COSMIX is a project developed at CEN Bordeaux-Gradignan aiming at providing high-school teachers with easy-to-use atmospheric-muon detectors. These detectors enable one to simply and quickly evidence the existence of cosmic rays. They take advantage of the recycling of Cesium iodide scintillator logs (CsI) and their associated electronics, used for tests preceding the launch of the Fermi satellite in 2008. Each detector is robust, light, easily transportable in a small case and only requires USB for its power supply. The scintillation light created by a muon passing through the bars is collected by a photodiode converting it into an electronic pulse, which is then amplified via dedicated circuits. The pulses from the bars can be visualized by an oscilloscope available to most high schools and the single and coincidence counts are displayed on a small screen, driven by an Arduino microcontroller. The counting is recorded on a simple SD microcard, together with the data from a GPS, an altimeter and a thermometer. The bars detect approximately one muon per second each. The basic experience, aimed at proving that the highly-penetrating detected particles have close-to-vertical trajectories, is very simple. When the bars are sitting side-by-side, coincidences, due to the same particle passing through the two bars, are very rare (about 1% of all counts). When one bar is placed on top of the other, the rate increases to about 40 %, proving that the particles come mostly from above.
The recorded data can be used for assessing the attenuation provided by concrete or rock shielding (in a building basement or a tunnel) or the enhancement related to higher altitudes (on a mountain top, an airplane or a balloon).
A total of 51 detectors have been built over the years. About half of them circulate in high-schools, located mostly in France but also abroad (Spain, Switzerland, Canada, Vietnam…). The other detectors are used either for education at colleges/universities or for outreach activities at research facilities.