Real-time Digital Pulse Processing Research Articles

FPGA implementation of a real-time digital pulse processing analysis for radiation detectors

A new universal, flexible firmware has been implemented on field -programmable gate array (FPGA) for gamma-ray spectroscopy. The firmware of the FPGA runs on a digitizer that we developed ourselves. The present paper describes the detailed architecture of the firmware, including the trapezoidal shaper, peak detection, pulse height analyzer, and pile-up rejection. Gamma-ray spectroscopy measurements are made using a NaI(Tl) detector, CdZnTe detector, and HPGe detector.

High-rate dead-time corrections in a general purpose digital pulse processing system.

Dead-time losses are well recognized and studied drawbacks in counting and spectroscopic systems. In this work the abilities on dead-time correction of a real-time digital pulse processing (DPP) system for high-rate high-resolution radiation measurements are presented. The DPP system, through a fast and slow analysis of the output waveform from radiation detectors, is able to perform multi-parameter analysis (arrival time, pulse width, pulse height, pulse shape, etc.) at high input counting rates (ICRs), allowing accurate counting loss corrections even for variable or transient radiations. The fast analysis is used to obtain both the ICR and energy spectra with high throughput, while the slow analysis is used to obtain high-resolution energy spectra. A complete characterization of the counting capabilities, through both theoretical and experimental approaches, was performed. The dead-time modeling, the throughput curves, the experimental time-interval distributions (TIDs) and the counting uncertainty of the recorded events of both the fast and the slow channels, measured with a planar CdTe (cadmium telluride) detector, will be presented. The throughput formula of a series of two types of dead-times is also derived. The results of dead-time corrections, performed through different methods, will be reported and discussed, pointing out the error on ICR estimation and the simplicity of the procedure. Accurate ICR estimations (nonlinearity < 0.5%) were performed by using the time widths and the TIDs (using 10 ns time bin width) of the detected pulses up to 2.2 Mcps. The digital system allows, after a simple parameter setting, different and sophisticated procedures for dead-time correction, traditionally implemented in complex/dedicated systems and time-consuming set-ups.

Xenon gamma-ray detector for ecological applications

A description of the xenon detector (XD) for ecological applications is presented. The detector provides high energy resolution and is able to operate under extreme environmental conditions (wide temperature range and unfavorable acoustic action). Resistance to acoustic noise as well as improvement in energy resolution has been achieved by means of real-time digital pulse processing. Another important XD feature is the ionization chamber’s thin wall with composite housing, which significantly decreases the mass of the device and expands its energy range, especially at low energies.

Construction and implementation of a TDCR system at ENEA

A new 4π (LS) TDCR system was built at ENEA-INMRI. Three photomultiplier tubes, arranged in a planar 120° geometry around a spherical optical chamber, were directly linked to a CAEN Desktop Digitizer DT5720. This module, based on the Field Programmable Gate Array (FPGA) technology for real time Digital Pulse Processing (DPP), allowed to replace all the classical TDCR electronics by only one device. The activity of 3H and 63Ni standard sources were successfully measured by the new detector.

Energy resolution and throughput of a new real time digital pulse processing system for x-ray and gamma ray semiconductor detectors

New generation spectroscopy systems have advanced towards digital pulse processing (DPP) approaches. DPP systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog pulse processing electronics, ensuring higher flexibility, stability, lower dead time, higher throughput and better spectroscopic performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse shape and height analysis. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors, coupled to resistive-feedback preamplifiers, highlight the excellent performance of the system both at low and high rate environments (up to 800 kcps). A comparison with a conventional analog electronics showed the better high-rate capabilities of the digital approach, in terms of energy resolution and throughput. These results make the proposed DPP system a very attractive tool for both laboratory research and for the development of advanced detection systems for high-rate-resolution spectroscopic imaging, recently proposed in diagnostic medicine, industrial imaging and security screening.

Real time digital pulse processing for X-ray and gamma ray semiconductor detectors

Digital pulse processing (DPP) systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog electronics, ensuring higher flexibility, stability, lower dead time and better spectroscopic performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse height and shape analysis. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors highlight the excellent performance of the system both at low and high rate environments (up to 800kcps). These results make the proposed DPP system a very attractive tool for both laboratory research and the development of advanced detection systems for high-rate-resolution spectroscopic imaging, recently proposed in diagnostic medicine, industrial imaging and security screening.

Implementation of a truncated cusp filter for real-time digital pulse processing in nuclear spectrometry

In this work the transfer function for a truncated cusp infinite impulse response (IIR) filter has been derived. The truncated cusp filter, when given an exponential pulse in the presence of white noise, outputs a truncated cusp pulse which is optimum pulse shape under the constraint of finite pulse duration. However it features a pole outside of the unit-circle and is therefore inherently unstable. To overcome this instability a switching algorithm with two alternating poles has been applied. The filter has been simulated with MATLAB and Simulink and implemented on-board a FPGA. The pulses from a waveform generator and silicon drift detector (SDD) have been also processed by the filter and results compared with theory. We find that the simulation and measurements were in agreement and show that energy resolution due to electronic noise can be improved by up to 7.5% using a truncated cusp instead of triangular filter. An improvement of up to 2.8% in overall energy resolution was measured with a typical X-ray spectrometer based on a SDD detector with a nominal energy resolution of 150eV at energies of MnKα line.

Parallel processing method for high-speed real time digital pulse processing for gamma-ray spectroscopy

A new data acquisition (DAQ) system was developed to fulfil the requirements of the gamma-ray spectrometer (GRS) JET–EP2 (joint European Torus enhancement project 2), providing high-resolution spectroscopy at very high-count rate (up to few MHz). The system is based on the Advanced Telecommunications Computing Architecture™ (ATCA™) and includes a transient record (TR) module with 8 channels of 14 bits resolution at 400 MSamples/s (MSPS) sampling rate, 4 GB of local memory, and 2 field programmable gate array (FPGA) able to perform real time algorithms for data reduction and digital pulse processing. Although at 400 MSPS only fast programmable devices such as FPGAs can be used either for data processing and data transfer, FPGA resources also present speed limitation at some specific tasks, leading to an unavoidable data lost when demanding algorithms are applied. To overcome this problem and foreseeing an increase of the algorithm complexity, a new digital parallel filter was developed, aiming to perform real time pulse processing in the FPGAs of the TR module at the presented sampling rate. The filter is based on the conventional digital time-invariant trapezoidal shaper operating with parallelized data while performing pulse height analysis (PHA) and pile up rejection (PUR). The incoming sampled data is successively parallelized and fed into the processing algorithm block at one fourth of the sampling rate. The following data processing and data transfer is also performed at one fourth of the sampling rate. The algorithm based on data parallelization technique was implemented and tested at JET facilities, where a spectrum was obtained. Attending to the observed results, the PHA algorithm will be improved by implementing the pulse pile up discrimination.

Towards real-time digital pulse processing based on least-mean-squares algorithms

The high potential of digital least-mean-squares methods in high-resolution nuclear spectroscopy cannot be fully exploited at present due to its heavy calculation burden which makes difficult a real-time implementation. A method for reducing the mathematical complexity of least-mean-squares algorithms used for deriving energy and arrival time of detected events, is presented here. It yields an easier path toward real-time implementation. The availability of the time information of each event allows the realisation of a statistical digital pile-up rejector based on the values of a Chi-square distribution associated to the measurement algorithm: this rejector is very sensitive to piled-up low-energy events.