Exploring Existential Questions about the Universe... Pioneering the Search for Exotic Nuclei

There is a scientist who transcends space and time in search of the origin of the universe. This nuclear physicist observes synthetic elements that do not exist naturally on Earth for a fleeting moment lasting zeptoseconds (10 to the power of -21 seconds), gaining hints regarding the origin of the universe, which is now 14 billion years old. He defines his research as "the humble process of a human challenging the wonder of the universe and nature."

HWANG Jongwon, a researcher at the Institute for Basic Science (IBS) Center for Exotic Nuclear Studies, stated, "Nuclear physics research seeks the origin of the vast universe by looking at its smallest building blocks - atoms. In terms of time, nuclear physics experiments explore the universe, ranging from the shortest ranging from zeptoseconds to the birth of the universe hundreds of billions of years ago."

In August, Hwang published a paper on 'Oxygen-28' in the international journal Nature in collaboration with researchers from the RIKEN Nishina Center for Accelerator-Based Science and the Tokyo Institute of Technology. Oxygen-28 is an unstable rare isotope that does not exist on Earth; most of the oxygen found in nature is in a stable state as oxygen-16.

Elements as seen in the periodic table are the basic building blocks of materials around us and its smallest unit is an atom. The atom consists of a nucleus and electrons, and the nucleus is composed of protons and neutrons. Depending on the number of protons and neutrons, the type of atomic nucleus is determined, and Hwang is studying the properties of these nuclei and the principles of interaction between protons and neutrons that underlie them.

Oxygen-16 has 8 protons and 8 neutrons, but oxygen-28 has 8 protons and 20 neutrons. Although they have the same number of protons, oxygen-28 is an 'isotope' with a different number of neutrons. The numbers 2, 8, 20, 28, 50, 82, 126, etc., are called 'magic numbers,' representing the specially stable numbers of protons or neutrons in the atomic nucleus. While they are stable, the reason for this stability is unknown, hence the term 'magic.'

Until now, oxygen-28 has been considered to be one of those isotopes that are at the limit of existence. Since isotopes that do not exist in nature disappear in an instant even if artificially created, the experiment itself was difficult. However, Hwang and the research team used RIKEN's heavy-ion accelerator, the Radioactive Isotope Beam Factory (RIBF), to observe oxygen-28 for the first time in the world and revealed that it does not possess the magic numbers for neutrons. Currently, Hwang is conducting pioneering research to find other exotic atomic nuclei such as zirconium-80.

Here is a Q&A session with HWANG Jongwon:

Q: Please introduce yourself.

A: I graduated from Seoul Science High School and received my bachelor's, master's, and doctoral degrees in physics from Seoul National University. During high school, I explored overseas research institutes and visited the High Energy Accelerator Research Organization (KEK) in Japan. When I saw the research conducted in such large facilities, I thought, 'This seems interesting,' 'I want to try it too,' 'I’d be able to explore the origin of the universe.' When I entered graduate school, I heard the construction plan for the IBS Rare Isotope Science Project (RAON) was announced, so I decided to enter the nuclear physics field.

I joined the WCU project at Seoul National University's graduate school, which brought Professor Sato YOSHITERU to Korea. Under his guidance, I started research on rare isotopes. I experimented with various rare isotopes, including oxygen-28 using Japan's SAMURAI (Secondary particle Array for Measurement of Unstable nuclei), and I graduated by utilizing the data for papers. From May 2017, I spent three years as a postdoctoral researcher at the Center for Nuclear Study (CNS) at the University of Tokyo and joined IBS in April 2020, continuing my follow-up research.

Q: What is the IBS Center for Exotic Nuclear Studies.

A: First of all, basic science is a kind of existential exploration of why nature is the way it is, why the universe has this structure, and how substances exist. Rare isotope research mainly seeks the origin of elements. Humans do not know exactly how all elements were created. Especially, the process of creating heavy nuclei like iron to uranium is not well known. Rare isotopes are closely related to the creation of elements in the process, and through rare isotope research, we aim to better understand how elements are created in the universe. Specifically, we perform experiments on astrophysically important nuclear reactions, such as the protons and neutrons capture processes. We also conduct studies on nuclear structures, such as the proton-neutron dripline where stable atomic nuclei exist and new magic numbers.

Q: We would like to know about your research area.

A: One representative example is the research on unstable rare isotopes that do not exist in nature, such as oxygen-28. Oxygen-28 consists of 8 protons and 20 neutrons. It has 12 more neutrons than oxygen-16, which is the stable isotope that is abundant in nature. Recently, research on zirconium-80 has also been underway. Zirconium-80 has more protons than neutrons. I am also studying isotopes with structures opposite to those of oxygen-28.

Q: Why is research on isotopes like oxygen-28 or zirconium-80 necessary.

A: The atom is the basic unit that represents the properties of matter. Atoms are composed of a nucleus and electrons. We focus on the atomic nucleus which contains most of the mass of the atom. The atomic nucleus is composed of protons and neutrons, and all types of atomic nuclei are created by the combination of these two particles, showing different properties. The combination of these two particles alone has contributed to the diversity that we see in the world. Nuclear physics research explores the interaction between these particles. Understanding the various phenomena created by this interaction and examining stable or unstable atomic nuclei is a crucial aspect of nuclear physics.

Q: Can you explain the significance of the research on oxygen-28.

A: Revealing the characteristics of atomic nuclei beyond the existence limit is significant. Atomic nuclei, when a specific number of protons or neutrons satisfies, often show stable characteristics. The numbers like 2, 8, 20, 28, 50, 82, and 126 in the atomic nucleus are called 'magic numbers.' Even though oxygen-28 is extremely unstable, there was some hope it would have a long enough half-life to be detected since it was a nucleus with two magic numbers, due to its composition of 8 protons and 20 neutrons. By using RIKEN's RIBF, we observed oxygen-28 for the first time in the world, and it was discovered that the concept of magic number did not apply to oxygen-28. This means that we experimentally revealed the properties of very rare isotopes beyond the limit of existence.

Q. The process of creating theoretical oxygen-28 wouldn't have been easy.

A. That's correct. Oxygen-28, considered to exist beyond the existence boundary, can exist as a quantum resonance state for only about a zeptosecond, or 10 to the power of -21 seconds. We created oxygen-28 by colliding an accelerator beam with a target to remove some portions from the atomic nucleus. In brief, we achieved this through the conversion process of calcium-48 → fluorine-29 → oxygen-28, to obtain oxygen-28. There was no predicted magic by scientists. The properties of atomic nuclei in extreme regions, unlike the majority of stable atomic nuclei, were unknown. Experimental data on extremely unstable atomic nuclei like oxygen-28 will serve as a foundation for understanding the interactions between protons and neutrons.

Q. Can this basic research be applied.

A. The greatest significance of basic science, in my opinion, lies in expanding humanity's horizons. While the term "science and technology" is commonly used, I believe that science and technology should be separated. Science is one of the various methods to understand the world, and basic science, in particular, is closely related to the humanities and arts. While the advancement of the humanities or arts is not directly linked to the survival of humanity, it contributes to the spiritual richness and cultural prosperity of humanity. Similarly, by broadening the horizons of knowledge, basic science contributes to the cultural development of humanity. As for applicability, we may not know it immediately, but in 100 or 1000 years, who knows it can be the foundation for new developments in engineering and technology. Just as things unimaginable 100 years ago are happening now, with the backing of engineering and technology, there could be many areas that can be applied extensively in the future.

Q. Isn’t it challenging to conduct research on something that doesn't exist in nature.

A. I found I fit quite well with conducting nuclear physics experiments. In nuclear physics experiments, researchers often design and manufacture detectors themselves. This involves drawing diagrams, designing circuits, and programming to make the electrical signals from the detectors readable by computers. Various knowledge is required, and my background in programming as a minor during my undergraduate years and my childhood interest in disassembling electronic devices helped a lot. In nuclear physics, research leaders often have to design the entire experiment and be well-versed in various aspects necessary for the experiment. Since there are many things I can do, nuclear physics research seems more appealing to me.

Q. Please share your recent memorable moments or experiences during the research process.

A. Recently, I experimentally created rare nuclear isotopes using the beam from RAON, a particle accelerator operated by the IBS. Watching that, I thought, 'Now Korea can do this too.' Of course, it will take more time to build global capabilities, but it was a proud and enjoyable memory. Another memorable research is about reprocessing nuclear waste using accelerators. Nuclear reactors generate lots of nuclear waste, and using accelerators to transform it into less hazardous elements makes it easier to handle. I am conducting research on this concept and writing a paper. It's somewhat like alchemy, and I aim to complete the paper within the year.

Q. How was your childhood.

A. Since elementary school, I wanted to become a scientist. I was exposed to science books a lot during my childhood. In elementary school, a neighbor gave us about two to three years' worth of the science magazine that her son had outgrown. It had fascinating content, and since it was colorful, I read a lot. From that time, I enjoyed reading science books, and I liked experimenting with various things, such as dismantling electronic devices. Asking fundamental questions eventually led to curiosity about the origin of nature and the universe, which led me to choose physics.

Q. You spent three years as a postdoctoral researcher in Japan, did you feel the need for international collaboration.

A. Over the course of the international collaboration, I strongly felt the importance of research facilities. Large research facilities like heavy-ion accelerators are essential for nuclear physics experiments. Even now, while RAON in Korea is nearing completion and open to users, Korean researchers had to conduct experiments mainly overseas in the past due to the lack of experimental facilities. There were some constraints during my graduate school research as well. I hope to utilize the network built over the years to engage in various collaborative research using domestic accelerators.

Q. Can you explain what nuclear physics means to you.

A. The reason I love nuclear physics, or basic science in general, can be broadly categorized into two aspects. First is the awe of nature and the universe, and second is the potential that humans, despite being small and insignificant, have in exploring it. Nuclear physics deals with various scales. Nuclei are so small that they are invisible, yet they are related to the universe. Supernova explosions or the evolution of stars are ultimately related to nuclear reactions or the creation of elements. Although the age of the universe is over ten billion years, experiments deal with scales as small as nanoseconds or microseconds. Engaging in such research makes me ponder existential questions about the universe and nature. Considering the limited time of human existence within the vastness of the cosmos, the curiosity of humans in exploring it is quite admirable.

Q. How about your life outside of research.

A. I play the viola. When conducting research, it's not easy to find direction. After completing one research paper, you need to find another topic. I have a lot of career-related concerns as well. Playing an instrument helps alleviate some of these concerns. Apart from that, I mainly engage in reading. For those entering the field of basic science, I recommend Carl Sagan's "Cosmos" and “Pale Blue Dot”. Richard Feynman's physics lectures can also help provide a perspective on physics.

Q. Despite discussing basic science, you've shared many philosophical thoughts. How would you like to be remembered as a person.

A. I want to be remembered as a hardworking person. Achievements in the field of basic science may not always turn out as intended. Being recognized for research achievements is not entirely up to the researcher. I have. I want to be remembered as someone who consistently and diligently conducted research and never gave up. I also hope to be remembered by my colleagues as someone who they enjoyed collaborating with.

Q. Please share your aspirations for the future and the fields you wish to explore.

A. Through the Young Scientist Fellowship (YSF) at the Institute for Basic Science, I am currently conducting research on zirconium-80. The YSF program provides support of up to 900 million KRW for a maximum of three years. I aim to experimentally verify the coexistence of different forms of atomic nuclei. In the long term, I want to discover new elements. Like the Japanese researchers who discovered nihonium (Nh, element 113) in 2016, I would like to participate in the research to discover new elements. Even if I am not leading the project, I want to be part of the research that discovers new elements someday.