Turn your smartphone into a cosmic ray detector

Researchers from the University of Wisconsin-Madison (UW-Madison) have developed a smartphone app that can turn Android phones into detectors to capture the light particles created when cosmic rays crash into Earth’s atmosphere. The project was led by Justin Vandenbroucke, a UW-Madison assistant professor of physics and researcher at the Wisconsin IceCube Particle Astrophysics Center (WIPAC).

Cosmic rays are energetic subatomic particles, believed to be created in cosmic accelerators like black holes and exploding stars. When the particles crash into the Earth’s atmosphere, they create showers of secondary particles called muons. When a muon strikes the semiconductor that underpins a smartphone camera, it liberates an electric charge and creates a signature in pixels that can be logged, stored and analysed.

The smartphone project, known as DECO (Distributed Electronic Cosmic-ray Observatory), includes a data logger and the DECO app. After downloading the app, the user should cover their phone’s camera lens with duct tape. The phone can then be placed screen-up just about anywhere - even in a desk drawer, as muons can penetrate matter much like X-rays.

Left running, an idle phone can be set to record an image every couple of seconds. It will then analyse the image and, if enough pixels light up, it gets recorded as a particle event. Particle tracks from both cosmic rays and radioactivity in the environment can be recorded, and events may sometimes be matched to cosmic phenomena detected by more sophisticated observatories. The data logger meanwhile routes event information - time, location and observations - to a central database.

Vandenbroucke said the idea behind the pocket cosmic ray detector is primarily educational. His WIPAC group, with grant support from the national program QuarkNet, plans to engage high-school teachers to develop curricular materials around the use of the detector.

“It would be great to get students and the public interested in gathering data and understanding the particles around them; things they ordinarily don’t get a chance to see,” Vandenbroucke said. He believes that if enough people use their old smartphones to capture muons, the project could one day evolve into a meaningful citizen science initiative.

To download the data logger and app, visit http://wipac.wisc.edu/learn.

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