Nuclear fusion is a tantalizing prospect. It theoretically offers boundless, zero-carbon energy. Yet the challenges in realising fusion on earth are formidable. Fusion initiates when deuterium and tritium reach extremely high temperatures; somewhere above 100 million degrees Celsius, to be precise. Also, the superheated plasma formed from the initial reaction must be densely confined long enough to complete the process. This is a key area of fusion research. Beyond academic hurdles, there are still questions of economic feasibility. For these reasons and more, fusion has long been deemed out of reach.

Fusion science is once again under the microscope as scientists seek a solution to the global energy and climate crises. Researchers are finally pushing the boundaries of achievable fusion on Earth. The recent experiment at Lawrence Livermore National Lab is a testament to this development. In this context, boron nitride (BN) is being examined for its potential contributions to help make fusion a scalable reality.

Neutron Absorption and the Advantages of Boron Nitride

Boron nitride, a compound formed from boron and nitrogen, has been used successfully as a neutron absorber in nuclear fission reactors, neutron detectors, and neutron beam lines. The effectiveness of BN can be attributed to the properties of boron, particularly its isotope, Boron-10. Boron is an element of interest in the nuclear field because it has two stable isotopes, Boron-10 and Boron-11. Both are naturally occurring and abundantly available.

Materials like boron carbide (B₄C), boric acid (H₃BO₃) and boron nitride (BN) are all candidate materials to utilize the benefits of boron. However, boron nitride has advantages for certain applications. The qualities that make BN attractive in traditional neutron absorption applications may be of interest for future fusion reactor systems.

Overview of Neutron Absorption

When a neutron collides with an atom, one of two outcomes will occur: either the neutron is absorbed into the atom or the atom undergoes nuclear fission, splitting into two new atoms. If the atom absorbs the neutron, it will transform into a new isotope. The energy released is minimal when a stable isotope is formed. However, if the isotope is unstable, it becomes radioactive and enters a process of nuclear decay.

Generally, elements with a large neutron cross section and a propensity to form stable isotopes are considered good neutron absorbers. The neutron cross section is the radius that will interact with a neutron as it approaches the atom. As it increases, the probability that a neutron will be absorbed also increases. 

Benefits of Boron Nitride

Neutron Absorption Efficiency

One of the notable characteristics of boron, especially Boron-10, is its large neutron cross section. It is very efficient for absorbing thermal neutrons in particular. Furthermore, boron emits lower energy gamma radiation than other common absorbers, such as gadolinium or cadmium, after absorbing a neutron. This can simplify radiation shielding considerations.

Machinability and Design Flexibility

BN's machinability offers potential advantages in design applications. It can be shaped into various forms precisely, providing design options that might be more limited with materials like boron carbide.

Potential in Polymer Integration

Another aspect of BN's versatility is its potential as a filler in polymers. By incorporating BN powder, certain polymers might exhibit enhanced neutron-absorbing properties, leading to the development of specialized components.

Proton-Boron Fusion: An Emerging Area of Interest

The fusion research landscape is diverse, with proton-boron fusion being one of the areas under investigation. In this context, hexagonal boron nitride (hBN) is being studied as a potential boron source. In this case, Boron-11, is the isotope of interest. Both isotopes are found in Saint-Gobain hexagonal BN products according to the natural abundance of each isotope.

BN is a material to consider for research centers, start-ups, and international reactor initiatives like the International Thermonuclear Experimental Reactor (ITER) in France. The characteristics that BN exhibits make it interesting as a traditional neutron absorbing material, but it could have a greater role to play in the evolving landscape of fusion research.

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References and further reading:

1.    Rolfs, C.E. (2010). Hans A. Bethe Prize Talk: LUNA: a Laboratory Underground for Nuclear Astrophysics. Bulletin of the American Physical Society.
2.    Stephen, Shankland. (2023). What the Fusion Ignition Breakthrough Really Means for Energy. CNET. (Available at: https://www.cnet.com/science/what-the-fusion-ignition-breakthrough-real…) 
3.    Ryan, Jackson and Ravisetti, Monisha. (2022). Major Energy Breakthrough: Milestone Achieved in US Fusion Experiment. CNET. (Available at: https://www.cnet.com/science/major-energy-breakthrough-milestone-achiev…)