Small neutron source

[Rapp Instruments]

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.

Ionbeam without target

Ionbeam with target and accelerating voltag on, glas is fluorescating by high speed secundary electrons

Tube with opened parafine moderator

the two counter tubes

measurements with silver and indium


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

[Dennis P Brown]

The rules clearly state use your real name to post.

[Chris Bradley]

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)?

[Dennis P Brown]

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]

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

[Chris Bradley]

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.

[Richard Hull]

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

[Rapp Instruments]

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

[Richard Hull]

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

[Rapp Instruments]

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).

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.

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

[Richard Hull]

At such a low beam current, and with the Russian 3He tube's low NV value. I would be surprised if you saw anything much, even if the tube was good.

Richard Hull

[Peter Schmelcher]

Thomas your equipment dilemma is probably very common. Effectively does my used stuff actually work? I have suffered from a non functioning Russian tube, failing electronics, as well as bad welds, and many rookie mistakes. Put them all together and progress is challenging.

I built several preamp designs that you can find on this site. These exposed the system dilemma, if it works great, but if it doesn’t how do you know which part is not working. Ultimately I went “All In” and designed my own high performance preamp which I could independently functionally verify, and then I knew the Russian tube was bad. So all dressed up and no place to go.

In hindsight if I were to do it again I would simply buy a new commercial preamp circuit board for about $50 and avoid suffering. Regrettably the very best low noise preamps are the easiest to destroy.

My preamp design was engineered, it is overkill with 15KeV rms of noise in the output signal (CERN would be closer to 12KeV). I used a Geiger mode He3 tube biased as a proportional tube with no issues.

The big advantage of proportionality IMHO is that you can verify that the neutron detection system is working using cosmic ray generated neutrons. Without a moderator your signal includes the initial neutron kinetic energy. With a moderator the neutrons are stripped of their kinetic creation energy and the output signal amplitudes show a distinct grouping or banding at the He3 neutron capture and dissociation energy. The catch is that fast neutron detection probability decreases dramatically with increasing kinetic energy so after you know the system is working you want a moderator.

FWIW
-Peter

[Rapp Instruments]

Hi,
I have builded preamps myself, which worked very well with a home-made prop counter for EDX analysis (1.5keV res at Mn K alpha)

http://www.rapp-instruments.de/Radioakt ... ounter.htm

The amplifiers should also work with the corona tube. I just ordered a new tube from Ebay.

Anybody knows about the spatial distributions of the neutron radiation from a flat target. If I suspect a homogen distribution I can calculate the minimun flux from the scintillators data.
Distance from source 25 cm > surface of the sphere 1963 square cm
surface of the scintillator 1 square cm
flux 14 n/s * 1963 = 27,000 n/s
assuming 100% detection effiency of the scintillator,
the real flux value should be somewhat higher.

Thomas

[Peter Schmelcher]

Nice project and preamp. I used the same preamp approach but picked the ADA4817 op amp.

My pre amp is battery powered and gets used with a scope that has a telecom test mask feature. The mask gets violated every time the displayed preamp signal crosses a mask boundary, and this increments a counter. So the scope becomes a multi channel analyzer with 8 adjustable channels.

-Peter

[Rapp Instruments]

hi,
at the end I got the corona counter to work. First I measured the voltage/current field of the tube (CHM 42)


The tube behave like it should regarding the data sheet (Starting voltage nom 600V, max 700V)
for the neutron counting I used a rather high working resistance with 1 Gigaohm.


The parafin moderate tube gave following counts

I supose the strong decay of counts after switching the target voltage on results from the large time constant of the RC-network or a change at target surface.
The neutron pulses have about twice the height then the corona noise amplitudes.

Happily after the measurement I broke the tube by handling it a little bit to hard. Anyone also using the CHM42, be carefull, there is a weak spot at the lower end of the tube, maybe the spot where it was evacuated and filled.
After the accident I opened the tube to have a look inside.

The tube is constructet like a normal counter tube with a thin central wire. What I'm wondering about is the black powder layer on the inside wall. The data sheet clearly says that the CHM42 should be a He3 counter, but this looks like a boron lined counter

Thomas

[Chris Bradley]

It might just be sputtered material from the wire, as these work by a continuous corona generation.

Yes, I bought a pile of these too and wondered what I had wasted my money on! After 10's of hours of effort, decided they didn't work. Some months later looked again once I had access to an oscilloscope of sufficient input impedance. Then I saw the signal, and then I could make some electronics to detect those signals!

Don't give up trying to make them work, simply that you have to get the right electronics in place. They do seem quite delicate.

[Richard Hull]

This discussion has moved into the area of neutron detection and might be better suited to the Radiation detection forum.

Richard Hull

[Rapp Instruments]

Okay, back to the accelerator,

I have increased the target bis from -50kV to arround -90kv, actually the voltage jumps between 80kV and 100 kV because of micro discharges along the tube walls. The increase of indium activation is remarkable, arround threefold



What would be the next, easy to activate element, beside silver and indium ?

Thomas

[Dennis P Brown]

Your current is low but you might want to check the x-ray output just to be on the safe side.

[Rapp Instruments]

Hi Dennis,

I don't worry about x-rays because I have a 5 mm lead shield to the operator side. Thick enough for low intensity 50 to 100 keV xrays I found with geiger counter.

Are there really no more elements beside silver and indium to activated with low neutron flux?

Thomas

[George Schmermund]

Have you given any thought to detecting protons from the DD fusion? That should be doable and you could then petition to be the first candidate to be enrolled into the 'Proton Club'!

[Richard Hull]

Rhodium is excellent if you can get it! But those are the big three.

Richard Hull

[Dennis P Brown]

Protons from any fusion events wouldn't travel through any significant amount of material (a few microns to tens of microns at best) if I recall from my calculations; be rather difficult to measure any considering that limitation even if they were accessible. Detector windows except for maybe beryllium wouldn't generally work for such low energy protons (a few MeV.)

Glad the x-ray radiation is not an issue!

Again, very nice experiment both for the design and confirmation method - your neutron flux is much higher than I would ever have expected considering such a simple apparatus.

I am curious about your target of zirconium - how did you fill it with deuterium?

[Rapp Instruments]

Hi George, hi Dennis

in the early days of nuclear research desintegration was mostly proved by protons. Researchers used a scintillator screen (ZnS) and counted the flashes with a microscope. The screen was mounted on the vacuum side of the tubes, you so only need a optical window. They were able to discriminate the protons flashes from the continous glow from x-rays, human multi chanel analyzers.
But I think with the most probably D-D reaction D + D > n + He3 there no proton emitted, the second reaction chanel with much lower probability D + D > p + H3 a proton would be emitted.

Zirkonium like some other metalls ( Titan, Palladium) readily absorb hydrogen/ deuterium from surrounding atmosphere, also the ion beam helps to load the surface layer with deuterium.

Hi Richard

altough the price for rhodium has fallen the last years it is still very expensive, but I can try my luck with rather cheap rhodium plated coins, maybe there enough material to see it.

Thomas

[Chris Bradley]

But I think with the most probably D-D reaction D + D > n + He3 there no proton emitted, the second reaction chanel with much lower probability D + D > p + H3 a proton would be emitted.

Those two routes are approximately (not quite) equal. It is the D+D->4He + hv reaction that is rare, about 1/20000 as likely as the others.

It could be a challenge to look out for the very high energy 24MeV gamma out of that rare reaction.

If you have that level of gamma spectrometry sufficient to discriminate this, another possible case for an interesting experiment is to mix your D with H, and try to detect the D+H->3He + hv gammas. Your linear target setup might lend itself better to that reaction. That would be the first detected amateur non-DD fusion if you could.