The influence of plasma effects on the timing properties of surface-barrier detectors for heavy ions

Abstract

Detecting ions from He to Xe at various accurately determined energies with surface-barrier detectors, the dependence of the timing signal on field strength, resistivity, area and thickness of the detector has been studied. Deviations of the measured time-of-flight from the calculated one in the order of up to several ns have been found for slow heavy ions. A variation of the field strength may also cause a time shift of several ns, depending on mass and velocity of the detected ions and the properties of the detector. Above a critical field F min a linear decrease of this “plasma delay” with increasing field strength has been observed. By linear extrapolation to infinite field strength a value for the minimum charge-collecting time of each detector has been determined. The experimental data allow to extract a set of empirical formulae that are able to describe the “plasma delay” as a function of the energy, mass and effective charge of the detected ions and of the thickness, area and resistivity of the detector.