Muon Camera

Using muons created by cosmic rays to see into pyramids, mountains, collapsed mines, damaged nuclear reactors or active volcanos.

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Surprisingly, using muons to see into large dense objects like pyramids and nuclear reactors is not a new idea, but they are very expensive and complex devices not easily accessible to researchers and emergency agencies. Building muon detectors is something I've been doing successfully for over 8 years and so I thought I'd like to give this a go. Recently, I'd been developed a low-cost solid-state muon detector using available components and voltage summing coincidence methods in order to reduce the cost for my Cosmic Array project and realised this same method could be used to make a virtual collimator, similar to how the Ommatidium functions in a compound eye of an Arthropod.

Fast moving high energy muons created in the upper atmosphere by cosmic rays rain down across the entire surface of the surface of the earth. They do this continuously at approximately 200 muons per second, per square metre across the entire surface of the earth. When counting muons over time the average flux is nearly uniformly and isotopic varying little over time, other than small gradual variations due to the solar magnetic cycle every 11 years.

Muons lose their energy gradually, as they have little mass and travel nearly at the speed of light 0.98c meaning they can travel through large amounts of matter before being stopped.  When averaging muon flux over time from a specific direction, it is unlikely to be any different from any other direction. Except where it is passing through different densities of matter like a mountain.  

The heart of the muon camera are low-cost Si Pin Photodiodes commonly used in low cost geiger counters.  However, the Si Pin Photodiodes are stacked in an array to create a collimator that amplifies muons detections coming from one specific direction. 

It does this using an array of 8 detectors that are enclosed in copper shielding to reduce background radiation, rfi and other interference.  This creates a virtual collimation effect as each Si Pin Photodiode is stacked one above the other, where the signal from each is added together using a voltage summing operational amplifier.  

Consequently, when a muon travels directly through the entire length of 8 detectors they will be triggered simultaneously, and so will have the highest signal amplification.  Whereas, muons or local background radiation passing through at other angles will have a lower signal and so can be filtered.

Similarly a single element in the compound eye of an arthropod focusing light from one direction on the ommatidium where as light from other angles is absorbed by its dark sided walls.

An array of 16 virtual collimators each grouped together to form a simple compound eye camera will be the first test. Increased to 32 depending on the results of field testing.

The image will be created based on the summed count rates of each virtual collimator spanning a number of week/days for a specific elevation angle and location coordinates.  Possible caverns or thick dense material concealed within a mountain may result in lower count rates than the surround detectors or in different locations and/or elevation angles. 

This design is not solely limited to use as the AMC: 

  • As it could also be used individually as a single cosmic ray telescope.  
  • In a small coincidence bundle like I have used in my Cosmic Array art project  ( the impetus that created this new design).
  • In other linear array configurations using raster scanning methods or,
  • Meridian drift scanning for an "all of sky" muon mapping. 

The design also lends itself to be arranged into a flat matrix of Si Pin Photodiodes and used as a beta, gamma and X-ray monitoring.  Also enhanced with the use of larger aperture Si Pin Photodiodes and/or scintillators. Consequently suitable for gamma ray spectroscopy.


Low-cost Si PIN photodiode with 7.7 mm2 sensitive area.

Adobe Portable Document Format - 151.03 kB - 04/17/2018 at 06:08



Dual Ultra Low Noise Wideband Operational Amplifier

Adobe Portable Document Format - 2.04 MB - 03/18/2018 at 09:01


  • 8 × TEMD5080 Low-cost Si Pin Photodiodes with 7.7 mm2 sensitive area.
  • 1 × LMH6624 Ultra Low Noise Wideband Operational Amplifier
  • 1 × TinyFPGA A1 TinyFPGA boards are a new series of low-cost, open-source FPGA board
  • 8 × 200mm x 20mm Dia Copper Tubing Light-proof shielding for array stack

  • A very big project indeed

    Robert Hart08/12/2018 at 01:00 0 comments

    Although I'm optimistic that it is possible to build such a muon camera.  The project is much bigger than I imaged, despite the small aperture size the cost and time required.  This project is significant and so I'm unlikely to have this project close to operational any time soon without additional free time, financial and complex, FPGA, software development support.  Here is an overview.

    Along with the above compound muon camera there will also need to be precision GPS location and time stamping information as more than one location and camera will be required to provide suitable resolution.   

  • Preparing for prototype build array element

    Robert Hart04/23/2018 at 11:35 0 comments

    After building many, breadboard, ratnest and prototype designs to test out a number of different approaches. It's become very clear that I need to knuckle-down and start developing a number of PCB prototypes on a multilayer pcb using all SMD components. 

    As both the input impedance and gain required on each Si Pin Photodiodes is extremely high and so not only is noise an issue including feedback, crosstalk and vulnerable to RFI, it is also affected by static electric fields. This will becoming an even greater problem when arranged in a multi element array.  

    From my last project experience I found that although the PCB CAD package I was using was fast, very easy to use and free, I couldn't import component footprints CAD files nor export Gerber pcb files.  Meaning I had to a number of custom footprints and could get competitive pricing when needing to have multiple PCBs manufactured.  As will be the case again for this project I'm making a move over to KiCad EDA.  The disadvantages are learning a new CAD package but so far so good. 

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Marcin Wachowiak wrote 07/23/2018 at 19:28 point

An amazing project! I'll keep my fingers crossed for your success. Hope you achieve best performance. Do you intend to use LMH6624 as a transimpedance amplifier?

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Robert Mateja wrote 04/19/2018 at 19:38 point

Mr.Alvarez would be proud.Keep cool project going!

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Robert Hart wrote 03/17/2018 at 10:02 point

Thank you David it should be interesting to try :)

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David H Haffner Sr wrote 03/16/2018 at 16:32 point

Wow! I really hope U get this project up and running, this is completely facinating :)

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