Measuring the "measuring device"｜リガクル[RIGAKU-RU]

From the biggest scales…

Science and nature have always surrounded me. I am from Kagoshima, a prefecture known for Sakurajima, a still active volcano. Seeing small volcano eruptions was an everyday experience. I could also see the stars in the sky at night as Kagoshima was far away from the most urbanized parts of Japan. The prefecture had a space center (Tanegashima Space Center) with a rocket launcher. Unlike volcano eruptions, however, rocket launches were a rare experience. I still remember it clearly, even though it happened years ago. I watched it with my family as the rocket lit up against the background of the dark morning sky. This experience got me interested in science and the cosmos in particular. In junior high and high school, I also learned about the small elements crucial for understanding the cosmos, the elementary particles. Thus, my interest shifted toward physics and intensified after visiting the particle accelerator in Tsukuba when I was a high school student. The sheer size felt unreal and piqued my interest in experimental physics. I knew many scientists at the University of Tokyo were using particle accelerators, so I decided I wanted to study there. I also visited many laboratories during high school. Seeing all those scientists enjoy their work left an impression on me. All of these experiences together led to my dream of becoming a physicist. So, continuing my studies in graduate school was a straightforward decision.

…to the smallest

So, I chose to major in nuclear experimental physics and now study the structure of the nuclei, a small unit of matter. If you look “inside” matter and go beyond the level of atoms, you can “see” nuclei and electrons. Nuclei consist of protons and neutrons. At the lab I am a member of, we aim to measure how strongly neutrons and protons interact with each other and how strong the forces acting between them are. This area of study is called high-energy nuclear physics because the main method of investigation uses high-energy particles to knock out particles from the nucleus. Then, we can make inferences about the structure of the nucleus based on the measurements we make about the emitted particles. However, many tasks need to be completed to make successful measurements. One such task is creating a beam of high-energy particles used in the experiments.

Focusing on beams

As previously mentioned, we investigate the nucleus of an atom by “calculating backward” from the knocked-out particles we can observe. This means that we have to precisely measure not only the particles coming out but also the particles going in, in other words, the particles that make up the beam used in the experiment. If we do not have precise data about the beam we are using, we could be wrong about our inferences just as if we did not have accurate data about the particles we knock out. This is my current research area: how we can ensure that we make accurate measurements about the beam itself. Interestingly, this research area found me rather than the other way around. At first, it was merely a task that my supervisor assigned me. However, as I studied this area for the past two years, I found the many complications that arose fascinating and got hooked. This area of research also appealed to my interests as primarily an experimental physicist. I do think theoretical physics is beautiful. But ultimately, the most important thing is whether we can validate theories against reality.

A unique method of “quality control”

A good quality beam that makes experiments easier is small in diameter and has a very stable energy distribution throughout the beam. Although both electrons and protons can be used to create such a beam, it is much more difficult to do so with protons, as heavier particles are more challenging to adjust and control. Thus, in our lab, we use electrons for our beams. Moreover, our lab emphasizes precision. So much so that we might have the highest precision in the world thanks to our unique method. Some researchers doubt its validity. We are confident, however, and keep collecting new data to demonstrate the method's validity. When the electron beam bends, the acceleration causes some radiation, a part of which is visible light. We then observe this emitted light and extract information about the beam’s energy, ensuring its quality. This method of observing light is common in many other research fields, but we are the first to apply it to making measurements of beam energy. I am currently working on analyzing the data we collected in Germany this spring.

Physicists meet in Mainz

I am so lucky. I got to travel to Mainz, Germany, funded by the laboratory I am a member of. I went to the University of Mainz (full name: Johannes Gutenberg University Mainz) because they have a well-known particle accelerator called Mainz Microton (MAMI). As accelerators cannot be relocated, it is we, the researchers, who “relocate." So, I was one of the many nuclear and particle physicists working temporarily at the accelerator in Mainz. As I mentioned earlier, the lab I belong to has developed a unique method to measure the beam's energy used for high-energy physics experiments. I went to Germany to collect data using their equipment to validate our method by demonstrating its precision using novel data. This project was the first time the physicist and the accelerator teams worked together. So, even though I focused on ensuring our measurements were taken appropriately, and other collaborators focused on the nuclear physics experiment itself, we still had daily, several-hour-long discussions about the details of the experiment. I have two distinct memories of this fun period.

On one occasion, a crucial component of the particle emitter broke down and we could not take any measurements. We had to contact our supervisor in Japan to discuss how we could repair this component. As we were only students, we needed him to contact our supervisors in Germany about how to proceed. However, I noticed a difference between Japanese and German culture. I felt like German researchers were much more optimistic. Whenever an issue arose, German researchers would only work on it until the end of the workday and feel confident about solving it the next day. I found the difference intriguing.

When in active use, the accelerator often has to be run 24/7. We worked six-hour shifts, sometimes in the middle of the night. Of course, the senior researchers had already gone home, and only students were left at the facility. So, I got to work with many people around the same age as me, which made communication easier. It was a great experience.

Advice to students

Sometimes, as an undergraduate student, you might feel like you have to study some subjects merely to pass an exam as a necessary step in your studies. You might have already experienced this in school, as you sat in class, listening to a school teacher teach about a specific subject. However, if you are studying something you are genuinely interested in, you will realize that what the professors are teaching is just one perspective within a field. This is true for the whole curriculum as well. So, feel free to explore your subject of interest outside of the bounds of the classroom as well. The discoveries will only motivate you more to continue your studies.

In the same vein of “discoveries”: do not fear going abroad. Going to Germany was my very first time traveling abroad. But thanks to FoPM (Forefront Physics and Mathematics Program to Drive Transformation), I got to chat with many upper-grade students who talked about doing research abroad and encouraged me to take a leap. As I did not speak German, sometimes I had trouble communicating outside the research center. However, I discovered the magic word “bitte,” or “please” in German, which helped me through most situations. Living in Germany was a great experience. I encourage students who might be hesitant to take up the challenge.

※Year of Interview:2024
Photography:KAIZUKA Junichi
Text:Belta Emese
/ The interview was edited for brevity and clarity.

NISHI Kotaro

2nd-year master’s student, department of physics

Kotaro Nishi is a 2nd year master’s student majoring in physics. His experimental research bridges the gap between the team of physicists using accelerators and the team of engineers responsible for the accelerator itself. He plans to continue his studies and enter a doctoral program.