[Reading Science] "All Humanity is Starry Love"... Accelerator Exploring the Atomic World

From Cancer Treatment to the Secrets of the Universe's Birth
Active Use of Accelerators Researching the Atomic World

"My Love from the Star." It was a popular drama from 2013 to 2014. Although it literally means "an alien," actual scientists view all of humanity as "My Love from the Star." This is because the elements that make up humans and all life on Earth were created during the 13.8 billion-year history of the universe through the birth, growth, explosion, and death of stars. Even the oldest sun in the solar system was not formed in the early universe but was created by the gathering of hydrogen and helium atoms produced when a distant star exploded long ago. Studying the origin and characteristics of elements is a major task in physics today, aimed at uncovering the history and essence of the universe and life. In particular, basic scientific research using accelerators to discover rare atomic nuclei not found on Earth is actively conducted worldwide for applications in semiconductors, medicine, and new material development.

▲Completed RFQ linear accelerator. [Photo by Ministry of Science and ICT]

The World of Femto Science

Elements, that is, atoms, consist of electrons and atomic nuclei (protons + neutrons). The distance between electrons and the atomic nucleus is relatively large, comparable to the distance from the heart of Seoul’s Jongno district to Uijeongbu, and the space between them is mostly empty. Protons, which make up the atomic nucleus, carry a positive charge and theoretically cannot bind together. However, multiple protons and neutrons are held together by the "nuclear force," which is stronger than electromagnetic force. Physicists determine the atomic number by the number of protons in an atom, which defines the chemical properties of the element. The mass of the element is considered as the sum of the number of protons and neutrons. Protons themselves are made up of quarks and gluons. The world of atoms is only about femtometers (one quadrillionth of a meter), much smaller than nanometers (one billionth of a meter). The tool used to explore this femtometer world is the accelerator. It is a device that accelerates charged particles by applying microwaves (electromagnetic force). Accelerators are classified by the type of particles (protons, heavy ions, electrons), their form (linear, circular), and the type of electromagnetic waves (DC, AC). Among these, synchrotron radiation accelerators accelerate electrons close to the speed of light to produce light, and recent research and development (R&D) achievements have been noteworthy.

The SLAC National Accelerator Laboratory at Stanford University in the United States completed and began operating the world’s most powerful X-ray laser (linear synchrotron radiation accelerator) on the 12th. It can capture the movement of atoms occurring at the moment of chemical reactions and record videos at 100,000 frames per second. The existing synchrotron radiation accelerator LCLS-I (Linac Coherent Light Source) was upgraded to LCLS-II with an investment of $1.1 billion. The number of X-ray pulses per second increased from 120 to an astonishing 1 million, more than 8,000 times, enabling video recording at 100,000 frames per second. The brightness of the laser also increased by more than 10,000 times on average. This allows molecular motion to be filmed with unprecedented clarity. The international journal Nature stated, "It is possible to image the extremely fast movements of materials, including electrons orbiting atoms during chemical reactions," and added, "This will help uncover the secrets of photosynthesis and develop new electronic devices for computing systems."

Particle Accelerator at the Particle Therapy Center

South Korea has been utilizing the 3rd and 4th generation Pohang synchrotron radiation accelerators since 1994. Currently, a 4th generation multipurpose synchrotron radiation accelerator is being constructed in Ochang, Chungbuk, with an investment of 1 trillion won. It will accelerate electrons to 4 GeV (4 billion electron volts) at the picometer scale to produce light about 1 trillion times brighter than the sun.

The heavy ion accelerator (RAON), which accelerates heavy ions such as uranium to create new isotopes, completed the first phase of the low-speed section (one-tenth the speed of light) at the end of last year with an investment of 1.5 trillion won. After further R&D, a high-speed section (about 150,000 km/s) is expected to be established in the 2030s. This will be applicable not only to uncovering the secrets of the universe’s birth but also to fields such as semiconductors, secondary batteries, chemistry, bio, and medicine. Recently, medical institutions have gained attention for adopting cancer treatment technology using heavy ion accelerators. The principle involves accelerating carbon ions to near the speed of light to precisely destroy cancer cells. Yonsei University Severance Hospital began its first treatment in May, and Seoul National University Hospital is also planning to build a heavy ion accelerator treatment center in Gijang-gun, Busan. The Korea Atomic Energy Research Institute operates a proton accelerator in Gyeongju.

Find New Atoms

Accelerators are called "Nobel Prize veins." Among over 100 Nobel Prizes in Physics awarded historically, more than 20 are related to accelerator research. Discovering a new element immediately places one on the Nobel Prize candidate list. Recently in Japan, a research team succeeded in observing for the first time the theoretically predicted oxygen isotope (oxygen-28, 28-O) using an accelerator, attracting attention. The Tokyo Institute of Technology research team published a related paper in Nature on the 30th of last month. It has been known that the atomic nucleus of oxygen (O2) consists of 8 protons and 3 to 18 neutrons. Oxygen-28 has 20 neutrons and was observed for the first time. The peculiar thing is that oxygen-28 decayed immediately after being created. This result differs from previous theories about atomic composition. Scientists have believed that atomic nuclei with certain numbers of neutrons?2, 8, 20, 28, 50, 92, 126, called "magic numbers"?are stable elements with long decay periods. Therefore, scientists who predicted and sought to observe oxygen-28 expected it to be a stable substance with a long half-life because it has 20 neutrons, a "magic number." Although further verification is needed, the scientific community regards this as a revolutionary finding that may require rewriting existing atomic composition theories. It may mean that "20" should be removed from the magic numbers.

▲4th generation synchrotron radiation accelerator.

South Korea’s accelerator research has reached a world-class level in terms of facilities and resources. However, field researchers point out that while major powers like the United States are increasing their research investments and achievements, Korea’s budget has rapidly decreased recently, putting it in a retreat phase. On the 14th, Han In-sik, head of the Rare Isotope Research Division at the Institute for Basic Science, said, "In the case of RAON, only the first phase low-energy section has been completed, and without the second phase high-energy section, winning a Nobel Prize is almost impossible." He added, "Since it is the world’s first to use both online isotope separation (ISOL) and in-flight fragmentation (IF) methods, expectations are high, but with only the first phase, it is difficult to make ‘first’ discoveries or significantly expand existing research areas." The Pohang synchrotron radiation accelerator and Osong multipurpose synchrotron radiation accelerator are limited because they use circular rather than advanced linear methods, making dynamic observation impossible. The proton accelerator at the Korea Atomic Energy Research Institute is also at 100 MeV, lower than major powers (500?3000 MeV), and lacks neutron utilization facilities, so upgrades are being considered.