Modern neutron detection - Ludlum's new scintillator

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.
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

I’m out of town, but see that mine was left in front of my door (Ring camera), so I can’t yet comment on condition…Has anyone said anything to the Seller yet?
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Update: Got mine opened up and looked at. It’s a little dirty, but in pretty good shape. It’s definitely not new, but doesn’t look like it saw much use, if any at all. It fired up and started making enough noise to upset my dogs…

I don’t have any neutrons yet, but do have some really really hot Uraninites as well as some radium. How should I test?
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Richard Hull
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

Have you been reading what we want? Put the thing on neutron only count with nothing radioactive near it. Get a long reading on counts and divide proportionally to arrive at a neutron background CPM. That is the number we want!

You might just throw hot uranium against the detector in neutron only mode and count again. The CPM value should be virtual background reading.

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: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Okay so here are some results, excuse anything that comes off as newbish as I am very newbish!

I reset the ID count, set for N only mode, x1, and ran for 10 mins. ID was 0.0 after 10 mins and 0.0 after 60 mins.

I then reset the ID count, same settings as before. This time, I placed a 3lb piece of nearly pure uraninite up against the area that has the GM tube. The gamma reading for this configuration/orientation is approximately 27mR/Hr (per the internal GM tube).

After just 10mins, I get a 3.2 for the ID.

Something seems off? No ID for Neutrons, but a high one with the uraninite present?

Edit: Ran the same test with uraninite and gamma only mode this time. Got the same ID of 3.2 after 10mins.

-Matt
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Richard Hull
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

Whoa, that is not good. You should count the rare cosmic in neutron only mode 3-8/minute. The internal gamma tube seems good. Really hot U rock can give off the mR/hr that you report. (internal tube) however, with that hot a rock jammed against the instrument, the neutron count should maybe double or triple the background in neutron mode. (10-20 cpm)

Ultimately you will need a neutron source and may have to back off the discrimination a bit. Again, this assumes the neutron detector is fully functional. The HV may also be set too low. Is a puzzlement. (yul Brenner in the "King and I")

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: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Hi Richard,

I am confused by what I am seeing from the uraninite. I expected the ID to stay at 0.0 while in Neutron only mode…

-Matt
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Richard Hull
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

As you can see I erased my original above in 30 seconds after posting and reposted.

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: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

While testing in neutron only mode, no uraninite present, I did see plenty of “events” that would come in every few seconds. These would range from 0.06 to 0.11 mR…Laying the uraninite on the scintillator hammer would increase the “events” rate and the max to 0.45 mR.

-Matt
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Andrew Seltzman »

Hi Matt,

The readings you are getting are plausible and likely indicate no problem. While the selector switch can select to display the gamma, neutron, or neutron+gamma dose RATE combined, the ID (integrated dose) records the sum of gamma and neutron dose independent of the selector switch position.

Unless you have a neutron source of reasonable strength (operating fusor), the ID for background neutron+gamma will be very low, or near zero even after extended periods of time, while a resonable gamma source will produce a response on the ID. If operating in a gamma only environment the ID will be he same independent of the selector switch position.
Don't mess with the discriminator for now.

The only way to effectively tally background neutron counts and gamma rejection is through the serial port and the ludlum software.
Check the internal dip switches are set in the following config:
Dip1: off (disable calibration date check)
Dip2: on (enable dual tone, high for N, low for gamma)
Dip3: off (enable serial autodump function)

Then install the ludlum software on your computer, connect the counter and run the software. Go to the autodump function and log data with and without the uranite present for about 30min each, and safe each file separately. Run the matlab code I appended to my previous post for each log file to extract the neutron background counts.

My counter is known working, my numbers were:
For background neutron rate only:
Average CPM= 6.9302 over 32.4667 min

For background neutron rate with 30uCi CS137 check source on detector:
Average CPM= 7.7958 over 54.5167 min
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Matt_Gibson
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Hi Andrew,

That explains it then…

Matlab, eh? This project has been bringing me back to my college days, more and more :-)

Interestingly, putting my uraninite up to the GM tube when outside of the case produced a very high reading of 80mR/hr! Didn’t think this hunk was that hot!

Off to order some rs232 stuff.

-Matt
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Okay, here are my results from Matlab:

Neutron only run:
CPM: 5.43, 10mins
With Uraninite:
CPM: 19.04, 10mins

I chose the 1/2second read rate on the Ludlum for both runs.

-Matt
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Richard Hull
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

This is much more like what is expected. sounds OK now. The software saved the day. Use it in future for counting. Analog metering in dose rate units is fine but the averaging is just no good for background. Nothing beats a digital count increment per detection pulse.

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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Finn Hammer
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Finn Hammer »

It would appear that Matlab is the tool of choice, in utilizing this new counter.
A home license is up and around 200USD, and I have no experience using Matlab.
In the light of a steep learning curve, I am interested i knowing if Matlab is the absolute essential tool to display the data, or whether there are other packages available, for example Excell.
My item is due for delivery tomorrow, hoping for a functional unit.

Cheers, Finn Hammer
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Matt_Gibson »

Hi Finn,

While I don’t know if there’s an alternative to using Matlab, I could definitely run your log file for you, so don’t worry about that :-)

-Matt
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Andrew Seltzman »

There's GNU Octave which "should" be inter-compatible with Matlab and is free, however in my opinion Matlab is likely the much better option. There's an enormous amount of resources, drivers, code packages, support, etc.. for matlab.
https://www.gnu.org/software/octave/index
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Richard Hull
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

I have always felt that software, in the many variants, revisions, updates, and failed corporate structures that no longer support it coupled with platform specific issues and hardware issues coupled to software controlled systems would, at some point, be a causative agent in a doomsday event. We already see hacking creating major disruptions in modified software updates from outside. we are too connected in critical infrastructures that run 100% on software internally. While we here are just annoyed by the above and would never create the doomsday event, we will be forced to barely survive of die due to its result once it is set in motion. Too much easily transportable malware on a thumb drive brought in from outside. Think about it. Thus far, in this posting, most seem to have software that works and Ludlum is still very much alive and well, (One of the few old line radiation measuring firms that were not gobbled up by a rather uncaring Thermo.)

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: Modern neutron detection - Ludlum's new scintillator

Post by Bruce Meagher »

Finn,

Would it not be a trivial exercise to take the ascii log file produced by the meter and process it with any modern language you're comfortable using (Matlab, Python, C, Java, Excel, etc.)? I'm not sure why Matlab would be more ideal except Andrew provided the solution for you.

Bruce
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Andrew Seltzman »

I compiled a updated standalone program that will run without Matlab, I believe you will have to install the matlab runtime.
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Finn Hammer »

First of all, a warm and heartfelt thank you to you, Andrew, for the compiled special, which enabled even me to report fast and efficient, in a timely manner.
You are a true friend, Andrew.
Hope is such a great thing, when reports of a less than accurate item description in a group buy are starting to emerge, and ironically enough, near the end hope was all there was to cling to.
But then, I was the fortunate one, and received a near mint item, with only minor scratches from 8 years of shelf life, the original readout protective sticker in place, the cable laced to the handle in a fasion I imagine only a Ludlum employee would device, and hardly any dust at all.

Near mint Ludlum 2362
Near mint Ludlum 2362
It powered up and with the dips set as advised, very soon the numbers started to roll in.
Around 3UTC, 29/12/2021 in Skoerping, Denmark, 80 meters above sea level, it recorded:
Average CPM= 7.0869 over 29.35 min

1st smoothed.JPG
1st smoothed.JPG
1-st smoothed.JPG




A stable gamma source is not at hand at the moment, so this will have to wait till I get one.

Eager to see the fusor raise the numbers above background, the probe was put next to the fusor with 10mm of lead in between, and let it rip.

20211229_163906.jpg


The following graph shows the raw numbers out of the ascii file, and is more for entertainment than anything else, as I can't say how they translate to neutron output, but I hope this thread will evolve into presenting a recipy on how to calibrate this counter.

FirstRawNumbers.JPG


Cheers, Finn Hammer
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Richard Hull »

Nice report Finn! You background is exactly what mine hovers around using the big 3He 4ATM detector. You got a good one for sure. Thanks for the high quality report, as usual.

Richard Hull
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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: Modern neutron detection - Ludlum's new scintillator

Post by Finn Hammer »

This is a report of the run this morning, Skoerping, Denmark, 11:00 - 12:00 UTC
I placed the probe so that it is 80mm from the center of the fusor, see attached photo, and ignore the parallax, I did not want to back off and use a tele.

Prescila probe jammed right close up to the fusor.
Prescila probe jammed right close up to the fusor.


Publishing the number from center of fusor, to face of the Prescila probe, may already be controversial, since there doesn't seem to be an agreement about exactly where the fusion takes place in a cube fusor, with a tube kathode. Is it in the center, perhaps mainly on the internal surface of the endplugs, or is it just randomly distributed allover the goddamn place?
Well, hopefully, this is something we are about to find out, by strategically placing the probe, extracting the numbers and subjecting these numbers to math.
I ran the fusor for 10 minutes at 43kV, 30mA, 32Microns and activated silver to 20kCPM.

Remote during the run. Notice that the 901P which delivers data to the oled readout, is 6 microns off the reading from the calibrated baratron.
Remote during the run. Notice that the 901P which delivers data to the oled readout, is 6 microns off the reading from the calibrated baratron.


After this run, the 2363 Interface crashed, so I did not get the numbers from that run.
Instead I ramped the fusor up to the same level again, over a minute, to grab the numbers from the probe.


Still a bit of water in the chamber, there is a leak that needs to be fixed.
Still a bit of water in the chamber, there is a leak that needs to be fixed.


This time I got the numbers, allright, and here they are. The output in mrem/hr are translated to cpm via the LANL-endorsed 350 conversion factor


rampup.JPG

The counts top out at 49000cpm at time 51.5 secs.
In a previous post, Andrew writes:

-----------------------------------------------------------------------------(block quote substitute, hehe)

A fusor producing 1e5n/s will generate 0.27mrem/min at 8cm from the center (equivalent to a BTI bubble detector placed on the surface of a 6" diameter sphere), or ~16.2mrem/h. At this dose rate the PRESCILA probe would be indicating 5670cpm.

------------------------------------------------------------------------------(EBQ)

Since my numbers are close to an order of magnitude higher, this should work out to a neutron output around 8.6e5n/s, in this run.


But something is bothering me, and that is the decay factor of 0.6 which creates a tail in the time domain, and what I presume is similar to the pile up seen in spectography from the tail from the shaping amplifiers, try to look at the numbers from one of the background runs:

hits and mis.JPG

The red dots indicate a hit by a neutron, creating an increase in reading by 0.08mrem/hr.
As an isolated event, this 0.08mrem/hr should decay to 0 in 4 seconds. But here during a fusion run, we are hammering the probe continously with hits and this must leave an elevated level of reading which should be compensated for.

The question is how?

I am probably messing things up here, from lack of understanding of the math involved. It sure would be easy if it is possible to take the reading at face value and conclude the 8.6e5n/s .


Edit:
Having an electronically recorded neutron rate available makes it much more efficient to create runs for higher numbers. This is the best up to now, with a calculated 1.54e6n/s. Frankly, I thought I was doing better than that and I guess a set of bubble detectors has to be brought in to deliver the last word.

Pouring 2kW+ in to it,  for hardly over the megamark makes this fusor the most inefficient model in history.
Pouring 2kW+ in to it, for hardly over the megamark makes this fusor the most inefficient model in history.
Second edit:

I do have some heavy stuff, and pulled out the 3phase variac, to get a higher voltage out, in this case, I got to 75kV.
The fusor gets rather temperamental at this point, and can shoot up above 50mA in a glimps of the eye, and you will see this behaviour reflected in the graph, where I have to turn the voltage down to abruptly, after the psu has tripped the over current protection. There is still plenty of headroom in the PSU, but for now, I think it is better to tend to the rather bad leak I have, which limits the bottom pressure to 4e-4torr
75kV run.JPG
I don't quite understand these numbers, I think others have reached 2ish meganeuts/s at much lower currents,

Cheers, Finn Hammer
Last edited by Finn Hammer on Thu Dec 30, 2021 10:02 am, edited 1 time in total.
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Andrew Seltzman »

Hi Finn,

The tail in time domain is a function of the time constant filtering in the meter and is not a problem; this is exactly how it is designed to work and does not need to be compensated for. The filter takes the discrete pulses and filters it to an average value displayed on the meter face and in the output removing the "noise" of the individual pulses. When the count rate is sufficiently large, the filtered value appears as a smooth constant dose rate. At very low dose rates you see a "blip" in the dose rate after each individual pulse followed by an exponential decay with the filtering time constant. For count rates high enough that the effects of individual pulses are not visible in the output, the calibration should be taken at the displayed value in mRem/h, at very low (background) dose rates the dose due to an "individual" neutron count does not have much meaning. Unfortunately this counter does not have a scalar function as it is designed to only be used as a rate meter / integrated dose meter making background counting over long intervals difficult.

The code I wrote takes advantage to the blips in dose rate after discrete neutron counts to provide a scalar function for background dose rate. It first takes the derivative of the dose rate with respect to time and divides by the peak increase in rate per pulse (0.08). This provides a spike of ~1 at the leading edge of each pulse. Then it thresholds any values <0 due to the decay tail and sets them back to 0. Then it rounds counts to the nearest integer value, and adds the tally of counts over the logging period and divides by time.

Question on your 901p: is the calibration factor set to hydrogen?
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Re: Modern neutron detection - Ludlum's new scintillator

Post by JoeBallantyne »

Finn, have you checked to see if the orientation of the probe makes any difference in your numbers.

In the only picture you have that shows the probe orientation, you have it with the end opposite the handle facing the fusor.

I'm not sure if there is a Hornyak button on that face of the probe.

If I were you, I would try putting one of the other 4 useable faces of the probe (each of which has a button in it for sure) up against the fusor. (ie: rotate your probe 90 degrees in the horizontal plane, or sit it on its end so the handle is vertical, and then jam one side up against the fusor)

See if your numbers change - and if so how.

Joe.
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Finn Hammer
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Finn Hammer »

Thanks, Andrew,

Answer is: no, nitrogen. Setting it to hydrogen returned the 901P to track the baratron with remarkable accuracy.

20211230_161833.jpg


Edit:

Joe, sounds like a must do, although the manual shows this graph to verify the dependence on rotation. "They" have taken every measure to make this probe omnidirectionally sensitive.

orientation.JPG
Cheers, Finn Hammer
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Re: Modern neutron detection - Ludlum's new scintillator

Post by Liam David »

Not to interrupt Finn's work, I just finished a 3-day background count with the Ludlum. Total counts were 39736, yielding a mean of 9.198 CPM.

Matlab code used:

s = serial('COM3','BaudRate',38400,'Terminator','CR/LF','Timeout',1);
fopen(s);

neutronData = zeros(86400*3*2,1);

for i=1:86400*3*2
t0 = tic;
fprintf(s,'RR');

try
data = fscanf(s);
nums = regexp(data,'[0-9.]+','match');
neutronRate = str2double(nums{1})/100;
neutronData(i) = neutronRate;
catch
disp('Connection Error');
fclose(s);
fopen(s);
end

dt = toc(t0);
pause(max(0,0.5-dt));
end

mRem_per_hour_count = 0.08;
counts = [0;diff(neutronData)]./mRem_per_hour_count;
counts(counts<0) = 0;
counts = round(counts);
counts(counts>10) = 0;
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