Ballistic Deficit Pulse Processing in Cadmium–Zinc–Telluride Pixel Detectors for High-Flux X-ray Measurements

Abstract

High-flux X-ray measurements with high-energy resolution and high throughput require the mitigation of pile-up and dead time effects. The reduction of the time width of the shaped pulses is a key approach, taking into account the distortions from the ballistic deficit, non-linearity, and time instabilities. In this work, we will present the performance of cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors equipped with digital shapers faster than the preamplifier peaking times (ballistic deficit pulse processing). The effects on energy resolution, throughput, energy-linearity, time stability, charge sharing, and pile-up are shown. The results highlight the absence of time instabilities and high-energy resolution (<4% FWHM at 122 keV) when ballistic deficit pulse processing (dead time of 90 ns) was used in CZT pixel detectors. These activities are in the framework of an international collaboration on the development of spectroscopic imagers for medical applications (mammography, computed tomography) and non-destructive testing in the food industry.

Advances in High-Energy-Resolution CdZnTe Linear Array Pixel Detectors with Fast and Low Noise Readout Electronics

“…Using the Amptek PX5 DPP, 1-h acquisitions were performed with the Am source at the shortest available peaking times (50 and 100 ns), to further back the results of stability over time performance of the detection system even in presence of ballistic deficit pulse processing [ 37 ]. Measurements showed 774 eV FWHM on the 59.5 keV line (377 eV FWHM on the pulser) for the 50 ns peaking time and 744 eV FWHM (309 eV FWHM on the pulser) for the 100 ns peaking time acquisition.…”

Window-Based Energy Selecting X-ray Imaging and Charge Sharing in Cadmium Zinc Telluride Linear Array Detectors for Contaminant Detection

“…However, this allowed us to demonstrate that charge sharing between adjacent pixels produces moderate distortions in X-ray images and, therefore, the ERPC prototype (equipped with a slit collimator) can operate at high rates without charge sharing detection. Moreover, we foresee it working at high rates by coupling the detectors to new front-end electronics, recently developed by our group [ 18 ], allowing excellent energy resolution (<1 keV) even with very fast peaking times (<50 ns); this would allow us to work with very short-shaped pulses ( ballistic deficit pulse processing approach [ 42 ]), ensuring excellent energy resolution and high throughput at high-rate measurements.…”

Potentialities of CdZnTe Quasi-Hemispherical Detectors for Hard X-ray Spectroscopy of Kaonic Atoms at the DAΦNE Collider

“…The height (i.e., the photon energy) and the peaking time (i.e., the pulse shape) of the pulses are calculated after SDL and trapezoidal shaping, as shown in Figure 6. In this case, the delay of the SDL shaping (acting as the shaping time constant of a shaping amplifier) is always selected to be longer than the peaking time of the CSP pulses, thus avoiding ballistic deficit effects [57]. To minimize the degradation of the spectroscopic response at different input counting rates (ICRs), a baseline recovery was implemented using the running average of a fixed number of samples preceding each pulse.…”

“…The spectroscopic response of the detector was measured at the laboratory of ionizing radiation detectors at the DiFC of University of Palermo (Italy). The detector was irradiated through the cathode electrode with uncollimated radiation sources (main X-ray and gamma lines: 109 Cd, 22.1, 24.9, and 88.05 keV; 241 Am, 59.5 keV; 57 Co, 122.1 and 136.5 keV; 137 Cs, 661.7 keV). We used two different 241 Am sources: one emitting the Np L X-ray lines (13-21 keV) and the 26.3 keV gamma line, and the other one with these lines shielded by…”

“…The coincidence events between the anode and cathode electrodes were fully detected within 50 ns, as shown in Figure 8c. The spectroscopic performance of the detector was investigated at room temperature (T = 20 °C) using uncollimated radiation sources ( 109 Cd, 241 Am, 57 Co, and 137 Cs). Figure 9a shows the energy resolution (FWHM) vs. the cathode bias voltage measured at various photon energies.…”