Small neutron source

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Rapp Instruments
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Real name: Thomas Rapp
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Small neutron source

Post by Rapp Instruments » Sat Aug 23, 2014 10:57 pm

High,
I builded a small neutron source. It use an simple canal ray ion-source with post accerleration. The ion-source runs with 25 kV, 200µA, the zirconium target is biased with -50 kV. The moderator enclosing the target is made from parafin. As detector I use two russian GM-counter tubes, one wrapped with indium wire, the other with an silver sheet. The activation of both materials is clearly seen.
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Ionbeam without target
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Ionbeam with target and accelerating voltag on, glas is fluorescating by high speed secundary electrons
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Tube with opened parafine moderator
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the two counter tubes
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measurements with silver and indium
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A bit more information can be found on my homepage http://www.rapp-instruments.de/Beschleu ... neugen.htm

future plans are to build a high frequency ion-source like Carl Willis to get more fraction of atomic ions and to build a higher voltage power suppy

Thomas

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Dennis P Brown
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Re: Small neutron source

Post by Dennis P Brown » Sun Aug 24, 2014 11:05 am

The rules clearly state use your real name to post.

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Chris Bradley
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Re: Small neutron source

Post by Chris Bradley » Sun Aug 24, 2014 11:23 am

Dennis. Thomas is well known for describing his excellent work here, and has always given is name 'Thomas Rapp', albeit in two parts, in every post.

Thomas, another well crafted execution. Thanks for sharing. One question I have is centred around your 'activation counters'. I have the same Russian tubes and was planning to do likewise with both those and to try it out with a plastic scintillation sandwich. Jon R has previously described his real-time activation counter with In, which I've asked him about off line. Can you let us know if it was possible/how well you found the In counter was able to detect the *onset* of neutrons (via the shorter 116(m2)In 2s half life, and not just via the longer half-life 116In and (m1) activations)?

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Dennis P Brown
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Re: Small neutron source

Post by Dennis P Brown » Sun Aug 24, 2014 1:26 pm

Sorry, didn't know the rules don't apply to all and understand how difficult it is to comply (lol; really, heard it is.) Yes, appears to be interesting and relevant work. The silver/In activation is very nicely done - simple but appears effective.

Rapp Instruments
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Re: Small neutron source

Post by Rapp Instruments » Sun Aug 24, 2014 2:12 pm

Hi Dennis,
I'm sorry, I didn't know about the 'real name rule'. It's some years ago that joined the forum. I just changed my profil, my real name should be visible now.

Hi Chris,
I have to disconnect the counter tubes from the electronics during the activation, because of interference from the high voltage. After the activation time I switch off the voltage supply and transfer the part of the moderator which contains the couter tube to the table with the electronics. This takes about one to two seconds so the short lifed nuclides have mostly gone. But of course the decay measurements contains also their radiation, in the case of silver also the radiation of the 2.4 minute nuclide Ag 108.
I will try to insert a electrostatic and x-ray screen between accelerator tube and moderator with countertube to be able to measure online.

Thomas Rapp

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Chris Bradley
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Re: Small neutron source

Post by Chris Bradley » Sun Aug 24, 2014 4:31 pm

Dennis P Brown wrote:Sorry, didn't know the rules don't apply to all
The clear purpose of the name rule is to attempt to ensure people are not acting behind pseudonyms. Thomas' identity is one of the most transparent on the forum, and his posts on his experiments are valued and exemplary. But I note he has seen fit to exercise his usual good judgement to pre-empt any further such pedantry.

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Richard Hull
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Re: Small neutron source

Post by Richard Hull » Mon Aug 25, 2014 2:15 pm

Thomas,

If you would post a bit more data, like the run time, accelerator deuterium pressure and and the -50kv current to target, I would like to place your name in the neutron club as it appears you have satisfied the bulk of the requirements for being in that limited group. Thanks and a very nice setup.

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.

Rapp Instruments
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Re: Small neutron source

Post by Rapp Instruments » Mon Aug 25, 2014 7:58 pm

Hello Richard,

1. in the beginning I exposed the samples for 4 minutes, but later I found that 1..2 minutes a quit enough for the short life nuclids.
2. the pressure in the ion gun I can only estimate, because of the feeding capillary and the small diameter ion chanel, it should be arround 0.01 mbar
the pressure in the accelerator tube is estimated < 10-3 mbar, because I get no sign of discharge with -50kV if the ion gun is switched off.
3. I could not measure the target current because of troubles with small discharges outside the tube. But tomorrow I'm going to measure it in an old fashioned
way. I use a small neon bulb with a capacitor and count the flashes. I already calibrated it, with 10nF,
0.2 µA 0.6 Flash/s
1 µA 2.7 Flash/s
2 µA 6.0 Flash/s
10 µA 20.0 Flash/s
for higher currents I will use a bigger capacitor. This small indicator should also work on high potential

Thanks for placing to neutron club, but I think I'm already listed since 2009 with my fusor experiments

Thomas

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Richard Hull
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Re: Small neutron source

Post by Richard Hull » Tue Aug 26, 2014 7:12 am

Thomas, You are correct! You have already been assigned to the neutron club. Your current project is most interesting and shows that fusion can be had from a number of simple sources, like your small beam tube.

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.

Rapp Instruments
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Joined: Mon Mar 23, 2009 11:22 pm
Real name: Thomas Rapp
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Re: Small neutron source

Post by Rapp Instruments » Tue Aug 26, 2014 1:32 pm

Hello

I made the meassurement of the target current. It's arround 30µA. The genious way to meassure small current on high potentials I found in American Scientific 1972 ( C.L. Stong).
Image Image
I made a video with Exilim EX-FH20 highspeed camera with a framerate of 420 pictures/second. By viewing the single frames I found a flash on every 40th images so the blink rate is arround 10/s which correspond to a target current of 30µA (ion source current 500µA).
A smarter way would be to use a lightguide fiber and to count the flashes with a photodiode.
Next I made meassurements of the neutron flux with a plastic scintillator (1x1x1 cm) without the moderator . The Scintillator was screened with a leed box, arround 1 cm leed.
Image Image
The count rate with deuterium is arround 16 c/s, the background 2 c/s, if I use air in the ion gun the count rate is 5 c/s, maybe from residual deuterium in the system.
Measurements with a russian He3 neutron counter CNM 32 showed no result, maybe I got a deaf tube

Thomas

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