Large Pulse-Height Loss due to Capacitive Decay in the Detector-Circuit During Collection of Charges

Abstract

Ionization chambers produce voltage pulses across the load having rise-time characteristics dependent upon the electron transport. During the rise-time of a pulse, the effect of the capacitive decay in the detector-circuit during charge collection on the pulse-height is invariably ignored. This is quite reasonable as long as the detector-circuit time constant is appreciably large compared to the collection time of electrons. In a real situation, however, the capacitive decay can be very important. In order to understand the effect of capacitive decay in the detector-circuit during collection of charges on the pulse shapes and pulse-height spectra, we have recently made Monte Carlo simulations of the response of two-electrode parallel plate ionization chamber and gridded parallel plate ionization chamber for energetic heavy ions. Simulations have shown that the capacitive decay in the detector-circuit during rise-time of each pulse produces large pulse-height loss, if the detector-circuit time constant is of the order of maximum electron collection time. There, however, exists no data in support. So, we have carried out measurements on the pulse-height loss due to the capacitive decay in the detector-circuit during collection of charges for two-electrode parallel plate ionization chamber. Experimental data on the pulse-height loss match reasonably well with the theoretical predictions.