An Electrostatic Generating Voltmeter for Measurement of Very Small e.m.f.'s

Abstract

N EW and hitherto unrealized potentialities of vibrating reed capacitative commutators (electrostatic generating voltmeters) for the stable measurement of very small electromotive forces have been explored and offer outstanding advantages in measurement of ionization currents. Low parasitic capacity (order of 10 micro-microfarads) is secured, making quick responses possible with high valued resistors coupling the source of current. Minimum detectible current (parasitic capacity X rate of drift of zero) is 10~1 8 ampere or better, and can easily be improved further.Amplifier tubes are employed coupled with negative feedback to increase further the energy of the generated signal. The extreme stability of the contact potential of pure gold with respect to pure gold, or of graphite with respect to graphite, is made use of by employing a null system for the measurements using the generating voltmeter composed of these materials as a null indicator. Electrical performance superior to that of the Hoffman electrometer is secured with nearly complete immunity to mechanical and thermal abuse. Long term zero stability allows comparable absolute measurements to be done in resistance coupled systems as well as in rate of drift arrangements.These engineering developments which began in the oil industry in 1938 were brought to the Metallurgical Laboratory in 1942 in a high state of perfection after extensive industrial applications in all major U. S. oilfields. A SERIES of investigators have found in cloud cham-bers a number of tracks of light positively charged particles originating in or near natural and artificial betaray emitters. 1 Sources which have been investigated for the production of these particles are Ra(B-fC), RaE, Th(C+C'+C"), UX, AcC, and P 32 . The particles have been found in all cases, and to approximately the same extent. The rate of occurrence is about 1X10" 2 per decay electron, far too great to be accounted for by the pair production by the gamma-and beta-rays from the source. zo AS r * £t4.ctro»i> 0 i 2 3 + S % G /tvtroac /fttttat Momentum x /0' % FIG. 1. Momentum loss vs. momentum for the positive particle and electrons.The tracks still occur when the source is surrounded by enough material to absorb all positrons of the energies indicated by the curvature measurements. The momentum spectra do not resemble the characteristic beta-decay spectrum; for the same maximum momentum, the average momentum is much lower. It is apparent from the properties of these particles that the phenomenon is quite distinct from branching, i.e., the alternative decay of an isotope by the emission of a positron (e.g., Cu 64 , As 74 ). The apparent penetrating power and the apparent absence of annihilation radiation, which should occur if the particles are positrons, led Bradt, Heine, and Scherrer 1 to suggest that the particles have a mass considerably less than that of the electron. This suggestion seemed to us to be inconsistent with a part of the experimental facts. We have performed experiments in which the behavior of the...

Mass Spectrometry

“…Consequently, new methods of detection or improvements in old ones are of immediate interest. One development that has been announced since the end of the war is the capacitativo commutator or dynamic condenser electrometer (119,120,130,131). This has extremely low drift, low background current, and high sensitivity.…”

“…Many workers have been interested in studying the relation between lens defects and image clarity (12,14,19,87,130). Others (16, 18, 28, 108, 132) have concerned themselves with studies of the theoretical resolving power of an electron microscope as determined by the maximum available contrast in the images.…”