Pulse-height Defects in Semiconductor Detectors for Fission Fragments

Measurements have been done of the response of surface-barrier detectors to fission fragments as a function of the bias voltage applied to the detectors. It is found that the reciprocal of pulse height decreases linearly with decrease of the reciprocal of average electric field strength within the depletion region. In accordance with such saturation characteristics, the pulse height defect for fission fragments is shown to decrease approximately linearly with decrease of the reciprocal of the electric field. By extrapolation of the linear relation to the infinite field strength, the pulse height defect for each group of light and heavy fragments is separated into field-dependent and field-independent components. The defect obtained at a finite field strength is a few MeV greater for heavy fragments than for light ones, and this difference comes mainly from the field-independent component. The field-independent defect seems to be smaller than the ionization defect in gas. Possible causes of the pulse height defect are discussed.