News Excerpt:
A recent study on plutonium isotope fission has provided significant updates that have implications for various fields, including nuclear reactor design and nuclear medicine.
More about the research:
- This research, conducted at the Los Alamos Neutron Science Centre, focuses on the Prompt Fission Neutron Spectrum (PFNS) of plutonium-240 (Pu-240), revealing key differences between predicted and observed outcomes.
- The study is only the second attempt to measure the PFNS of induced fission in Pu-240 and the first to use neutrons with energy greater than 0.85 mega-electron-volt (MeV).
The Experiment:
- The researchers used a particle accelerator to bombard a tungsten disc with pulses of protons, producing neutrons with energy ranging from 0.01 to 800 MeV.
- These neutrons were then directed to a chamber containing a highly pure Pu-240 sample, weighing just 20 milligrams, to minimize the emission of alpha particles.
- An array of liquid scintillators, substances that emit flashes of light when struck by energetic particles, tracked the fission products emitted by the Pu-240 sample.
- The researchers meticulously subtracted contributions from spontaneous fission, alpha particles, and other sources to isolate data relevant to neutron-induced fission, focusing on incident neutrons with energies between 1 and 20 MeV.
Key Findings:
- The study revealed significant deviations between the predicted and observed PFNS after induced fission in Pu-240.
- Additionally, the researchers reported a higher-than-expected rate of second-chance fission, where a nucleus becomes fissionable after losing a neutron.
- They also found indications of third-chance fission, though these were less clear in the data.
Significance and Applications:
- In the context of nuclear power, understanding the behavior of Pu-240 is particularly relevant for India's second stage of its nuclear power program, which focuses on plutonium fission.
-
- The prototype fast breeder reactor (PFBR) at the Madras Atomic Power Station, which uses plutonium recovered from spent CANDU (Canada Deuterium Uranium) fuel, will contain significant quantities of Pu-240. Insights from this study will aid in improving reactor design and safety.
- Moreover, the updated data on Pu-240 fission will benefit various applications that rely on nuclear reaction models.
- These include designing nuclear reactors, radiation shielding, calculating radiation doses in nuclear medicine, and even tracing the origins of elements in the universe.
Future Scope:
- The study's findings highlight the need for ongoing research to refine nuclear reaction models.
- Current models are based on data libraries compiled from various experiments, reactor operation records, and simulations.
- The discrepancies observed in this study suggest that these data libraries, including ENDF, JEFF, and JENDL, need to be updated to incorporate new data on multi-chance fission and pre-equilibrium neutron emission processes.
- Future research will likely focus on further experiments to clarify the contributions of different fission processes and refine the energy thresholds for pre-equilibrium neutron emission.
- These efforts will enhance the accuracy of nuclear reaction models, ultimately leading to improved applications across nuclear science and engineering.
