Gating of charge sensitive preamplifiers for the use at pulsed radiation sources

The development of a switch circuit to gate charge sensitive preamplifiers for use at pulsed radiation sources will be presented. This development was used for the $^{16}$O(n,$\alpha$)$^{13}$C reaction measurement with a Double Frisch Grid Ionization Chamber (DFGIC) at the neutron time-of-flight facility CERN n_TOF in Geneva, Switzerland. Intense instantaneous radiation which is produced in the spallation target of the n_TOF facility ($\gamma$-flash) can saturate charge sensitive preamplifiers and prevent signals from being registered in the detection system. The switch circuit made it possible for the first time to perform a measurement with the DFGIC with -flash gated off at n_TOF. Nano-second gating of charge sensitive preamplifiers has a wide range of applicability at pulsed radiation sources, where short bursts of radiation must be gated off to avoid saturation, e.g. with HPGe detectors for -ray detection. Nano-second gating requires the stray-capacitance of the wideband reflective switch to be compensated to avoid a strong signal during the switch operation. Spectral analysis of the switch circuit shows that additional noise is insignificant.