Pulse Pile-up Correction Research Articles

Pulse pile-up correction by auto-regression on linear operations (ARLO) method: A comparison with integration-based algorithms

Radiation detection at high count rate suffers from pulse pile-up, where the counting data and energy information of the system are affected by the overlapping of the system output pulses. There exist various pile-up correction strategies to recover the true information of the pulses, among which pulse-tail extrapolation is a well-known method focused on in this study.Present work aims to use a mono-exponential model for extrapolating the pileup-distorted trailing edge of a pulse, to provide a reference line for calculating the true amplitude of its subsequent overlapping pulse. To this goal, the auto-regression on linear operations (ARLO) method is examined and compared with two integration-based methods (the Foss and the Matheson methods), as well as the non-linear least squares (NLS) method.Despite a higher sensitivity to noise, the ARLO method was able to provide a simple, non-iterative solution with a performance over 400 times faster than the NLS algorithm, according to the analysis of a high count rate set of experimental pulses from a NaI(Tl) detection system. Foss and Matheson methods also provided solutions reasonably faster than NLS (but not surpassing ARLO), performing exactly the same as each other with results very close to NLS, benefiting from their non-iterative nature.

Simultaneous photon counting and charge integrating for pulse pile-up correction in paralyzable photon counting detectors

Objective. In photon counting detectors (PCDs), electric pulses induced by two or more x-ray photons can pile up and result in count losses when their temporal separation is less than the detector dead time. The correction of pulse pile-up-induced count loss is particularly difficult for paralyzable PCDs since a given value of recorded counts can correspond to two different values of true photon interactions. In contrast, charge (energy) integrating detectors work by integrating collected electric charge induced by x-rays over time and do not suffer from pile-up losses. This work introduces an inexpensive readout circuit element to the circuits of PCDs to simultaneously collect time-integrated charge to correct pile-up-induced count losses. Approach. Prototype electronics were constructed to collect time-integrated charges simultaneously with photon counts. A splitter was used to feed the electric signal in parallel to both a digital counter and a charge integrator. After recording PCD counts and integrating collected charge, a lookup table can be generated to map raw counts in the total- and high-energy bins and total charge to estimate pile-up-free true counts. Proof-of-concept imaging experiments were performed with a CdTe-based PCD array to test this method. Main results. The proposed electronics successfully recorded photon counts and time-integrated charge simultaneously, and whereas photon counts exhibited paralyzable pulse pile-up, time-integrated charge using the same electric signal as the counts measurement was linear with x-ray flux. With the proposed correction, paralyzable PCD counts became linear with input flux for both total- and high-energy bins. At high flux levels, uncorrected post-log measurements of PMMA objects severely overestimated radiological path lengths for both energy bins. After the proposed correction, the non-monotonic measurements again became linear with flux and accurately represented the true radiological path lengths. No impact on the spatial resolution was observed after the proposed correction in images of a line-pair test pattern. Significance. Time-integrated charge can be used to correct for pulse pile-up in paralyzable PCDs where analytical solutions may be difficult to use, and integrated charge can be collected simultaneously with counts using inexpensive electronics.

Preface to the Special Issue on Signal Processing, Data Acquisition and Front-end Systems for Radiation Detection and Measurements

This special issue of the Journal of Signal Processing Systems focuses on advancement of signal processing and data-acquisition for radiation detection and measurements. The seven articles cover diverse topics within the scope of radiation detection ranging from understanding of fundamental fission process, instrumentation, and application of radiation interaction (e.g., tomography and imaging). The articles focus on signal processing for fission spectrometer, neutron and gamma-ray computed tomography and artificial intelligence methods, dynamic neutron imaging system, pulse-pileup correction in x-ray spectroscopy and calibration methods in radiation measurement.

Pulse Pile-up Correction by Particle Swarm Optimization with Double-layer Parameter Identification Model in X-ray Spectroscopy

Pulse Pile-up Correction by Particle Swarm Optimization with Double-layer Parameter Identification Model in X-ray Spectroscopy

Neutron–gamma pulse pileup correction based on mathematical morphology and optimized grey model

A new neutron–gamma pulse pileup correction algorithm based on mathematical morphology and optimized grey model is proposed. The pulse characteristic information is extracted through basic mathematical morphology operations to perform pileup discrimination and correction. The hyperbolic tangent function transformation is used to optimize the grey model, and the class ratio dispersion is reduced without reducing the initial sequence smooth ratio, resulting in improved model prediction accuracy. Through experiments, the feasibility of the proposed algorithm is verified and a good correction effect is achieved.

Identification and correction method of nuclear detector pulse forming pile-up

Gaussian forming has good time, response and SNR, Gaussian shaping is widely used in nuclear signal processing because of its simple realization and good comprehensive performance. When working in high counting rate environment, the output pulse signal of nuclear detector often appears pile-up phenomenon, which leads to the nuclear spectrum measurement system cannot accurately extract the pulse amplitude, and then the energy spectrum measurement error. In order to solve this problem, a method of pulse pile-up identification and correction is proposed. A test system consisting of signal generator, detector, communication circuit and oscilloscope is designed. Experiments show that this method can accurately identification and correct the pile-up waveform., and increase count rate by 3%–30% compared with the traditional method.

Pulse pileup correction method for gamma-ray spectroscopy in high radiation fields

Abstract The detector suffers from pulse pileup by overlapping of the signals when it was used in high radiation fields. The pulse pileup deteriorates the energy spectrum and causes count losses due to random coincidences, which might not resolve within the resolving time of the detection system. In this study, it is aimed to propose a new pulse pileup correction method. The proposed method is to correct the start point of the pileup pulse. The parameters are obtained from the fitted exponential curve using the peak point of the previous pulse and the start point of the pileup pulse. The amplitude at the corrected start point of the pileup pulse can be estimated by the peak time of the pileup pulse. The system is composed of a NaI (Tl) scintillation crystal, a photomultiplier tube, and an oscilloscope. A 61 μCi 137Cs check-source was placed at a distance of 3 cm, 5 cm, and 10 cm, respectively. The gamma energy spectra for the radioisotope of 137Cs were obtained to verify the proposed method. As a result, the correction of the pulse pileup through the proposed method shows a remarkable improvement of FWHM at 662 keV by 29, 39, and 7%, respectively.

Pulse Pileup Correction of Signals From a Pyroelectric Sensor for Phase-Insensitive Ultrasound Computed Tomography

This paper describes the application of a pulse pileup correction algorithm based on maximum likelihood estimation to simulated and experimentally acquired signals from a pyroelectric ultrasound sensor. The sensor forms part of a prototype phase-insensitive ultrasound computed tomography (piUCT) system for breast cancer detection that generates quantitative maps of acoustic attenuation. The effectiveness of the piUCT technique has been previously demonstrated through imaging of cylindrical, polyurethane phantoms. For the technique to be applied clinically, the system must be capable of measuring high acoustic attenuations (>30 dB) and completing a scan in a clinically acceptable time frame of approximately 5 min. High attenuations present a challenge because the sensor responds directly to acoustic power and therefore, an attenuation of 30 dB causes a drop in signal level of three orders of magnitude, resulting in a large dynamic range in the received signal set. Completion of a scan in 5 min requires a period between measurements shorter than the response time of the sensor, causing pyroelectric pulse pileup. The maximum likelihood estimation method recovers the amplitudes of closely spaced superimposed pyroelectric signals while improving the coefficient of variation of the measurement by a factor of two compared to direct pulse amplitude measurement, simultaneously increasing the maximum measurable attenuation and measurement rate of the system.

The Design and Performance of the Real-Time Software Architecture for the ITER Radial Neutron Camera

The neutron detection system for characterization of emissivity in ITER Tokamak during DD and DT experiments poses serious challenges to the performance of the diagnostic control and data acquisition system (CDAcq). The ongoing design of the ITER Radial Neutron Camera (RNC) diagnostic is composed by 26 lines of sight (LOS) for complete plasma inspection. The CDAcq system aims at meeting the ITER requirements of delivering the measurement of the real-time neutron emissivity profile with time resolution and control cycle time of 10 ms at peak event rate of 2 MEvents/s per LOS. This measurement demands the generation of the neutron spectra for each LOS with neutron/gamma discrimination and pile up rejection. The neutron spectra can be totally processed in the host CPU or it can use the processed data coming from the system FPGA. The number of neutron counts extracted from the spectra is then used to calculate the neutron emissivity profile using an inversion algorithm. Moreover, it is required that the event based raw data acquired is made available to the ITER data network without local data storage for post processing. The data production for the 2 MEvents/s rate can go up to a maximum data throughput of 0.5 GB/s per channel. The evaluation of the use of real-time data compression techniques in RNC is also depicted in another contribution. To meet the demands of the project a CDAcq prototype has been used to design and test a high-performance distributed software architecture taking advantage of multi-core CPU technology capable of coping with the requirements. This submission depicts the design of the real-time architecture, the spectra algorithms (pulse height analysis, neutron/gamma discrimination and pile-up correction) and the inversion algorithm to calculate the emissivity profile. Preliminary tests to evaluate the system performance with synthetic data are presented.

Pulse pileup correction in the presence of a large low-energy background

Pulse pileup correction is required for high count rate experiments. Spectral distortion due to pileup is strongly affected by the distribution of pulse heights. Methods used to limit the digitization rate – including energy thresholds and coincidence requirements – adversely affect attempts to correct the pileup-induced distortion. A simplified method for correcting the spectral distortion using a general pileup function can be used when the spectrum is dominated by a low-energy background. This method has particular relevance for nuclear resonance fluorescence experiments.

Multi-shape pulse pile-up correction: The MCPPU code

In spectroscopic measurements with high counting rate, pulse pile-up (PPU) is a common distortion of the spectrum. It is fully ascribable to the pulse handling circuitry of the detector and it is not comprised in the detector response function which is well explained by a purely physical model. Since PPU occurs after the transport inside the detector, this is the first correction to perform in case of spectrum unfolding. Many producers include electronic rejection circuits to limit the appearance of PPU, but it is never suppressed completely. Therefore, it is always necessary to correct PPU distortions after the measurement. In the present work, it is described the post-processing tool MCPPU (Monte Carlo Pulse Pile-Up), based on the MC algorithm developed by Guo et al. (2004, 2005). MCPPU automatically determines the dead time of the counting system and corrects for PPU effects even in the presence of electronic suppression. The capability of allowing a user defined pulse shape makes the code suitable to be used with any kind of detector. The features of MCPPU are illustrated with some examples.

FPGA-Based Pulse Pile-Up Correction With Energy and Timing Recovery

Modern field programmable gate arrays (FPGAs) are capable of performing complex discrete signal processing algorithms with clock rates well above 100 MHz. This, combined with FPGA's low expense, ease of use, and selected dedicated hardware make them an ideal technology for a data acquisition system for a positron emission tomography (PET) scanner. The University of Washington is producing a high-resolution, small-animal PET scanner that utilizes FPGAs as the core of the front-end electronics. For this scanner, functions that are typically performed in dedicated circuits, or offline, are being migrated to the FPGA. This will not only simplify the electronics, but the features of modern FPGAs can be utilized to add significant signal processing power to produce higher quality images. In this paper we report on an all-digital pulse pile-up correction algorithm that has been developed for the FPGA. The pile-up mitigation algorithm will allow the scanner to run at higher count rates without incurring large data losses due to the overlapping of scintillation signals. This correction technique utilizes a reference pulse to extract timing and energy information for most pile-up events. Using pulses acquired from a Zecotech Photonics MAPD-N with an LFS-3 scintillator, we show that good timing and energy information can be achieved in the presence of pile-up utilizing a moderate amount of FPGA resources.

Triangle bipolar pulse shaping and pileup correction based on DSP

Programmable Digital Signal Processing (DSP) microprocessors are capable of doing complex discrete signal processing algorithms with clock rates above 50 MHz. This combined with their low expense, ease of use and selected dedicated hardware make them an ideal option for spectrometer data acquisition systems. For this generation of spectrometers, functions that are typically performed in dedicated circuits, or offline, are being migrated to the field programmable gate array (FPGA). This will not only reduce the electronics, but the features of modern FPGAs can be utilized to add considerable signal processing power to produce higher resolution spectra. In this paper we report on an all-digital triangle bipolar pulse shaping and pileup correction algorithm that is being developed for the DSP. The pileup mitigation algorithm will allow the spectrometers to run at higher count rates or with multiple sources without imposing large data losses due to the overlapping of scintillation signals. This correction technique utilizes a very narrow bipolar triangle digital pulse shaping algorithm to extract energy information for most pileup events.

A high performance reconfigurable hardware platform for digital pulse processing

This paper presents a new reconfigurable hardware platform which uses both digital signal processors (DSP) and field programmable gate arrays (FPGA) to attain high resolution and real-time processing in nuclear spectrometry experiments. The module was designed in order to provide a high digital pulse processing (DPP) yield with the capacity of being reconfigurable according to the experimental conditions and the desired data output. This allows unprecedented real time processing capabilities implemented in the FPGA such as pulse pileup correction through adaptive filtering and effective signal-to-noise ratio (SNR) control and optimization. The module uses a Virtex-II Pro FPGA (Xilinx) and a DSP from the TMS320C64xx family (Texas Instruments) and is implemented on a PCI board to be used in a host workstation. Special emphasis is given to the scalability of the module along with the potential capacity of being used as a portable stand-alone instrument. This reconfigurable hardware platform allows us to simultaneously benefit from the advantages of the hardware based digital spectrometers, namely, their high throughput, and of the flexibility of the software based configurations. Besides, this same platform can be used as a general purpose high-speed data acquisition and processing unit.

Examination of the traditional Raman lidar technique. I. Evaluating the temperature-dependent lidar equations.

The essential information required for the analysis of Raman lidar water vapor and aerosol data acquired by use of a single laser wavelength is compiled here and in a companion paper [Appl. Opt. 42, 2593 (2003)]. Various details concerning the evaluation of the lidar equations when Raman scattering is measured are covered. These details include the influence of the temperature dependence of both pure rotational and vibrational-rotational Raman scattering on the lidar profile. The full temperature dependence of the Rayleigh-Mie and Raman lidar equations are evaluated by use of a new form of the lidar equation where all the temperature dependence is carried in a single term. The results indicate that, for the range of temperatures encountered in the troposphere, the magnitude of the temperature-dependent effect can reach 10% or more for narrowband Raman water-vapor measurements. Also, the calculation of atmospheric transmission, including the effects of depolarization, is examined carefully. Various formulations of Rayleigh cross-section determination commonly used in the lidar field are compared and reveal differences of as much as 5% among the formulations. The influence of multiple scattering on the measurement of aerosol extinction with the Raman lidar technique is considered, as are several photon pulse pileup-correction techniques.

Pulse pileup correction of large NaI(Tl) total absorption spectra using the true pulse shape

The usefulness of a simple numerical correction method of electronic pulse pileup distortion in measured energy spectra is investigated. The algorithm only requires the knowledge of the true pulse shape. The accuracy of the correction achieved for total absorption gamma-ray spectroscopy measurements with NaI(Tl) detectors is demonstrated.

Variability in the distribution of selenium in healthy heart tissue measured by neutron activation analysis

Chronic dietary deficiency of selenium has been shown to be associated with degenerative heart disease in production animals in the U.S. and in the human in parts of China. In the latter, subjects in the endemic areas suffer high rates of a cardiomyopathy known as Keshan's Disease which is normally fatal in early adulthood and can be prevented, or reversed in its early stages, via selenium supplementation. Selenium, as the active moiety in the enzyme glutathione peroxidase, protects against oxidative attack of cell membranes by peroxides formed during normal metabolism. In this study, we investigated the distribution of selenium in healthy porcine and bovine heart tissue freshly collected at slaughter. The whole heart was perfused with DI water and carefully de-fatted. Representative samples of left and right atria and ventricles and the interventricular septum were collected, lyophilized and homogenized prior to preparing replicate samples for analysis. Replicates were analyzed for selenium via an INAA scheme employing a 5, 15 and 25 second irradiation (φth = 8·1013 n·cm−2·s−1), decay and real-time count (77mSe,T1/2=17.4 s), respectively, using high-resolution gamma-ray spectroscopy with Westphal pulse pile-up correction. Selenium distribution will be discussed relative to differentiated function and oxygenation of the specific tissues.

Application of the digital pulse processing technique to gas proportional scintillation counters

Digital signal processing techniques have been developed to analyze the signals from a gas proportional scintillation counter (GPSC). Compared to analog systems, the digital technique is a very simple and powerful tool for manipulating and improving pulse-height distributions with no additional electronic components. Among the features inherent in digital signal processing are pulse risetime discrimination, pulse pileup correction and rejection, and background rejection. By allowing the rejection of signal pulses from X-ray interactions within the scintillation region and/or near insensitive regions of the detector, an improvement in the pulse-height distribution has been effectively achieved. Using this technique the energy resolution for the 22.1 keV line of a /sup 109/Cd X-ray source improves from 5.6 to 5.1% and the peak-to-background ratio increases from 30 to 170.

Determination of the silver content of ancient silver coins by neutron activation analysis

A reactor neutron activation analysis procedure for the determination of the silver content of silver coins is described. The samples are irradiated for 1 s, cooled for 85 s and measured for 60 s with a Ge-detector. The analysis is based on the measurement of110Ag and108Ag. Aluminium is used for flux monitoring and pulse pile-up correction. A calibration curve is prepared by irradiating and measureing a series of discs with known silver contents. An average precision of ±2.1% is obtained. The analysis of coins with known silver contents shows good agreement with the given values. The analysis time is 2.5 minutes per sample.