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Hacking SBM geiger tubes

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Conundrum

Wed Feb 06 2013, 06:43AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.
I noticed that many of the cheaper tubes are of the "linear" type, using essentially a thin brass walled tube
with the gas fill or are the "mini" SBM21 type with lousy efficiency.

So has anyone else tried to modify these to detect more efficiently, etc?

Ideas so far:-
To use neodymium iron boron (NIB) magnet pairs swiped from dead PS3 optics around the edge of the tube to generate a field gradient and increase the detection threshold.
To use an HV device to "blow out" the centre of the filament then remove the unused end cap and make a 2x tube for direction sensing.
Modify the sense circuit to detect sub threshold events and mount a linear CCD behind the tube so that coincidence detecting can be done.
Use a paraffin/boron doped wax block to make a neutron counter for the fusor folks.
Use rolled indium foil and some sort of biasing circuit to make a neutron activation counter.
Charge up the tube until the count rate skyrockets then back it down until a given CPS is reached.
Insulate the tube with antistatic foam to make it "coil proof"

Bluray based laser pre-ionisation on end window type tubes?!?!
Add a charged plate inline to accelerate alpha particles onto one of two tubes for direction sensing...
"Pre-nuke" the tube with an RF heater to increase internal pressure if they are messed up..
Build a "Life Signs detector" using the characteristic gammas from decaying K-40

Feel free to add to this.
-A

Proud Mary

Wed Feb 06 2013, 05:56PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Have you still got those blue Rumanian glass GM tubes I gave you a few years ago, AndrÃ©? Despite their poor terminations, clunky UX4 base, 900 V anode supply and general fragility, they are far more sensitive than the metal wall SBM-21.

GM tubes are used in fewer and fewer new designs, and while there will probably always be a niche for them, it would be much easier for someone starting afresh to experiment with PIN photodiodes, or RADFETs, which is where the action is today.

Conundrum

Wed Feb 06 2013, 06:43PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Not sure, can you send me a picture please?
I don't recall anything like that, top hats maybe.

-A

Proud Mary

Wed Feb 06 2013, 09:48PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

This Romanian GM tube is often described as the worst GM tube of the whole Cold War, and seems to have been made in a great hurry. The top caps fall off all on their own, and the bakelite base adhesive, long gone hard, cracks, so the base rotates around the glass, snapping off the very brittle wires where they enter the glass.

Nonetheless, they work very well indeed. The glass is as thin as can be, and the tube will fire erratically on UV photons if the metallic blue paint is removed.

I was wrong when I said above that the working voltage is 900V. This particular example was manufactured in October 1960, and has Vthresh 980V, centre plateau 1060V, and Vmax 1140.

I had a few dozen of them at one time, and gave half of them away. I thought I'd sent you a few of them, perhaps three or four years ago, but I may be mistaken.

I have a box of miniature steel GM tubes with miniature HV supplies (3V:450V) and will send you a couple if you'd like to experiment with them. The PSUs will fail at once if you try to get more than a few Î¼A out of them!

Conundrum

Sun Feb 10 2013, 08:52AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Sure PM, thanks!
I have a few goodies here if you'd like to trade, including a Gen 0 night vision tube and (if its intact) a flat Sony CRT that "bounced" from the invalid address.

Proud Mary

Sun Feb 10 2013, 05:17PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conundrum wrote ...

Sure PM, thanks!
I have a few goodies here if you'd like to trade, including a Gen 0 night vision tube and (if its intact) a flat Sony CRT that "bounced" from the invalid address.

I was mistaken when I said the PSUs were 3V to 450V - they are actually 9V in ~500V out, and I was thinking of something else. Do you still want them?

The GM tubes are the relatively insensitive Phillips ZP1313 compensated personal dosimeter types. (A tin filter is incorporated into the design to compensate for the very non linear energy response of GM tubes below 150 keV.)

GENERAL SPECIFICATIONS
Gas filling Ne +Halogen
Cathode material 446 Stainless Steel
Maximum length (inch/mm) 1.26/32.1
Effective length (inch/mm) 0.63/15.9
Maximum diameter (inch/mm) 0.38/9.7
Effective diameter (inch/mm) 0.19/4.83
Connector Pin
Operating temperature range Â°C -40 to +75

ELECTRICAL SPECIFICATIONS
Recommended anode resistor (meg ohm) 3.3
Maximum starting voltage (volts) 380
Recommended operating voltage (volts) 500
Operating voltage range (volts) 450 - 650
Maximum plateau slope (%/100 volts) 15
Minimum dead time (micro sec) 15
Gamma sensitivity Co60 (cps/mr/hr) 1.5
Tube capacitance (pf) 3
Weight (grams)
Maximum background shielded 50mm Pb + 3mm Al (cpm) 2
Minimum anode resistor (meg ohm) 2.2

FILTER SPECIFICATIONS
Material Sn
Thickness (inch/mm) 0.08/2.0

WALL SPECIFICATIONS
Areal density (mg/cmÂ²) 100
Thickness (inch/mm) 0.005/0.13

And no, I don't want anything in trade for them. I have more parts and bits and pieces than could ever be used in a single lifetime! Put a couple of quid in an RSPCA box next time you see one.

Conundrum

Tue Feb 12 2013, 08:24AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Cool, will do. Its a shame that my goodie box to Ash went missing, as this had a few useful Tektronix parts in it.

We should start a few more "roving junk boxes" but this time require exchange of postcards or something to verify that the address actually exists

I have the same problem here, still can't figure out a use for a gen 0 Nv tube as the picture is too dim for anything but a night scope and my original plan of using it as a "poor man's CRT" flopped due to the -13.5KV messing up the LCD panel.

Also

-A

Proud Mary

Wed Feb 13 2013, 03:35PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've found a small jiffy bag to put the two ZP1313 GM tubes and HV PSU modules in, and will see if I can find time to post them tomorrow, or Friday. I'll throw in some suitable anode resistors for them if I can find them. 3.3 MÎ© is the recommended value for ZP1313, so we could do three 10 MÎ© in parallel if I can't find any single resistors at or near the specified value.

I've tested the ZP1313s, and they both motor along nicely at 500V, logging about 9 cpm for background gammas.

Conundrum

Thu Feb 28 2013, 11:07PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I got the Tek box back.
Also just received five IN-9 Russian bargraph tubes, tested one and they seem to work fine.
The are essentially a current indicator, firing at about 170V and the length of the bar reaches full scale at 9mA.
Any use?
-A

Ash Small

Fri Mar 01 2013, 12:15AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Conundrum wrote ...

Its a shame that my goodie box to Ash went missing, as this had a few useful Tektronix parts in it.

Conundrum wrote ...

I got the Tek box back.

I'm glad you've got this box back now, but we hadn't even finalised what was going in it, let alone price, before you posted it without checking I was still at my old address.

I felt I should comment as my name had been mentioned.

BTW, have you worked out a price for 'that other box of goodies' yet?

EDIT: Include me if you do start a junkbox. I've plenty to put in. You have my new address.

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