Cosmic Ray Research During The 2017 Solar Eclipse
How It All Started
In 2007 an opportunity arose through the Quarknet organization to attend a week-long workshop with students in which we would construct four muon counters to bring back to our school. As a physics teacher, I was looking for ways to incorporate real-world research into our physics curriculum and this seemed like an excellent way to accomplish just that. Muons are particles (like electrons, but heavier) that are streaming down from above. They result from the collision of cosmic rays with the Earth’s atmosphere. If you hold out your hand, about four muons will pass through that space every second. So, there are plenty of muons to detect! But what’s really interesting is that they only occur in high-energy collisions. Everyday matter is not made of muons. Typically we build giant particle colliders like the LHC at CERN to make exotic particles, but these cosmic ray collisions are even more energetic… and free!
In between now and then, the muon counters were only used sparingly. There would occasionally be groups of students that would want to learn how to set up the counters. I would run a couple of training workshops where students would learn how to use a computer to communicate with the microprocessor that controls the muon counters. We would also learn about how to count in hexadecimal, since all of the output was in base-16. At most, these groups of students spent time calibrating the counters. One of the biggest obstacles to getting a research project going was having a dedicated space for the detector. In the old Academy building, there was little space in any of the labs to keep this equipment running for weeks undisturbed.
In December of 2015, we moved into a new building designed for 21st century learning. During the design phase I made sure to account for what would be needed to make the muon detectors a part of our plans. The GPS and temperature sensors were installed on the roof above the lab in November of 2016. Students began to notice when they waked into class, because the ceiling tiles were removed and all these wires were bundled up on the lab tables. That turned out to be a great recruitment tool. I explained to my classes that they could use this opportunity to learn about high-energy physics and research. It was under this vague banner of “Let’s do science!” that a few students expressed interest, but three students kept coming in after school and made the commitment to learn about muons and how to operate the detectors.
The three students started their journey with a couple of after school lectures I gave on high-energy physics, the standard model, and how to understand a histogram. Each student made an online account on Quarknet’s Cosmic Ray E-lab webpage and used the on-line resources to learn more about these topics. We then started setting up the detectors and testing all the connections. The first important accomplishment was to make sure the GPS beacon was detecting enough satellites to make the very accurate time measurements needed. This involved installing and learning the software that communicates with the microprocessor, which controls the muon detectors, GPS, temperature and barometric pressure sensors. Once we determined that everything was working as expected, we set our sights on getting the detectors ready for an extended data run.
Getting the Detector Up And Running
So how do you detect a muon? We have four separate detectors (called counters) and they detect muons by looking for the faint light emitted as they travel though a slab of scintillator. Each counter has a light sensor that had to be calibrated so we are recording muons at optimal efficiency. This process is called plateauing the detector, and it was the next big step in getting operational. The students spent a day after school going over the time-intensive procedure and exploring a spreadsheet to analyze the data. The process involved taking measurements at various operating voltages for the light sensor (photomultiplier tube, or PMT) and plotting count rates versus voltage. That data is then compared to a control detector set to a fixed voltage. A plot of rates for muons that hit both detectors is then made, and used to set the optimal voltage. The students did all of the setup and analysis for this project. Data was complied on a google spreadsheet for easy sharing. Students also began keeping a logbook. They found that with people coming in to work at different times it was confusing to know what was done without having all activity recorded.
This brings us to February of 2017. The students began talking multiple day runs using all four counters stacked atop one another. The idea is to establish baseline readings for each counter to use for “blessing” our future data. It was about this time the students were getting very familiar with the equipment and became more comfortable with asking questions and thinking about what all this data means. The student were perplexed as to why one counter would read more counts than another even though they were stacked on top of each other. They also became curious as to how the computer actually figured out when a muon, which is traveling near the speed of light, was detected by all four counters. The students reached out to Quarknet scientists for insights into these questions. This led to a greater understanding of the difference between signal and noise in data. There are many times when the computer will tell you that a muon hit all four detectors, but it could have been caused by two separate muons hitting at similar time intervals. The very concrete idea of an object being “seen” and a more abstract idea of measurement through statistics involving many “events” was a challenge for them because it never comes up in the standard high school curriculum. This is one of the great lessons from this experience.
It was also around this time that the Quarknet group let us know about an idea for an experiment measuring muon rates during the solar eclipse. They asked a bunch of schools with detectors to think about how the counters could be arranged to look at a small section of the sky. Our students decided to take up this challenge.
Here is a picture of myself and two of the students setting up a couple of counters above the drop ceiling in our lab.
And here is an example of one of the plateau plots made by the students
The Experimental Question
Is cosmic ray radiation affected by a solar eclipse? One of the Quarknet advisors who was helping us get our detectors operating posed this question and couldn’t find much research on it. The students were excited to participate in an investigation of a question that so little is known about. What was an after school activity quickly morphed into a research team. The students started by testing different arrangements of the four counters to see how muon counts depended on separation distance and overlap. The eclipse would only take place across half of a degree of the sky, so it would be important to try and minimize the region of the sky from where we are detecting muons. Our data for these proof-of-concept experiments was uploaded to the Quarknet server so teams from other schools could have access and compare results.
The students found that the number of muons that hit two stacked counters did decrease proportionally with decreasing the area of overlap. They also found that counts for increasing separation between two counters fit well with a theoretical expectation for decreasing the amount of sky that a muon could come from and hit both counters. The last concern was about in increase of noise from a large separation of two counters. A large separation will decrease the rate of muons hitting both counters, but might have little effect on the noise of two different muons registering like a single event according to the computer. The data that our students took led to the optimal spacing and overlap of the counters needed to construct the muon telescope. It was during this time that we picked up a forth member of our team. A freshman student with an interest in science had heard about the experiment and wanted to participate. We now had the whole team that would eventually build our telescope and conduct the experiment.
We called ourselves Team Muon Team. The group consisted of three juniors from my AP Physics 1 class and one freshman with a keen interest in math and science. In June of 2017, the students and I attended a week-long workshop to collaborate with students from four other schools in building the telescopes for the experiment. There were multiple designs. The one that the students worked on was made of a long 2×4 with two plywood ledges separated by about six feet to hold the counters. This telescope would be pointed at the location of the eclipse for the three days preceding the eclipse, and during the eclipse itself. For the days preceding the eclipse we would be able to get data for the sun and the moon passing solo across the field of vision. We could then compare that data to the day of eclipse data to look for changes. Of course, there would also be many hours of empty sky data to use as a baseline.
These workshops were the first opportunity for my students to talk about this project with students from other schools. They presented their data on the proof-of-concept trials to an audience of fellow student researchers and Quarknet scientists. The students discovered that they knew more than they thought they knew. Yes, other students had the same questions they had. Sometimes our students had answers that others were looking for. They learned that it was okay not to know the answer to a question. It was a time when the students started feeling like they belonged and had something to add to the discussion.
This workshop also provided one of our first major setbacks. We use our counters to build a telescope that would take some test data for an hour so outside. We set up the telescope so the computer and electronics were under an awning, but the telescope itself was uncovered so it could be pointed at the sky. We went inside to our meeting room in the interior of the building. No windows. When I took a break to check the telescope, there was a steady rain giving out telescope a shower of water along with the muons. I sent a text to one of the Quarknet leaders and began to frantically disconnect power to the telescope. Within a minute, a rush of students came down to assist. The rain water caused one of our counters to eventually fail. A replacement was provided by Quarknet and needed to go through the plateau process yet again. This experience led to a discussion about how we should plan for rain at the eclipse site. The telescopes would need to be exposed to the elements for 80 hours straight with no breaks during the experiment.
Here is a picture of the telescope before the rain hit.
Here we see two of our students in the workshop constructing the telescope
Students presenting data from the proof-of-concept
Preparing for Missouri
The team at Quarknet found a location along totality where the experiment could be performed. There were unique requirements. Since hotels were booked by tourists and massive amounts of people were expected to flood areas of totality, we needed to be more-or-less self-contained. Jefferson College in Hillsboro, MO gave us access to their field house area during the eclipse and the three days prior. We could sleep on wrestling mats in the field house and use the concessions refrigerator and coolers to store perishables. Outside the field house was a covered apron where computers and other electronics would be reasonably protected from rain, but with easy access to an uncovered area for setting up the four muon telescopes. The team now had two tasks to accomplish: To build and test the telescope we were bringing to Missouri and to plan the out the logistical realities of spending five days in the country.
On the scientific end of the spectrum, the team constructed the fixed muon telescope in our physics lab and took days of data with it pointed at at the correct altitude angle with the horizon. Muon counts decrease as you point the telescope toward the horizon, and we needed a baseline reading for the angle at which the experiment would be run. The team also took measurements with various overlap schemes to make sure we were still seeing the same relationships. This amounted to a trial run at the real experiment. All of this preliminary data was recorded in our log book and uploaded to Quarknet servers.
On the logistical end of the spectrum, we needed to figure out a way to keep kosher over five days in the middle of rural Missouri. We were arriving on Thursday and the eclipse was on Monday, so Shabbos arrangements also needed to be worked out. The sleeping arrangements changed suddenly when the university decided that it was a bad idea to let the students sleep in the gym for four nights. Fortunately, the university was able to book us reasonably-priced rooms at a nearby motel. This was a big deal since tourists had booked most of the rooms across the path of the eclipse months in advance, and the rooms that were available were going for huge premiums. In fact, we also packed extra water and snacks just in case of emergency. This was going to be one of the largest sudden movements of people across the country in recent memory, and FEMA was worried about rural resources being stretched thin. We were able to arrange for our students to stay with families in the St. Louis area during Shabbos. Our principal investigator, also a Quarknet fellow, is observant and worked with the students in making these arrangements. I set up a spreadsheet for planning meals and snacks for the five days of the experiment. Students contributed ideas and ultimately wanted to have some hot meals, so we brought along a gas camping stove and kosher cookware. A genuinely lovely moment was watching our students explain keeping kosher to students and advisors who were not Jewish. The sharing of cultural experiences was an unexpected moment of learning for the whole group.
Here is a picture of the students testing the fixed telescope in our lab before the eclipse
Arriving in Missouri
We were in Hillsboro, Missouri from Thursday, August 17th until about three hours after the eclipse on Monday, August 21st. Most of Thursday was spent driving to the site and setting up equipment. We had to construct four telescopes, connect all the wiring, and start taking data. Three of our students focused on building and maintaining the fixed telescope. One our our students set up and maintained a fixed stack of four counters that pointed directly upward the entire time for purposes of gathering background readings. Our students also helped construct two telescopes that tracked the sun and moon in the sky during the day. All the practice and preparation made the setup a breeze. These students were experts by now and everything was up and running well before nightfall. There was no rain in the forecast all the way through the eclipse. However, temperature were hovering around 100-degrees Fahrenheit and the humidity was very high. Over the next few days we would need to take frequent breaks in the air-conditioned gym. The telescopes did not have this luxury. The muon counters are wrapped in black, light-blocking material and were continuously exposed to sunlight. We had never tested how extreme temperatures and humidity would affect the counters, and we were frequently seeing counters with fluctuating rates. Like true scientists, the students had to make quick decisions and triage all the problems that developed. Many counters were replaced with spares that were brought along. An entire telescope spectacularly crashed to the ground after being in the sun for the entire day. Wires and connections were failing. In the end, we rarely got data runs where all four counters were functioning properly. Some decisions would need to be made about how best to use the data we could collect. This is another example of a real-world research problem that is challenging to recreate in an academic setting.
The University was hosting an eclipse watching party for the public. We were one of the many stations that visitors were encouraged to visit on campus, along with a booth set up by NASA and other educational experiences. We set up our experiment posters close to the telescopes so the public could see what we were doing. As it turns out, they had many questions. The students found themselves acting as experts in cosmic ray research! I imagine it was a first for all of the students. What an incredible feeling to get to share your many months of work with interested strangers, and to be treated like a scientist… not a student.
The event itself was beyond expectation. We were very fortunate to have clear skies. It was truly magical, and an emotional conclusion to many months of work. The fixed telescope and the “stack” took data throughout the eclipse, however the fixed telescope had one counter that fluctuated wildly. The students worked diligently all day to stabilize all the counters, but during the eclipse you basically just let it be and take in the once-in-a-lifetime show.
About two and a half hours after totality we shut down the computers, took down all the telescopes, packed the busses and vans, and made our way to St. Louis for a celebratory dinner. The drive home was made longer due to the incredible traffic of eclipse tourists heading back to the Chicago area. It was a great time for reflecting on all the amazing things that were accomplished. The students conveyed a sense of pride that comes from setting big goals and seeing them through. They were excited about moving onto the next stage, which was to try and make sense of all the data they had collected.
Videos And Pictures From The Eclipse
This YouTube video was made for our school to show everyone what the student were doing leading up to the eclipse. They students explain the experiment and some of the equipment.
The students prepare one of the meals for the whole team
Setting up the fixed telescope
Putting the fixed telescope into place
Setting up the stacked muon counters
A student explaining the experiment to people gathered to view the eclipse
A team picture of the students, Quarknet advisors, and myself
The eclipse at totality (Photo taken by Tony Valsamis of Glenbrook North High School)
Data Meetings & Presenting Our Findings
Shortly after returning we decided that we should begin to look at the data and plan to present it at the winter meetings of the American Association of Physics Teachers. This would provide a capstone experience for the students of presenting their research to their peers. A “data party” was set up for early September in which we made preliminary plots of muon rates for various counter combinations. Although we had no results to report, we needed to get abstracts together to make the deadline for paper and poster submission for the conference. The students looked at example abstracts and worked out who be the lead author on each paper. Here are the three paper abstracts that were submitted and approved for the 2018 Winter Meetings:
Baseline Data Collection for Analysis of Muons Flux During a Solar Eclipse
by Michelle Matten,* Tamar Dallal, Ezra Schur, Jacob Miller, Allen Sears
While it is true that scientists have been detecting muons for decades, trying to detect a change in muon counts during a total solar eclipse is more challenging. How and where should one arrange the muon counters in order to maximize results? What special conditions need to be taken into account? In this presentation we will discuss the approaches used to collect data before and during the solar eclipse of August 2017, the reasoning behind these methods, and how the data were used in order to help determine whether the eclipse had any effect on muon flux.
Baseline Studies for Cosmic Ray Solar Eclipse Experiment
by Tamar Dallal,* Clarissa Carr, Jacob Rosenberg
A cosmic ray experiment was proposed to measure muon flux changes during a total solar eclipse. Before the eclipse, baseline studies of empty sky, lunar transit, and solar transit needed to be collected. In accumulating these baseline data, various methods of collection were implemented. Specific results of these investigations and reasons for each in preparation for the solar eclipse will be explored.
Study of Muon Flux During a Solar Eclipse Results
by Jacob Miller, Ezra Schur, Nathan Unterman, Allen Sears
Using QuarkNet cosmic ray muon detectors during the recent August 2017 solar eclipse, experiments were conducted to measure the change of muon flux during the eclipse. Using a fixed array of counters, data on muon flux was captured from a 30 degree cone of acceptance centered at the point of totality of the eclipse. Additionally, a tracking telescope of counters was used to capture a 22 degree angle of acceptance, following the sun throughout the day. Finally, a small stack of counters was used to establish a control measure of muon flux. Pre-eclipse team discussions included the sun as a significant source of cosmic rays showing changes during the occultation, a decrease in cosmic rays due to the blocking of rays by the sun and moon, and an increase in cosmic rays due to atmospheric changes unique to an eclipse. Specific methods and findings will be presented.
All of these papers are being presented on Sunday, January 18th, 2018 at the American Association of Physics Teachers Winter Meetings in San Diego, California.
We decided as a group to post all of the data and generated graphs to Google Sheets. I gave the students a crash course in using spreadsheets to do iterative calculations and make graphs. It did not take them long to pick it up. We had to decide how to look at the data, and our practice in making histograms and adjusting bin size was an important part of the analysis. Quarknet provided a computational script that would organize all of the counts for each detector into ten minute bins that the students could easily transfer into a spreadsheet. It was the task of the students to use the spreadsheet to create calculations of single counter rates and many different combinations of rates for coincidence hits of multiple counters. They then made scatter plots of all the data to get a better visual of how the muon counts changed over time.
Two other data meetings have taken place to work out final plots and to discuss if our data shows a relationship between muon flux rates and the eclipse. Some of the findings so far are more procedural. The stack counter showed that temperature and atmospheric pressure did not warrant any statical corrections to our data. The fixed telescope had one counter with unusable data, so we had to rely on the three other counters to piece together any change in muon flux rates. This changed aspects of the experiment, but opened up new questions as well. With the remaining counters being offset from each other, the opposite pairs pointed at different regions of the sky. We could look for echo patterns in the sets of functioning counters as the moon, sun, and the combination moved across their field of vision. This experience taught the students that failure is really just a natural part of being ambitious. Although the original plan didn’t work out, there was still a way to take what was working and make something of it.
As of this writing we have plane tickets and hotel rooms booked for the conference. Shabbat arrangements in San Diego are being finalized. The students are taking breaks from college applications to finish the data analysis. We are close to coming to a conclusion about what the data is telling us about muons and the eclipse. This teacher is eagerly awaiting the next chapter in this scientific adventure.
Connection To The Classroom
Data collected from proof-of-concept phase of the experiment yielded some very useful data for teaching about measuring speed. Students in regular and AP-level classes typically learn about measuring speed from looking at slopes of position versus time graphs. One of our trials collected data for three counters that were separate at one to two meter intervals. The Quarknet analysis tools allowed us to get “time of flight” data between each counter reading. We are essentially using a stopwatch to time how long it takes for muon to go through two detectors. This allows us to measure the average speed of a muon! Students are given the histogram time-of-flight distributions for three different sets of counters. They then plot the separation distances versus the peak time on the distribution, the slope of which should yield the speed of a muon. The number they get is approximately the speed of light. I developed an online version of this activity for the Inspiring Science Education portal and it can be found at: http://portal.opendiscoveryspace.eu/en/edu-object/measure-cosmic-ray-muon-speed-848516
Mr. Sears is in his 19th year of teaching physics at Ida Crown. He is a practitioner of the modeling method of physics instruction. His professional memberships include the American Association of Physics Teachers, Quarknet, Physics Northwest and the Illinois State Physics Project.