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Digital Pulse-Processing Techniques for X-Ray and Gamma-Ray Semiconductor Detectors
Published in Renato Turchetta, Krzysztof Iniewski, Analog Electronics for Radiation Detection, 2017
Leonardo Abbene, Gaetano Gerardi, Fabio Principato
Recently, the high performance of analog-to-digital converters (ADCs) have driven physicists and engineers to realize electronics in which the analog-to-digital conversion is performed as close as possible to the detector. Several groups [3–6] have proposed hybrid (i.e., both analog and digital) pulse-processing chains, in which the shaped pulses from an analog amplifier are sampled by a digitizer (with sampling frequencies > 10 MHz), thus eliminating the dead time of MCAs (Figure 6.4a). The digitized shaped pulses are processed offline for pulse height analysis and pileup inspections. These systems showed good spectroscopic performance up to photon-counting rates of approximately 100 kcps, a limit due to the finite width of the shaped pulses and the difficulties on baseline restoration. At higher counting rates, the direct digitization of the preamplifier output pulses (DPP approach) is a very appealing solution, as reported in several works [7–17]. In a DPP system, the preamplifier output (CSP) signals are directly digitized by ADCs (with sampling frequencies ≥ 100 MHz) and then processed by using digital algorithms (Figure 6.4b). A DPP system leads to better results than the analog one in terms of parameters such as stability, flexibility, reproducibility, energy resolution, throughput, dead time modeling, and the possibility of shape preservation of the pulses for further analysis. In a DPP system, the direct digitizing of the detector signals minimizes the drift and instability that are normally associated with analog pulse processing. Once digitized, the pulses are immune to distortions that are caused by electronic noise and temperature instabilities. Moreover, it is possible to use complex algorithms for adaptive processing and optimum filtering, which are not easily implementable in a traditional analog approach. A DPP analysis also requires considerably less overall processing time than the analog ones, ensuring lower dead time and higher throughput. In a DPP system, there is no additional dead time that is associated with digitizing the pulses, and so there is no MCA dead time (conversion time and data storage time). Preservation of the detector pulse shape for pulse shape analysis is also very important for performance enhancements, photon tracking, or particle identification. Some DPP systems are composed of a digitizer and a personal computer for data recording and analysis (offline analysis) [3–6,10,12–16]. Real-time data processing [7–9,17,18], in which the signals are acquired, recorded, and processed online, is obtained by using digitizers with local memory and field-programmable gate arrays (FPGAs) wherein pulse-processing algorithms can be implemented (DPP firmware).
The Effect of Wavelength Shifting Fibers on Cherenkov Glass Detectors for Gamma-Ray Measurements
Published in Nuclear Technology, 2022
Since the discovery of Cherenkov radiation in 1934, Cherenkov detectors have been developed and used in several fields, such as astrophysics experiments, radiochemistry, and biology.1 In these fields, the detectors have been used in many applications, like ring imaging Cherenkov detectors, time-of-flight positron emission tomography, detection of antineutrino by neutron sensing, threshold discrimination and particle identification, and X-ray imaging systems.1 Moreover, several types of Cherenkov detectors have been reported, including water, silica aerogel, gas, and glass. The most widely studied and used is the glass type, especially lead glass because of its high refractive index and high density. Cherenkov detectors have several advantages compared with other detector types, such as low noise due to the low-energy threshold of Cherenkov radiation and short decay constant. However, the yield of Cherenkov photons is low. Only several hundred Cherenkov photons can be generated per megaelectron-volt in several media, as shown in Fig. 1. This means about 10−3 of the particle’s energy is converted into Cherenkov photons, and this conversion is a factor of 100 smaller than scintillators.2