Abstract

Spectroscopy of γ-quants with large area silicon-detectors (≈ 1 cm 2) has a lower limit of about 40 keV (fwhm ≈ 20 keV) at room temperature. This limit can be lowered considerably by using multiplying detectors, which amplify the signal fully but not all of the noise components. Obviously preamplifier noise does not depend on multiplication and also according to the individual geometry of the diode the noise of the reverse current is not multiplied up to 90% in silicon ( α ⪢ β). In spite of the statistical Fano-noise and two other other contributions it is possible therefore to lower this limit down to about 1 keV for quantum spectroscopy. These two additional noise contributions are generated by the statistical character of the multiplication itself and by local fluctuations of the multiplication factor owing to diode inhomogeneties; their influence on the signal to noise ratio (snr) is observed to be important only for greater multiplication factors respectively higher γ-energies. The individual noise contributions were measured in detail. Considering all noise components the optimal multiplication factor was found to be about 20. For greater multiplication factors the snr decreases. This agrees with experiment.

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