A Comparison of the Charges of the Electron, Proton and Neutron

Abstract

IT has recently been suggested by Bondi and Ly ttleton^1,2 that the magnitudes of the electric charges on the proton and electron may differ by a little more than one part in 10¹⁸, in which case electrostatic forces would cause the universe to expand. In fact, Piccard and Kessler³ attempted to detect such a difference in 1925, and found that a molecule of carbon dioxide did not have an electric charge greater than 2×10⁻¹⁹ e, where —e is the electronic charge, from which they concluded that the magnitudes of the proton and electron charges were the same to within 5 parts in 10²¹, assuming that matter was built entirely of protons and electrons. Since matter also contains neutrons, they have assumed in effect that the neutron has a charge equal to that of a hydrogen atom; but the neutron might equally well have a charge opposite to that of a hydrogen atom, in which case their experiment does not settle the point at issue, since carbon dioxide contains equal numbers of protons and neutrons (to within 0.1 per cent). It therefore seemed desirable to find whether matter in which there is an excess of neutrons is electrically neutral. We have found that the charge on an argon atom (18 protons, 18 electrons and 22 neutrons) is not greater than 8×10⁻²⁰ e and that on a nitrogen molecule (14 protons, 14 electrons and 14 neutrons) is not greater than 12 × 10⁻²⁰ e. Treating the charges on nitrogen and argon as the sums of charges on protons, electrons and neutrons, it is deduced that the proton charge is (1±4×10⁻²⁰)e and the charge on the neutron is less than 4 × ⁻²⁰ e.