Radiation Detector?

[ghost]

I was at my local antique electronics store, and I came across a box labelled "radiation detectors". They were $5, so I bought one.

It is made by Lind, Inc. and has a "Tube Type" of 7311/8767. The actual device is labelled:

LIND, INC.
P115
MADE IN USA
86-16

See the pictures.

What is this? How does it work?

Thanks!

 

[10fttall]

If it turns brown on one side and blackish on the other, you have been exposed to too much radiation and will grow 14 fingers.

 

[OverlordvI]

Dude - that is awesome! I've been tinkering with the idea of sending up a rocket with a USEFUL payload - things like radiation detectors (based off sun cycles, etc.), temperature sensors, and so on. Can you image how much data there is still to collect?

Send it up with your rocket a few times and see what happens =). I doubt it's sensitive enough, and I'd really cringe if it changes color - think about what must be happening to you when you fly on an airplane...

 

[10fttall]

I was just doing a bit of googling and found the product page and company web site. You could call and ask them what it does. I'd be curious to find out how much it retails for also.

https://www.lndinc.com/products/389/

 

[Pem Tech]

Thin membrane?
Hmmmmm
Sounds like it may be an Alpha probe, of some sort. Let me look and check around the office to see if I can confirm that. I work for the Department of Health, Radioactive Materials program, so SOMEONE should know something.

 

[ghost]

This is really cool! I'm excited to see what it does!
https://www.lndinc.com/products/pdf/389/ is definitely the datasheet. Good find!
So does this change color when exposed to too much alpha/beta/gamma radiation? Or does it need to be hooked up to a circuit (as shown in the diagram). If it's a circuit, I know what my next electronics project is going to be

EDIT: It looks like the store doesn't list them on their website (allelectronics.com). But they were definitely selling a box of about 20 of them for $5 each!

 

[ghost]

Oh and the metal cap on the end unscrews to reveal.... a glass thingy. Opinions?

 

[SCE to AUX]

What you have there is a "pancake" type Geiger-Muller (GM) tube, the sensing element of a "Geiger counter".

https://en.wikipedia.org/wiki/Geiger-M%C3%BCller_tube

Handle the tube VERY carefully, as the thin mica window is exceedingly fragile, and if you crack it, the gas fill will leak out and the tube will be worthless.

The circuit shown in the datasheet is only the "front end" of a counter, and will give short pulses out when the tube detects an alpha/beta/gamma. To actually count particles or calculate a dose rate, more electronics will be needed.

You will need a high voltage (900V) power supply to provide proper operating bias for this tube. Fortunately, the current requirement is nearly zero (microamp range).

 

[10fttall]

What a coincidence! I also need a 900V power supply for my new 342 engine cluster.

 

[TWRackers]

What a coincidence! I also need a 900V power supply for my new 342 engine cluster.

Maybe, but how many amperes would it source?

 

[ghost]

What you have there is a "pancake" type Geiger-Muller (GM) tube, the sensing element of a "Geiger counter".

https://en.wikipedia.org/wiki/Geiger-M%C3%BCller_tube

Handle the tube VERY carefully, as the thin mica window is exceedingly fragile, and if you crack it, the gas fill will leak out and the tube will be worthless.

The circuit shown in the datasheet is only the "front end" of a counter, and will give short pulses out when the tube detects an alpha/beta/gamma. To actually count particles or calculate a dose rate, more electronics will be needed.

You will need a high voltage (900V) power supply to provide proper operating bias for this tube. Fortunately, the current requirement is nearly zero (microamp range).

Oh cool! So if I follow their circuit, what would the output look like? And where do I even attach the ground and positive wire for 900 volts? There doesn't appear to be a connector.
Yes, this implies I'm going to (try to) build my own geiger counter
Any advice on reading those pulses (besides an oscilloscope?)

EDIT: what do you think it's worth?

 

[SCE to AUX]

Oh cool! So if I follow their circuit, what would the output look like?

The circuit shown will produce sharp negative-going pulses at the "signal" output.

And where do I even attach the ground and positive wire for 900 volts? There doesn't appear to be a connector.

Ground would be the metal case, the high voltage (through the 3.3M resistor shown in the diagram) would go to the small metal cap.

Yes, this implies I'm going to (try to) build my own geiger counter
Any advice on reading those pulses (besides an oscilloscope?)

The easiest thing to do would be to apply the pulses to an audio amplifier/speaker, to get the typical "clicking" output associated with a Geiger counter.

If you want to actually determine counts per minute, you will need some type of electronic counter circuit. This could be a simple analog integrator driving a moving needle meter, or a true digital counter.

If you want to be able to distinguish between alpha/beta/gamma, you need to place different shields over the tube window. Placing a thin aluminum foil over the window will block alphas, allowing beta/gamma only, and a thicker metal shield will block betas, only allowing the gammas through. A standard GM tube will not detect neutron radiation, you need a special type of tube for that.

EDIT: what do you think it's worth?

Probably a couple hundred dollars. At $5 each, you stole it!

 

[ghost]

The circuit shown will produce sharp negative-going pulses at the "signal" output.



Ground would be the metal case, the high voltage (through the 3.3M resistor shown in the diagram) would go to the small metal cap.



The easiest thing to do would be to apply the pulses to an audio amplifier/speaker, to get the typical "clicking" output associated with a Geiger counter.

If you want to actually determine counts per minute, you will need some type of electronic counter circuit. This could be a simple analog integrator driving a moving needle meter, or a true digital counter.

If you want to be able to distinguish between alpha/beta/gamma, you need to place different shields over the tube window. Placing a thin aluminum foil over the window will block alphas, allowing beta/gamma only, and a thicker metal shield will block betas, only allowing the gammas through. A standard GM tube will not detect neutron radiation, you need a special type of tube for that.



Probably a couple hundred dollars. At $5 each, you stole it!

Oh wow this is pretty cool. I know selling it would be the SMART thing to do, but I want to try building my own geiger counter! Oh and wouldn't a piece of plexiglass be better for blocking beta emissions? Then you don't have to worry about the thickness of the metal?

At this point, if I could get a circuit that "clicks" when it is exposed to radiation, I'd be thrilled. So if I hook up around 900V as specified in the datasheet, where would I hook up the audio amp and speaker? Also, any suggestions on the specific audio amp or speaker?
And to get 900V, I guess I just have to build a circuit with a transformer or look up some high voltage power supplies online? Any suggestions for a circuit? For testing, my school has a bunch of kilovolt power supplies I can use (they go down to about 0.5 kvolt). But to make it portable, I guess I'd have to do some googling....

Thanks!!

 

[SCE to AUX]

There is a good article (including a schematic) on building a basic Geiger counter available here:

https://www.imagesco.com/articles/geiger/01.html

You will need to make a few modifications to suit your particular tube. In particular, you will need to add a stage or 2 to the voltage multiplier in the HV supply(or use a transformer with a higher output voltage), and add 2 more 1N5281 zener diodes to the regulating string (their tube needs 500V, rather than 900V). Running the HV supply directly from the 9V battery rather than the 5V output of the 7805 would help boost output, as well. I would use the LND recommended 3.3M resistor in the anode circuit (rather than the 10M that the schematic shows).

At any rate, their schematic should provide a good starting point for a design. It gives an idea of how to build a suitable HV supply and audio chain.

https://www.imagesco.com/articles/geiger/schematicl.jpg

About the only part in that schematic that isn't readily found would be the HV transformer T1. Suitable transformers would be found inside a discarded photoflash, or even a flash from a single-use disposable camera.

Do you have a suitable radioactive source available to verify that the counter is working? If you are headed back to that store anytime soon, would you be willing to pick up a couple more tubes? Would gladly pay you a few $ over cost + shipping to get one for my own use...

 

[ghost]

Thanks for the links!
My high school has several radioactive samples I can test it with (alpha, beta, and gamma emitters). They also have a few professional geiger counters so I could test it with those.
Next time I'm at the store I'll buy a few more of them. I'll def give it to you for $5 (cost of it) + shipping.

 

[bobkrech]

Oh wow this is pretty cool. I know selling it would be the SMART thing to do, but I want to try building my own geiger counter! Oh and wouldn't a piece of plexiglass be better for blocking beta emissions? Then you don't have to worry about the thickness of the metal?

At this point, if I could get a circuit that "clicks" when it is exposed to radiation, I'd be thrilled. So if I hook up around 900V as specified in the datasheet, where would I hook up the audio amp and speaker? Also, any suggestions on the specific audio amp or speaker?
And to get 900V, I guess I just have to build a circuit with a transformer or look up some high voltage power supplies online? Any suggestions for a circuit? For testing, my school has a bunch of kilovolt power supplies I can use (they go down to about 0.5 kvolt). But to make it portable, I guess I'd have to do some googling....

Thanks!!

Be very carefull with kilovolt power supplies. They can be lethal if they generate a lot of current. You really should use a low current, high voltage battery powered power supply. The supplies below are suitable but the directions need to be followed exactly. (You need to have a capacitor and resistor in parallel across the outputs to stabilize operation and load the output.)

https://www.picoelectronics.com/dcdclow/pe65.htm

Part number 5AV900 [5+/-0.5 Vdc in, 900 Vdc out] would work well with (4) NiMH batteries.

These detectors use low current. - max current < 300 microamps at 1 KV using the recommended resistance values shown on the datasheet.

https://www.lndinc.com/products/389/

When ionizing radiation breaks down the gas in the tube, the tube becomes conductive and generates an output pulse. The pulses sent to headphone or small speaker will an audio indication of the activity. Put a 50 uamp current meter in series with the speaker and you'll have a visual indication as well.

https://www.allelectronics.com/make-a-store/item/PMD-50UA/50UA-DC-PANEL-METER/-/1.html

Here's a plan you can modify to make your detector usable. https://www.imagesco.com/articles/geiger/01.html

Bob

 

[ghost]

Ok then a kilovolt power supply might not work (though we do have all the proper safety equipment).

Those DC-DC converters look great, except for the price I have experience with modding the flash circuit in disposable cameras, but that only produces ~300DCV. Is there a cheaper way to get 900V from battery power?

So it seems like if I have the power supply, I can hook it up following the geiger-muller tube's schematics, and then just attach the current meter on the ground wire on either side of the resistor.
This seems relatively simple.

Am I missing anything?

Thanks!

 

[SCE to AUX]

The schematic I posted shows a circuit containing 2 diodes (D2, D3) and 2 capacitors (C4, C5) on the secondary side of the step-up transformer T1. This configuration is known as a voltage doubler. By adding additional diodes and caps, you can achieve even higher degrees of voltage multiplication. Such circuits are called Cockroft-Walton multipliers, and are commonly used to generate very high voltages for everything from bug zappers and CRT type TV sets to huge particle accelerators and X-ray machines.

https://home.earthlink.net/~jimlux/hv/cw1.htm

A battery powered photoflash works by chopping the DC from the battery into pulsating AC, and then driving a small stepup transformer to generate 2-300 V for the flashtube. The Geiger counter schematic I posted works the exact same way. The 4049 inverter is set up as an oscillator (U1A and U1B), which feeds an inverting buffer (U1 C+D) which drives the primary of the T1 transformer through the MOSFET Q1.

To modify a photoflash, I would disconnect the circuitry (rectifier, capacitor, "ready" light, trigger coil, etc.) from the secondary side of the DC-DC converter transformer, and use the transformer secondary to supply AC to a 3-stage multiplier. A photoflash may contain a lot of other circuitry that you won't need/want, so you might want to just salvage the tiny stepup transformer from the flash, and use it to build something like the posted circuit.

A 3 stage voltage tripler on the output side of a photoflash transformer should get you somewhere in the 1kV range without a problem. You actually want the no-load voltage to be higher than the tube will require, because you will be regulating it down using a shunt string of zener diodes.

If you end up using a photoflash as the basis of your power supply, you need to make sure to REMOVE the main energy storage capacitor (discharging it carefully before handling, of course). A Geiger tube does NOT need a power supply that stores a lot of energy, and leaving the photoflash capacitor in creates a needless hazard. The capacitors in the tripler circuit will provide sufficient filtering for this application.

 

[ghost]

The schematic I posted shows a circuit containing 2 diodes (D2, D3) and 2 capacitors (C4, C5) on the secondary side of the step-up transformer T1. This configuration is known as a voltage doubler. By adding additional diodes and caps, you can achieve even higher degrees of voltage multiplication. Such circuits are called Cockroft-Walton multipliers, and are commonly used to generate very high voltages for everything from bug zappers and CRT type TV sets to huge particle accelerators and X-ray machines.

https://home.earthlink.net/~jimlux/hv/cw1.htm

A battery powered photoflash works by chopping the DC from the battery into pulsating AC, and then driving a small stepup transformer to generate 2-300 V for the flashtube. The Geiger counter schematic I posted works the exact same way. The 4049 inverter is set up as an oscillator (U1A and U1B), which feeds an inverting buffer (U1 C+D) which drives the primary of the T1 transformer through the MOSFET Q1.

To modify a photoflash, I would disconnect the circuitry (rectifier, capacitor, "ready" light, trigger coil, etc.) from the secondary side of the DC-DC converter transformer, and use the transformer secondary to supply AC to a 3-stage multiplier. A photoflash may contain a lot of other circuitry that you won't need/want, so you might want to just salvage the tiny stepup transformer from the flash, and use it to build something like the posted circuit.

A 3 stage voltage tripler on the output side of a photoflash transformer should get you somewhere in the 1kV range without a problem. You actually want the no-load voltage to be higher than the tube will require, because you will be regulating it down using a shunt string of zener diodes.

If you end up using a photoflash as the basis of your power supply, you need to make sure to REMOVE the main energy storage capacitor (discharging it carefully before handling, of course). A Geiger tube does NOT need a power supply that stores a lot of energy, and leaving the photoflash capacitor in creates a needless hazard. The capacitors in the tripler circuit will provide sufficient filtering for this application.

I'm building the circuit right now.
I took a flash camera, and I removed the cap. The place where the cap used to be seems to be outputting aroun 1000V (it's jumping around on my multimeter).
So the cap obviously HAD a positive 1000V lead and a ground (0V) lead.
Using this schematic: https://www.lndinc.com/products/389/
It shows 3 connections - 2 high voltage leads and one ground wire. Where do I get the ground wire from? Should i connect it to that same 0V wire I'm using for the HV lead?

 

[ghost]

And where do I attach the millamp meter (analog)?

 

[SCE to AUX]

The node marked "HV" (free end of the 330K resistor) in the LND schematic goes to the positive output of the HV supply. You have it connected to the negative on yours.

The negative side of the power supply goes to the case of the tube. The schematic assumes the HV power supply is referenced to ground.

The "signal" node (free end of the 50pF cap) is where the output pulses will be present. It does NOT connect to the power supply. Make SURE that this capacitor has a voltage rating at least as high as the HV supply voltage!

You may need to adjust your HV supply down to the recommended 900V to get proper operation. A Geiger tube operates right on the edge of self-breakdown, and excessive voltage may result in the tube self-firing or failing to quench between pulses. Operating the tube in continuous ionization mode will ruin it in a very short time.

There is no place in the LND circuit to directly connect an analog meter. To use an analog meter, you would need to connect the input of some sort of amplifier and integrator circuit to the "signal" node, and connect the meter to the amplified output.

About the only thing that you can directly drive with the LND circuit is an oscilloscope or a high impedance (crystal) headphone or earphone. A modern type voice coil headphone will NOT work here. Whatever you use, it connects between the "signal" node and ground (negative end of HV supply).