Building Nuclear Reactors @Â Radiant Industries
High-Altitude Muon Detection Balloon
Freshman Project by Team "The Cow that Jumped over the Muon"
A high-altitude balloon was launched with the muon-detection sensor, primarily utilizing a plastic scintillator and a silicon photomultiplier (SiPM), in order to detect muons at varying altitudes in the troposphere and stratosphere. On board the payload, a micro-controller collected the data and sent it to a transmitter, which in turn relayed the data to a ground station.
The Sensor
When charged particles interact with a scintillating material, the electrons of the atoms in the scintillator are excited to a higher energy state. Afterwards, the electrons fall back to their lower energy state, resulting in an emission of an electron. These photons are emitted around the "emission maximum" wavelength, which is determined by the type of scintillating material. A few dozen photons are emitted by the scintillator per muon.
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The silicon photomultiplier is an electrical network of avalanche photo-diodes (APD). When photons interact with a photo-diode, photoelectrons are emitted (thanks to the photoelectric effect), resulting in a minuscule current. These photoelectrons collide with other electrons, creating an avalanche. This results in a measurable current and voltage spike.
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The video to the right demonstrates the output of the sensor, before (blue) and after filtering and amplification (yellow). The small spikes and bumps are due to parasitic capacitance of the breadboard that the circuit was built on.
The Device
The amplified signal is detected by a comparator in the analog-to-digital converter on the PIC. The signal is measured against a threshold value supplied by the DAC. If the comparator returns that the spike was above the threshold, then the program concludes that a muon was detected, and increments the muon count. The PIC then sends the spike count encoded as a PWM signal to the transmitter. The transmitter then AM modulates the data onto a 433MHz carrier wave. The ground station picks up and demodulates the signal.
"Muon detector" is technically a misnomer, as the sensor will pick up any energetic charged particle that can penetrate the electrical tape and aluminum foil shielding. Testing was done in a building at sea level, so the sensor detected a lot of ambient radiation.
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The video (best with audio) to the right demonstrates the entire system. The transmission is picked up on the hand-held transceiver. As the data was encoded on a PWM signal with frequencies in the range of human hearing, the detection of a particle can be heard!
Uranium Tests
Schrödinger's Cat is probably alive. It has 18 half-lives.
We acquired some uranium dioxide. Because the sensor detects any energetic charged particles, it detected the alpha radiation from the decaying uranium.
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The video to the right demonstrates the uranium source placed on the sensor. Note that the spikes on the oscilloscope occur appear at a far greater rate than in the ambient settings in the above videos.
The Flight
After the semester ended, we prepared our and other groups' payloads to be attached to a high-altitude balloon. Then, we drove to an airfield in Eastern Washington to launch the balloon. A base station was set up to acquire the signals from the payloads. A search party later followed the balloon for pickup.
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The video to the right is the balloon and its payloads lifting off.