Amplifiers for Use with P-N Junction Radiation Detectors

The signal on radiation pulse detectors is in the form of a charge on a capacitor. An ionizing particle produces a charge pair for each 3.6 ev dissipated in silicon. The capacitance of a p-n junction is proportional to the area and inversely proportional to the square root of the bias potential. Three similar preamplifier circuits are described. Negative charge feedback is employed so that the output amplitude is essentially independent of the value of the detector capacitance. The amplifiers have a high open loop gain, a fast response, and show little tendency to oscillate. Best overall performance, a noise line width of 5 kv, is achieved using WE417A or equivalent tubes in cascode at the input. RCA 7586 tubes give a line width of 8-10 kv with low capacitance detectors. The line width with transistors is 20-30 kv.