The atomic-beam magnetic-resonance method was used to measure the nuclear gyromagnetic ratios and hyperfine-structure separations of the radioactive isotopes Cs 134 , Cs 135 , and Cs 137 . A surface ionization detector was used.The hyperfine-structure separations were obtained by direct AF=±l transitions near zero field. The values of Av found for the three isotopes are: Av(Cs 134 ) = 10 473.626±0.015 Mc/sec, A^(Cs 135 ) = 9 724.023±0.015 Mc/sec, Av(Cs 137 ) = 10 115.527±0.015 Mc/sec. STROKE, JACCARINO, EDMONDS, AND WEISS

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The problem of finding the resistance between two circular contacts on an infinite conducting plane is related to that of the capacity between paraxial cylinders. The general formula for the capacity between two such cylinders is obtained, resulting in a solution for the resistance between any two circular contacts, including the case in which one is inside the circle formed by the other. This approach suggests a new experiment for the undergraduate laboratory using the electrodes and electrolytic tank often found in such laboratories intended for the usual field plotting experiment. The setup for the resistance experiment is described and some results presented.

A compact annular-cathode electron gun which allows direct, efficient injection into the accelerating structure of a racetrack microtron has been designed, built, and tested. The gun operates under pulsed conditions with applied high voltages of 40 kV or more and delivers an output current in excess of 1 A. Design and construction details are presented for both a basic gun and a gun with built-in output current monitor. Gun performance in a test chamber and in the multicavity racetrack microtron at the University of Western Ontario is described.

This paper describes a simple, yet accurate, vacuum-tube electrometer that has proved very useful in the teaching laboratory for measuring the small currents involved in various modern physics experiments. Details of the circuit design and construction are given. In addition, an electrometer test setup is described and the results obtained with the electrometer here considered are presented. The results indicate that this unit has an over-all precision of better than 4% on its 10−10 A full-scale range and a response time (including the recorder) of less than 12 sec for full-scale travel following application of a step function input. A simple modification allowing measurement of resistances up to 1011 Ω is also indicated.