Final Results on the Nature of the Pulse-Height Spectrum from Semiconductor Detectors

An analysis of the shape of the pulse-height spectrum is carried out. The se quence of the physical processes which participate in shaping signals in a detector is taken into consideration. The main attention is paid to the charge collection process and to the spread in the amplitude Co(q) due to incomplete collection. A generalized analytical expression is obtained for the quantity q and the function Co(q) for detectors of the most widely used configurations (planar, coaxial, spherical). An analysis is given of the difference in two conventional approaches 6,8 to the problem of calculating the total pulse-height spectrum shape. It is noted that under ordinary conditions of gamma spectrometry the spectrum undergoes essential symmetrization due to multiple scattering (Compton scattering with subsequent photoabsorption). This brings the results of calculations outlined in refs. 6,8 closer to one another. However, in a single-step interaction (resulting, for instance, in the double escape peak) simple summation of dispersions for the spectrum components in 6 would lead to considerable errors. The scheme outlined in 8,12 is shown to permit using a pulse-heght analyzer in calculations of the spectrum shape. Presented in the Appendix are the results of an experiment showing that the signal across the detector electrodes is connected with potential differences traversed: Δq~Δv/v This relationship was used to calculate the charge q and the spectrum Co(q).