Moderated neutron sources for calibrating neutron dosimeters for reactor environments

Neutron dosimeters used around reactor environments are often calibrated with (..cap alpha.., n) sources or /sup 252/Cf sources. Since these sources emit neutrons which are more energetic than those outside power reactors, the readings of dosimeters calibrated in this manner may be erroneous because of the variation in their energy response. To produce calibration sources whose neutrons approximate those to be monitored, certain groups have embedded sources in spheres of various materials. Recently, Environmental Measurements Laboratory (EML) has also decided to have such moderated sources for calibration. The assemblies chosen are spheres of polyethylene, 20.3 cm and 45.7 cm in diameter which can be enclosed by Fe shells 10.2 cm thick. The center of these assemblies has a cavity 1.2 cm in diameter containing a /sup 252/Cf source 0.8 cm in diameter. This paper discusses the calculation of leakage spectra for these 4 assemblies