CosmicWatch detector makes invisible space particles visible: youtube.com/watch?v=HeaMo__873Y
Making the invisible visible
Photos by Evan Krape and courtesy of Musarate Shams | Photo illustration by Jeffrey C. Chase | Video by Sam Kmiec and Paul Puglisi January 07, 2026
UD physicist’s invention expands our knowledge of the universe, particle physics
You can’t see, feel, hear, taste or smell them, but tiny particles from space are constantly raining down on us.
They come from cosmic rays — high-energy particles that can originate from exploding stars and other extreme astrophysical events far beyond our solar system. When the rays collide with atoms high in the Earth’s protective atmosphere, they trigger a cascade of secondary particles. Among the most important of these new particles are muons, which can pass through the atmosphere and even penetrate into the ground.
An invention by University of Delaware physics professor Spencer Axani called CosmicWatch is putting the science of muons in the palm of experienced scientists and high school students alike.
About the size of a box of animal crackers, CosmicWatch is a particle detector. Made from electronic components that cost around $100, it lights up and counts each time a muon passes through it, storing the data so it can be downloaded and analyzed.
Originally designed as a low-cost educational tool to introduce students to particle physics, CosmicWatch is also used in international astrophysics experiments that are teaching us more about the universe.
“CosmicWatch detectors allow us to do far more physics at a dramatically lower cost, in a compact and portable form, opening the door to many new kinds of experiments and outreach opportunities,” Axani said.
Birth of a detector
Scientists study muons to learn more about some of the universe’s most extreme phenomena, including supernovae, gamma-ray bursts and blazars. Through the muons, scientists can infer the energy, mass and direction of the incoming cosmic ray. This same muon flux also provided one of the earliest experimental confirmations of Einstein’s theory of special relativity in the early 1940s.
Muons can also tell us more about objects here on Earth. Like some superheroes, the tiny particles can pass through solid objects — walls, rock or humans, for example — without causing damage. The energy trail they leave behind makes them ideal for imaging through large amounts of matter that would otherwise be inaccessible. In 2016 muon technology uncovered an unknown corridor in the Great Pyramid of Giza.
But most muon detectors are large and expensive, limiting the kinds of physics experiments that could be done and the number of schools that could use them.
“A typical undergraduate physics lab course uses a rack of electronics about the size of a small bookshelf to measure muons,” Axani said.
Axani created CosmicWatch in 2017 while a graduate student at MIT. He originally intended to build a small, low-power muon detector to be used at the IceCube observatory in Antarctica. IceCube is a huge detector under the ice that tracks neutrinos, another type of subatomic particle. Having a detector for muons helps the scientists filter out which particles are actually neutrinos.
The project morphed into an educational outreach program when Axani realized he could make a portable detector for a low price.
Axani continued improving CosmicWatch after joining the UD faculty in 2022 and just released its third version. Upgrades to the device, which were published in an article in the Journal of Instrumentation in October, allow it to monitor its local environment, withstand high levels of radiation and collect data faster.
“Even though I had studied cosmic rays, I didn't fully appreciate the rich physics behind the working of these detectors to actually ‘see’ the world and atmospheric particle production,” said Masooma Sarfraz, a doctoral student in Axani’s lab and primary author on the journal article. “For a student like me who has been working on theoretical ideas, this was a perfect opportunity to dive into the experimental side. It also connects beautifully to my current broader research work with particle physics.”
The new version is ideal for calibrating large scale detectors and is being used in the NuDot experiment at UD and the Coherent CAPTAIN-Mills (CCM) dark matter detector in Los Alamos, New Mexico. Another version of the detector is being developed to measure primary cosmic rays onboard rockets and spacecraft.
Science in action
CosmicWatch is still being used for education. At UD, Axani uses it to teach students about particle, nuclear and astrophysics. The students build the devices from scratch, learning how to create high-speed electronics, and then use them in experiments they design.
Musarate Shams, a doctoral student in the quantum science and engineering program, customized the CosmicWatch he built, adding temperature and pressure sensors to investigate cosmic rays in the Earth’s upper atmosphere.
In May, his device was launched on a high-altitude balloon that rose to 100,000 feet, just at the edge of space. After analyzing the data, he was able to show how the flux of cosmic rays coming from outer space changes with altitude.
“It’s a very cool thing to build something in the lab in a couple of days that’s able to detect these cool particles from hundreds of light years away,” he said.
UD students aren’t the only ones learning from CosmicWatch. Natasha Holmes, the Ann S. Bowers Associate Professor of Physics at Cornell University, has students in her introductory physics courses build the detectors and use them in experiments, too. She said the hands-on experience of using the device brings the science to life.
“The students seem really excited about doing this thing that is more like what particle physicists and experimental physicists actually do,” she said. “They get to learn some coding with it, and sometimes they break the devices and then we have to talk to them about being careful with your equipment. It’s very different from a typical physics lab. We’ve had students say they’re doing ‘real science’ after using it.”
Worldwide physics
Axani estimated thousands of CosmicWatches have been built since the first version was released eight years ago. He would love to see that number multiply in what he envisions as a global “citizen science” project, where people from around the world monitor muon rates in their locations and transmit it to a central area on the internet.
In the meantime, he’s working on an offshoot of the detector that would make groups of satellites “smarter” by enabling them to communicate with each other about their environment. For example, the detectors would alert the satellites about solar flares so the satellites could power down if needed.
He never imagined that what started as an educational outreach project would one day be used for bigger experiments.
“Although it started as an educational program it’s found a use in a lot of different areas of physics,” Axani said. “It’s pretty cool.”
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