mbed Cosmic Ray Detector

I'm currently working on an mbed based data acquisition system for a scintillator + silicon photomultiplier cosmic ray / radiation detector. Hopefully this will result in a portable, low cost device that could be used in ground based or high altitude experiments.

Basic Design

When a high energy charged particle goes through the scintillator a small amount of light is emitted. This is detected by a silicon photomultiplier, resulting in a 10 mV, 25 ns pulse. An opamp is used to raise this signal to 50 mV. A fast comparator is used to trigger when the amplified photomultiplier signal raises above a comparison voltage which can be set by the mbed's AnalogOut pin. The comparator triggers a monostable which gives a 3.3 or 5 V pulse that is a few microseconds long. This pulse can be used to interrupt the mbed or could be used for triggering a coincidence between multiple photomultipliers, which in turn could interrupt the mbed.

In the initial design the mbed will just set the comparison voltage and count the triggers in a given time period. The trigger rate will then be sent over USB serial for logging on a PC. Planned upgrades include storing the data to an SD card, controlling the power power supply for the silicon photomultiplier, transmitting the data to another microcontroller (such as a flight computer), transmitting data over ethernet, time/position tagging the triggers using GPS, etc.

Status

I'm currently testing my prototype comparator/monostable circuit board and running some preliminary experiments to show that the detector is working.

I update my Monday Geekery G+ page at least weekly with the current status and developments.