New tests with neutron detector - EMI rejection

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Silviu Tamasdan
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New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 12:03 am

I refined my detector a bit. It's now enclosed in a Faraday cage to reduce electromagnetic interference (well it's been for a while but didn't have time to test). The cage is a 3/4" copper tube from a home improvement store plumbing section; ID of 3/4 copper is 19.5mm, OD of SNM-11 tube is 18mm. The SNM-11 was sanded carefully over its whole length and wrapped in several layers of aluminum foil, enough to make a tight fit (but not too tight to allow for disassembly). One end of the copper tube has a lid soldered, the other end is a tight-fitting lid with a hole for BNC connector, and is held over the end of the copper tube with a metal hose clamp.

The connections of the tube are: cathode/aluminum foil/copper tube/BNC jacket, and anode/copper fitted connector/soldered to central BNC connector. Everything is nice and tight with no mechanical play at all.

As a source of EMI I used a high voltage arc in air; it's produced between 2 copper electrodes about 1cm apart, fed by a NST nominally 3.2kV/30mA (but it doesn't get anywhere close to that). The NST is specced for 220V primary, so I also use a upconverting transformer 110V-to-220V/500W. Using a kill-a-watt type device the total power used by this chain is 52VA, so allowing for losses in the 2 transformers I will assume that no more than 25W is fed into the arc. That's why I said above "doesn't get anywhere close" - but good enough for this test.

Setup:
- tube + Faraday cage held in a fixed position above bench in a lab clamp, with the other end supported by a metal ruler which is exactly 15cm. (because the lab clamp isn't strong enough). It's connected to the MCA then to acquisition computer.
- arc is set 30cm away from the tube between electrodes as described above, supported by a flower pot for insulation.
- neutron source placed in relevant experiments at predetermined position, 15cm away from the tube. The source I have posted about before, built from a 5mCi 210-Po source + beryllium. Calculated current activity of the source is 3.68mCi.
- moderator built around the detector tube in certain parts of the experiment, consists of a 4x5x20inch block of HDPE and 12 quarts of mineral oil.

Counted neutrons 8 times, 10 minutes each; recorded all data including pulse and baseline waveforms.

Experiment truth table (and quick results for the impatient):

Code: Select all

test        EMI(HV arc)         source        moderator    |  counts in 10 minutes
N1               0                 0             0         |               3          
N2               1                 0             0         |               3             
N3               0                 1             0         |               5              
N4               1                 1             0         |               5            
N5               0                 0             1         |               4             
N6               1                 0             1         |               2                  
N7               0                 1             1         |              29                            
N8               1                 1             1         |              27                    
(where 0=not present/not turned on, 1=present/turned on)

I think the numbers speak for themselves. I did not notice any abnormality of the baseline when the electric arc was turned on. The SNR remained excellent even in the presence of interference.

I'm attaching the full datasets to this post.
The next post will contain screenshots of the final result for each of the 8 datapoints above. Post #3 will contain pictures of the experimental setup.
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12-01-2017.zip
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Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 12:05 am

Screenshots
Attachments
N1.JPG
no arc, no source, no moderator
N2.JPG
arc, no source, no moderator
N3.JPG
no arc, source, no moderator
N4.JPG
arc, source, no moderator
N5.JPG
no arc, no source, moderator
N6.JPG
arc, no source, moderator
N7.JPG
no arc, source, moderator
N8.JPG
arc, source, moderator
There _is_ madness to my method.

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Dennis P Brown
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Re: New tests with neutron detector - EMI rejection

Post by Dennis P Brown » Sat Dec 02, 2017 12:10 am

A good start on working with more realistic issues (except, maybe failure issues with a fusor ;) . I've had my fill of those today with my own system.) A bit limited data - could use more runs with the source and moderator (say, ten) and maybe five runs without a moderator. Also, 29 counts in 10 minutes is rather low. I thought the source was more active then that - or is that the result of the detector bias circuit applied to the detector tube? Flynn was asking about that and as I only far too recently discovered, not an insignificant effect on the output signal.

Aside: a fusor can also cause issues with ground loops and feed-back problems along power lines within the house resulting in complex interference issues with detector systems, besides the RF signature that you are partly simulating.
Last edited by Dennis P Brown on Sat Dec 02, 2017 12:18 am, edited 2 times in total.

Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 12:15 am

Pictures
Attachments
20171201_112818.jpg
Baseline setup: in the middle detector tube suspended; to the left HV arc setup including flower pot with electrodes, NST and upconverting transformer; to the right MCA, laptop, mouse and coffee cup.
20171201_114237.jpg
average arc about 1cm
20171201_121113.jpg
Test N4: arc on, source to the right (inside the plastic sleeve taped to the side of the brown box) but no moderator
20171201_122532.jpg
Test N5; arc off, no source, moderator in place.
20171201_125712.jpg
Test N6; arc on, moderator in place, source absent
20171201_130220.jpg
Test N7; no arc, source to the right, moderator in place
20171201_132509.jpg
Test N8; arc on, source to the right, moderator in place
There _is_ madness to my method.

Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 1:41 am

Dennis P Brown wrote:
Sat Dec 02, 2017 12:10 am
A good start on working with more realistic issues (except, maybe failure issues with a fusor ;) . I've had my fill of those today with my own system.) A bit limited data - could use more runs with the source and moderator (say, ten) and maybe five runs without a moderator. Also, 29 counts in 10 minutes is rather low. I thought the source was more active then that - or is that the result of the detector bias circuit applied to the detector tube? Flynn was asking about that and as I only far too recently discovered, not an insignificant effect on the output signal.
The detector is optimized already. With this system it's the best I can get. Poor sensitivity but can detect enough neutrons to see a difference. I am not trying to achieve high quality neutron flux measurement, but rather obtain reliable detection of thermalized neutrons above background. Precision will come later, with a completely different system that I've already started working on.
Aside: a fusor can also cause issues with ground loops and feed-back problems along power lines within the house resulting in complex interference issues with detector systems, besides the RF signature that you are partly simulating.
I can run the detection system disconnected from any power supply, just off the laptop battery. It runs for about 90 minutes this way. If I need more I can rig a car battery based charger. No ground loops, measuring system air-gapped.
There _is_ madness to my method.

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Richard Hull
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Re: New tests with neutron detector - EMI rejection

Post by Richard Hull » Sat Dec 02, 2017 4:56 am

Is your source a nucleospot? If so you should have many more counts in 10 minutes in moderator. If it is how is the Be placed on the source.

Richard Hull
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Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 7:46 am

There _is_ madness to my method.

Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Sat Dec 02, 2017 8:31 am

Of course I get a lot more counts with the source placed inside the moderator block right next to the detector as opposed to 15cm away from it.


But again, that wasn't the point of this test.
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Dennis P Brown
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Re: New tests with neutron detector - EMI rejection

Post by Dennis P Brown » Sat Dec 02, 2017 11:15 am

That is good work - just the statistics are low for the limited data sets. That is, if one is counting between 2 and 3 events a minute, then the data rate isn't terribly significant relative to counting over ten minutes )count rate is just 10% of the total data set.) However, your noise floor is very low and your source is a known, which certainly indicates your data is solid - just sparse. Of course, for most fusion proofs, where the source isn't a given, and noise can be significant, higher data rates are necessary.

Do look forward to you doing fusion when you either build or locate a fusor class x-former or power supply - then you will have far more counts and a very strong & (hopefully!) better signal. My mentioning of the ground loops & feed-back issues on power lines was more a FYI for readers since this isn't always considered by people and can cause problems. A battery operated neutron detector system has a number of advantages.

Silviu Tamasdan
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Re: New tests with neutron detector - EMI rejection

Post by Silviu Tamasdan » Tue Dec 05, 2017 1:50 pm

I am working on 3 power supplies now. One is the switching PS that I discussed in the other section. Another is modifying a Spellman PS for higher output current. The third is based on a more conventional iron-core transformer. The trigger points for more work on those are in order: 1.ferrites being shipped from China and free time; 2. resistors for appropriate power load being shipped from Russia, and time; 3. huge capacitors being shipped from China, and time.
In the best case scenario if all 3 are successful they wouldn't be wasted; I have enough ideas for using all 3 and more.
There _is_ madness to my method.

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