Jaime Gomez (on the left) and Keegan Kelly are seen engaged in the preparation of the Chi-Nu experiment, which involves calibrating the distance of detectors and installing the gas lines needed for the fission-counting target at the center. Image courtesy of Los Alamos National Laboratory.
The experiment is designed to analyze the energy distribution of neutrons produced through neutron-induced fission.
The Chi-Nu physics experiment, conducted at the Department of Energy’s Los Alamos National Laboratory, has yielded invaluable and hitherto unrecorded data that is crucial for augmenting nuclear security measures, comprehending criticality safety, and advancing the design of fast-neutron energy reactors. The Chi-Nu experiment, which spans several years, is focused on evaluating the energy range of neutrons that are emitted when fission is induced by neutrons. It has recently completed an unprecedented, thorough uncertainty analysis on the three key actinide elements—uranium-238, uranium-235, and plutonium-239.
“Though the discovery of nuclear fission and its associated chain reactions dates back just over eight decades, researchers continue to pursue a comprehensive understanding of fission processes for major actinides,” stated Keegan Kelly, a physicist with Los Alamos National Laboratory. “Throughout the project’s duration, we have identified explicit markers of fission processes that, in numerous instances, were never detected in earlier experiments.”
The final Chi-Nu study by the team at Los Alamos, focusing on the isotope uranium-238, was recently published in the academic journal Physical Review C. This experiment analyzed the prompt fission neutron spectrum of uranium-238: both the energy of the neutron that initiates the fission—essentially the neutron that collides with and divides the nucleus—and the subsequent varying energy levels (the spectrum) of the emitted neutrons. The Chi-Nu project zeroes in on fission induced by “fast neutrons,” with the inciting neutron energies calculated in millions of electron volts, an area where measurements have traditionally been scant.
Physicist Keegan Kelly is seen assembling a fission-counting target that contains approximately 100 milligrams of a subject actinide for a Chi-Nu experiment. The setup includes 54 liquid scintillation neutron detectors and 22 lithium-glass detectors that capture neutrons across various energy bands. Image courtesy of Los Alamos National Laboratory.
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Pivotal Data for Fission-Related Research
Combined with similar studies on uranium-235 and plutonium-239, the Chi-Nu experiment’s results have become, in many cases, the primary source of empirical data steering contemporary initiatives for evaluating the prompt fission neutron spectrum. The data serve to refine nuclear models, perform Monte Carlo calculations, assess reactor functionality, and more.
Actinide elements and their potential for chain reactions are crucial for both nuclear weaponry and energy reactors. Actinides are a set of 15 radioactive elements with atomic numbers ranging from 89 to 103. When a nucleus undergoes fission, multiple neutrons are liberated, which could potentially initiate fission in adjacent nuclei, leading to a chain reaction. The likelihood of subsequent reactions in this chain is contingent on the energy levels of the emitted fission neutrons.
Experimental Procedure at LANSCE
The Chi-Nu experiment was executed at the Weapons Neutron Research facility situated within the Los Alamos Neutron Science Center (LANSCE). The advanced setup involved tests across multiple energy spectrums. The LANSCE proton beam strikes a tungsten target, producing neutrons that proceed along a trajectory towards the Chi-Nu apparatus. When these neutrons encounter the uranium-238 isotope, fission may be induced, and this event is documented. The emitted neutrons are then gauged using either liquid scintillation or lithium-glass detector arrays, depending on the energy spectrum pertinent to the experiment, and both types of detectors register light emissions stimulated by the neutrons.
Future Avenues for the Utilization of Chi-Nu Expertise
Ongoing research aims to complete the characterization of actinide isotopes. In related projects funded by the Nuclear Criticality and Safety Program, the Chi-Nu research team is presently compiling and scrutinizing data on plutonium-240 and uranium-233.
Following the conclusion of measurements by the Office of Experimental Sciences, the team is considering the application of their acquired knowledge and methodologies in fission neutron measurements to a range of additional isotopes. They are also diverting their focus towards capturing data on neutrons emitted from neutron scattering reactions. Within these reactions, neutrons transit through a material and deposit energy. Both the emitted neutron and gamma-ray energy, along with their angular distributions, are recorded, as is the probability of the reaction occurring, generally termed as the neutron scattering cross-section.
Reference: “Measurement of the 238U(n, f) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons with 1.5–20 MeV energy” authored by K. J. Kelly et al., published on 14 August 2023 in Physical Review C.
DOI: 10.1103/PhysRevC.108.024603
Funding: The research has been financially supported by the U.S. Department of Energy via the Los Alamos National Laboratory’s Office of Experimental Science.
Frequently Asked Questions (FAQs) about Chi-Nu experiment
What is the primary objective of the Chi-Nu experiment?
The primary objective of the Chi-Nu experiment is to measure and analyze the energy spectrum of neutrons emitted from neutron-induced fission. This data is crucial for advancing nuclear security measures, understanding criticality safety, and improving the design of fast-neutron energy reactors.
Who conducted the Chi-Nu experiment?
The experiment was conducted by a team of researchers at the Department of Energy’s Los Alamos National Laboratory.
What elements are primarily studied in the Chi-Nu experiment?
The Chi-Nu experiment focuses on the three major actinide elements—uranium-238, uranium-235, and plutonium-239.
Where was the experiment conducted?
The Chi-Nu experiment was conducted at the Weapons Neutron Research facility within the Los Alamos Neutron Science Center (LANSCE).
How does the Chi-Nu experiment contribute to current nuclear models and calculations?
The results from the Chi-Nu experiment serve to refine existing nuclear models, aid in Monte Carlo calculations, and assess the performance of reactors. In many cases, the data from the Chi-Nu experiments have become the dominant source of experimental data for these purposes.
What types of detectors were used in the experiment?
The experimental setup included 54 liquid scintillation neutron detectors and 22 lithium-glass detectors to capture neutrons across various energy bands.
What is the significance of actinide elements in the Chi-Nu experiment?
Actinide elements and their potential for chain reactions are crucial for both nuclear weaponry and energy reactors. The likelihood of subsequent reactions in a nuclear chain is contingent on the energy levels of the emitted fission neutrons, which the Chi-Nu experiment aims to measure.
What are the future applications of the data gathered from the Chi-Nu experiment?
The expertise and methodologies acquired from the Chi-Nu experiment will be applied to a range of additional isotopes. Researchers are also shifting their focus towards capturing data on neutrons emitted from neutron scattering reactions.
Who funded the Chi-Nu experiment?
The research was financially supported by the U.S. Department of Energy via the Los Alamos National Laboratory’s Office of Experimental Science.
Where can I find the published results of the Chi-Nu experiment?
The final study focusing on the isotope uranium-238 was recently published in the academic journal Physical Review C.
More about Chi-Nu experiment
- Los Alamos National Laboratory: Official Website
- Physical Review C: Academic Journal
- U.S. Department of Energy: Official Website
- Nuclear Criticality and Safety Program
- Actinide Series: Scientific Overview
- Neutron-Induced Fission: Scholarly Articles
- Monte Carlo Methods in Physics
- Neutron Scattering: An Overview
- Nuclear Reactor Design: Basics
8 comments
While the science is cool, I hope all this research also considers the environmental impacts of nuclear energy.
This is so complex but fascinating. Anyone know where I can read the full article in Physical Review C?
didnt know that actinides had such a big role in chain reactions. Guess I got something new to read about tonight.
kudos to the team at Los Alamos. This level of detail in the research can totally redefine how we look at nuclear reactors and security.
If this enhances nuclear security, then it’s a win in my book. Anything that makes the world safer is a step in the right direction.
I’m amazed that we’re still getting groundbreaking data even 80 years after discovering nuclear fission! The actinide info is especially interesting.
If this can improve reactor design, it could be a game-changer for the energy market. Worth keeping an eye on.
Wow, the Chi-Nu experiment sounds like a big deal for nuclear science. crazy how they can measure neutrons with such precision.