Electron multiplier for the measurement of an ion current on a mass spectrometer

The apparatus described is designed to measure weak ion currents received at the collector of a mass spectrometer. The report describes successively the study of electron paths in the multiplier by the method of analogy, using rubber membranes, and the practical details of construction of the apparatus. The variation with surface treatment of the secondary emission coefficient of the alloy CuBe containing 2 per cent Be, which makes up the dynodes, and the influence of the voltage on the gain per stage, are discussed. Results of tests regarding: the influence of the ion mass on the gain, the background of the instrument and the energy distribution of the impulses coming out on a high gain multiplier (q.q. 107) are given. Finally the performances of the multiplier are reported. 1- For a low gain (104), precision and reproducibility comparable to the electrometer valve, sensitivity 100 times greater, currents capable of detection 10-17 Ampere. 2- For a high gain (107) and measurement by impulse counting, currents capable of detection 10-19 Ampere. Mounting difficult to use on a mass spectrometer. (author)