Altitude dependence of cosmic rays through scintillation detection

Research Group: Moab Croft, Ty Patterson, and Zachary Washburn

Launch: Whitworth Spring 2022

''The goal of our project was to determine the number of cosmic particles that come into contact with our pod every 30 seconds through scintillation detection. Cosmic particles have the potential to interfere with computer software if they have enough energy, and because of this, it is extremely important to collect data on their concentrations within our atmosphere to avoid any future complications. We planned to use 2 scintillators with light sensitive receptors that could measure the quantity and intensity of incidents, but due to problems with the circuitry, we used a LabQuest with a radiation detection component instead that could only detect quantity of incidents. The data showed that the number of incidents increased as altitude increased, ranging from around 20 incidents at ground level to about 300 at a heigh of approximately 78,000 feet. Moving forward and looking at future projects that use the same methods of radiation detection, it would be beneficial to spend more time researching and testing the circuitry components of the design to ensure that the project is functioning.''

Background
Cosmic particles were discovered in 1911 by Victor Hess who made the realization while studying radiation during an eclipse. During the eclipse he realized that the radiation levels did not drop while the sun was obstructed, meaning that another source of radiation was present.

Later, after further experiments, it was discovered that these particles travel through space near the speed of light. They are comprised of atom fragments ejected from the sun or other stars, with those with the highest energy coming from the collapse of supernovae. As they barrel through Earth's atmosphere, they collide with particles and break apart further, losing more energy the closer they travel to the surface.

Previously unnoticed, further studies revealed that cosmic particles were found to have a significant impact on our planet. These cosmic particles have a profound impact on technology, which can lead to issues with sensitive equipment. One well known example is a famous malfunction upon the Voyager 2 space probe. A cosmic particle struck the probe's computers, flipping a single digit in the binary code, resulting in problems with the probe's operations. As humanity progresses closer and closer towards manned, deep space missions, it is extremely important to have a strong understanding of the impact the highly charged particles have on technology, as well as where they can be found, because it can be the difference between life and death.

The discovery of cosmic particles spurred the development of many detectors, with the Massachusetts Institute of Technology having created a publicly-available cosmic ray detector instruction manual known as Cosmic Watcher. We will be testing Whitworth's radiation detection equipment with a plan originally created by a launch group from 2020 named "Adaption of the MIT cosmic ray detector for Whitworth's balloon system," which was heavily inspired by the Cosmic Watcher project. The main piece of equipment being used will be a scintillator, which is a plastic matrix including luminophores suspended in a transparent polymer. Scintillators give off light when muons strike them, and the changes in light will be measured with a SiPM detector. The data collected will include the amount of cosmic incidences(counts of spikes in energy), the average energy levels of incidences, and the standard deviation between the points of interest. This data will be analyzed against the altitude data collected from the command module, allowing us to construct a model comparing the concentration of particles at different altitudes.

Mechanical Design
Our design was meant to be utilizing the Cosmic Watcher - Amplifier and Peak Detector that has been used by many schools and organizations in order to conduct cosmic ray experiments. Although we did not send this part of the system up, we did complete a test design that proved to be unsuccessful. We then switched to a more reliable source of testing by using the LabQuest 2 and its geiger counter attachment to conduct the flight.

Intended Design
Our test design includes the Cosmic Watcher circuity as well as the flight computer containing mbed LC1768 microcontroller, battery pack and control switch. If this design had worked, the pod would have contained the circuit, flight computer, two boxes with scintillators, two PCB connectors, and cardstock shelving to separate the components. The scintillator boxes would be ziptied to the side of the pod with the zip ties going through the walls of the pod to secure the boxes inside the pod. The flight computer would be strapped down in the same way, only it would be laying flat on the bottom side of the inside of the pod. A hole would be cut in the exact shape and size of the control switch through a side wall of the pod to allow the control switch to be manipulated without taking the harness and lid off.

Used Design
The design that was ultimately used was much simpler in terms of assembly and data collection. It involved two components, including a Vernier LabQuest 2 data logger and a Vernier Radiation Monitor. These two components were attached to the inside of the pod using zipties much like the intended design described above. The LabQuest 2 was attached to a side wall with zipties and the radiation detector was added in the same way but on the opposite wall to account for weight distribution. The cord going from the LabQuest 2 to the radiation detector stuck out the LabQuest too far and was being interfered with by the lid of the pod. A hole going through just the first layer of foam on the lid was cut to accommodate for the cord and allowed for a more secure connection between the two components.

Intended Design
Figure 1 shows the intended circuit design. It includes the DC-DC Booster, Peak Detect, Amplification, 5V Regulator, Interrupt Generator, and all ports. However, the following change was made to the circuit without updating the diagram:
 * R5 was changed to 13.7 kΩ

Figure 2 shows the breadboard construction of the electrical circuit shown in figure 1, but with the aforementioned changes.

Used Design
While the intended design was to use the breadboard in figure 2 to test Whitworth’s new scintillator detectors, there was an unknown flaw in the circuit design which was unable to be fixed. Due to this, and time constraints, the intended design was scrapped in favor of a Vernier LabQuest 2 Datalogger, to which a simple Geiger counter was attached to measure hits per 30 seconds.

Validation and Calibration
Due to aforementioned issues with the original circuit design, no testing or calibration was done past basic voltage and current measurements. These tests, which consisted of measuring current through certain portions of the circuitry to ensure that the different components of the circuit were operating correctly, yielded poor results. We used an external power supply to power our breadboard and then used a multimeter to determine if our connections were in fact connected and/or were getting the correct voltages. We also conducted a test with an oscilloscope to test the signal being transmitted from our SiPM circuit to the rest of our breadboard. Although we received good voltage readings during the multimeter test, the oscilloscope results proved less fruitful. We concluded with the cause being an unknown error in the layout of the circuit itself. Due to the constraints of time, a choice was made to switch to a LabQuest system.

Following the decision to transfer efforts to a LabQuest 2 system matched with a Geiger counter, validation and calibration were completed with a series of trial runs. The detector was connected via the Channel 1 port, and then was collected for approximately 2 minutes in order to make sure the device was counting reasonable numbers of events on ground level (10-20 counts per 30 seconds). Following this brief test run, the battery then needed to be tested to ensure that it had an adequate length of life to allow data collection to run for the maximum flight time of around 2.5 to 3 hours. This test was conducted by starting data collection at approximately 8am and letting the device run until around 11am. Prior to starting this trial, the collection time constraints for the device were edited, raising run time from 600 seconds to 14400 seconds (4 hours), with data being recorded every 30 seconds. This allowed for the LabQuest to collect data for the longest possible flight time. Following a successful 2nd trial, with the battery only going down approximately 10-15% and the overwhelming majority of the data points being within the previously established reasonable boundaries, the LabQuest was calibrated and ready for flight and data collection.

Summary
Given the successfulness of the experiment, the only data we were able to collect during the flight was the amount of radiation counts per 30 seconds. Ideally this data would have been crossed with the altitude data. However, due to a malfunction in the command module, we were unable to recover any altitude data from the flight. Instead we were able to calculate the data and produce a rough estimate of the altitude at different times during the flight. By crossing our radiation counts with the calculated altitude measurements, we can create a model that shows us the amount of radiation at different heights in the atmosphere.

Calculating Ascent Altitude
By observing the Stabilization Group’s video data, time of ascent was found to be 77.7 minutes, or 4662 seconds. Using a linear balloon ascent rate of 1000±10 feet/minute, found through personal communication [5/5/2022], the altitude data was thus calculated. Note that highest altitude was therefore 77700±777 feet.

Relative Hits/30sec Rate of Change
The relative rate of change is the slope between two datapoints. In this context, the datapoints are the Hits-per-30sec points in figure 1.

Conclusion
Cosmic Rays are high energy particles that are broken up the elements in the atmosphere. This shields the surface from harmful amounts of radiation and keeps the radiation levels at a healthy amount. Radiation counts during ascension into the atmosphere will increase until you reach the altitude at which the cosmic rays are colliding with atmospheric particles. At that point, the amount of radiation counts will decrease to an amount slightly smaller than that of the collision zone. The area above the collision zone will have less counts but higher energy levels, while the area below will have higher counts and lower energy levels.