Decode Cosmic Ray, One Muon At a Time
I built a Compact Cosmic Ray Muon Detector for my undergraduate research project. It can “capture” muon particles from cosmic rays and display statistical information to the small OLED screen. It can also perform muon coincidence detection with two different photon sensors.
This blog series aims to document my research journey and share my relatively limited knowledge about muon and particle detection.
Why Do We Care About Muons?
Source of Muon
When cosmic rays, high energy astrophysical particles, collide with the Earth’s atmosphere, muons are formed as indirectly decay products.
Let’s back up a bit, where does cosmic ray come from?
Supernova explosions of stars produce most cosmic rays in the galaxy and travel through space at nearly the speed of light. “About 90% of cosmic rays are protons, 9% are helium nuclei, and the remaining 1% are heavier nuclei.” (CosmicWatch, 2017) As the nuclei of the atmosphere and cosmic rays interact, a scatter of particles is generated consisting of pions and kaons — ancestors of the muons.
Mean Lifetime
As cool as it may sound, due to the volatile nature, muons are destined for decaying to an electron, a neutrino, and an anti-neutrino. The mean lifetime of muon particle is approximately 2.2 microseconds, much longer than many other subatomic particles.
Provided that the formation of muons after a collision happens at the altitude of 10 kilometers above the Earth’s surface, the probability of muons’ survival and reaching detector on the Earth surface is miniature, according to theoretical calculations of Galilean relativity. However, relativistic time dilation prolongs muons’ lifetime because of their creation at high energies. Therefore, Earth-surface detectors are able to “capture” them, thanks to their relatively longer survival duration.
What Do Muons Tell Us?
Abundant information can be extracted from the study and detection of muon particles. As they are direction-dependent, muons’ detection can further scientific research about the origins of these particles. While 90% of muon creation can be explained via supernova or solar energy, the remaining source remains a mystery (Wikipedia, 2020). There exists the speculation of dark energy producing cosmic rays. In the education end, such detection serves as an effective tool to study relativistic time dilation.
Muon Detection
Detection Process
The first stage of the muon detector is the scintillating material. Such material absorbs muon’s partial energy and converts it to photons when a charged muon hits the scintillator.
A silicon photomultiplier (SiPM), a light-sensitive sensor, is used to capture emitted photons and output an electrical signal — a pulse that represents the muon’s energy.
An electronic system, which comprises a voltage amplifier, peak-holding circuitry, and a microcontroller unit (MCU), is built to process such output pulses for extracting insights. The pulse’s amplitude determines the number of photons generated, and the instance of the pulse capture conveys the timing of muon incidence.
Existing Solutions
IceCube
With international collaboration among 300 physicists from 52 research institutions representing 12 countries, the IceCube Neutrino Observatory — located at the South Pole in Antarctica — is the most cutting-edge detector to observe cosmological events and study astrophysical sources, such as supernovas, gamma bursts, black holes, and neutron stars. IceCube also probes cosmic rays interacting with the Earth’s atmosphere to examine muon’s behavior and unveil fascinating discovery about the cosmos.
The IceCube lab was constructed to serve elaborated scientific research and push the boundary of human knowledge. Due to its complex design, large-scale infrastructure — extremely lab-oriented and immobile — is needed to support and maintain its operation. It also requires enormous energy, powering a plethora of gigantic photomultiplier tubes and their corresponding electronics. Overall, an excessive funding source is demanded to keep the lab functional and operative
CosmicWatch (MIT Physics Project)
A few years ago, a group of graduate researches and scientists from MIT came up with a simple and DIY solution — CosmicWatch — to “catch” falling muons.
This $100 detector can be constructed with off-the-shelf components, such as plastic scintillator, silicon multiplier, and fabricated in the university’s widely accessible electronics shop. Its prominent feature is battery power, thus a portable device to observe interesting physics phenomena.
The device can track when a muon particle hits the detector and displays how many times it has been hit on the OLED screen. However, solely for educational purposes, the design is too simplistic for more advanced physics experiments and research, including timing and energy resolution and coincidence measurement.
Our Solution to Bridge the Gap — Educational & Research Purposes
As existing solutions fall short on both educational and research purposes, we bridged the gap by introducing the Compact Cosmic Ray Muon Detector.
We redesigned the muon detector with the following criteria:
· Compact:
With the advancement in silicon multiplier and scintillator technology, small-size components are utilized to significantly reduce the size of the detector.
· Portable:
Operated as a standalone unit, our detector can be taken to field trips and installed in remote areas due to its mobile nature.
· Low-noise:
Advancement in integrated circuits and printed circuit boards can reduce noise and interference.
· Low-power:
Our detector can be powered via small batteries or mobile power bank.
· Flexible:
The system can be configured to perform different tests and experiments. For example, timing and energy resolutions.
· User-friendly:
Out detector is easy to assemble and interface. It has the potential to serve as an educational platform to benefit other college students, professors, and researchers.
Part 2: From Muons to Electrons is now public.
I’d like to receive your feedback, comments, and inquiries. Please drop me a message on Linkedin, with a 100% response rate.
References
CosmicWatch. (2017). CosmicWatch. Retrieved July 07, 2020, from CosmicWatch: http://www.cosmicwatch.lns.mit.edu/about#:~:text=About%2090%25%20of%20cosmic%20rays,the%20progenitors%20of%20the%20muons.&text=As%20a%20result%2C%20muons%20can%20survive%20to%20be%20detected%20on%20Earth.
Wikipedia. (2020, July 03). Wikipedia. Retrieved July 07, 2020, from Wikipedia: https://en.wikipedia.org/wiki/Muon#Muon_sources
Figure 1 Source: http://www.scienceinschool.org/sites/default/files/articleContentImages/14/cloud/issue14cloud5_large.jpg
Figure 2 Source: https://www.ahmadabdulnasir.com.ng/category/physics/?page=3
Figure 4 Source: https://icecube.wisc.edu/science/icecube/detector
Figure 5 Source: http://www.cosmicwatch.lns.mit.edu/about
