Open source Gamma spectrometer (MCA) discussion

[Sigurthr]

Good to see progress coming along so quickly! Unfortunately my hobby budget is totally burnt for a while. My scaler just died the other day and I rebuilt the pancake in to a very basic clicker/blinker for now, as it is perfectly good.

Hopefully one day I'll be able to pick up a nice scint probe and get an MCA going out of it.

 

[Seoul_lasers]

Good to see progress coming along so quickly! Unfortunately my hobby budget is totally burnt for a while. My scaler just died the other day and I rebuilt the pancake in to a very basic clicker/blinker for now, as it is perfectly good.

Hopefully one day I'll be able to pick up a nice scint probe and get an MCA going out of it.

Hey, do you have a picture of your scaler? Knowing a fair bit myself about GM counters... how did it die?

What kind of tubes you running? 900V?

 

[Sigurthr]

450V russian 3" pancake.

I was using a G8RPI PIC Scaler Unit, I'm not sure where it went south yet, the unit just stopped responding to pulses. I'm terible with digital electronics, lol.

 

[Seoul_lasers]

450V russian 3" pancake.

I was using a G8RPI PIC Scaler Unit, I'm not sure where it went south yet, the unit just stopped responding to pulses. I'm terible with digital electronics, lol.

hmm strange... I'm not sure I'm familiar with this unit.
Do you have a picture of the unit and the circuit.

The HV is still present? Have you tested the output for 450V?
What happened when the scaler went dead? What were you doing.

If not HV present then I suspect you blew one of the HV power supply transistors.

Post some pics.

 

[Sigurthr]

The G8RPI PIC Scaler is a PIC microcontroller based scaler unit that was designed by one of the list members a year or two ago. He made several small batches and sold them over the list. His unit consists solely of a PIC board and an LCD board; you supply the detection board, HV board, and probe. HV on my board is fine and the pancake is responding as normal; I built a quick and easy analog blinker circuit to monitor pulses (2N2222 + dc blocking cap + resistor + LED) to check my pulse network and it looks fine.

I'm thinking exposure to a high RF or HV Electric field may have corrupted the coding or zapped some surface mount part on the PIC Scaler board.

I had the unit in storage on my shelf, pulled it out to check for contamination on a NST I just recently bought from a member here who happens to own a box of Thorium Nitrate powder, and observed no response... not even a background count. I ran two full 10 minute surveys, total of zero counts. Normal should be about 260c/10min. Dissassembled it and threw together the blinker, and the tube + HV + pulse is working fine. Negligible contamination on the NST, btw. Just 1 to 2 cpm higher than background.

 

[Seoul_lasers]

Woa, yes that does sound like a pic problem.
Any way you are able to check the pic? Is the pic removable?

 

[Sigurthr]

Aye. Yeah the PIC is removable, but I don't have any tools to test it. Tbh it didn't work all that beutifully to begin with, the nice part was the price ($58). When I can afford to I may just pick up a used scaler from eBay and use that instead.

This one only had 4 modes:
6sec sliding window and average of last 60sec.
5minute total count.
10sec sliding window and average of last 5min.
10min total count.

The 1st and 3rd modes were useless for pretty much everything. I only used the total count times. Also, a good 20% of the pulses were missed by the PIC, so you lost some sensitivity on the lower activity side.

 

[Seoul_lasers]

OMG! That sounds just about useless.
Sorry to hear that. Do you have a pic of the unit?
Also there is another integrated scaler you can get.
Vender root makes a totalizer that is very fast
You could use this. You'd be limited to cps or cpm.
Timer can be set to cut the pulses after an x amount of time.
I know because I made one for my LENi for calibration.

 

[Sigurthr]

Ya, I'll whip up a picture of it soon. Got my hands full with a CW Mult + NST project at the moment, hehe, and I don't want my camera out and around the HV field. If it works well I should see ~-90kV DC. Currently solving flashover issues.

Thanks for the suggestion of the totalizer, I'd heard of it before but didn't know who made it.

 

[Seoul_lasers]

A Cockcroft–Walton (CW) generator? Cool what are you building with that? Smashing some atoms? X-ray flashlight.... kidding.

 

[Sigurthr]

Aye, haha, no, just a replacement ionizer for my air filter XD. Nothing grandiose, haha. I could always repurpose it though, heh.

I do miss smashing atoms... neutron shielding is a nightmare though...

I used cheap Chinese parts though so I don't think this one could break 100kV, even after I potted the entire thing In high dielectric plastic.

 

[Seoul_lasers]

I'd highly recommend using mineral oil or Shell Dialex for your CW multiplier. Repotting it in plastic is risky because of air pockets. Are you using epoxy or polyester resin ?

 

[Sigurthr]

Multitemp Hotglue actually! Haha, I tested this stuff up to 120kV/cm with no arcing. I couldn't go any higher. If I need to remove the glue I can bake the parts at 120F for a couple hours and it will all drip off, haven't had to yet though.

I did the whole oil submersion thing about a decade ago... wow what a mess. I had a proton accelerator back then.... what fun! I never did find out the mean free path of the protons.... I may have irradiated some neighbors. I got rid of it because it got old (boring) and was a huge honker of a machine. Plus, I hate working with H2 gas.

I'll take a pic of the setup for ya as well. It's only temporary, the NST is due for some HV-powered Low Pressure Sodium lamp experiments as soon as the bulb arrives.

PIC scaler pics to come, once I dig it out.

 

[Seoul_lasers]

Sounds like lots of fun.
Proton accelerator （＾∇＾）

Btw, have you ever had the urge to play with neutrons?