An Advanced Cold Moderator Using Solid Methane Pellets

摘要

This paper reports developments of the pellet formation and transport technologies required for producing a liquid helium or hydrogen cooled methane pellet moderator. The Phase I USDOE SBIR project, already completed, demonstrated the production of 3mm transparent pellets of frozen methane and ammonia and transport of the pellets into a 40cc observation cell cooled with liquid helium. The methane pellets, formed at 72K, stuck together during the loading of the cell. Ammonia pellets did not stick and fell readily under vibration into a packed bed with a 60 percent fill fraction. A 60 percent fill fraction should produce a very significant increase in long-wavelength neutron production and advantages in shorter pulse widths as compared to a liquid hydrogen moderator.