Education

原子核は様々な量子現象の舞台です。一粒子運動と集団運動の拮抗、自発的対称性の破れ（回転対称性、反転対称性、ゲージ対称性…）、コヒーレンス、量子もつれと干渉現象…。原子核の実験技術は飛躍的な発展のさなかにあります。私たちは最先端のガンマ線トラッキング検出器と希少原子核ビームを組み合わせて原子核の種類や励起エネルギー、さまざまな量子数を変化させることで原子核に現れるさまざまな量子構造を研究しています。

一例として回転対称性や反転対称性を自発的にやぶった状態の探索があります。原子核は中性子と陽子（あわせて核子）が自己束縛する孤立した有限多体系であるため、太陽系における太陽のような中心を持たず、その形状をその構成要素である核子たち自身で「民主的に」決めることになります。回転対称な空間に浮かぶこの系は古典的には回転対称な形状、すなわち球形をとりますが、原子核の場合、量子性のために多くの場合変形していることが分かっています。これは量子系における自発的対称性の破れの典型例で、ゲージ空間における対称性の破れと理解できる物性における超伝導現象など、さまざまなスケールの量子系とのつながりがあります。原子核の変形はよく研究されていますが、これまでに実験で知られているのは主として軸対称四重極変形、すなわち、ラグビーボール型変形（プロレート変形）やミカン型変形（オブレート変形）で、理論的にはもっと変わった変形も多数予言されています。例えば、非軸対称（三軸非対称）の四重極変形や、空間反転対称性すら破る洋梨形変形やテトラポット型変形（八重極変形）、軸対称四重極変形のなかでも非常に変形度の大きなハイパー変形などがあげられます。こうした形状は中性子数と陽子数の関数として変化していきますが、原子核科学研究センターがRIビームファクトリーにもつ OEDO/SHARAQ ビームラインで広い領域の中性子数と陽子数の原子核を生成し、ガンマ線トラッキング検出器で測定することを目指しています。

We study the disappearance of antimatter, the nature of dark matter, and the very origins of matter in the early universe—framing all of these in terms of fundamental symmetry breaking. Heavy nuclei with extreme shapes serve as quantum-amplifiers of unknown symmetries and interactions, acting like microscopes for the tiniest symmetry-violating effects. By combining accelerator beams and laser techniques, we’re pioneering quantum-sensing methods—most notably optical-lattice atom interferometry—to probe the properties of hypothetical particles. Current research directions include:

• Francium EDM Search: Using an optical-lattice interferometer to measure the permanent electric dipole moment of francium atoms.
• Anapole Moment Studies: Investigating how the weak interaction propagates through a nuclear medium.
• Laser-Cooled Polar Molecules: Developing Fr–Sr molecules for precision tests of fundamental symmetries.

Through these efforts, we aim both to discover phenomena beyond the Standard Model and to unravel how symmetry breaking emerges and evolves in quantum many-body systems—using extreme nuclei as our experimental laboratory.

Approximately 3,000 nuclides have been confirmed experimentally, and nuclear‐structure models predict another 3,000 yet to be observed. Most of these are radioactive isotopes—bound by the strong force but decaying via the weak interaction—and over ten radioactive-beam facilities worldwide are racing to study them. As the host laboratory for the world-unique slow-beam system OEDO coupled with the SHARAQ magnetic spectrometer, we collaborate with users from around the globe to unravel how nucleons self-organize in finite quantum many-body systems.

In particular, we’re experimentally probing recently discovered phenomena such as shape coexistence, exotic deformations, and the Bose–Einstein-condensate to BCS crossover. We also investigate the astrophysical origins of heavy elements by measuring neutron-capture cross sections on neutron-rich nuclei. To support these programs, we are developing advanced detector technologies—high-efficiency γ-ray arrays, recoil-particle detectors based on silicon strip sensors, and ultra-thin diamond detectors—to deliver the timing, position resolution, and radiation hardness these experiments demand.

Nuclei—finite many-body systems made up of only a few dozen to around a hundred nucleons—exhibit a rich variety of structural modes determined by their proton–neutron composition. As finite systems, they possess macroscopic attributes such as surface and shape. By probing a nucleus via nuclear scattering, one can induce rotational and vibrational motion; these processes, known as nuclear collective excitations, directly reflect fundamental properties like nuclear stiffness. The Exotic Nuclear Reactions Group investigates these responses to uncover the interactions that generate novel collective behaviors and exotic structural phases.

With unstable beams from RIBF, we can now study highly asymmetric nuclei in scattering experiments—systems that were previously inaccessible. Our core focus is on their spin and isospin responses. To enable these measurements, we have developed specialized neutron detectors such as the PANDORA array, and we periodically produce new unstable beams (for example, spin isomers). We also use one exotic nucleus to probe another—searching for new resonant states via in-beam scattering. Experimental nuclear physics is entering a golden era in which straightforward ideas—like using high–angular-momentum beams to efficiently populate high-spin states—can be tested and realized.

In the moments following the Big Bang, the universe was filled with an ultra–high-temperature quark–gluon plasma (QGP). By recreating this QGP in the laboratory and probing its properties, we aim to unravel the mysteries of matter creation in the early universe—specifically the QCD phase transitions: quark confinement, chiral-symmetry breaking, and hadron mass generation. The only way to produce and study this extreme state of matter experimentally is via high-energy heavy-ion collisions. We pursue this program through the ALICE experiment at CERN’s Large Hadron Collider (LHC).

The mechanism by which stars shine in the universe and explosive phenomena such as supernovae occur can be explained by the action of small atomic nuclei inside atoms. "Nuclear astrophysics" is a research field that connects celestial bodies floating in the vast universe with tiny atomic nuclei. The power of nuclear astrophysics is needed to answer questions such as how the elements around us were synthesized throughout the history of the universe, and how stars in the universe burn and explode.

Yamaguchi Lab./Nuclear Astrophysics Group is working with researchers from all over the world to solve various mysteries of the universe, from the Big Bang nucleosynthesis, the first element synthesis in the universe, to the frequent explosive phenomena in the universe, such as X-ray bursts, using a unique device "CRIB" that can generate unstable nuclear beams at the temperatures of explosive stellar environments.

Nuclear astrophysics has become a major theme in nuclear physics worldwide. While the main research of Yamaguchi Lab. is based in Japan, we are conducting unique research in a highly international research environment.