Digital Multi-channel Analyzer Research Articles

Development of a Compact Digital Multichannel Analyzer based on FPGA

Development of a Compact Digital Multichannel Analyzer based on FPGA

Development of the digital multichannel analyzer for liquid scintillation detection

The new digital multichannel analyzer (DMCA) based on field programmable gate array (FPGA) technology is successfully developed, and it is used for liquid scintillation detection. The performance of this system has been evaluated. The analog signal output emanating from the photomultiplier tube (PMT) is transformed into digital signals through the utilization of an amplifier and a high-speed analog-to-digital converter (ADC). Information about the energy, timing, and pulse shape characteristics of the radiation event is contained in the digital signal. Subsequently, this digital signal is directed towards the FPGA for digital signal processing. In order to reduce the thermal and electronic noise, the dual-channels configuration and the signal coincidence function are added to DMCA for optimizing the validity of signal. The signal coincidence unit is designed within the FPGA, optimizing the synchronization of signals. The measurement data is transmitted to a computer via USB interface. The energy spectra of gamma sources, namely 22Na, 60Co, and 137Cs, as well as the alpha source 232Th, were measured utilizing the newly developed system. Notably, thermal and electronic noise interference is reduced in the coincidence measurement mode, and the coincidence energy spectra are improved compared to the singles measurement. In contrast to commercially available systems, the advantages of our design in terms of miniaturization, cost-effectiveness, and expandability are demonstrated.

Flexible and low-cost FPGA-based multichannel analyzer for handheld measurement devices

This study proposes a flexible, low-cost digital multichannel analyzer (DMCA) based on a field-programmable gate array (FPGA). Digital signal processing modules, including a digital Sallen-Key filter, an energy reconstruction (trapezoidal) filter, a baseline restorer, a timing trigger, and a pulse pile-up rejector, are implemented on FPGA. The proposed DMCA is coupled directly to the detector pre-amplifier without any analog signal conditioning circuit for a simple, compact, and cost-effective hardware design. The parameters of the filtering modules were optimized using MATLAB/Simulink and pulse data digitized using a high-speed analog-to-digital converter. The proposed DMCA also includes a digital gain compensation module to stabilize measured gamma spectra against temperature variation. In addition, software with a user-friendly graphical user interface has been developed for gamma spectrum acquisition and analysis. This prototype DMCA is highly promising for developing handheld radiation measurement devices in terms of performance, cost, and size.

Toroidal soft x-ray array on the EXL-50 spherical tokamak

A toroidal soft x-ray array system for spectrum and intensity measurements on the EXL-50 spherical tokamak is described. Silicon drift detectors and digital multichannel analyzers are adopted for all 21 channels of the array, and an average energy resolution of 147eV at 5.89 keV has been achieved at count rates over 500 kcps. In total, 20 channels of the array are symmetrically observed in both co- and counter-current directions on the EXL-50 mid-plane with a spatial resolution of around 10cm, and the remaining one serves as a background reference channel. Tungsten emissions from tungsten coating of the limiters on the central post are observed. The influence of hard x rays on measured soft x-ray spectra and system operation is discussed.

SOFTWARE AT MOBILE SPECTROMETER WITH CZT-DETECTOR

The technology is based on a semiconductor CdZnTe-portable (almost the size of a mobile phone) gamma-ray spectrometer with high resolution, which provides high efficiency of rapid identification of radionuclides and assessment of radiation dose from low to moderately high levels. The CdZnTe gamma-ray spectrometer is a highly efficient device based on the use of CdZnTe(CZT) semiconductor detectors operating at room temperature with very low power consumption, a digital multichannel analyzer, and amicrocomputer. CdZnTe-portable spectrometer is a self-contained device and consists of three modules -a detector module, a multichannel analyzer, and a microcomputer. The detector module contains a high-quality CdZnTe detector, a preamplifier, and a high voltage power supply for the detector. There are detector modules with different volumes of the CZT detector from 5mm3to 1600mm3. It is possible to use a multi-detector system. The analyzer module contains an amplifier, a digital signal processor, a low voltage power supply, and a computer interface. The microcomputer software interacts with the multichannel analyzer, analyzes gamma spectra, and provides the accumulation of time profiles of the dose of gamma radiation, communication with other information systems. Spectrometric measurements in real-time make it possible to use "electronic collimation" technologies to build a map of the radiation field and localize sources of ionizing radiation, with the subsequent certification of identified sources, creation of an effective radiation monitoring system with the functions of certification of ionizing sources radiation. The corresponding software allows you to solve the following tasks –building a three-dimensional map of the fields of ionizing radiation of various degrees of spatial detailing, taking into account the radiation energy, localization, and certification of gamma radiation sources. The special laboratory kit is based on μSPEC microspectrometers. A LattePanda single board computeris used to control the operation of spectrometers, collect and analyze data. LattePanda –A Windows10 Computer with integrated Arduino. This explains the choice of LattePanda. Windows10 applicationallows you to use the WinSPEC software to control the multichannel analyzer operation supplied with the spectrometer. The built-in Arduino allows you to remote control the movement of the radiation source during laboratory experiment. Both the traditionalproblems of calibrating spectrometers (energy calibration and efficiency curves), including those for various source geometries, processing the measured spectra using standard programs, calculating the activity of sources, and the problem of creating a spectra processing program and a spectrometer control program are considered. The values of the minimum detectable activity are given.

Experimental Study on Fusion Neutron Activation of Metal Materials in EAST

Fusion neutron activation experiments have been carried out to investigate the activation of metal materials in Experimental Advanced Superconducting Tokamak (EAST). Some cylindrical samples made of stainless steel 316L, carbon steel (A3), high purity cadmium (Cd), oxygen-free copper (Cu), and high purity aluminum (Al) were transported to Port G in the EAST hall for neutron irradiation. The characteristic gamma rays emitted by activated samples were measured with a spectrometer consisting of a digital multichannel analyzer (MCA) and a high purity germanium (HPGe) detector. Qualitative identification of the dominant radionuclides and quantitative measurement of the specific activity have been performed. The experimental results indicated that the high radioactive nuclides with short half-life were produced, such as 56Mn in 316L and A3, 28Al in Al, 66Cu in Cu, and 111m Cd in Cd. Moreover, the long half-life radionuclides were generated in 316L, A3, Cu and Cd samples, which will become the major factors on environment and personnel. In addition, the normalized dose rate at 10 cm in the air of 316L, A3, Al, Cd, and Cu was $1.53\times 10^{-23}$ , $4.83\times 10^{-24}$ , $5.57\times 10^{-23}$ , $4.90\times 10^{-\mathrm {24}}$ and $1.10\times 10^{-\mathrm {23}}$ Sv/h/n, respectively. Finally, the comparison between the experimental neutron activation results and the predicted quantities calculated with FISPACT-2007 was discussed.

Response to 14 MeV neutrons for single-crystal diamond detectors

Single-crystal diamond (SCD) detectors promise to have applications in neutron spectrometers and fusion neutron monitoring under high flux deuterium plasma. The response to 14 MeV neutrons for the SCD detector is studied in this paper. A high-performance SCD neutron detector is developed by processing cleaning wafer, depositing metal electrodes, annealing and wire-bonding. A fast-neutrons monitoring system containing the detector, preamplifier and digital multichannel analyzer is constructed, and the response to 14 MeV neutrons for the detector is measured on the K-400 neutron generator supported by China Academy of Engineering Physics. In addition, computational simulations of the energy deposition and detection efficiency of 14 MeV neutron through diamond are performed via Geant4 toolkit based on evaluated nuclear data libraries of ENDF-VIII.0, JEFF-3.3, BROND-3.1, JENDL-4.0u and CENDL-3.1. The methods of widening the simulation spectrum and calibration of measuring spectrum are presented in order that simulation results are in reasonable agreement with measured values. The results indicate that the energy deposition of 14 MeV neutrons incident on the <sup>12</sup>C can be more accurately calculated with CENDL-3.1 than with other data libraries. The elastic scattering and reaction of <sup>12</sup>C(n, 3α) are described more accurately with the CENDL-3.1, and the characteristic peaks of <sup>12</sup>C(n, α)<sup>9</sup>Be matched well the calibrated testing spectrum and the after-widening simulation spectrum, with a difference between the simulated detection efficiency and measuring results being as low as 0.61%. The outcome measures are described as the standardized mean difference, with a detection efficiency of (3.31 × 10<sup>–4</sup> ± 0.11 × 10<sup>–4</sup>) counts/n, an energy resolution of 4.02% ± 0.09%, and a peaking channel of 1797.24 ± 0.80, which suggest that the detector keeps stable well under a high neutron flux of 2 × 10<sup>10</sup> n/s for as long as 2 h. The results demonstrate that the SCD detector can be a promising candidate for monitoring 14 MeV D-T neutrons.

Digital Multi-Channel analyzer for detection and analysis of radiation in nuclear spectroscopy

Radiation caused by radiation sources due to ionization in the form of alpha, beta, gamma, X-ray and neutron radiations is harmful to human health. Multi-Channel Analyzers (MCAs) are incorporated in nuclear instruments for various applications like Isotope identifiers, Alpha/Gamma spectroscopy and liquid scintillators etc., that demand wide resolutions. Analog signal which is detected by the detector from radiation source is converted into digital using Analog-to-Digital Converter (ADC). Trapezoidal shaping is done by the Digital Signal Processor (DSP) using the proposed algorithms. This work targets the design and implementation of Digital Multi Channel Analyzer implemented on FPGA that can be used in nuclear spectroscopy instruments. The MCA system is designed by using trapezoidal recursive algorithm with the help of Lower Level Discriminator (LLD) and Upper Level Discriminator (ULD) detection using peak detection. The height of the pulse is the proportional to the energy of the particle which is used for peak detection. The peak detection data is counted, and histograms are generated for data analysis. This system is designed and realized by using Verilog Hardware Description Language (HDL) with low power and high profile SmartFusion2 FPGA SoC that can be used in nuclear spectroscopy instruments. The peak detection and counting are done by the modules developed using Hardware Description language (HDL) aiming the target device to be the Smart Fusion 2 Field Programmable Gate Array (FPGA) which has in-built Digital Signal Processor (DSP).

A Confident Configuration for an Environmental Radiation Monitoring System

This work presents a high-resolution, high-confidence, and high-temperature-stabilization prototype environmental radiation monitoring system (ERMS) with integrated digital filter, peak-finding algorithms, and real-time analyses. Through measuring <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co radiation sources with the same NaI(Tl) detector, the features of the digital multichannel analyzer (DMCA) in our system, including throughput, energy resolution, and peak shape, were compared with those of a commercial instrument, namely the DSPEC jr 2.0 from ORTEC, USA. The results indicate that the full-width at half-maximum (FWHM) and peak heights obtained with our DMCA are better than those obtained with the DSPEC jr 2.0 up to 12%. The ERMS also integrates a solar power supply, multimodal data transmission, and a weather channel, thus facilitating its deployment in boundary areas or far islands for monitoring and forecasting radioactive propagation. Therefore, the proposed configuration system is highly promising in terms of performance and low cost of maintenance.

Factors affecting the minimum detected activity of the GAMMAVISION software report protocol

The article presents the results of a gamma- spectrometer study with a low- capacity scintillation (NaI(Tl)) detection unit, with software GammaVision v.8, adopted to solve certification problems, including for measuring activities close to zero. The list of factors influencing the presentation of the minimum detected activity (MDA) in the report protocol is analyzed software GammaVision v.8. To perform the measurements, the company´s ORTEC gamma-spectrometer with a low-capacity detection unit a type digiBASE-RH, in which a high-voltage power supply unit, amplifier, digital multi-channel analyzer with USB-connection to a computer with the installed driver are installed, was used. The peak search in the library was performed using a compressed version of the library, which contains two nuclides 137Cs and 40K. Methods of calculating MDA are based on the intensity of accounts. Nuclide activity is calculation for all peaks in the library, the energy of which is in the selected energy ranges for analysis. Measurements and calculations MDA under the given conditions of research for five methods depending on time of measurement and geometry of measurements are carried out. It is shown that the level of MDA can be reduced by choosing the optimal conditions, time of measurement and geometry of measurements. Recommendations are given for the use of capacity for counting sample, which will reduce the amount of substance required for analysis and optimize the time spent on measuring the counting sample. In a prospect it is expedient to undertake a study of dependence of MDA from the physical properties and radionuclide composition of the substance for the counting sample and the dependence from the uncertainty in the equation MDA.

Sparsity-based pulse-processor for digital α-particle spectroscopy with Si-PIN-Diode detector

Nowadays, digital methods are used in nuclear detection instruments which are more popular than conventional signal processing. In this work, a digital α-particle spectrometer, compatible with the low-cost digitizers, was designed and constructed. Similar to the analog pulse-height analyses, the digital signals must also be carefully shaped. Here, the charge pulses induced by alpha particles were measured in a silicon PIN-diode detector. Then, a digital sparsity-based pulse-processor was introduced for shaping the charge signals that were digitized by a low sampling rate digitizer. To this end, a charge-sensitive pre-amplifier was designed and fabricated for coupling to the digitizers. To perform off-line analysis, the detector pulses were stored through a combination of a fast-digital oscilloscope and the LabVIEW software. Finally, the pulse-height spectrum was obtained by a digital multi-channel analyzer block. The performance of the designed filter was examined for Ra-226 alpha spectrum by comparing its output with those of other conventional filters. Our results show the advantages of the sparsity-based filter in high-resolution measurements. The designed filter achieved an energy resolution of 12.3% at 4.78 MeV alpha particles.

Design and Construction of a Digital Multichannel Analyzer for HPGe Detector Using Digital Signal Processing Technique

The outstanding advantage of digital signal processing (DSP) techniques and Field Programmable Gate Array (FPGA) technology is capable of improving the quality of the experimental measurements for nuclear radiation. In this article, a compact DMCA 8 K was designed and manufactured using DSP technique based on FPGA technology. In particular, the output of the preamplifier is completely processed by digital techniques which are obtained from the analog-to-digital converter (ADC) to calculate the baseline, DC offset, energy peaks, pile up, threshold discrimination and then the form of energy spectrum. The Spartan-6 board is used as a hardware for the development of the digital multichannel analyzer (DMCA), which is equipped with the 14-bit AD6645 with 62.5 Msps sample rate. The application software for instrument control, data acquisition and data processing was written under C++ builder via the RS-232 interface. The designed DMCA system has been tested with a HPGe detector using gamma sources of 60Co and 137Cs and a reference pulser.

Baseline restoration method based on mathematical morphology for high-pressure xenon detectors

The shift of baseline has always existed in high-pressure xenon (HPXe) detectors because of the influence of external acoustic noise. This problem seriously influences the spectrometric characteristics of these detectors. A special baseline restoration method is required to remove the shift of baseline in real time. This study demonstrated that the top hat transform based on mathematical morphology can restrain the shift of baseline in digital multichannel analyzer. An improved baseline restoration (IBLR) method based on mathematical morphology was proposed and implemented in field programmable gate array (FPGA) to obtain superior baseline restoration. The structuring element of the IBLR method can be adjusted automatically in real time according to the characteristics of the baseline. Experimental results show that the IBLR method can maintain an excellent energy resolution over a wide shift range of baseline. To strengthen our conclusion, we carried out an external acoustic noise experiment on a HPXe detector. The HPXe detector with IBLR was virtually unaffected by external acoustic noise.

Analog rise-time discriminator for CdZnTe detector

Due to variable time for charge collection, energy resolution of nuclear detectors declines, especially compound semiconductor detectors like cadmium zinc telluride (CdZnTe) detector. To solve this problem, an analog rise-time discriminator based on charge comparison principle is designed. The reference charge signal after attenuation is compared with the deconvoluted and delayed current signal. It is found that the amplitude of delayed current signal is higher than that of the reference charge signal when rise time of the input signal is shorter than the discrimination time, thus generating gating signal and triggering DMCA (digital multi-channel analyzer) to receive the total integral charge signal. When rise time of the input signal is longer than discrimination time, DMCA remains inactivated and the corresponding total integral charge signal is abandoned. Test results show that combination of the designed rise-time discriminator and DMCA can reduce hole tailing of CdZnTe detector significantly. Energy resolution of the system is 0.98%@662 keV, and it is still excellent under high counting rates.

Experiment and modeling of scintillation photon-counting and current measurement for PMT gain stabilization

Scintillation detectors with light readout are used for gamma, x-ray and particle detection. Where applicable, photon counting is principally superior to charge integration with regard to accuracy. Most scintillation detectors, however, generate a large number of photons per microsecond for a typical scintillation pulse resulting in significant amounts of pileup. This precludes the separation, and thus direct counting of single photoelectron charges.The algorithm developed and presented in this paper quantifies the coarseness of fast digitized current tracks to construct a photon count dependent, however, electron gain independent charge calculation function. Underlying photoelectrons are interpreted as noise components and retrieved by a modified statistical variance calculation. This method is verified for modeled scintillation pulses and scintillation detector data. It provides a new means for PMT gain stabilization in digital multi-channel analyzers by pulse current analysis.

Rapid Response Sensor for Analyzing Special Nuclear Material

Rapid in-situ analytical techniques are attractive for characterizing Special Nuclear Material (SNM). Present techniques are time consuming, and require sample dissolution. Proof-of-principal studies are performed to demonstrate the utility of employing low energy neutrons from a portable pulsed neutron generator for non-destructive isotopic analysis of nuclear material. In particular, time-sequenced data acquisition, operating synchronously with the pulsing of a neutron generator, partitions the characteristic elemental prompt gamma-rays according to the type of the reaction; inelastic neutron scattering reactions during the ON state and thermal neutron capture reactions during the OFF state of the generator. The key challenge is isolating these signature gamma- rays from the prompt fission and β-delayed gamma-rays that are also produced during the neutron interrogation. A commercial digital multi-channel analyzer has been specially customized to enable time-resolved gamma-ray spectral data to be acquired in multiple user-defined time bins within each of the ON/OFF gate periods of the neutron generator. Preliminary results on new signatures from depleted uranium as well as modeling and benchmarking of the concept are presented, but this approach should should be applicable for virtually all forms of SNM

Reset charge sensitive amplifier for NaI(Tl) gamma-ray spectrometer

The time constant of the output signal of the front-end readout circuit of a traditional gamma-ray spectrometer with a NaI(Tl)+PMT structure is affected by temperature, measurement environment and the signal transmission cable, so it is difficult to get a good resolution spectrum, especially at higher counting rates. In this paper, a reset charge sensitive amplifier (RCSA) is designed for the gamma-ray spectrometer with a NaI(Tl)+PMT structure. The designed RCSA outputs a step signal, thus enabling the acquisition of double-exponential signals with a stable time constant by using the next stage of a CR differentiating circuit. The designed RCSA is mainly composed of a basic amplifying circuit, a reset circuit and a dark current compensation circuit. It provides the output step signal through the integration of the PMT output charge signal. When the amplitude of the step signal exceeds a preset voltage threshold, it triggers the reset circuit to generate a reset pulse (about 5µs pulse width) to reset the output signal. Experimental results demonstrated that the designed RCSA achieves a charge sensitivity of 4.26×1010V/C, with a zero capacitance noise of 51.09fC and a noise slope of 1.98fC/pF. Supported by the digital shaping algorithm of the digital multi-channel analyzer (DMCA), it can maintain good energy resolution with high counting rates up to 150kcps and with a temperature range from −19°C to 50°C.

Efficient Digital Implementation of Signal Processing Algorithms in State-Of-The-Art Field-Programmable Gate Arrays for Gamma-Ray Spectroscopy

In this work, a board based on a Spartan-3 field-programmable gate array was designed as a hardware prototyping platform for development of a multichannel digital gamma spectrometer. The device is compatible with various detectors like high-purity germanium, NaI, and CsI detectors. Before implementing the hardware, the method for digital signal processing for gamma spectroscopy was developed. The aim of this paper is to introduce a robust tool suitable for optimizing the design of complicated systems. The characteristics of this method, such as its ability to implement adaptive shaping, are investigated. The optimum conditions for digital filtering were determined using MATLAB/Simulink. This scheme can be useful for commercial production. Simulation was used to examine each processing unit in the whole signal processing procedure including cusplike shaping. The proposed method can be used as a computer design tool for optimizing digital multichannel analyzers or digital nuclear spectrometers.

The Design of Digital Multi-channel Analyzer based on FPGA

A Digital Multi-Channel Analyzer (DMCA) based on FPGA(Field Programmable Gate Array) is introduced. The nuclear signals are processed by EP3C40Q240. It uses digital signals acquired by ADC to do calculus,seek the peaks,discriminate the threshold,and then form the energy spectrum. DMCA communicates with energy spectrum processing terminal(for example: PC) by high-speed RS485 bus interface. The software on PC can control DMCA and display energy spectrum. And the energy spectrum of 137Cs is given,which is obtained from NaI(Tl) detector and processed by DMCA.

A Non-linearity Correction Method for Fast Digital Multi-Channel Analyzers

Fast digital multi-channel analyzers (FDMCA) which based on flash ADCs have been intensively used recently. The FDMCA is different from traditional MCAs which based on Wilkinson ADCs. The non-linearity, including the integral non-linearity ( INL ) and differential non-linearity ( DNL) , mainly arising from flash ADCs, degrade the accuracy of fast digital MCAs. To improve the non-linearity of FDMCA, a practical off-line correction method has been proposed in this paper. The non-linearity features of the FDMCA system is obtained by a special measurement previously. In light of that the non-linearity of a system is inherent; the non-linearity can be eliminated by comparing the data between the general measurement and the special one.