A low-cost cosmic muondetector

The core of the muondetector consists of a Raspberry Pi mini computer combined with a u-blox NEO-M8 GNSS module. They are coupled to a plastic scintillator, which acts as the active sensor material and a SiPMs for light detection.

The software is designed to be user-friendly. It takes care of synchronizing the accumulated data with a central server, requiring minimal effort from the user. Nonetheless, a graphical user interface allows to precisely control and debug the muondetector if desired.

Make sure to check out the Mediawiki if you are interested in more background information.

Time accuracy of tens of nanoseconds

The "timemark" feature of the u-blox NEO-M8N GNSS module allows the muondetector to reach a time stamping accuracy of several tens of nanoseconds. The high time resoltuion is benefitial for correlating events in multiple individual detector units.

Hardware

Plastic scintillator

The plastic scintillator is the active sensor material of the muondetector. When charged particles like cosmic muons pass through the detector, they may excite electrons of its scintillating material to higher but unstable atomic energy levels. The de-excitation of the atom leads to the emission of light, which can then be detected by the SiPM.
To avoid any influence on the measurement caused by ambient light, the system has to be impermeable to light which is why the plastic scintillator is wrapped in reflective foil (Teflon + VM2000) and black tape.

SiPM and preamplifier

The SiPM (short for silicon photomultiplier) detects the light generated by the plastic scintillator. It is a pixelated matrix of photodiodes, which are semiconductor devices used to convert light pulses to an electrical current. The response of the individual pixel cells are added discretly to form the output signal. Since this signal amplitude is rather small, an additional preamplifer is needed to increase the SiPM output before it can be processed by the custom board.

Custom board

The printed circuit board (PCB) is designed as a plug-on board for the Raspberry Pi and features all necessary electronics to measure muons with high precision timestamps.
There are two individual input channels on the MuonPi board, so the measurement can be performed with up to two detectors. It provides the necessary voltage to run the preamplifier and SiPM sensor.

Raspberry Pi

We use a raspberry pi to control all components on our custom board via i2c, uart and gpio.