When Atomic Worlds Collide: Exploring the Role of Shape and Breakup in Nuclear Fusion

From Atomic Bonds to Nuclear Fusion

Everything in the universe is made of atoms and at the heart of every atom lies its nucleus, held together by incredibly strong nuclear forces. When two nuclei come close enough to each other, they can merge and form a heavier nucleus, a process called nuclear fusion.

Fusion is nature’s way of producing energy. It powers the Sun and stars, where extreme temperature and pressure allow light nuclei like hydrogen to fuse into helium, releasing enormous energy in the process.

In the laboratory, however, the scenario is far more delicate. Scientists use particle accelerators to make nuclei collide at high speeds to study how they interact. These studies not only help us understand how elements are formed in stars, but also how to harness fusion energy and produce useful isotopes for medicine and industry.

Fusion as a Window into Nuclear Structure

When two heavy nuclei collide, several outcomes are possible. Sometimes, the two merge completely to form a single, highly excited nucleus — this is called Complete Fusion (CF).

But often, especially when the incoming nucleus (the projectile) is weakly bound, it breaks apart before or during the collision. In that case, only a part of it fuses with the target nucleus, while the rest escapes. This process is known as Incomplete Fusion (ICF) or Break-Up Fusion (BUF). These fusion processes are not just about forming new nuclei, they provide a unique way to probe how nuclear forces, angular momentum, and internal structures influence the dynamics of a reaction.

The AMU Tradition of Nuclear Research

The Department of Physics at Aligarh Muslim University (AMU) has a long and distinguished history of research in nuclear physics, dating back to the early 20th century. Started with fabrication of GM counters and electronic setup counters for measuring Shor lived activities produced with Indigenous Cockcroft Walton 14 MeV neutron generator. The neutron generator was built by a team lead by Prof P S Gill. Prof H S Hans and Prof Khurana played a key role in is development accelerator facilities and legacy continued with Prof R. Prasad, that later we moved to various other National Accelerator facilities. With advanced facilities like HPGe detector systems, GDA+ CPDA systems and collaborative experiments conducted using national accelerators such as the 15 UD Pelletron at IUAC, New Delhi, AMU’s experimental nuclear physics group has contributed extensively to understanding nuclear reactions, structure, and decay dynamics. Also used many facilities abroad to study the reaction dynamics at various energy regimes. Continuing this tradition, our recent work explores how two key factors, target deformation and projectile breakup, shape the outcome of fusion reactions.

15 UD Pelletron accelerator at IUAC, New Delhi

The Science Behind the Study

In our experiments, we investigated the fusion of oxygen-16 nuclei with targets like ytterbium-174 and thulium-169.These reactions occur near the Coulomb barrier — the energy threshold where the repulsive electric force between the positively charged nuclei is just overcome. We discovered that when the target nucleus is deformed (that is, not perfectly spherical), the incoming projectile experiences uneven nuclear forces. This distortion makes it more likely for the projectile to break up into smaller fragments, leading to incomplete fusion. Conversely, for more spherical nuclei, complete fusion is more probable. Thus, the shape of the target plays a decisive role in determining the fusion dynamics.

Probing the Process: The Role of Gamma Rays

To study these reactions, we used high-purity germanium (HPGe) detectors to capture gamma rays emitted by the excited nuclei formed during the reaction. These gamma rays act as a “signature,” helping identify the reaction products and measure how much of the projectile actually fused. By comparing the observed data with theoretical models (such as PACE4 simulations), we could clearly see how ICF strength — the proportion of incomplete fusion — varies with both beam energy and target deformation.

Experiments were performed using the 15 UD Pelletron accelerator at IUAC, New Delhi. Gamma-ray detectors helped identify the reaction residues and quantify fusion probabilities.

Key Findings

• Target Deformation: More deformed nuclei (like ¹⁶⁹Tm) enhance projectile breakup, increasing ICF probability.

• Projectile Stability: Weakly bound projectiles, which have low breakup thresholds, contribute more to ICF.

• Energy Dependence: The fraction of ICF rises with increasing beam energy, reaching around 25–30% above the Coulomb barrier.

• Angular Momentum: Breakup fusion serves as a mechanism for shedding excess angular momentum, influencing the final nuclear state.

  
  

Beyond the Lab: A Step Toward Medical Applications

Interestingly, these nuclear reactions also produce radioactive isotopes that can be used in medicine. One such example is platinum-186 (¹⁸⁶Pt), a theranostic isotope that can be used for both diagnosis (via gamma-ray imaging) and therapy (through low-energy electron emission).

“Radioisotopes like ¹⁸⁶Pt produced in such fusion studies have potential applications in cancer diagnosis and therapy.”

This bridges the gap between fundamental nuclear physics and applied nuclear medicine, highlighting how experiments on nuclear structure can lead to real-world benefits.

Looking Ahead

The next phase of our research will employ advanced detector arrays (like INGA) coupled with charged-particle detectors to examine how angular momentum and breakup processes evolve with different nuclear combinations. Such studies are crucial, not only for understanding fusion hindrance and energy dissipation but also for advancing nuclear technology, astrophysics, and isotope production

In summary the fusion reactions are like a cosmic conversation between nuclei, and their outcome depends as much on their shape and structure as on their energy. Through precise experiments, AMU’s research has shown that target deformation and projectile breakup play intertwined roles in deciding whether nuclei fully unite or part ways. In reveling these microscopic mysteries, we take another step toward understanding how matter, energy, and the elements themselves are forged, both in the stars above and in the accelerators here on Earth.

Author is a senior experimental nuclear physicist at the Physics Department, Aligarh Muslim University, ALIGARH, INDIA

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