Solid State Ionising Radiation Detector

Geiger–Müller tubes and Photomultipliers are all well and good but have limitations. Solid State is great but there are other limitations.

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Current project areas I've been experimenting with such as: cosmic ray detectors and x-ray crystallography have relied heavily on Geiger–Müller tubes or photomultipliers and Scintillators as the detector. The issue with using these detectors are a limited life and high voltages between 300 to 1600V DC which must also be low noise and regulated. Further, without going into detail here, there are significant cost issues when using new components and even more so when needing to measure the energy level of the radiation being detected.

Solid state devices particularly Si Pin Photodiodes are capable of measuring both gamma rays and their energy level but also come with their own issues and compromises such as : more complexity, noise, cost and small aperture size. But also have the benefit of low voltage, power, and greater longevity. The aim of this project is to develop a relatively cost effective detector that can measure gamma rays and also offer some energy measu

Low-cost of-the-shelf SiPin photodiodes such as the BPW34F which have been featured in many DIY projects over the years seems the obvious choice. However these require significant amplification, very noisy and very susceptible to RFI. So can only be practically used as a simple gamma counter, with no energy resolution and has very low sensitivity having a very small aperture.

There are also specialist SiPin Photodiodes designed specifically for gamma ray and xray detection, but these are very expensive and difficult to source in small quantities. So the next best candidate are the medium range detectors usually with a 10mm x 10mm aperture. Current detectors I am testing include:

  • Manufacture First Sensor Part # 5014450 - has visible light filter
  • Manufacture First Sensor Part # PS100B-7-CERPINE - has visible light filter
  • Hamamatsu Part # S3590 - no visible light filter

New part : as used in the Cosmic Pi 3x3mm Silicon PhotoMultiplier (SiPM) Manufactured by AdvanSiD - Part number - ASD-RGB3S-P, ASD-NUV3S-P this detector has to be used with a larger plastic or crystal scintillatior.

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sparks.ron wrote 01/05/2017 at 17:10 point

Hi Robert, I am very interested in your project.  A couple of years ago I built a simple detector published by Elektor magazine using the BPW34F.  I had trouble with it breaking into self-oscillation when I hit a launch deadline and dropped the project.  This year I moved to building a Scintillation-PMT unit instead (project on  In response to discussion there I looked into a SiPM but found the cost too high for my tiny hobbyist budget.  For that reason I opted to go with a traditional PMT.
I am not knowledgeable enough yet to understand how to accurately capture the gamma energy levels from the pulses, so I have not finalized any design for the detector electronics.
I have two questions for you: Is there a way to use your approach to measure the pulse energy (relative, not absolute)?  And can you point me to any references on the subject of using the PMT pulse to measure the gamma energy (eV) ?

I wish you the best in your project and its continued success.

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Robert Hart wrote 01/05/2017 at 23:59 point

I understand, the Pin Photo-diodes have their problems with noise and feedback and SiPM costs and scintillators also, I'm working on a cost-effective solution "coming soon", well sort of, as its taking time due to new job and lower budgets.   Have a look at the cosmic pi project it uses a lower cost  SiPM  -  For your traditional PMT/scintillator stuff check out - suplus parts are the quickest way in try 

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fjjablonski wrote 01/08/2016 at 13:09 point

Hi Robert. Is the polarization of the photodiode in the schematics +24 V?  Should it not be -24V?

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Robert Hart wrote 01/08/2016 at 21:23 point

Oops - sorry placed the diode incorrectly in the circuit, I've now corrected it :P  Yes you are correct it would need to be -24V and it would work as  I started that way but then found I had a inverted output, also +24 regulators are more easier to come by than -24V regulators.   

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Brian wrote 01/07/2016 at 03:04 point

Why not use a large single crystal silicon solar cell in a light tight enclosure? Or better yet, a semiconductor with higher density, and therefore higher gamma efficiency, like CIGS, Cadmium Telluride, or Gallium Arsenide? There is no reason the junction needs to be sensitive to optical wavelengths. Stacking the devices gives a larger interaction volume, and a higher chance of gamma ray detection.

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Robert Hart wrote 01/07/2016 at 09:24 point

I really do wish it was that simple, but alas there is a lot more involved.  There is much difference between a gamma ray and optical light as there is to radio waves. So the method of measurement is as vastly different.  Although both a solar cell and photo diode are essentially a pn junction there construction and the way they are used is vastly different almost opposite.  A photodiode is designed to maximize photo current, minimise dark current, noise and capacitance to make it sufficiently fast. While a solar cells are optimized for the maximum conversion of incident light into electrical energy.   Further to increase sensitivity to the fast pulses of ionising radiation the electrical method of detection is not by amplifying anything coming out the cell, but rather applying a reverse bias to the junction and measuring impedance change, so one has to employ all kinds of jiggery pokery electronics to get it to work.

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A. M. Aitken wrote 07/29/2014 at 18:58 point
Should the first part number be 50144501? Should the Op Amp be AD8616?
Where are you getting the sensor prices from?
What is the idea behind the preamp board, it seems to be doubly integrating?

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Robert Hart wrote 07/30/2014 at 10:43 point
Sorry typo 50144501 corrected, the circuit is quite conventional I've tried a few variations and this currently seems to do a good job. The first stage is a charge amplifier the next is Integrator amplifier. I may consider adding more stages and decreasing the gain of each stage to increase pulse detection over the noise floor. Although these diodes are small in the photodiode world they have a large-area which tend to have higher capacitance, which increases the noise gain of the circuit. Similarly, a higher bias voltage means higher leakage current. Leakage current also generates noise. Prices are what I managed to buy them, with fast talking and promises to share results.

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A. M. Aitken wrote 07/11/2014 at 15:28 point
I'm surprised First Sensor is citing ;There is a lot to like about the attempt but it's ruined by some major mistakes and the engineers at First must know that. Fundamentally I don't believe spectroscopy is possible with the X100 at 600kev.

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A. M. Aitken wrote 07/11/2014 at 15:34 point
I should qualify that. I don't believe it's possible with the bare sensor at 600kev. With a scintillator it's certainly possible.

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A. M. Aitken wrote 07/08/2014 at 20:02 point
This is relevant and very cool,
Clicking on the polish version gives some complimentary information.
There is no circuit diagram. Some more details,
I think there is enough information to replicate, I've not tried contacting them yet.

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Robert Hart wrote 07/07/2014 at 23:37 point
Would really appreciate any information you have acquired. I'm interest in detectors in the low xray and high gamma regions.

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A. M. Aitken wrote 07/08/2014 at 17:22 point
What I have is fragmented, several attempts at gathering info over 2 or 3 years. Potentially useful trick for PIN diodes is the parallel plate approximation - divide the number of square millimeters of area by the capacitance in pf and multiply by 117 to get the depletion depth in um. Not reliable for very small area sensors, probably because stray and terminal capacitance dominates. Add the SFH206K to your list to test, I read good things despite metrics.

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Robert Hart wrote 07/07/2014 at 23:31 point
Hi Marvin yes it is very much a skeleton, just sharing, as I have different needs for different projects, and yes you are right it is S3590 (corrected) I was looking at the other for xray use but it was too expensive. I haven't got around to writing anything up, its very much a work in progress, with rat-nest test different amplifier designs and different detectors, so haven't even got around to look at energy calibration at all. This is currently the cheapest choice but am awaiting samples to test.

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A. M. Aitken wrote 07/07/2014 at 16:29 point
Picture looks more like an S3590. How are you testing energy resolution? What are the criteria? What were the mediocre and worst candidates? I'm interested in this project, but right now it's just a skeleton :)

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