In the "Compact carbon AMS" system it counts 14C ions
of 975 keV energy. For samples of modern material, the detector counts ca. 12,000 14
C ions per minute. For samples of old material, it gives less than 10 counts per minute
is a semiconductor silicon detector with surface barrier. It has sensitive area of 1 cm2
and energy resolution of 25 keV. Semiconductor detector is built like a large semiconductor diod. It is polarised with a constant voltage so that it does not conduct electric current. Passing-through high-energetic charged particle (like 14
C ion in the AMS spectrometer), releases some number of free carriers of electric current (electrons and "holes") and produces small scale discharge in the semiconductor volume. This can be detected as a single short-lasting voltage drop (pulse).