Cloud Chamber for Precision Measurements

Abstract
A cloud chamber has been constructed in which accurate measurements of ionization and momentum can be made simultaneously. The chamber has a useful volume of 18 in. by 12 in. by 5 in., contains helium, and is in a magnetic field of 7500 gauss. Procedures have been developed to measure momentum and ionization and to determine the errors. Measurements on 40 protons indicate an average probable error of 7 percent for an individual measurement of mass by the comparison of ionization and momentum. A calibration technique is used for the determination of the minimum ionization for each case.