Response of Lithium-Drifted Silicon Radiation Detectors to High Energy Charged Particies

The measured response characteristics of lithium-drifted silicon radiation detectors at 295°K and 79°K are presented for protons with energies from 315 to 3.5 MeV; for positive pions with energies from 50.2 to 206 MeV; and for electrons with energies from 265 keV to 767.2 MeV. Analysis of the energy loss spectra confirms that the energy is being deposited by the protons and pions in the silicon purely through collision losses, whereas it appears that the silicon absorbs additional energy lost by the high energy electrons through interaction of the bremsstrahlung radiation in the depletion region. The charge collection efficiency determined by gamma rays is shown to agree with the charge collection efficiency determined by minimum ionizing particles. Nonlinear effects caused by unequal electron and hole trapping lengths and surface effects lead to reduced charge collection efficiencies for low energy electrons which do not completely penetrate the detector depletion region, in agreement with theory and with observations in the X-ray region. Apparent recombination effects also lead to reduced charge collection efficiencies at low fields or for protons with energies below about 100 MeV under constant bias conditions. The present data support the conclusion that the charge conversion factor ¿ at any one temperature is constant to within 1% for electrons, pions and protons over the entire energy span measured.