Pocket Photodiode Geiger Counter

RobMan
Pocket Photodiode Geiger Counter

Detects alpha, beta and gamma rays within its range by lighting an LED and producing a ticking noise as the rays get stronger. Uses a photodiode instead of an expensive Mueller tube. Helps to detect harmful environments, but not recommended for extreme cases.

COMMENTS

user
Shyam (Jul 22, 2012)

Large area about 10mmx10mm PIN photodiodes with Scintillator coating on top can sense Cosmic Radiation and also man made radiation. However, electronics is not easy as charge or bunch of electrons that form pulse are very low and thermal noise at room temperature is high, and diode leakage current run into 100s of pA which makes it very difficult. I think people already having good electronics background can try such idea. Sources for such PIN diodes are companies like Hamamatsu Japan, Detection Technology Finland, IRD Inc USA (www.ird-inc.com). etc. You can't pick up some photodiode and get results. It is very tricky business and highly professional companies manufacture these items. I will say good luck if you wish to try these.. PIN Detectors cost about US$100 plus. and then sensitive electronics may also cost that much and one also requires some kind of metering device. like pulse counter with displayor count rate meter etc. It should be expensive project and chances of success depends on material and how you make it. I am in this line and have about 1000 such detectors that work well but they are expensive. Working with GM Tubes is simple but they require high voltage 400-500V and are bit unsafe as they can give shock. One can purchase from LND Inc USA or Philips etc.

user
RVAWEB (Jun 14, 2012)

Need to see more, can we move forward, how many votes are needed?

user
lenright (Jun 24, 2012)

I need more info on TIA, not familiar with this device, 30v reverse bias? I do not understand the reverse bias trick, probably de-sensitices the diod, does the Diode end up on a knee close to break down?

user
koosh (Jun 26, 2012)

The TIA is a transimpedance amplifier circuit. It is the op-amp which converts the very small current pulse from the photodiode into a larger voltage pulse output. Reverse biasing the diode decreases its capacitance by increasing the thickness of the depletion layer. It allows you to parallel multiple diodes, and/or achieve a higher bandwidth.

user
koosh (Jun 13, 2012)

A few suggestions that I learned building one of these myself: Use a well-soldered metal shield to entirely enclose the photodiode (array) and transimpedance amplifier to avoid swamping the signal with noise. Make sure the PCB is thoroughly cleaned after soldering, since any residue near the TIA will leak current and mask your signal. Use a guard ring around the high-impedance node to further shield it. Use three or more resistors in series rather than one for the large TIA feedback, to reduce parasitic capacitance which will otherwise limit your bandwidth and TIA gain. Buy a check source (United nuclear sells a bunch) for testing. Cs-137, Eu-152, and Co-60 work pretty well. Am-241 from a smoke detector produces a very low energy gamma which is close to the noise floor of the circuit, and challenging to detect. You can significantly increase bandwidth and the active volume in the detector by reverse biasing the diode by 30V or more. If you do a good job, you'll even be able to estimate the energy of the particle by measuring the height of the output pulse. Good luck! It's a fun project.

user
Wolfstone (Jun 05, 2012)

The mantle from a white gas lantern (e.g. Coleman) usually contains Thorium, an alpha emitter.

user
Crumpite (Jun 05, 2012)

Aluminum foil is too thick/dense to let alpha's through. You'd need something like radfilm which is expensive and hard to find. You'll likely need something conductive to shield the diode to keep hum pickup down. I had to build mine in a Altoids box and use Al foil over a hole to keep hum down so the circuit would work. Also, unless the diode has no covering over the bare silicon surface, it will filter out the alpha's anyway... Also, I wouldn't recommend using the Am241 pit from a smoke detector for any testing. You can do it, but it's very, very illegal to do. If you put that into your instructions, I'm quite sure you'd get unwanted attention from the authority's ! A piece of uranium ore would work quite well and is inexpensive and legal.

user
Xanatos (Jun 05, 2012)

Is this the one that uses the BPW34 or 61? I've tried to breadboard this one but I think the interlead capacitance around the LM358 kills it... Looking forward to seeing if we're working from similar schematics. I may just have to go ahead and PCB this one.

user
Shyam (Apr 11, 2013)

Most important factors are Dark current <100pA @ 25C is normally OK Charge generated in the sensitive layer and charge collected <100pF capacitance for 1cmx1cm area is normally OK. Ti OPA129 or AD549LH of ADI <100fA bias current amplifier are great Smnall amount of CsI:Tl Scintillator layer abouve Photodiode is good. Use Charge Injection reverse bias mode for pulse counting Use photodiode or photo cell mode for DC- Current measurement Vishay photodiodes are not meant for such purpose. They have small area too much dark current and large capacitance. More to be answered by the kit designer, however if anyone has a question then write to me as I can't often see this club discussions very frequently. Dr. Shyam www.sensorstechnology.com/

user
Luther (May 16, 2012)

Does the photodiode get a cover? If so what is it? Is it transparent to Alpha, beta, and Gamma rays yet opaque to near IR and visible light? Or do you just use it in a dark room?

user
user ClubRob (May 16, 2012)

I haven't completed it just yet, but the photodiode might be covered with aluminum foil. Beta particles should be able to get through easily as well as most alpha particles (hopefully). Anyone know any good household appliance to test this with?

user
WarSpigot (May 20, 2012)
@ClubProRob
First thing that comes to mind is a smoke detector if you can find the Americium. It's probably a pretty small amount of radiation though. From Wikipedia, it looks like a lot of things that are "permanently illuminated" without batteries use tritium, which emits beta particles.
user
Shyam (Apr 11, 2013)

Photodiode must not be covered for beta rays or electrons and for Alpha ZnS coating on top can help in converting charge to light. For X-rays and gamma rays white reflective paint is oftem applied to seal the external light and reflect back internal light photons generated by any scintillation process if scintillator is used. .

user
Kelvin (May 15, 2012)

I built one about 35-40 years ago. Worked well; very compact. Large-area photodiode was expensive and hard to find, and required risky modifications to the TO-5? package, to be capable of detecting alpha radiation. I still have the schematic, etc. somewhere in my files.

user
FredW (May 15, 2012)

Are you going to make this project available in a schematic?

user
user ClubRob (May 16, 2012)

Yes, there will be a schematic available. It's pretty straightforward and only requires a few components

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captainron (Jun 24, 2012)

Could it be waterproofed and adapted for marine aplications? check out my ROV brief

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RHAYASHI (Jul 06, 2012)

ebay has Geiger-Muller tubes SI3BG for $50

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CodeDalek (Jul 06, 2012)

I have a bunch of SI3BG Russian glass tubes. They do not seem as sensitive as the old Lionel CDV-700 tubes. I have some rocks that I can detect radiation with a CDV-700 but not the Russian tubes in the Chinese circuits.