Joe Gayo's lab tour

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Joe Gayo
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Lukas - If you are talking about the small oscillations that follow a trendline, then this is a result of the statistical nature of neutron measurement. The counts are averaged over 500 msec but I only report rates that have been averaged over 5 seconds or more and not a single measurement spike.

@everyone - Above 90kV I'm having a saturation (maybe?) issue with my detector where the counts increase asymptotically and the numbers become very high. Is this because of a lack of deadtime? I would assume it would stop counting if the BF3 tube just constantly discharged because the signal would be constantly high. Or is it saturated but there is enough of an AC component to the current that it's registered as erroneously high counts? I need to set up an additional detector at a greater distance...

I have tried reducing shaping time (which seemed to help) on the amplifier to allow higher count rates. With a shaping time of 4usec, I would think it would support many kHz of rates. The detector seems fine to 3 kHz count rate.
Last edited by Joe Gayo on Mon Jul 01, 2019 8:07 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Lukas Springer »

Damn statistics, ruin everything! :D

That sounds like signal pileup in your detector, have you tried just using a higher distance to your reactor?
faster shaping can do only so much and most gas proportional detectors are not made for high counting rate.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Yes, I’m going to set up an additional detector at a greater distance (The present detector location is calibrated and gives nice resolution for low current/voltage operating conditions), but I was curious about typical resolving time for a BF3 detector system. I could setup a signal generator to test. I would think dead time issues would reduce the count rate, not increase (I found a paper citing dead-time under 10usec).

https://www.tandfonline.com/doi/pdf/10. ... 96.9732021

Another question: I understand how pile-up can distort spectroscopy measurements but in pure counting situations how does the count rate multiply?
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Re: Joe Gayo's lab tour

Post by Robert Dwyer »

I think there should be decent dead time in your system that can cause pulse-pileup, but I am unsure why that would make you have multiplying count rates. I think there are three places that will give you dead time, and measurements of these with an o-scope could help diagnose this issue:

1. Tube dead time: This stems from the recovery period due to the voltage drop across the tube when a current flows from a pulse. The current needs to drop far enough so there is sufficient voltage to cause a large enough pulse to be formed for the amps and shaping electronics to detect the event.

2. Electronics Dead time: This will come from the any NIM or other electronics used for pulse shaping and analysis suhc as amps, scas, etc.. there is a time were the electronics are busy with a single event and cannot resolve any other inputs that come into the electronics. On many NIM modules there is an output on the back labled 'DT' which sends a logic signal while the module is busy with an even allowing you to better track deadtime on the electronics front.

3. Scaler Dead time: I am putting this in a different category than the 'electronics' category, as it has less to do with pulse shaping, but more the counting end of thing. This could include hardware such as physical counters or scalers, but also could extend to digitizers, mca's or even software, that adds deadtime to the system were, at high count rates, pulses may be lost.

As your tube is a gas tube, I think Lukas is right in suggesting most of your issues are stemming from the tube itself (if it is a pileup related event). The deadtime, if not found on manufacturer's sheet, can be measured using an oscilliscope. Setting the oscilliscope to trigger on a pulse from the detector each event, but not clear the screen. After about 50-100 pulses, you should see the time between the pulses (dead time). There are many mathematical models you can find that have been done on correcting for dead time, but the easiest way is to move the detector farther back. These models, and more in depth explanations of dead time can be found online. I suggest Glenn Knoll's book which is great investment for both the hobbiest and professional interested in radiation counting, as it explains things far more in-depth and better than I ever could.

Below is an image showing both the dead-time and recovery time in a geiger tube, which will be similar to what is probably happening in your tube.
Dead_time_of_geiger_muller_tube.png
The dead time should keep you from seeing too high count rates. If your tube is not properly quenched, then perhaps there may be an issue there. If there is nothing erroneous in your dead time measurments or pulse traces, then I suspect an issue with counting electronics such as your scaler. At 90kv sufficient noise may be entering your system as well. Both the dead time measurements and a farther detector will give you a good start as to figuring out this issue.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

I have a bubble dosimeter reading of 4.8E+7 which seems ridiculous...

@Robert
I have Knoll’s book and agree it’s a must. There are several things I’m going to investigate with the counting electronics (plus add the greater distance detector)
Last edited by Joe Gayo on Mon Jul 01, 2019 9:18 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Robert Dwyer »

Does this reading corellate with the high count rate from the BF3 tube? If so then you may be seeing real counts. I think setting up both a bubble dosimeter along with another tube at a greater distance at the same parameters of voltage, current, and pressure and see if you get the same yield. If the dosimeter is reading these results I think the likelihood of real events is true. At those neutron numbers pileup events would still be visible, but a trend should still be seen with the BTI with regards to a count rate.

If you do see evidence of these numbers being real, my next suggestion is activation of some kind. Silver, Rhodium, Silvers, etc... to verify these yields.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Yes, but I want a lot more data. I’ve had some runs where the rates were much higher but unfortunately I didn’t have a bubble dosimeter present.

I’ve activated silver, indium, and manganese quite easily to many times background. The device can run at 5E+6 for extended periods (60 minutes).
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Re: Joe Gayo's lab tour

Post by Richard Hull »

I would take three routes here with large numbers you are apparently getting.

BTI at some increased range. (BTI dosimeter needs to be fresh and trusted, obviously.) If in excellent shape, different ranges should jibe based on inverse square law plus or minus a bit, but not to an extreme.

Silver activation - Always a true indicator of Neutrons. Should hold to some semblance of the inverse square law as well.

Definitely move the BF3 tube out farther. The suggestion about an o'scope picture of the preamp output is a must.... To eliminate the issue of noise. due to proximity. If I were there, I would be all over the preamp output with a good DSO like ugly on a gorilla. Electronic counting is tough and noise loves a home in long cables that are terminated poorly or not at all. Even with good technique, the energy and RF at 90kv in a fusor might be an issue. This is especially true if the moderator and tube are in close proximity to the fusor. If all is fine with the electronics its count at various ranges should obey the inverse square law just like the dosimeter. Neutrons, while they can scatter somewhat in air, have decent straight line ranges much like gamma rays over laboratory distances.

Sometimes I find I just can't do it all to a degree that make some of my efforts payoff like I want. I have knowledable friend in the HEAS here that I can call upon in critical endeavors, mostly in data gathering.

Much of the above that I have suggested should rely on a good lab assistant as you will have your hands full with controlling the fusor in the experiment. This is especially true for the multiple capture and saving of screen images on the DSO during the experiment. The lab assistant is almost a must have and should have some familiarity with the process and equipment. A third person could be a "step-and-fetch-it". Such a person need not have any experience, just a willingness to help the two researchers in whatever small intermediate tasks that are menial yet immediately helpful. (log book entries called out to him.)

I have even used a large cadre of very experienced fusor people at the HEAS gathering in October for a lot of tasks I fret over when alone.

Richard Hull
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

I'll post more details in the near future, but I was having issues of gamma/x-ray pile-up above 90kV. These normally low amplitudes pulses pilled up to such an extreme level that they crossed the discriminator threshold. This was resolved in the typical fashion with increased distance, shielding, and discriminator level.

I have re-validated the results below 90kV and my previous numbers stand. I have some new record results that I will be posting ...
Last edited by Joe Gayo on Mon Jul 22, 2019 5:32 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

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Indeed, X-rays get vastly more intense as the voltage advances. There is a trade off which Joe is helping to quantify here. His chambers are of low Z aluminum which typically reduce X-ray production, but at high voltages, what x-rays are produced make the chamber absolutely transparent to the higher energy x-rays that are produced. Interesting....

Richard Hull
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Fusion is the energy of the future....and it always will be
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Getting Serious ... added a turbo and RGA
IMG_2249.jpg
IMG_2250.jpg
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

Initial Pump Down versus Base Pressure After Multiple Heating Cycles
Pressure (Torr).png
Before and After Run
Pressure (Torr) (1).png
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Re: Joe Gayo's lab tour

Post by Scott Moroch »

Are you sure your units are right? I have never heard of anyone reaching 1E-10 with a turbo. Best I have seen is E-8. Perhaps someone with more experience can weigh in.

What are the time units? Minutes? Days?

Nice work though!

Scott
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

The x-axis is AMU ... these are all single scans that take about 1 minute
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Re: Joe Gayo's lab tour

Post by Scott Moroch »

Ah, I see. I apologize, I misunderstood. Thought time was the x-axis . Nice plots.

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Re: Joe Gayo's lab tour

Post by Richard Hull »

SRS! Top drawer stuff. I picked up a brand new, in-box SRS 0-3kv digital controlled PMT, Proportional tube power supply. List price $1900 at a hamfest for $250. Best supply I have ever seen. I powers my 5" Bicron NaI:Tl gamma spec tube into my canberra gamma spec. with it.

I have always lusted after an SRS RGA but lacked the $3000 to own a new one. But...who an I kidding... I would have to completely redo my system to hit 10e-6 torr.

Great system Joe ...

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Joe Gayo's lab tour

Post by ian_krase »

I actually wonder what the cheapest RGA out there is. It looks like many are available for a couple thousand...
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

After a high power run, interesting peaks at 5 and 6 amu
Peaks5-11.png
Last edited by Joe Gayo on Sun Jul 28, 2019 8:39 pm, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

More interesting data ... any guesses for amu 21 (DTO ?)
D2 Plasma Run - 90kV 15mA - 2.8mPa - 3.03E7 n_sec.png
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Re: Joe Gayo's lab tour

Post by Dan Knapp »

D2OH+
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Re: Joe Gayo's lab tour

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I find it interesting that even after an hour it’s still there and it didn’t show up in lower fusion rate runs

What’s an alternate explanation for mass 5 if tritium isn’t present ?
Last edited by Joe Gayo on Mon Jul 29, 2019 12:35 am, edited 1 time in total.
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

@Dan - I’m trying to complete the following list of possible detected species that’s relevant for fusors

AMU: Possible Species
1: H+
2: H2, D+
3: H3, HD, 3He, T+
4: D2, 4He, TH
5: D2H+(?), TH2+(?), DT
6: D3+, T2, C+

19: DHO, H2OH+, NHD2, CH3D
20: D2O, ND3, CD4
21: D2OH+, DTO
22: D2OD+, T2O
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Re: Joe Gayo's lab tour

Post by Richard Hull »

Tricky work! The RGA in the depths of what a multiplier can sniff out below 10e-7 might be showing stuff that can't be produced or exist outside of an active fusor environment. Still, it's fun to try and figure it all out. We really don't know what stressed molecular chemistry might slap together in rare moments in vacuuo, and in an energetic environment.

Good start on a listing. My head hurts just reading that first pass of molecular offerings.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Joe Gayo's lab tour

Post by Joe Gayo »

This search helps: https://webbook.nist.gov/chemistry/mw-ser/

The strong presence (2.86E-7 Torr) of 5 amu correlated with high fusion rate runs temps me to believe this is DT.
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Re: Joe Gayo's lab tour

Post by JoeBallantyne »

Half of the D-D fusion that happens should be producing T + p. The other half is producing He3 + n.

Some of the T that gets produced may also get burned. So you should see some 14Mev neutrons coming out if you are actually burning DT.

Probably most of the T is getting buried in the walls of your fusor, since it will not be confined by 90KV.

But if you bury enough T in the walls, some of it will likely outgass.

I wouldn't be surprised if you see some DT after a long high power run. Figuring out how much you should be seeing will likely be non trivial.

Joe.
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