The bottom picture shows an instrumented test fixture I designed for analyzing the performance of beta radiation sensor systems. The top picture is an ion chamber that was created under my direction. Versions of this were used with beta-emitting isotopes of strontium, krypton and promethium to measure the weight per unit area of plastic films (and other hydrocarbon materials) ranging in thickness from 0.0002 to 0.250 inches in thickness. At the low end of the thickness range, the air in the measurement gap had as much weight per unit area as the plastic film. So, provisions were made for compensation of changes in air density.