Energy Resolution and Response Function of Electron Detectors

2 Energy Resolution and Response Function of Electron Detectors 

The best energy resolution for electrons is obtained using silicon semiconductor detectors, with the possible exception of magnetic spectrometers. Silicon detectors may be surface-barrier or Si(Li) detectors. The surface-barrier detectors operate at room temperature, while the Si(Li) detectors give best results when cooled to liquid nitrogen temperatures. The energy resolution of semiconductor detectors is determined by the electronic noise alone. It deteriorates as the area and the sensitive depth of the detector increase. For commercial detectors the full width at half maximum (FWHM) ranges from about 7 to 30 keV. 

The energy resolution of scintillators, plastic scintillators in particular, is much worse. It is of the order of 8-10 percent at 1 MeV, which gives a FWHM of 80-100 keV. For scintillators the FWHM is roughly proportional to / . Plastic scintillators have two advantages over semiconductor detectors the backscattering fraction is less for scintillators because of their lower atomic number, and the timing characteristics are extremely useful for certain types of measurements. The pulse risetime is about 0.1 ns for a plastic scintillator, while for a silicon detector it is between 1 and 10 ns. 

The response function of electron detectors is of the form shown in Fig. 

Because of the low-energy tail, if one measures a continuous spectrum (e.g., one beta spectrum or a mixture of beta spectra), the measured spectrum will be higher than the source spectrum at the low-energy end and lower at the 

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