Star Safari Observatory has a Muon Detector made by mDetect. The detector consists of two stacked scintillators that record coincident events. Muons are the product of cosmic ray interactions with atoms in the upper atmosphere. Muons are similar to electrons but about 200 times heavier. Cosmic rays come from very distant events in the universe, like supernovae and supermassive black holes.

The graphs display the muon detections, which are higher-energy than the other background radiation detections. To isolate the muon detections, the raw data has to be corrected for temperature drift in the detector. The ambient temperature affects the amplitudes measured by the detector. The most pronounced effect is in the top detector. To reduce the impact of this variation, the lower detector is used to select which coincident events are most likely to be muons.

The top graph shows the rate of coincident events happening every minute. Coincident events are flashes detected simultaneously in both scintillators. The events have been selected to include only muon-related amplitudes, and the plot covers 7 days. The daily variation is mainly due to environmental temperature and pressure effects.

The second graph is a longer-term plot of the rate of muon detections since the detector was switched on (and a small gap where I accidentally turned it off – that’s the first big decrease in rate on the left side of the plot). The aim of this plot is to see if there is any long-term variation.

The third two graphs show a histogram plot of the coincident events in scintillators A and B. These scintillators are stacked on top of each other. The first peak in the graph corresponds to non-muon events, which are primarily background radiation detections. The second bump is the muons.

The last two graphs show barometric pressure and temperature. The rate of muon detection is influenced by barometric pressure and, to a lesser extent, temperature. 

The final graph shows all the data collected so far, overlaid and stacked into a single 24-period graph. It shows the variation in muon rate over a day. Now that most of the detector-based variation has been removed, this plot is now quite flat.