neutron detection by indirect method of Ag activation

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Post Reply
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 2:16 pm
Real name: Shireesh Apte

neutron detection by indirect method of Ag activation

Post by Shireesh Apte » Sat Nov 04, 2017 8:08 pm

I have posted previously in the vacuum forum. I want to be able to detect neutrons by thermalizing them through a water batch subsequently impinging on a silver foil. I will detect the emitted beta particles with a Geiger counter. I have calculated the amount of neutrons that I would need to produce in the fusor so that my beta radiation counts are at least 10 times above background radiation. Unfortunately, it turns out to be a huge number (187 kiloNeutrons/second) if I keep the silver foil at a total distance of 10 cm away from the fusor. Most of the posts I have read indicate that reasonable values of deuterium induced neutron production are approximately 50 kiloneutrons/second at 35 KV, 5 mA and 35 mTorr (and that number is on the high side).
Can I reduce the distance between the fusor and the silver foil by placing the water bath ON TOP of the stainless steel cross (in its prone position)? That way, I can reduce the distance to 5 cm and the maximum neutron counts at 50 kiloneutrons/second - which seems doable. Please see photos of JPGs of calculations and the 2.75 inch SS cross that I plan on using for my fusor.
Best,
Shireesh Apte
20171104_144744.jpg
20171104_144735.jpg
20171104_144729.jpg
20171101_155428.jpg

Silviu Tamasdan
Posts: 147
Joined: Wed Jun 28, 2006 11:17 pm
Real name: Silviu Tamasdan
Location: Connecticut

Re: neutron detection by indirect method of Ag activation

Post by Silviu Tamasdan » Sat Nov 04, 2017 9:30 pm

While detecting the beta decay by geiger counter should be feasible, you have to make sure the Geiger counter you use is actually sensitive to beta (many aren't). An adequate check source for your counter would be Sr-90.
Alternatively you could look into a liquid scintillation setup.
There _is_ madness to my method.

Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 2:16 pm
Real name: Shireesh Apte

Re: neutron detection by indirect method of Ag activation

Post by Shireesh Apte » Sat Nov 04, 2017 11:10 pm

Thanks Silviu,

I was reading the posts and came across a recommendation to type in "activation". That takes me to Garrett's post - among others. It appears that Garrett's fusor (in a 2.75 inch SS cross) is similar to mine and he has obtained counts of well over 200 Kneutrons/sec. He has also used silver activation as one of his detection methods. I should have added to that post instead of opening a new one. However, this is encouraging as it leads me to believe that I can achieve neutron production and activation with my Silver apparatus set up in my 2.75 inch SS cross.

Best,
Shireesh Apte

User avatar
Dennis P Brown
Posts: 1521
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: neutron detection by indirect method of Ag activation

Post by Dennis P Brown » Sat Nov 04, 2017 11:20 pm

Your calculated numbers appear to be in agreement relative to what people here post for actual fusor neutron rates and Ag activation. My fusor delivers near 100 k/neutrons/sec and I cannot detect any activation by silver. Then again, my Geiger counter is both very old and touchy so being so low on the flux range my detector isn't likely to give me measurable results from Ag. I did buy a scintillation detector for this very purpose but that is yet another project waiting for me to get time to re-address this question.

Nothing wrong with a new thread on this topic and one concerning this area of study. Also your providing those calculations can be very helpful to others who are also interested in this very question.

As for getting enough neutrons, the key is having a power supply with enough wattage; then, getting experience to keeping the plasma stable (can get tricky until some practice and a clean system.) Otherwise, I believe your goals are very attainable (again, as long as you can obtain sufficent power levels) - best of luck and do continue to post as you develop your system.

User avatar
Richard Hull
Site Admin
Posts: 10904
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: neutron detection by indirect method of Ag activation

Post by Richard Hull » Sun Nov 05, 2017 8:05 pm

With nearly a million neutrons per second rate in my less than perfect moderator, while running fusor IV, I only get about 4-6X background on activated Ag. This is easily counted and detected with a 2" diameter mica windowed pancake GM detector. I do this every year at HEAS with my fusor for all to see.

Your calculation of only 187K neuts per second for 10X above background count are ideal and do not reflect real world scenarios and a number of highly variable parameters.

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.

Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 2:16 pm
Real name: Shireesh Apte

Re: neutron detection by indirect method of Ag activation

Post by Shireesh Apte » Mon Nov 06, 2017 7:01 pm

Thanks Dennis, Richard,

Garrett could do >1e6 n/s in his 2.75 inch SS cross with 'reasonable' voltage and current ( I have reproduced his post below). Although I am a bit apprehensive about such a high number - it appears that it is doable - in a similar apparatus with similar power and vacuum levels that I plan ton achieving. Therefore; I will trudge on this trajectory.
Best,
Shireesh Apte

by Garrett Young » Mon May 01, 2017 12:25 am

Acquired a new power supply capable of -60kV and 11mA and have performed several lower power runs and the results are very exciting.

Pressure: 33 mTorr
Cathode Voltage: 44.1 kV
Cathode Current: 10.9 mA

TIER: 1.30 E+6 n/sec (!!)
Q: 3.16 E-9

ian_krase
Posts: 455
Joined: Mon Nov 28, 2016 7:48 am
Real name: Ian Krase

Re: neutron detection by indirect method of Ag activation

Post by ian_krase » Tue Nov 07, 2017 8:17 am

Thomas Rapp apparently used this as his main method of neutron detection.

User avatar
Richard Hull
Site Admin
Posts: 10904
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: neutron detection by indirect method of Ag activation

Post by Richard Hull » Tue Nov 07, 2017 4:45 pm

If one has the neutron numbers and good instrumentation, silver activation is a fine way to prove fusion.

Most people never get the neutron numbers, at first, to do silver activation or fail in any number of ways to give convincing data. Accomplished fusioneers know what to expect and can detect poor statistics and off-base reported numbers.

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.

Post Reply