sesselmann » Sat Nov 21, 2009 10:54 am

Carl,

Once again, an excellent and informative video. I think it deserves a new post.

FAQ - Neutron Activation and Gamma Spectrometry

Steven
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https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

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Chris Bradley
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Re: FAQ - Neutron-detection videos - another one

Post by Chris Bradley » Sat Nov 21, 2009 1:05 pm

Thanks Carl. All lovely work and well presented.

It makes me wish I lived in the US where I might be able to get this kit. Never seen a NIModule here in the UK to buy, we don't get the standard of surplus stores and hamfests here. I'll have to make do with just watching you do it instead!!..

Quicky question; was the half-life count the total net counts, and if so (or if not, vice versa) do you think it could be improved by using only the counts over time as detected around the peak?

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Re: FAQ - Neutron-detection videos - another one

Post by Carl Willis » Sat Nov 21, 2009 7:42 pm

Hi Chris,

The time spectrum is collected through an SCA that coarsely windows the 850-keV gamma peak, in order to improve the statistics as you suggest.

With the ADC in the bin, it's quite easy to use the timing SCA in this manner without calibration. I take the bipolar output of the delay-line amp to the SCA with a very short cable. I take the fast negative output of the SCA to the coincidence gate on the ADC with a very short cable. Then, the unipolar output from the delay-line amp is sent to the input of the ADC over a long cable so that it arrives by the time the gate can be opened. In this manner I can graphically adjust the window of the SCA relative to my calibration pulse-height spectrum and get it in exactly the right place. To take counts on the MCS, the SCA output to the ADC coincidence gate is then simply moved to the input on the MCS.

-Carl
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Mike Beauford
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Re: FAQ - Neutron-detection videos - another one

Post by Mike Beauford » Sun Nov 22, 2009 3:06 am

Hi Carl,

Another great video Carl, if I were you I'd start to think about writing a book about this stuff. I suspect you won't make a ton of money, but I think it will do wonders for your career.

Mike Beauford
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Re: FAQ - Neutron-detection videos

Post by richnormand » Mon Nov 23, 2009 3:47 am

As your videos are on youtube is there an easy way to get you to either post them on this site or have a way to download them. They are quite good and I would much like to have them burned on a CD than see them disappear in the future. If you do consider downloadable version make sure you embed a visible watermark on them so your copyright is safe.
Nice work Carl.

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