Dead Time Parameters Research Articles

FITEVT: A FORTRAN program for arrival-time analysis of nuclear-decay events

FITEVT is a FORTRAN program designed to analyze recorded arrival times of nuclear-decay events affected by dead-time. The primary goal of the program is precise and accurate determination of half-lives. Its method involves imposition of a known sufficiently long extending dead-time to the recorded event sequence, so that the original dead-time effects are completely obliterated and the remaining live-times of the survived events are known exactly. Upon completion of the analysis, the arrival-time spectrum and the live-time spectrum are predicted and compared to those constructed from the survived events. Program summaryProgram title: FITEVTLicensing provisions: MITCPC Library link to program files:https://doi.org/10.17632/scg6p9jxjk.1Programming language: FORTRAN (using double precision)Nature of problem: Accurate determination of the ideal event rate from the observed event rate in a nuclear decay can be a challenging task due to the inevitable presence of detection system's dead-time, whose nature and extent are typically unknown. Consequently, the results of nuclear half-life measurements may depend on the method used to correct for event losses due to dead-time. Therefore, there is a need for an exact method of data analysis and the means to apply it in order to ensure reproducibility, accuracy and optimized precision of the results.Solution method: FITEVT performs arrival-time analysis of the recorded events, in which a known, sufficiently large extending dead-time is imposed by means of software, so that in the resulting set of survived events the original dead-time effects are completely replaced by the effects of the imposed dead-time. As a result, the dead-time following each survived event and the remaining live-time preceding each surviving event are known exactly. This allows for application of the maximum-likelihood method of estimation, in which the half-lives as well as the other parameters of the ideal-decay-rate function can be accurately determined.Additional comments including restrictions and unusual features: In its original form the program can handle contributions from a constant event rate (i.e., a typical background) plus up to 4 different exponentially-decaying event rates. One of these 4 contributions is allowed to be negative, so that the program can be applied to the general case involving a single two-component decay chain. The employed method of analysis produces accurate results even when the product of the ideal event rate (ρ) and the extending dead-time parameter (τe) is as large as 51.2 [1]. Example used in the present paper involves simulated events having initial rate of 105 s−1, to which extending dead-time of 64 μs is imposed.Data analysis is based on maximum-likelihood principle, in which minimization of the deviance involves calculations in double precision and determination of its derivatives is based on analytical expressions. This is done in order to optimize precision and accuracy of the results as well as the program execution time.With the provided input data and a typical contemporary laptop computer, the program execution typically lasts about 5 minutes. Reducing the imposed dead-time to zero increases the number of survived events approximately by a factor of 6, but the program execution time increases by about a factor of 3.

Effective Dead Time of Two Non-Paralyzable Detector Components in Series

Detector dead time losses, caused by both physical components in the detection system and the electronic data acquisition system, are perhaps the most prominent effect in non-ideal detector behavior. Most mathematical modeling methods consider the detector as a single unit with a single dead time parameter, while a true physical detector is often comprised of several serially connected components, each suffering from independent dead time losses. In this study, we develop new formulas for evaluating the dead time losses in a detection system with two serially connected components, each component with a non paralyzing dead time, while assuming that the original count rate has a Poisson distribution. The analytic results obtained are first compared with numeric simulations (showing a very good correspondence) and are then used for numeric investigation of global boundaries of the dead time effect in serially connected systems.

Assessment of multi-energy inter-pixel coincidence counters for photon-counting detectors at the presence of charge sharing and pulse pileup: A simulation study.

Spectral distortion due to charge sharing (CS) and pulse pileup (PP) in photon-counting detectors (PCDs) degrades the quality of PCD data. We recently proposed multi-energy inter-pixel coincidence counters (MEICC) that provided spectral cross-talk information related to CS. When PP was absent, the normalized Cramér-Rao lower bounds (nCRLBs) of 225-µm pixel PCDs with MEICC was comparable to those of 450-µm pixel PCD without MEICC. The aim of this study was to assess the performance of PCDs with MEICC in the presence of both CS and PP using computer simulations. An in-house Monte Carlo program was modified to incorporate the following four temporal elements: (1) A pulse shape with a pulse duration of 20ns, (2) delays of up to 10ns in anode arrival times when photons were incident on pixel boundaries, (3) offsets proportional to a vertical separation between the primary and secondary charge clouds at the rate of ±4ns per ±100µm, and (4) a stochastic fluctuation of anode arrival times for all of the charge clouds with a standard deviation of 2ns. We assessed the performance of five PCDs, (a)-(f), for three spectral tasks, (A)-(C): (a) The conventional PCD, (b) a PCD with MEICC, (c) a PCD with one coincidence counter (1CC), (d) a PCD with a 3×3 analog charge summing scheme (ACS), and (e) a PCD with a 3×3 digital count summing scheme (DCS); (A) conventional CT imaging with water (i.e., linear attenuation coefficient maps), (B) water-bone material decomposition, and (C) K-edge imaging with tungsten. The tube current was changed from 1mA to 1000mA and the nCRLB was assessed. The recorded count rate curves were fitted by the non-paralyzable detection model with the effective deadtime parameter. The best fit was achieved by 25.8ns for the conventional PCD, 18.6ns for MEICC and 1CC, 140.5ns for ACS, and 209.0ns for DCS. The nCRLBs were strongly dependent on count rates. MEICC provided the best nCRLBs for all of the imaging tasks over the count rate range investigated except for a few conditions such as K-edge imaging at 1mA. PP decreased the merit of MEICC over the conventional PCD in addressing CS. Nonetheless, MEICC consistently provided better nCRLBs than the conventional PCD did. The nCRLBs of MEICC were in the range of 49-58% of those of the conventional PCD for K-edge imaging, 45-76% for water-bone material decomposition, and 81-88% for the conventional CT imaging (i.e., linear attenuation coefficient maps). ACS provided better nCRLBs than the conventional PCD did only when the effect of PP was minor (e.g., when the counting efficiency of the conventional PCD was higher than 0.95 with the tube current of up to 100mA). Besides a few cases, MEICC provides the best nCRLBs for all of the tasks at all of the count rates. ACS and DCS provide better nCRLBs than the conventional PCD does only when count rates are very low.

An applicable count rate saturation correction approach on gamma camera for I-131 labeled radiopharmaceuticals

Abstract Background Gamma camera count rate saturation and high-rate dead time are the most important problems of quantitative measurement in dosimetric studies. In this study, we aimed to assess an algorithm for correction of the measured counting rates in the entire energy spectrum (327–400 keV) for camera dead-time effects. Methods In our study, whole body (WB) scan was performed by using a tissue-equivalent phantom, and that the radioactive Iodine (I-131) source with activities of 0.3, 0.6, 1.2, 1.5, 2.07, 2.7, 3.7, and 5.55 GBq was applied. WB scans of the 20% width energy windows were acquired for 420 s. Results Camera dead-time parameters were obtained from different activities of I-131 in a tissue-equivalent thyroid Phantom, then the saturation curve and coefficients α and β were obtained by using those parameters. Conclusions We concluded that in high-administered activity, it is possible to determine actual count rate of the system in saturation areas. Operation and accuracy of our gamma camera were determined for high activities of iodine-131, which can contribute to various applications of dosimetry in different fields.

Estimating the effective system dead time parameter for correlated neutron counting

Neutron time correlation analysis is one of the main technical nuclear safeguards techniques used to verify declarations of, or to independently assay, special nuclear materials. Quantitative information is generally extracted from the neutron-event pulse train, collected from moderated assemblies of 3He proportional counters, in the form of correlated count rates that are derived from event-triggered coincidence gates. These count rates, most commonly referred to as singles, doubles and triples rates etc., when extracted using shift-register autocorrelation logic, are related to the reduced factorial moments of the time correlated clusters of neutrons emerging from the measurement items. Correcting these various rates for dead time losses has received considerable attention recently. The dead time losses for the higher moments in particular, and especially for large mass (high rate and highly multiplying) items, can be significant. Consequently, even in thoughtfully designed systems, accurate dead time treatments are needed if biased mass determinations are to be avoided. In support of this effort, in this paper we discuss a new approach to experimentally estimate the effective system dead time of neutron coincidence counting systems. It involves counting a random neutron source (e.g. AmLi is a good approximation to a source without correlated emission) and relating the second and higher moments of the neutron number distribution recorded in random triggered interrogation coincidence gates to the effective value of dead time parameter. We develop the theoretical basis of the method and apply it to the Oak Ridge Large Volume Active Well Coincidence Counter using sealed AmLi radionuclide neutron sources and standard multiplicity shift register electronics. The method is simple to apply compared to the predominant present approach which involves using a set of 252Cf sources of wide emission rate, it gives excellent precision in a conveniently short time, and it yields consistent results as a function of the order of the moment used to extract the dead time parameter. This latter observation is reassuring in that it suggests the assumptions underpinning the theoretical analysis are fit for practical application purposes. However, we found that the effective dead time parameter obtained is not constant, as might be expected for a parameter that in the dead time model is characteristic of the detector system, but rather, varies systematically with gate width.

An 18 V Input 10 MHz Buck Converter With 125 ps Mixed-Signal Dead Time Control

A highly integrated synchronous buck converter with a predictive dead time control for input voltages ${ > } 18\,\text{V}$ with 10 MHz switching frequency is presented. A high resolution dead time of ${\sim} 125\,\text{ps}$ allows to reduce dead time dependent losses without requiring body diode conduction to evaluate the dead time. High resolution is achieved by frequency compensated sampling of the switching node and by an 8 bit differential delay chain. Dead time parameters are derived in a comprehensive study of dead time depended losses. This way, the efficiency of fast switching DCDC converters can be optimized by eliminating the body diode forward conduction losses, minimizing reverse recovery losses and by achieving zero voltage switching. High-speed circuit blocks for fast switching operation are presented including level shifter, gate driver, PWM generator. The converter has been implemented in a 180 nm high-voltage BiCMOS technology. The power losses were measured to be reduced by up to 31% by the proposed dead time control, which results in a 5.3% efficiency increase at ${V_{\rm IN} = } 18\,\text{V}$ , ${V_{\rm OUT} = } 5\,\text{V}$ , and 0.45 A load. At ${V_{\rm IN} = }12\,\text{V}$ , the peak efficiency is 81.2% with an efficiency improvement of 6% with dead time control.

Development of “active correlation” technique

With reaching to extremely high intensities of heavy-ion beams new requirements for the detection system of the Dubna Gas-Filled Recoil Separator (DGFRS) will definitely be set. One of the challenges is how to apply the active correlations method to suppress beam associated background products without significant losses in the whole long-term experiment efficiency value. Different scenarios and equations to develop the method according this requirement are under consideration in the present paper. The execution time to estimate the dead time parameter associated with the optimal choice of the life-time parameter is presented.

COuntLOss in NEutron multiplicity assessment (COLONEMA)

An approach has been developed to model in a simple way count loss in Passive Neutron Coincidence and Multiplicity Counting (PNCMC) systems in order to determine dead time corrections. The approach does not require to simulate the full PNCMC system, but rather uses basic information from the PNCMC system such as the neutron detection efficiency, the counters cabling scheme and the dead times of different electronic components of the system. A good agreement is found between the measured dead time parameters of a neutron multiplicity counter described in the literature and the dead time parameters calculated using the presented approach. Program summaryProgram title: COLONEMACatalogue identifier: AEYS_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEYS_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 2900No. of bytes in distributed program, including test data, etc.: 18753Distribution format: tar.gzProgramming language: C++.Computer: Unix/Linux workstations and PC.Operating system: Unix, Linux and windows, provided a C++ compiler has been installed. Examples were tested under Debian Linux.RAM: Depends on the simulated neutron source strength and detector efficiency. !at most, the example presented in the article allocates about 2 GB of virtual memory.Classification: 11.7, 17.7.Nature of problem: To determine the mass of fissile materials inside an unknown object, a passive neutron multiplicity or coincidence counting is performed in which single, double and triple neutron rates are measured. The measured rates must however be corrected from count losses due to dead time when the count rate is large.Solution method: Unlike approaches based on time consuming Monte Carlo transportation of the neutrons in the inspection system combined with treatment that take into account count losses due to dead time, a versatile Monte Carlo approach is presented which uses only the detection efficiency of the system and the dead time of the electronics and counters.Running time: It takes about 109 min on an Intel Xeon X5550 2.676 GHz processor to run the example presented.

On oscillation reduction in feedback control for processes with an uncertain dead time and internal–external disturbances

This paper aims to find a practical solution to reduce oscillation on the Smith Predictor (SP) based design with the dead time (DT) uncertainty, making it less sensitive to DT change and more effective in disturbance rejection. First, a conditional feedback mechanism is introduced in SP to reduce the amount of oscillation caused by the model inaccuracies in the DT parameter. Then, to address the oscillation caused by the phase lag in traditional PI controller and uncertain dynamics, this conditional SP is combined with active disturbance rejection control (ADRC), assisted by the knowledge of process dynamics. A practical tuning method is provided for the practicing engineers. The proposed approach is validated in extensive simulation studies with different types of plants and in frequency domain analysis. The simulation results show significant improvements in performance robustness and transient response.

SU‐E‐I‐88: The Effect of System Dead Time On Real‐Time Plastic and GOS Based Fiber‐Optic Dosimetry Systems

Purpose:A methodology is presented to correct for measurement inaccuracies at high detector count rates using a plastic and GOS scintillation fibers coupled to a photomultiplier tube with digital readout. This system allows temporal acquisition and manipulation of measured data.Methods:The detection system used was a plastic scintillator and a separate gadolinium scintillator, both (0.5 diameter) coupled to an optical fiber with a Hamamatsu photon counter with a built‐in microcontroller and digital interface. Count rate performance of the system was evaluated using the nonparalzable detector model. Detector response was investigated across multiple radiation sources including: orthovoltage x‐ray system, colbat‐60 gamma rays, proton therapy beam, and a diagnostic radiography x‐ray tube. The dead time parameter was calculated by measuring the count rate of the system at different exposure rates using a reference detector.Results:The system dead time was evaluated for the following sources of radiation used clinically: diagnostic energy x‐rays, cobalt‐60 gamma rays, orthovoltage xrays, particle proton accelerator, and megavoltage x‐rays. It was found that dead time increased significantly when exposing the detector to sources capable of generating Cerenkov radiation, all of the sources sans the diagnostic x‐rays, with increasing prominence at higher photon energies. Percent depth dose curves generated by a dedicated ionization chamber and compared to the detection system demonstrated that correcting for dead time improves accuracy. On most sources, nonparalzable model fit provided an improved system response.Conclusion:Overall, the system dead time was variable across the investigated radiation particles and energies. It was demonstrated that the system response accuracy was greatly improved by correcting for dead time effects. Cerenkov radiation plays a significant role in the increase in the system dead time through transient absorption effects attributed to electron hole‐pair creations within the optical waveguide.

Measurement of dead time by time interval distribution method

Non-random event losses due to dead time effect in nuclear radiation detection systems distort the original Poisson process into a new type of distribution. As the characteristics of the distribution depend on physical properties of the detection system, it is possible to estimate the dead time parameters based on time interval analysis, this is the problem investigated in this work. A BF3 ionization chamber is taken as a case study to check the validity of the method in experiment. The results are compared with the data estimated by power rising experiment performed in Esfahan Heavy Water Zero Power Reactor (EHWZPR). Using Monte Carlo simulation, the problem is elaborately studied and useful range for counting rates of the detector is determined. The proposed method is accurate and applicable for all kinds of radiation detectors with no potential difficulty and no need for any especial nuclear facility. This is not a time consuming method and advanced capability of online examination during normal operation of the detection system is possible.

An exact discrete-time model and the bifurcation performance of single phase grid-connected inverter with L-filter considering dead-time nonlinearity

Grid-connected inverter system is recognized as a time-varying nonlinear system, and it has complex nonlinear behaviors in practice. However, the introduction of dead-time nonlinearity can make the nonlinear behaviors of the system more complex and harder to predict. In this paper, the proportional control single-phase grid-connected inverter with L-filter considering dead-time nonlinearity is investigated. The observation of current waveforms under fixed controller parameter and different dead-time parameters shows that the bifurcation phenomenon occurs with the increase of dead-time. According to the features of dead-time nonlinearity and the zero current clamping phenomenon caused by dead-time, an exact and complete discrete-time model is established by comprehensively considering the system from various aspects. And the theoretical analysis of bifurcation behaviors of system is carried out based on the proposed model. Moreover, the stability judgment has engineering significance. However, with the consideration of dead-time nonlinearity, analytical methods are difficult to use and the graphic methods do not have satisfactory accuracy. Therefore, a stability criterion based on equivalent duty ratio is proposed in this paper, which can accurately judge the stability boundary and provide reliable references for the parameter design of controller and dead-time.

Main Steam Temperature Modeling Based on Levenberg-Marquardt Learning Algorithm

Main steam temperature is one of the most important parameters in coal fired power plant. Main steam temperature is often describe as non-linear and large inertia with long dead time parameters. This paper present main steam temperature modeling method using neural network with Levenberg-Marquardt learning algorithm. The result of the simulation showed that the main steam temperature modeling based on neural network with Levenberg-Marqurdt learning algorithm is able to replicate closely the actual plant behavior. Generator output, main steam flow, main steam pressure and total spraywater flow are proven to be the main parameters affected the behavior of main steam temperature in coal fired power plant.

Mechanistic Studies of Hairpin to Duplex Conversion for Trinucleotide Repeat Sequences

The expansion of a trinucleotide repeat sequence, such as CAG/CTG, has been pinpointed as the molecular basis for a number of neurodegenerative disorders. It has been proposed that as part of the expansion process, these repetitive sequences adopt non-B conformations such as hairpins. However, the prevalence of these hairpins and their contributions to the DNA expansion have not been well defined. In this work, we utilized a molecular beacon strategy to examine the stability of the (CAG)(10) hairpin and also its behavior in the presence of the complementary (CTG)(10) hairpin. We find that the two hairpins represent kinetically trapped species that can coexist but irreversibly convert to duplex upon thermal induction. Furthermore, as monitored by fluorescence and optical analysis, modifications to the base composition of either the loop or stem region have a profound effect on the ability of the trinucleotide repeat hairpins to convert to duplex. Additionally, the rate of duplex formation is also reduced with these loop and stem-modified hairpins. These results demonstrate that the trinucleotide repeat hairpins can convert to duplex via two independent mechanisms as follows: the loop-loop interactions found in kissing hairpins or the stem-stem interactions of a cruciform.

A gamma camera count rate saturation correction method for whole-body planar imaging

Whole-body (WB) planar imaging has long been one of the staple methods of dosimetry, and its quantification has been formalized by the MIRD Committee in pamphlet no 16. One of the issues not specifically addressed in the formalism occurs when the count rates reaching the detector are sufficiently high to result in camera count saturation. Camera dead-time effects have been extensively studied, but all of the developed correction methods assume static acquisitions. However, during WB planar (sweep) imaging, a variable amount of imaged activity exists in the detector's field of view as a function of time and therefore the camera saturation is time dependent. A new time-dependent algorithm was developed to correct for dead-time effects during WB planar acquisitions that accounts for relative motion between detector heads and imaged object. Static camera dead-time parameters were acquired by imaging decaying activity in a phantom and obtaining a saturation curve. Using these parameters, an iterative algorithm akin to Newton's method was developed, which takes into account the variable count rate seen by the detector as a function of time. The algorithm was tested on simulated data as well as on a whole-body scan of high activity Samarium-153 in an ellipsoid phantom. A complete set of parameters from unsaturated phantom data necessary for count rate to activity conversion was also obtained, including build-up and attenuation coefficients, in order to convert corrected count rate values to activity. The algorithm proved successful in accounting for motion- and time-dependent saturation effects in both the simulated and measured data and converged to any desired degree of precision. The clearance half-life calculated from the ellipsoid phantom data was calculated to be 45.1 h after dead-time correction and 51.4 h with no correction; the physical decay half-life of Samarium-153 is 46.3 h. Accurate WB planar dosimetry of high activities relies on successfully compensating for camera saturation which takes into account the variable activity in the field of view, i.e. time-dependent dead-time effects. The algorithm presented here accomplishes this task.

The Mechanism of the Reverse Recovery Step, Phosphate Release, and Actin Activation of Dictyostelium Myosin II

The rate-limiting step of the myosin basal ATPase (i.e. in absence of actin) is assumed to be a post-hydrolysis swinging of the lever arm (reverse recovery step), that limits the subsequent rapid product release steps. However, direct experimental evidence for this assignment is lacking. To investigate the binding and the release of ADP and phosphate independently from the lever arm motion, two single tryptophan-containing motor domains of Dictyostelium myosin II were used. The single tryptophans of the W129+ and W501+ constructs are located at the entrance of the nucleotide binding pocket and near the lever arm, respectively. Kinetic experiments show that the rate-limiting step in the basal ATPase cycle is indeed the reverse recovery step, which is a slow equilibrium step (k(forward) = 0.05 s(-1), k(reverse) = 0.15 s(-1)) that precedes the phosphate release step. Actin directly activates the reverse recovery step, which becomes practically irreversible in the actin-bound form, triggering the power stroke. Even at low actin concentrations the power stroke occurs in the actin-attached states despite the low actin affinity of myosin in the pre-power stroke conformation.

Concurrent Measurement of Individual Gamma-Ray Spectra During and Between Fast Neutron Pulses

A fast commercial digital multi-channel analyzer (DMCA) with a 40 MHz sampling frequency, was modified for concurrent acquisition during the same data collection run, of two separate gamma-ray spectra induced during and between fast neutron pulses. The DMCA was programmed to monitor the incoming and observed count rates, and the resulting real times and dead times separately for each spectrum. We report here the performance of the DMCA in terms of it's monitoring capabilities for each channel when using a pulsed 14 MeV neutron generator. The losses in the incoming and observed count rates were modeled based on the basic dead time parameter of the system

Maximum Efficiency Point Tracking (MEPT) Method and Digital Dead Time Control Implementation

An adaptive control method, to be called maximum efficiency point tracking (MEPT), is presented in this paper. This method tracks system efficiency, which is dc-dc converter efficiency in this paper, and adaptively optimizes system parameters to maximize efficiency. The MEPT method is used in this paper to optimize the primary-to-secondary switches' dead-time parameter in an isolated topology to reduce the switches' body diodes conduction during commutation periods and to reduce body diodes conduction and reverse-recovery related losses in order to improve efficiency. MEPT tracks converter efficiency while changing the dead-time and detects the optimized dead-time value at the maximum efficiency point at different load and line conditions. In this paper, the MEPT method is discussed and analyzed, and its digital control algorithm and experimental implementation are presented

Measurement uncertainty in the presence of low-frequency noise

We discuss the measurement uncertainty in the presence of different types of fundamental noise processes, especially 1/f noise. The treatment is based on the Allan variance of an n-sample average with two deadtime parameters relevant in metrology. Some results applicable to situations that are common in metrology, e.g., international comparisons, are derived. Experimentally, the output of Zener voltage standards in the frequency range from 10/sup -6/ Hz to 10/sup 3/ Hz is studied and behavior closely resembling that of 1/f noise is found at all time scales of practical interest. The noise floor of a 10 V Zener standard was found to be 60 nV and the 1/f corner frequency 3.5 Hz. Environmental variations cause the long-term (>100 s) deviations of the Zener voltage to slightly increase from the limiting 1/f noise level.

Single- and multi-deadtime parameter corrections of one- and two-dimensional Rossi-alpha distributions for time interval analysis in neutron coincidence counting

Advanced neutron coincidence counting techniques applied for the assay of special nuclear materials additionally also determine the factorial moments of the detected neutron multiplicity distribution. From these factorial moments the actual neutron detection efficiency or neutron multiplication can be inferred via a so-called three-parameter-analysis in which the spontaneous fission rate together with two other unknowns can be determined. The factorial moments are generally obtained with data from multiplicity counters, but can also be derived by the Time Interval Analysis (TIA) technique based on Rossi-alpha distributions. In the past, the importance of accurate corrections for counting losses of the counting data from the multiplicity counters has already been shown and deadtime correction models for the three-parameter-analysis using multiplicity counters were presented. This article presents deadtime correction formulas for a three-parameter-analysis based on the recording of Rossi-alpha count-rate distributions. Whereas dead time correction formulas in neutron assay are generally based on a model with a single deadtime parameter, also a more general multi-deadtime parameter description is derived which can account for different counting losses in the different detection chains of a neutron counter. The multi-deadtime parameter correction formalism was tested experimentally using a fast Time Interval Analyser board which also allows to directly monitor the effect of counting losses and measure deadtime parameters.