An Electron Lens Type of Beta-Ray Spectrometer

A beta-ray spectrometer utilizing the focusing action of the homogeneous magnetic field produced by a long solenoid is described. The theory of the action of an instrument of this type is considered in some detail for the case of a point source of beta-rays, and the extension of the theory to cover the case of an actual source of finite area is discussed. Details of design are given, together with a number of experimental tests which have been made on the instrument. These tests include measurements of the absorption of beta-rays in the Cellophane window of the G-M counter used for detection, measurement of the resolution and efficiency of the spectrometer, calibration of the instrument, and an examination of the beta-ray spectrum of radium E. The beta-spectra of phosphorus ₁₅P³² and iridium ₇₇Ir¹⁹⁴ have been investigated. The forms of the distribution curves all agree better with the Fermi than the K-U theory. It is concluded that the spectrometer operates satisfactorily and possesses some definite advantages over the conventional designs.