SUMMARY

One method of producing a broad energy range of neutrons for experiments is through the use of accelerators. Accelerator production of neutrons can be accomplished via accelerating protons to high energies (40 - 3,000 MeV) and inducing spallation of nuclei in a target made of heavy metal. Several facilities, notably the Swiss Spallation Neutron Source (SINQ), the Los Alamos Neutron Science Center (LANSCE) in the United States and the ISIS Pulsed Neutron and Muon facility in the United Kingdom use solid metal targets, typically tungsten, for the production on the neutrons. While in the past decade, two other primer facilities, the Spallation Neutron Source (SNS) in the United States, and the Japan Proton Accelerator Research Complex (J-PARC), incorporate a liquid mercury target system. While liquid metal targets allow for efficient cooling of the target, they also present radiation safety challenges with radioisotopes from the resulting spallation reaction that circulate and deposit throughout the target system.
In 2008, the International Atomic Energy Agency organized a benchmark committee to develop a set of experimental benchmark data. The set of experimental data chosen covered the energy range of 40 – 3,000 MeV from several different targets, including iron, lead and uranium. The data incorporated the production of neutrons, light particles from protons to alphas, pions and spallation residuals. The methods of measurement of the production cross-sections for the spallation residuals ranged from x-ray and gamma-ray spectroscopy, to accelerator mass spectrometry, to fragment separation. The results of the experimental data were then compared to various computer codes to see how well the different physics models predict the experimental result. Missing from the set of experimental data was spallation residual production cross-sections from a mercury target.
This work involves the design of a liquid mercury target benchmark experiment. The developed target was irradiated at the LANSCE facility with the production cross sections of longer half-life residuals determined through a set of gamma-ray spectroscopy measurements. In addition to providing an initial set of production cross-section data for residuals from a mercury target. The distribution and plating of residuals on the stainless steel encapsulation material of the target will be studied to help determine long-term distribution of radionuclides in flowing mercury target systems.