A Multiwire Proportional Chamber for Imaging Thermal, Epicadmium, and Fast Neutrons

The 25 cm × 25 cm chamber described images thermal and epicadmium neutron beams using two boron-coated conversion screens, and fast neutrons using a single polyethylene converter. Sample images and quantitative attenuation and resolution data are presented. Measurements of neutron attenuation in lucite patterns give good agreement with expected values for thermal, epicadmium, and fast (Pu-Be) beams. The measured mean free paths were 0.30, 0.81, and 5.8 cm, respectively. Thermal neutron resolution (0.2 cm) depends upon α-particle range, but resolution for fast neutrons (0.4 cm) appears to be limited by chamber thickness (to approximately one-half of the chamber thickness). Measurements involving digital image storage and manipulation are also described and illustrated.