High-flux experiments and simulations of pulse-mode 3D-position-sensitive CdZnTe pixelated detectors

Abstract

In this work we present high-flux experiment and simulation results of 3D-position-sensitive CdZnTe pixelated detectors operated in pulse mode. Charge transport properties used in our simulations were carefully calculated through direct comparison between measured and simulated charge induced signals using two different methods: irradiating with a-particles on the lateral side surface of the detector at normal bias and irradiating with Mo-Kc"X-rays (Molybdenum) on the cathode surface at reverse bias. Measured and simulated spectra as a function of increasing flux showed energies shifting towards lower energy bins followed by complete absence of spectral information, which was found to be caused by positive space charge build up distorting and completely breaking down the operating field as flux increased. More importantly, we developed a complete 3D framework that can be extended to other semiconductor detector technologies to study and predict their performance under high flux scenarios.

3D prompt gamma imaging for proton beam range verification

“…Based on the beam delivery times, this correlates to a maximum estimated instantaneous count rates of ~54 000 (18 000 cps/0.276 second irradiation) and ~59 000 for the 180 MeV and 120 MeV beams, respectively, resulting in maximum measurement dead times of ~15% per CC stage. These instantaneous count rates are well within achievable count rate limits for CZT (Perez and He, 2001) and well below flux rates known to induce charge polarization effects within the crystals (Rodrigues, 2012). Table 2 shows, for each beam energy the number of measured double/triple scattered PG events used for reconstruction for the raw, unfiltered data and the data filtered with each filtering technique for the delivery of the 2 Gy pencil beam at each CC position and for the combined data.…”

Properties and spectroscopic performance of semiconductor detectors under high-flux irradiation

“…These simulations are capable of solving the charge trasport equations, cosidering multiple electron and hole trapping centers, coupled with Poisson's equation. 3,10 Positive space charge build up has been systematically studied by high-flux simulations. Different irradiation fluxes are achieved in simulations by considering events interacting in the detector volume at variable average interaction times, where initial interaction position and deposited energy are given by Monte Carlo simulations.…”

A Learning-Based Physical Model of Charge Transport in Room-Temperature Semiconductor Detectors

“…In [26], 9 defect levels and irradiation-induced variations of trap signatures for these levels were observed on CdZnTe:Al using TSC measurements. In [27] the average trapping and detrapping times for holes were derived using the average hole trapping time τ h as measured in [28]- [32] using statistical model of charge collection efficiency based on known electron average trapping time. Average hole de-trapping time τ dh is extracted by direct comparison between measured and simulated using only signals from holes measured by the cathode electrode.…”

“…[53] worked on techniques to measure more detailed properties of these materials using the charge transport equations driven by the charge continuity equations with multiple electron and hole defect levels -trapping centers -coupled with Poisson's equation [54]- [59]. The macroscopic equations in [60] describe the various phenomena occurring in the material when photons, X-rays or energetic gamma rays interact with the material usually by Photoelectric, Compton or Pair-Production type of interaction, creating electron-hole pairs. Once the electronhole pairs are created the following phenomena occur: (1) drift of charges (electrons and holes), (2) free charges getting trapped and de-trapped in defect levels within the material, (3) recombination of free charges, which is modeled as capture of free electrons followed by capture of free holes in the material [61].…”

“…15 is shown for one trapping center for both electrons and holes for illustration. However, we perform simulation experiments considering CZT detector with 2 trapping centers for holes and 1 trapping center for electrons [21], [60]. We generate the learning based model for CZT detector which is popularly used in radiation imaging systems.…”