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Integral Experiment on Polyethylene Using Radiative Capture and Inelastic Excitation in Indium Foils inside a D-D High Flux Neutron Generator.


Cross-sections nuclear data are invaluable to the nuclear community. As well as providing information on nuclear structure of matter and reaction dynamics, they provide practical support for applications including design and modelling of fission and fusion reactors, shielding geometry for radiation sources such as radiation treatment machines, etc. Evaluated cross section data in form of evaluated nuclear data are the products of experiment and theoretical modelling. Before they can be used, their reliability and accuracy need to be assured. This is done through integral experiments in which prediction from simulation using the evaluated nuclear data is compared to experimental value.

Integral benchmark experiments are used to test the accuracy and reliability of evaluated nuclear data. They are a rich source of information with which a wide range of validation and comparison exercises can be made [1]. Such benchmark experiments provide global measures of data performance for applications and are a valuable resource for nuclear data testing and evaluation efforts [2]. Integral experiments in reactors play an essential role in nuclear data validation and improvements [3].

Applications of integral benchmark experiments are found in fission and fusion reactors designs for safety, in fast neutron therapy for shielding calculation. They are a very powerful means of assessing the quality of nuclear data for specific applications, nicely complementing differential measurements [4].

Neutron generators such as D-D fusion generators can serve the purpose of performing integral benchmark experiment for validation of cross-section data. The Nuclear Engineering department of the University of California Berkeley has D-D neutron generator called the High Flux Neutron Generator (HFNG). It operates in the range of 100-125 keV of accelerating voltage. The generator produces neutron current of the order of 108 per second. These neutrons have energies between 2.2 – 2.8 MeV.

In this work, neutron elastic and inelastic scattering cross sections on carbon and hydrogen nuclear data in the evaluated nuclear database ENDF/B-VII.1 are compared to experiments via the observation of radiative capture and inelastic excitation of two long-lived isomeric state in 116In and 115In on a foil mounted in the center of the HFNG in order to benchmark scattering on a polyethylene moderator surrounding the generator.

Two different methods were used: single and double ratios of the products of the two reactions. Results from both methods show generally good agreement with the expected values, although some statistically significant differences are observed. These results highlight the utility of compact DD neutron sources such as the HFNG as integral benchmarks and suggest that further work should be done to improve the evaluation of scattering data on polyethylene due to its important role in shielding applications.

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