Habiba Abbasi
The properties of magnetism, protein structure analysis, stress and strain in jet engines, explosive materials, energy and matter are all essential domains for the development of our society that require research efforts and in-depth studies using neutron optics. The neutron chopper, invented in 1935, is a device that filters beams of neutrons at different energy levels using a rotating chopper blade. Neutron absorbing disks in the chopper rotate at high speeds to chop neutron beams, resulting in neutron beams at uniform energy levels. As you can imagine, with this high level of functionality, it is indisputable that an immense amount of heat and stress is generated. Extensive heat and stress can reduce the functionality of the neutron chopper and increase its risk of structural failure. Improving the design of the neutron chopper to accommodate the high heat and stress created can enable scientists to continue studying fundamental topics of human interest.
James Lu and colleagues from the Brown University School of Engineering investigated methods to design stable rotors and provide effective cooling for neutron choppers. This study was conducted by exploring advanced manufacturing for neutron chopper design. Advanced manufacturing is a technique used to make products more efficient and sustainable. The paper makes use of thematic analysis to address the problem of the current neutron chopper design. This means that as opposed to the commonly used statistical datasets to conduct research, this study analyses and interprets patterns or themes from qualitative data.
Lu, an undergraduate research assistant at Brown University School of Engineering emphasizes the advantage of using smart technologies to innovate the chopper design. “The usual advances in the field have been achieved by adding stages to the beamline, with narrow innovative possibilities. Advanced manufacturing and a family of smart technologies brings the design ability beyond conventional techniques and geometries of the neutron chopper design toward the ideal.”
The results of this study show that there are four advanced manufacturing technologies identified by the US Department of Energy that can be collectively implemented to improve cooling and handle the structural complexity of the neutron chopper. These four are outlined in figure 1 below.
Figure 1. Four advanced manufacturing technologies identified by the US Department of Energy can be implemented in the neutron chopper design.
These clean energy manufacturing techniques are advantageous compared to traditional manufacturing because they improve energy use and minimize environmental impacts associated with production, use and disposal of products.
Designing Stable Rotors
Using the advanced manufacturing techniques identified, Lu has suggested constructing rotor blades for the neutron chopper from light aluminum coated with Gadolinium-157, an elemental isotope. Advanced manufacturing can create far more complex devices with previously unattainable geometries compared to traditional “mold-and-cast” methods and is able to use materials that can withstand nuclear radiation as is the case with the neutron chopper. Together these technologies can improve filtering of the neutron beam energy distribution as they provide a high absorption cross section for neutrons, are non-toxic and efficiently exchange heat during high speed rotation.
Effective Cooling System
Using mathematical modeling, Lu approximated that the temperature of the neutron chopper motor would increase by approximately 0.45°C every minute and rise from 20°C to 47.2°C during the operating time. The current neutron chopper system utilizes a water-cooling piping system to cool motor components and the heat generated by the rotor must be dissipated via conduction. Lu compares coolant fluids based on four parameters and identifies methyl formate as an effective coolant for the rotor as it transfers heat at the same rate at which the rotor heats, has a high heat capacity, high thermal conductivity and satisfactory phase change temperature.
Future Directions
These findings suggest a new method for generating uniform energy neutron beams through advanced manufacturing and instrumentation which improve heat dissipation and component fabrication of the neutron chopper. Lu explains that “breakthroughs in neutron chopper design by advanced manufacturing have a broad impact on society. To name a few, biologists can scatter neutrons from DNA solutions; chemists can probe complexes for their molecular structures; physicists can exploit the universe beyond condensed matter. The sky's the limit!”
The study also aims to inspire the undergraduate audience to pursue nuclear engineering in relation to the development of clean energy. Lu is positive that “almost all sectors need people with skills in applied nuclear science: nuclear medicine in healthcare and nuclear materials in high tech.” This is vital for the future, particularly in light of global climate change–a major issue of our time and radioactive materials in the fight against cancer.
References
Lu, J., Sabharwall, P., Heidrich, B., and Christensen, R. (2020). Advanced Manufacturing and Instrumentation for Neutron Chopper Design. Journal of Young Investigators, 38(6), 60-67, available: 10.22186/jyi.38.6.60-67