Die zählratenabhängigkeit des verstärkungsfaktors und des auflösungsvermögens bei photomultipliern vom typ RCA 6810 A

Abstract

The variations in gain and resolution of RCA 6810 A photomultiplier tubes have been investigated with reference to changes in the illumination of the photocathode. The tubes were mounted to a NaI(Tl) crystal, irradiated with γ-rays of different energies and intensities. Changes in the counting rate result in reversible fast and slow variations in gain. An increase of the irradiation level causes a rapid positive initial change with a continuing slow rise followed by a gradual decline to a stable level. Magnitude and exact time dependence vary with multiplier load and past history. Moreover, the amplitude is different for every tube. A reduction of counting rate results in a sudden negative initial shift with a continuing slow decrease. The long-term instabilities are discussed in detail. They may be attributed to reversible changes in the secondary emission ratio of the dynode surfaces. The resolution was found to deteriorate with increasing irradiation intensity.