A position sensitive proportional counter for a beta-ray spectrometer II

Abstract

A position senstive proportional counter employing resistive charge division has been improved for use on the focal plane of an iron-free π√2 beta-ray spectrometer. This counter consists of three Nichrome anode wires of 10 μm in diameter which are stretched in parallel and connected in series. This allows three position spectra, divided in the direction of the magnetic field of the spectrometer, to be simultaneously measured, each of which covers the momentum range of about 4%. The spatial resolution (fwhm) obtained is 0.5 mm between 100 and 1000 keV, which corresponds to a momentum resolution of 0.016%. The momentum resolution obtained at 45 keV is 0.047%, and that above 10 keV is higher than 0.1%. The incident angles ( ø e and θ e) of electrons can be roughly obtained by placing a similar counter behind the first one and simultaneously measuring two-dimensional positions ( x 1, z 1) and ( x 2, z 2), respectively. With this two-counter system, a very low natural background count is obtained, smaller than one count/hour per fwhm of a peak. Experimental studies have effectively been made by using this counter to examine the focusing properties of this spectrometer, and these reveal that this spectrometer is suitable for use in the broad momentum range of about 4% if very high resolution, better than 0.08%, is not required.