No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Pulse pileup correction of large NaI(Tl) total absorption spectra using the true pulse shape
Abstract
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.
... Equally important was the development at Valencia of the computer programs needed to provide consistent and reliable analysis of the data acquired with the spectrometer. This involved finding a solution [15,16] to the inverse, ill-posed problem that is described later in this article in section 3.1, taking account of the nonlinearity of the light output in the scintillator [17] and the pile-up in the electronic circuits [18]. Figure 2 compares the B(GT) distribution for the decay of 156 Tm measured with the Russian TAgS and the GSI spectrometer. ...
... The exploitation of Lucrecia would have been much more difficult without the development of analysis methods and techniques [15][16][17][18] that we will briefly summarise here before going on to discuss some examples of Lucrecia in use. Since real TAS spectrometers are not 100% efficient it is necessary to consider the response to beta particles and the electromagnetic deexcitation cascades in unfolding the measured spectra. ...
... These authors have put the analysis of TAS data on a sound footing although in applying the methods due care and attention must be paid to the individual case. In addition to solving the 'ill-posed' problem the Valencia group also looked in detail at the effect of the nonlinearity in the light output of the scintillator [17] and of the pile-up in the electronic circuitry [18] and showed how they can be taken into account. ...
Here we present the experimental activities carried out at ISOLDE with the total absorption spectrometer Lucrecia, a large 4π scintillator detector designed to absorb a full gamma cascade following beta decay. This spectrometer is designed to measure β-feeding to excited states without the systematic error called Pandemonium. The set up allows the measurement of decays of very short half life. Experimental results from several campaigns, that focus on the determination of the shapes of β-decaying nuclei by measuring their β decay strength distributions as a function of excitation energy in the daughter nucleus, are presented.
... Generally, radiation detectors have an output in the form of a series of pulses. For example, a scintillator produces pulses with a rise and fall time typical for a given detection of nuclear radiation [1,2]. The quantity of radiation can be represented as the number of detected pulses; this can be measured using a counter. ...
... The counting rate was measured by PHA and corrected (actual) counting rate calculated by Equation(1). ...
A pulse height analyzer (PHA) is used to measure the frequency distribution of the signal output height of an event detector. However, the typical PHA algorithm has limitations in measurement; it cannot distinguish multiplet due to coincidence and singlet pulse. Coincidences will pile up the signals that make the pulse height value higher than it should be. Therefore, this study has developed a simple algorithm to calculate pulse height distribution with coincidence correction (PHA-CC). The developed algorithm firstly identified the coincidence pulse by considering its pulse width. The result shows that the developed algorithm could successfully distinguish multiplet and singlet pulses. The significance of pulse height distribution measured by the PHA-CC compared to regular PHA was also discussed in this paper.
... Il a été démontré dans la réf. [36] qu'un excellent accord avec les réponses mesurées pour plusieurs isotopes radioactifs peut être obtenu lorsque les réponses individuelles des rayons gamma sont produites par simulation Monte Carlo (code Geant IV). ...
... Cette possibilité est nouvelle comparée aux détecteurs TAGS précédents. L'objectif est de se servir de cette information additionnelle dans la résolution du problème inverse pour améliorer la fiabilité de l'analyse des données [35], [36] : ...
Today, nuclear energy represents a non-negligible part of the global energy market, most likely a rolling wheel to grow in the coming decades. Reactors of the future must face the criteria including additional economic but also safety, non-proliferation, optimized fuel management and responsible management of nuclear waste. In the framework of this thesis, studies on non-proliferation of nuclear weapons are discussed in the context of research and development of a new potential tool for monitoring nuclear reactors, the detection of reactor antineutrinos, because the properties of these particles may be of interest for the International Agency of Atomic Energy (IAEA), in charge of the verification of the compliance by States with their safeguards obligations as well as on matters relating to international peace and security. The IAEA encouraged its member states to carry on a feasibility study. A first study of non-proliferation is performed with a simulation, using a proliferating scenario with a CANDU reactor and the associated antineutrinos emission. We derive a prediction of the sensitivity of an antineutrino detector of modest size for the purpose of the diversion of a significant amount of plutonium. A second study was realized as part of the Nucifer project, an antineutrino detector placed nearby the OSIRIS research reactor. The Nucifer antineutrino detector is dedicated to non-proliferation with an optimized efficiency, designed to be a demonstrator for the IAEA. The simulation of the OSIRIS reactor is developed here for calculating the emission of antineutrinos which will be compared with the data measured by the detector and also for characterizing the level of background noises emitted by the reactor detected in Nucifer. In general, the reactor antineutrinos are emitted during radioactive decay of fission products. These radioactive decays are also the cause of the decay heat emitted after the shutdown of a nuclear reactor of which the estimation is an issue of nuclear safety. In this thesis, we present an experimental work which aims to measure the properties of beta decay of fission products important to the non-proliferation and reactor decay heat. First steps using the technique of Total Absorption Gamma-ray Spectroscopy (TAGS) were carried on at the radioactive beam facility of the University of Jyvaskyla. We will present the technique used, the experimental setup and part of the analysis of this experiment.
... The response function R depends on the detector and branching ratios B of the levels in the daughter nucleus and can only be calculated using MC techniques. The analysis of the data presented here was carried out using the methods of analysis established by the Valencia group [10][11][12][13]. The response function was determined by means of the GEANT4 code [14]. ...
... Pulse pileup also distorts the spectra. The pileup distortion was calculated as described in Ref. [10]. The second step in the analysis is the determination of the branching ratio matrix of the daughter nucleus (B). ...
The β-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely 102,104,105Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations.
... If more than one event arrives within the same analog to digital converter (ADC) event gate, a signal with the wrong energy is stored in the spectrum. Apart from the electronic pulse pileup effect for a single detector module [33] one must consider the summing of signals from different detector modules. A new Monte Carlo (MC) procedure to calculate their combined contribution has been developed. ...
... The procedure is based on the random superposition of two stored events within the ADC gate length. The normalization of the resulting summing-pileup spectrum is fixed by the event rate and the ADC gate length [33]. ...
Total absorption spectroscopy was used to investigate the beta-decay
intensity to states above the neutron separation energy followed by gamma-ray
emission in 87,88Br and 94Rb. Accurate results were obtained thanks to a
careful control of systematic errors. An unexpectedly large gamma intensity was
observed in all three cases extending well beyond the excitation energy region
where neutron penetration is hindered by low neutron energy. The gamma
branching as a function of excitation energy was compared to Hauser-Feshbach
model calculations. For 87Br and 88Br the gamma branching reaches 57% and 20%
respectively, and could be explained as a nuclear structure effect. Some of the
states populated in the daughter can only decay through the emission of a large
orbital angular momentum neutron with a strongly reduced barrier penetrability.
In the case of neutron-rich 94Rb the observed 4.5% branching is much larger
than the calculations performed with standard nuclear statistical model
parameters, even after proper correction for fluctuation effects on individual
transition widths. The difference can be reconciled introducing an enhancement
of one order-of-magnitude in the photon strength to neutron strength ratio. An
increase in the photon strength function of such magnitude for very
neutron-rich nuclei, if it proved to be correct, leads to a similar increase in
the (n,gamma) cross section that would have an impact on r-process abundance
calculations.
... It gets even worse because of the poorer energy resolution of the scintillator detectors and if the decay scheme is mostly unknown. A specific analysis method is followed to determine BFI from the TAGS spectrum as described in the Ref. [10][11][12][13][14]. ...
High Resolution Gamma-ray Spectroscopy (HRGS) and Total Absorption Gamma-ray Spectroscopy (TAGS) techniques of beta decay study and facilities for such techniques at VECC, Kolkata have been described. The preliminary results of the HRGS experiment performed at VECC to study the beta decay of 126Sb, an important nucleus for the reactor decay heat estimation, are presented. The observation of a 928-keV gamma ray confirmed the 2703.6 keV state in 126Te. The half-lives of both the beta-decaying states in 126Sb could be uniquely measured in this work. The results are useful for future TAGS measurements of the 126Sb beta decay.
... The traditional method to solve the pile-up is to use the pile-up rejection circuit to discard the pile-up pulses directly, but it will reduce the pulse pass rate and increase the dead time of the system. The majority pulse pile-up identification and correction methods needs full waveform [3][4][5], which is not available in many situations. ...
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.
... All of these studies assumed a mean pulse shape. The use of a mean pulse shape can reduce calculation time, and simplify the analysis process, but pulse shape estimated from the measured transient current can provide more accurate results in the entire energy range [16], [17]. In addition, for strip detectors, the energy collected on one strip varies significantly from photon to photon due to charge sharing effect, and, therefore, the use of a mean pulse shape to study pileup and energy distortion may introduce inaccuracies. ...
Due to pulse pileup, photon counting detectors (PCDs) suffer from count loss and energy distortion when operating in high count rate environments. In this paper, we studied the pulse pileup of a double-sided silicon strip detector (DSSSD) to evaluate its potential application in a mammography system. We analyzed the pulse pileup using pulses of varied shapes, where the shape of the pulse depends on the location of photon interaction within the detector. To obtain the shaped pulses, first, transient currents for photons interacting at different locations were simulated using a Technology Computer-Aided Design (TCAD) software. Next, the currents were shaped by a
CR
–
RC
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
shaping circuit, calculated using Simulink. After obtaining these pulses, both the different orders of pileup and the energy spectrum were calculated by taking into account the following two factors: 1) spatial distribution of photon interactions within the detector and 2) time interval distribution between successive photons under a given photon flux. We found that for a DSSSD with a thickness of
$300~\mu \text{m}$
, a pitch of
$25~\mu \text{m}$
, and a strip length of 1 cm, under a bias voltage of 50 V, the variable pulse shape model predicts that the fraction free of pileup can be >90% under a photon flux of 3.75 Mcps/mm
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
(million counts per second per square mm). The DSSSD is a promising candidate for digital mammography applications.
... Fig. 6(a) shows the spectrum measured without the absorber; the effect of response function was unfolded. The total counting rate was approximately 5 kCPS, and as clearly observed in the spectrum, a significant pile-up part was not shown in the high energy region (Debertin et al., 1977;Then et al., 1977;Cano-Ott et al., 1999). Fig. 6(b) shows four spectra with each absorber of soft tissue-equivalent phantom with 20.0 mm thickness, bone-equivalent phantom with 4.1 mm thickness, acrylic with 24.0 mm thickness, and aluminum with 1.9 mm thickness (see Fig. 5). ...
... The experiments were performed under the following irradiation conditions summarized in Table 1; phantom thicknesses were 1, 5, 10, and 20 cm; tube voltages were 40, 60, 80, and 120 kVp; and tube current-time products were 0.5-1000 mAs. The currents (mA values) were determined so as to provide a proper counting rate (less than 10 kilocounts per second) for the CdTe detector, and the effects of pile-up and dead time [18][19][20] were negligibly small for the experimental conditions. The spectra measured with the CdTe detector were unfolded with response functions derived by a Monte-Carlo simulation code (electron gamma shower ver. ...
Our aim in this study is to derive an identification limit on a dosimeter for not disturbing a medical image when patients wear a small-type optically stimulated luminescence (OSL) dosimeter on their bodies during X-ray diagnostic imaging. For evaluation of the detection limit based on an analysis of X-ray spectra, we propose a new quantitative identification method. We performed experiments for which we used diagnostic X-ray equipment, a soft-tissue-equivalent phantom (1–20 cm), and a CdTe X-ray spectrometer assuming one pixel of the X-ray imaging detector. Then, with the following two experimental settings, corresponding X-ray spectra were measured with 40–120 kVp and 0.5–1000 mAs at a source-to-detector distance of 100 cm: (1) X-rays penetrating a soft-tissue-equivalent phantom with the OSL dosimeter attached directly on the phantom, and (2) X-rays penetrating only the soft-tissue-equivalent phantom. Next, the energy fluence and errors in the fluence were calculated from the spectra. When the energy fluence with errors concerning these two experimental conditions was estimated to be indistinctive, we defined the condition as the OSL dosimeter not being identified on the X-ray image. Based on our analysis, we determined the identification limit of the dosimeter. We then compared our results with those for the general irradiation conditions used in clinics. We found that the OSL dosimeter could not be identified under the irradiation conditions of abdominal and chest radiography, namely, one can apply the OSL dosimeter to measurement of the exposure dose in the irradiation field of X-rays without disturbing medical images.
... A carbon scatterer was used in place of the ionization chamber (see Fig. 3). In our experimental conditions, the counting rate (counts per seconds: CPS) of the CdTe detector was kept below 1 kCPS to reduce the pulse pileup effect [23,24]. ...
We propose a new practical method for the construction of an accurate secondary X-ray field using medical diagnostic X-ray equipment. For accurate measurement of the air kerma of an X-ray field, it is important to reduce and evaluate the contamination rate of scattered X-rays. To determine the rate quantitatively, we performed the following studies. First, we developed a shield box in which an ionization chamber could be set at an inner of the box to prevent detection of the X-rays scattered from the air. In addition, we made collimator plates which were placed near the X-ray source for estimation of the contamination rate by scattered X-rays from the movable diaphragm which is a component of the X-ray equipment. Then, we measured the exposure dose while changing the collimator plates, which had diameters of 25-90 mm(ϕ). The ideal value of the exposure dose was derived mathematically by extrapolation to 0 mm(ϕ). Tube voltages ranged from 40 to 130 kV. Under these irradiation conditions, we analyzed the contamination rate by the scattered X-rays. We found that the contamination rates were less than 1.7 and 2.3 %, caused by air and the movable diaphragm, respectively. The extrapolated value of the exposure dose has been determined to have an uncertainty of 0.7 %. The ionization chamber used in this study was calibrated with an accuracy of 5 %. Using this kind of ionization chamber, we can construct a secondary X-ray field with an uncertainty of 5 %.
... The first is that the nanoDot OSL dosimeter has a low detection efficiency, therefore it was located at a minimum distance from the sample for the efficiency of the experiments. The second is that the CdTe detector causes a pile-up effect depending on the incident photon number, therefore the distance was determined as the photon number having the unit of CPS (count per second) which is less than 10000 cps [17][18][19]. In addition to the consideration of experimental settings, these detectors were covered with lead plates to prevent the detection of unnecessary scattered X-rays. ...
... The detailed irradiation conditions are also presented in the figure; the tube voltages are 40, 60, 80, 120 kV and the tube current-time products are 0.5 to 1000 mAs. The currents were varied so to obtain a proper counting rate (less than 10 kilocounts per second) for the CdTe detector in order to establish the sufficiently reduced effects of pile-up and dead time [13][14][15]. The spectra measured with CdTe detector were corrected by response functions derived by the Monte-Carlo simulation code (electron gamma shower ver. ...
... As part of the optimization procedure in the analysis, the cut energy and the parameters of the statistical model can be changed. Once the branching ratio matrix is defined, the R ij can be calculated recursively from previously calculated responses using Monte Carlo simulations [37][38][39]. Carlo simulations were validated with measurements of the spectra of well-known radioactive sources ( 24 Na, 60 Co, 137 Cs). Once the R response matrix is obtained, the expectation maximization (EM) algorithm is applied to extract the beta feeding distributions [40,41]. ...
The β decay of [superscript 192,190]Pb has been studied using the total absorption technique at the ISOLDE (CERN) facility. The β-decay strength deduced from the measurements, combined with QRPA theoretical calculations, allow us to infer that the ground states of the [superscript 192,190]Pb isotopes are spherical. These results represent the first application of the shape determination method using the total absorption technique for heavy nuclei and in a region where there is considerable interest in nuclear shapes and shape effects.
... Their accuracy is severely affected when two or more pulses are piled up. Such piled-up events are usually caused by high source activities, long pulse duration and etc. Pileup processing is important in the energy measurement (Tenney 1984, Germano and Hoffman 1990, Debertin and Schötzig 1977, Gardner and Wielopolski 1977, Cano-Ott et al 1999. Lots of researches have been focused on it over the past few decades, while the majority of them aimed at detecting the pileups for rejection (Moszyński et al 1967, Máthé 1963, Tenney 1984, Blatt et al 1968, Westphal 1979, Barradas and Reis 2006. ...
This work focuses on event energy measurement, a crucial task of scintillation detection systems. We modeled the scintillation detector as a linear system and treated the energy measurement as a deconvolution problem. We proposed a pulse model based iterative deconvolution (PMID) method, which can process pileup events without detection and is adaptive for different signal pulse shapes. The proposed method was compared with digital gated integrator (DGI) and digital delay-line clipping (DDLC) using real world experimental data. For singles data, the energy resolution (ER) produced by PMID matched that of DGI. For pileups, the PMID method outperformed both DGI and DDLC in ER and counts recovery. The encouraging results suggest that the PMID method has great potentials in applications like photon-counting systems and pulse height spectrometers, in which multiple-event pileups are common.
The β decays of the ground state (gs) and isomeric state (m) of Y96 have been studied with the total absorption γ-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the 8+ isomeric state from the 0− ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The β-intensity distributions of both decays have been independently determined. In the analyses the deexcitation of the 1581.6 keV level in Zr96, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the β-detector efficiency, influencing the β-intensity distribution obtained. Our results for Y96gs (0−) confirm the large ground state to ground state β-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to 96.6−2.1+0.3% of the total β intensity. Given that the decay of Y96gs is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of Y96m (8+), previously undetected β intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption γ-ray spectroscopy measurements of β decays with highly fragmented deexcitation patterns. Y96m (8+) is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average β and γ energies differ significantly from the previous values in evaluated databases. The discrepancy is far above the previously quoted uncertainties. Finally, we also report on the successful implementation of an innovative total absorption γ-ray spectroscopy analysis of the module-multiplicity gated spectra, as a first proof of principle to distinguish between decaying states with very different spin-parity values.
In this review we will present the results of recent β-decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain β-decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the γ cascades that follow the initial β decay. For this reason the technique requires the use of calorimeters with very high γ detection efficiency. The measurements presented and discussed here were performed mainly at the IGISOL facility of the University of Jyväskylä (Finland) using isotopically pure beams provided by the JYFLTRAP Penning trap. Examples are presented to show that the results of our measurements on selected nuclei have had a large impact on predictions of both the decay heat and the anti-neutrino spectrum from reactors. Some of the cases involve β-delayed neutron emission thus one can study the competition between γ- and neutron-emission from states above the neutron separation energy. The γ-to-neutron emission ratios can be used to constrain neutron capture (n,γ) cross sections for unstable nuclei of interest in astrophysics. The information obtained from the measurements can also be used to test nuclear model predictions of half-lives and Pn values for decays of interest in astrophysical network calculations. These comparisons also provide insights into aspects of nuclear structure in particular regions of the nuclear chart.
In β-decay studies the determination of the decay probability to the ground state (g.s.) of the daughter nucleus often suffers from large systematic errors. The difficulty of the measurement is related to the absence of associated delayed γ-ray emission. In this work we revisit the 4πγ−β method proposed by Greenwood and collaborators in the 1990s, which has the potential to overcome some of the experimental difficulties. Our interest is driven by the need to determine accurately the β-intensity distributions of fission products that contribute significantly to the reactor decay heat and to the antineutrinos emitted by reactors. A number of such decays have large g.s. branches. The method is relevant for nuclear structure studies as well. Pertinent formulas are revised and extended to the special case of β-delayed neutron emitters, and the robustness of the method is demonstrated with synthetic data. We apply it to a number of measured decays that serve as test cases and discuss the features of the method. Finally, we obtain g.s. feeding intensities with reduced uncertainty for four relevant decays that will allow future improvements in antineutrino spectrum and decay heat calculations using the summation method.
Under the condition of high counting rate, the phenomenon of nuclear pulse signal pile-up using a single exponential impulse shaping method is still very serious, and leads to a severe loss in counting rate. A real nuclear pulse signal can be expressed as a dual-exponential decay function with a certain rising edge. This paper proposes a new dual-exponential impulse shaping method and shows its deployment in hardware to test its performance. The signal of a high-performance silicon drift detector under high counting rate in an X-ray fluorescence spectrometer is obtained. The result of the experiment shows that the new method can effectively shorten the dead-time caused by nuclear signal pile-up and correct the counting rate.
Optimization algorithms are applied to resolve the second-order pileup (SOP) issue from high counting rates occurring in digital alpha spectroscopy. These are antlion optimizer (ALO) and particle swarm optimization (PSO) algorithms. Both optimization algorithms are coupled to one of the three proposed peak finder algorithms. Three custom time-domain algorithms are proposed for retrieving SOP peaks, namely peak seek, slope tangent, and fast array algorithms. In addition, an average combinational algorithm is applied. The time occurrence of the retrieved peaks is tested for an elimination of illusive pulses. Conventional methods are inaccurate and time-consuming. ALO and PSO optimizations are used for the localization of retrieved peaks. Optimum cost values that achieve the best fitness values are demonstrated. Thus, the optimum positions of the detected peak heights are achieved. Evaluation metrics of the optimized algorithms and their influences on the retrieved peaks parameters are established. Comparisons among such algorithms are investigated, and the algorithms are inspected in terms of their computational time and average error. The peak seek algorithm achieves the lowest average computational error for pulse parameters (amplitude and position). However, the fast array algorithm introduces the largest average error for pulse parameters. In addition, the peak seek algorithm coupled with an ALO or PSO algorithm is observed to realize a better performance in terms of the optimum cost and computational time. By contrast, the performance of the peak seek recovery algorithm is improved using the PSO. Furthermore, the computational time of the peak optimization using the PSO is much better than that of the ALO algorithm. As a final conclusion, the accuracy of the peaks detected by the PSO surpasses that for the peaks detected by the ALO. The implemented peak retrieval algorithms are validated through a comparison with experimental results from previous studies. The proposed algorithms achieve a notable precision for compensation of the SOP peaks within the alpha ray spectroscopy at a high counting rate.
Purpose:
The new lower eye lens dose limit is of relevance in interventional radiology, where higher dose procedures result in increased scattered radiation to staff. The eye lens dose may be monitored using the directional dose equivalent at 3 mm depth, Hp(3), or through Hp(10) or Hp(0.07) measurements and using conversion factors. However, there are a considerable range of factors which contribute to measurement uncertainties, one of which is the incident photon energy. This study investigated the energy spectra of scattered radiation in interventional radiology, and the dosimetry accuracy of dosimeter types, evaluating their energy dependence.
Methods:
Scatter X-ray energy spectra were recorded under varied conditions in a fluoroscopy imaging suite. Dosimetry accuracy of eye dosimeters, including TLDs (100 s, 100Hs), Landauer Hp(3), John Caunt ED3 and Electronic Personal dosimeters (EPDs) were compared to air kerma measurements across a range of tube voltages.
Results:
The variation of energy spectra with changing phantom thickness, spectrometer angulation and filtration are presented. The 100 and 100H TLDs, and EPDs showed a consistent air kerma response (within 10%) with changes in energy. The real-time silicon diode detectors showed a variable over response of between 10 and 25% across the energies investigated while Landauers dedicated Hp(3) eye dosimeters showed considerable variation between dosimeters for similar conditions, a 17% variation at 50 kVp.
Conclusion:
The work aimed to validate the scattered energy spectra typically encountered in interventional radiology and to further determine the accuracy of eye dosimeters in relation to energy response variations.
Using the ‘quadruple combination detection’ automatic calibration method to solve the traditional passive nuclear ash hopper material level meter calibration problem. The method adopts the ‘contour multistage measurement’ mode, fitted the ratio of absorbed dose rate detected by adjacent cascade probe with corresponding actual material level after measurement, then use the fitting parameters to calibrate automatically which do not need ash hopper stop working, And this can effectively save the calibration time and cost. The method can effectively eliminate the material level measuring error brought by the changes of radioactive activity in the coal ash, which improve the measuring precision and material level positioning accuracy. There are many factors affecting the radioactive activity of coal ash which vary in Different feeding period, or after refueling. And this may cause measurement error and misinformation. Using quadruple combination detection and contour multistage measurement mode, when the radioactive activity in the coal ash changes, the passive nuclear meter level gauge can be revised according to the calibration curve or calibrated automatically. Which eliminated the effects brought by the changing of coal ash radioactive activity, saved onerous repeatedly calibration procedure, also improve the accuracy of the calibration, avoid misjudgment, and can improve the accuracy of measurement.
The decays of the β-delayed neutron emitters I137 and Rb95 have been studied with the total absorption γ-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyväskylä allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption γ-ray spectrometer, a segmented detector composed of 18 NaI(Tl) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt γ rays and delayed neutron interactions to eliminate this source of contamination. Due to the sensitivity of our spectrometer, we have found a significant amount of β intensity to states above the neutron separation energy that deexcite by γ rays, comparable to the neutron emission probability. The competition between γ deexcitation and neutron emission has been compared with Hauser-Feshbach calculations, and it can be understood as a nuclear structure effect. In addition, we have studied the impact of the β-intensity distributions determined in this work on reactor decay heat and reactor antineutrino spectrum summation calculations. The robustness of our results is demonstrated by a thorough study of uncertainties and with the reproduction of the spectra of the individual modules and the module-multiplicity gated spectra. This work represents the state-of-the-art of our analysis methodology for segmented total absorption spectrometers.
The β-intensity distributions of the decays of Nb100gs,100m and Nb102gs,102m have been determined using the total absorption γ-ray spectroscopy technique. The JYFLTRAP double Penning trap system was employed in a campaign of challenging measurements performed with the decay total absorption γ-ray spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. Different strategies were applied to disentangle the isomeric states involved, lying very close in energy. The low-spin component of each niobium case was populated through the decay of the zirconium parent, which was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained β-intensity distributions for these zirconium decays. The β-strength distributions evaluated with these results were compared with calculations in a quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of Zr100,102. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The β-intensities of the decay of Nb102m, for which there were no previous data, were obtained. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported, and here we detail the significant impact on decay heat calculations.
Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of Nb100gs,100m and Nb102gs,102mβ decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.
Three observables of interest for present and future reactors depend on the β decay data of the fission products: the reactor decay heat, antineutrinos from reactors and delayed neutron emission. Concerning the decay heat, significant discrepancies still exist between summation calculations in − their two main ingredients: the decay data and the fission yields − performed using the most recent evaluated databases available. It has been recently shown that the associated uncertainties are dominated by the ones on the decay data. But the results subtantially differ taking into account or not the correlations between the fission products. So far the uncertainty propagation does not include as well systematic effects on nuclear data such as the Pandemonium effect which impacts a large number of nuclei contributing to the decay heat. The list of nuclei deserving new TAGS measurements has been updated recently in the frame of IAEA working groups. The issues listed above impact in the same way the predicted energy spectra of the antineutrinos from reactors computed with the summation method, the interest of which has been recently reinforced by the Daya Bay latest publication. Nuclear data should definitely contribute to refine and better control these calculations. Lastly, a lot of nuclear data related to delayed neutrons are missing in nuclear databases. Despite the progresses already done these last years with new measurements now requiring to be included in evaluated databases, the experimental efforts which still need to be done are significant. These different issues will be addressed here before to comment on recent experimental results and on their impacts on the quoted observables. Some perspectives will also be presented. Solving the issues listed above will require to bring together experimental, simulation, evaluation and theoretical activities.
In this work, decay spectroscopy of neutron-rich 43K has been performed at the Radioactive Ion Beam (RIB) facility at Variable Energy Cyclotron Centre (VECC), Kolkata by producing it with an 18-MeV alpha beam on 40Ar gas target. The beam was delivered from the K130 Cyclotron and the gas jet recoil transport system was used to move the products to a low-background site. The β-feeding intensities were measured by both high resolution γ -ray spectroscopy and total absorption γ -ray spectroscopy methods in order to address mainly the anomalies (if any) in the feeding to �J ≥ 1 levels reported earlier. The decay half-life of 43K was also measured to be 22.4(1) hrs.
The β decay of Tc100 has been studied by using the total absorption γ-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. In this work the new Decay Total Absorption γ-ray Spectrometer in coincidence with a cylindrical plastic β detector has been employed. The β intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double β decay of Mo100.
The beta decays of $^{86}$Br and $^{91}$Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyv\"askyl\"a and further purified using the JYFLTRAP. $^{86}$Br and $^{91}$Rb are considered to be major contributors to the decay heat in reactors. In addition $^{91}$Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam {\it et al.} assuming that this decay was well known from high-resolution measurements. Our results show that both decays were suffering from the {\it Pandemonium} effect and that the results of Rudstam {\it et al.} should be renormalized. The relative impact of the studied decays in the prediction of the decay heat and antineutrino spectrum from reactors has been evaluated.
We investigate the decay of Br87,88 and Rb94 using total absorption γ-ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ intensity, so far unobserved in high-resolution γ-ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for U235 fission at cooling times in the range 1-100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for γ emission from neutron unbound states populated in the daughter nucleus. The γ branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for Rb94, although much smaller, hints of the need to increase the radiative width Γγ by one order of magnitude. This increase in Γγ would lead to a similar increase in the calculated (n,γ) cross section for this very neutron-rich nucleus with a potential impact on r process abundance calculations.
This article describes a Monte Carlo event generator for the design, optimization and performance characterization of beta decay spectroscopy experimental set-ups. The event generator has been developed within the Geant4 simulation architecture and provides new features and greater flexibility in comparison with the current available decay generator.
This chapter provides an overview of the basic techniques for detection of positron-emitting radionuclides and subsequent image reconstruction of the isotopes’ distribution within the object being imaged. Areas covered include basic gamma ray detectors with an emphasis on scintillator-based detectors, corrections for photon transport and detector effects, and the basic image reconstruction techniques commonly used in positron emission tomography scanners.
Using the results of β-decay studies with two complementary techniques, level density parameters for the nucleus 150Ho were deduced.
The new Decay Total Absorption Spectrometer (DTAS) has been commissioned with low energy radioactive beams at the upgraded IGISOL IV facility. The DTAS is a segmented detector composed of up to 18 NaI(Tl) crystals and it will be a key instrument in the DESPEC experiment at FAIR. In this document we report on the experimental setup and the first measurements performed with DTAS at IGISOL. The detector was characterized by means of MC simulations, and this allowed us to calculate the response function of the spectrometer and analyse the first cases of interest.
Beta-decay experiments are a primary source of information for nuclear structure studies and at the same time complementary to in-beam investigations far from stability. Although both types of experiment are mainly based on γ-ray spectroscopy, they face different experimental problems. The so called Pandemonium effect [1] is a critical problem in β-decay. In this contribution we will present a solution to this problem using total absorption spectroscopy methods. We will also present some examples of experiments carried out with the total absorption spectrometers TAS at GSI and Lucrecia recently installed at CERN.
The Gamma-ray Burst Monitor consists of 12 sodium iodide and 2 bismuth germanate scintillation detectors designed to enhance the scientific returns from Fermi in the study of γ-ray bursts. It has a fixed non-paralyzing dead time of 2.604 μs for each detected event except for those in the overflow channel of the 12 bit analog to digital converter of each detector, which have a longer dead time of 10.42 μs. At very high counting rates the pulse pile-up effect in the detectors leads to spectral distortions and also to additional event losses. These effects are relevant for the spectral analysis of high-flux astrophysical events such as gamma-ray bursts, soft gamma repeaters and solar flares, as well as terrestrial gamma-ray flashes. In this paper we present the results of post-launch tests using engineering detectors and equipment on the ground, along with detailed simulations of these effects at very high counting rates. The simulations enable us to assess the qualitative and quantitative changes in spectral shapes and event losses at different count rates. The observed spectra at various count rates using high intensity radioactive sources such as Cs137 and Co60 agree well with the simulated spectra. We also re-test the analytical model developed previously to correct for the pulse pile-up effects in GBM detectors. We also study the expected spectral distortions of specific spectral models commonly used in GRB analysis, including the Band model and power-law models with and without a high-energy cutoff.
The beta decay of $^{192,190}$Pb has been studied using the total absorption
technique at the ISOLDE(CERN) facility. The beta-decay strength deduced from
the measurements, combined with QRPA theoretical calculations, allow us to
infer that the ground states of the $^{192,190}$Pb isotopes are spherical.
These results represent the first application of the shape determination method
using the total absorption technique for heavy nuclei and in a region where
there is considerable interest in nuclear shapes and shape effects.
An overview is given of our activities related to the study of the beta decay of neutron rich nuclei relevant for nuclear applications. Recent results of the study of the beta decay of Br-87,Br-88 using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy.
Preliminary results of the data analysis of the beta decay of 94Rb using a novel - segmented- total absorption
spectrometer are shown in this contribution. This result is part of a systematic study of important contributors to the decay heat problem in nuclear reactors. In this particular case the goal is to determine the beta intensity distribution below the neutron separation energy and the gamma/beta competition above.
The antineutrino spectra measured in recent experiments at reactors are
inconsistent with calculations based on the conversion of integral beta spectra
recorded at the ILL reactor. $^{92}$Rb makes the dominant contribution to the
reactor spectrum in the 5-8 MeV range but its decay properties are in question.
We have studied $^{92}$Rb decay with total absorption spectroscopy. Previously
unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding
was found to be 87.5(25)%. The impact on the reactor antineutrino spectra
calculated with the summation method is shown and discussed.
A new detector array, the Modular Total Absorption Spectrometer (MTAS), was commissioned at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). Total absorption gamma spectra measured with MTAS are expected to improve beta-feeding patterns and beta strength functions in fission products. MTAS is constructed out of hexagonal NaI(Tl) detectors with a unique central module surrounded by 18 identical crystals assembled in three rings. The total NaI(Tl) mass of MTAS is over 1000 kg. The response of the central and other 18 MTAS modules to γ-radiation was simulated using the GEANT4 toolkit modified to analyze the nonlinear light output of NaI(Tl). A detailed description of the GEANT4 modifications made is discussed. Simulated energy resolution of MTAS modules is found to agree well with the measurements for single γ transitions of 662 keV (137Cs) with 8.2% full width half maximum (FWHM), 835 keV (54Mn) with FWHM of 7.5% FWHM, and 1115 keV (65Zn) with FWHM of 6.5%. Simulations of single and multiple γ-rays from 60Co are also discussed.
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.
X-ray spectroscopy is widely used for in-situ applications for samples analysis. Therefore, spectrum drawing and assessment of x-ray spectroscopy with high accuracy is the main scope of this paper. A Silicon Lithium Si(Li) detector that cooled with a nitrogen is used for signal extraction. The resolution of the ADC is 12 bits. Also, the sampling rate of ADC is 5 MHz. Hence, different algorithms are implemented. These algorithms were run on a personal computer with Intel core TM i5-3470 CPU and 3.20 GHz. These algorithms are signal preprocessing, signal separation and recovery algorithms, and spectrum drawing algorithm. Moreover, statistical measurements are used for evaluation of these algorithms. Signal preprocessing based on DC-offset correction and signal de-noising is performed. DC-offset correction was done by using minimum value of radiation signal. However, signal de-noising was implemented using fourth order finite impulse response (FIR) filter, linear phase least-square FIR filter, complex wavelet transforms (CWT) and Kalman filter methods. We noticed that Kalman filter achieves large peak signal to noise ratio (PSNR) and lower error than other methods. However, CWT takes much longer execution time. Moreover, three different algorithms that allow correction of x-ray signal overlapping are presented. These algorithms are 1D non-derivative peak search algorithm, second derivative peak search algorithm and extrema algorithm. Additionally, the effect of signal separation and recovery algorithms on spectrum drawing is measured. Comparison between these algorithms is introduced. The obtained results confirm that second derivative peak search algorithm as well as extrema algorithm have very small error in comparison with 1D non-derivative peak search algorithm. However, the second derivative peak search algorithm takes much longer execution time. Therefore, extrema algorithm introduces better results over other algorithms. It has the advantage of recovering and measuring over 21,941 peaks per second. Although, 1D non-derivative peak search algorithm has better extraction of peak height than other algorithms.
Measurement of a resonance's integrated cross section using nuclear resonance fluorescence can be a valuable tool for verifying the properties of the resonance because of the clear and unambiguous physical connection to the spin, lifetime, and ground state branching ratio of the level. We demonstrate this idea by measuring the integrated cross section of the 3.004-MeV level in Al27 to 4% using the monoenergetic γ-ray beam at the High Intensity γ-ray Source. That level was the subject of much debate experimentally in the 1960s, especially its spin, and even now only has a current tentative spin assignment of J=(9/2). The consistency check between this integrated cross section and the known properties of the level indicate that one (or more) of the literature properties is incorrect. Based on the range of extent of each property, a reassignment of spin to a tentative J=(7/2) may be warranted, but this would need to be confirmed with other measurements. This result demonstrates the utility of NRF as a way to verify the properties of states in the literature before undertaking more extensive measurements.
Beta-decay is described here as an alternative to charge- exchange
reactions to populate spin-isospin excitations in nuclei. Its advantages
and disadvantages are discussed and the Total Absorption Technique, a
reliable method of measuring Gamow-Teller transition probabilities is
described. An illustrative example is given where single particle and
collective excitations are observed in the beta decay. Problems such as
the spreading width, mixing of the states and the high energy tail of
the resonance are discussed.
A study of the Gamow-Teller strength distributions B(GT) in the beta decay of 78Sr and 76,78Rb has been made using a total absorption spectrometer (TAS). Following the success in deducing the sign of the deformation for 76Sr, a similar approach is adopted for 78Sr based on a comparison of the measured B(GT) with quasiparticle random-phase approximation calculations. This work confirms its previously expected prolate deformation in the ground state. Conclusions about the structure of the odd-odd 76,78Rb isotopes have been drawn based on their measured B(GT) distributions.
Far from the line of stability, β-decay studies are often a primary source of information on nuclear structure. The measured β-strength distribution for a given decay can be used to verify the accuracy of our theoretical description of the parent nucleus ground state and the states populated in the daughter nucleus. Total absorption spectrometers based on large NaI crystals are well suited tools to determine the β-strength distribution over the whole QEC decay window. The newly built spectrometer TAgS, dedicated to such studies, is presented and its performances and possibilities are discussed in the light of experiments performed at the ISOLDE/CERN mass separator. The resulting information on ground state deformations for the 74Kr and 76Sr isotopes are discussed.
The response of a large NaI(Tl) total absorption spectrometer for β-decay studies is investigated.The accuracy of Monte Carlo simulations taking into account the light yield non-proportionality of NaI(Tl) and the detailed geometry is assessed through comparison with spectra measured for several radioactive sources.
The method of analysis of total absorption γγ-ray spectra obtained in ββ-decay measurements is studied. The analysis problem is reduced to the solution of a linear inverse problem. The performance and systematic uncertainties of different inverse algorithms are studied. The maximum entropy and the expectation-maximisation algorithms are found to be superior to the linear regularisation method.
The response of a large NaI(Tl) total absorption spectrometer for β-decay studies is investigated.The accuracy of Monte Carlo simulations taking into account the light yield non-proportionality of NaI(Tl) and the detailed geometry is assessed through comparison with spectra measured for several radioactive sources.
A method is developed for calculating the distortion in pulse-height spectra obtained from spectrometry systems caused by the peak pulse pile-up effect. A general expression for double pulse coincidences is derived from the interval distribution for calculating the observed spectrum in terms of the true (undistorted) spectrum, the allowable pulse width, and the pulse shape. A specific model with explicit solution is obtained by assuming that the pulse shape is parabolic. Good agreement is obtained between this model and experimental data on a specific system which has a pulse shape that is approximately parabolic. An iterative procedure can be employed with the present model to obtain true spectra from observed spectra that contain considerable pulse pile-up.
A detailed study of pile-up effects in a single acquisition channel has been performed. A computer code of the Monte Carlo type has been written to simulate the acquisition process taking into account both the detailed shape of the input signals to the ADC as well as the characterictics of an auxiliary pile-up rejection circuit. The results of the simulation are used to purge from pile-up effects our experimental data on the energy spectrum of the beta rays from a 35S source.
In a previous paper a method for calculating the distorted or observed high counting rate pulse-height spectra from spectrometry systems when the undistorted or true spectra are known from low counting-rate spectra was developed based on double sum pulses and approximation of the pulse shape by a parabola. The present Part I paper extends this to double sum pulses of any arbitrary shape by methods that are suitable for use on any spectrometry system. In Part II of this paper a method for performing the inverse calculation for obtaining true from observed spectra is developed that is based on the model predicting spectral distortion developed here and in the previous paper.
In the calculation of the partial spectrum caused by pile-up effects the influence of the pulse shape is considered by a convolution integral over the ideal analyser spectrum and a probability distribution representing the weight of the momentary pulse heights. The probability distribution can be determined experimentally. The good agreement of measured and computed pile-up spectra using the observed analyser spectra as a first approximation is shown for some practical cases of pulse shapes and rates.
Pulseheight spectra caused by pile-up effects have been calculated considering the influence of the pulse shapes of amplifiers and the dependence of analog-digital conversion on pulse duration. The results are compared with experimental pile-up spectra. A program has been made which enables the easy calculation and elimination of pile-up spectra in nuclear spectroscopy.
The energy spectrum containing the effects of all orders of pulse pileup is predicted for an idealized X-ray pulse height analysis system measuring randomly occurring events. Two simplifying assumptions used are (1) a fixed pulse resolution time, and (2) that the measured energy of piled-up pulses is the algebraic sum of the energy associated with each pulse.
The status of the GSI mass separator facility on-line to the heavy-ion accelerator UNILAC at Darmstadt is described, covering the technical development since the start of operation in 1976.
In recent years, it has become possible to study experimentally the properties of many nuclei with a neutron number differing greatly from that of stable nuclei [see, e.g., (FHR 67), (Ley 70)]. The present survey deals with the information about nuclear structure that may be gained from the investigation of the beta-decay properties of nuclei far away from beta stability, where the energy available for beta decay is very large. The decay can therefore proceed to a very large number of excited levels of the kind that are observed as resonance or final states in the neutron-capture process. Because of the large number and density of final states it becomes expedient to deal with high-energy beta decay in the language of the statistical model [for general reviews, see Lynn (Lyn 68) and Vogt (Vog 68)], and to discuss the beta-decay rate in terms of a strength function.
In the present Part II paper a method is developed and demonstrated for performing the inverse calculation for obtaining true from observed pulse-height spectra utilizing the model for predicting spectral distortion due to peak pile-up.
A total absorption γ-ray spectrometer (TAGS), based on a 25.4-cm diameter × 30.5-cm long NaI(Tl) well detector, has been developed at the INEL on-line isotope separator facility. A Si detector in the well of the NaI(Tl) detector allows one to collect β-particle-gated coincidence γ spectra in addition to singles γ spectra. From the analysis of these total absorption γ-ray spectra, β−-decay intensity distributions are obtained. The analysis methodology is based on response functions that simulate the response of the NaI(Tl) detector to the γ-rays and electrons (including external bremsstrahlung) from a radioactive source in the detector well. These response functions are computed with a Monte Carlo photon and electron transport code. This methodology has been completely upgraded since it was first developed and now provides very good simulations of both singles and coincidence spectra. As an example of the application of this methodology, the Iβ distribution for the decay of 141Cs is determined from the TAGS spectra.
Peak pileup decrease the counting efficiency and distorts the recorded spectral shape in a pulse-height spectroscopy system. To correct for counting efficiency, it is common to estimate the photon detector input count rate by adding a pulse generator peak, wth known count rate, to a spectrum. A rigorous set of equations is developed to predict the number of piled up counts when either a periodic or a random pulser is used. Using these equations and an empirical treatment of ADC dead-time, expressions for the input count rate are derived for two cases: (1) “sparse” spectra dominated by one or a small number of photon peaks, and (2) “dense” spectra in which photon events occupy most of the spectral channels. Only the first has been treated previously. We provide formulae for the second case both for the situation where the pulser peak is superimposed on the photon region, and where it is separate from the photon region. The pileup equations are incorporated in an iterative routine which corrects for spectral distortion. The analysis has been applied to spectra of 99mTc and medical bremsstrahlung, measured with a high-purity germanium spectroscopy system.
A total absorption spectrometer, constructed and briefly operated at the on-line isotope separator OASIS at Lawrence Berkeley Laboratory, has been moved and installed at the on-line mass separator of GSI Darmstadt. At GSI, the spectrometer has been used for β-decay strength function measurements of nuclei in the vicinity of 100Sn and 146Gd.
The times between pulses generated by a radiation detector are
known as the interarrival times. When the pulse amplitudes are sorted by
an analog-to-digital converter (ADC) to produce a radiation energy
spectrum, a minimum interarrival time is required for the ADC to make an
error-free conversion. This is dependent on the pulse shape and
duration, among other factors. When interarrival times are less than
this minimum, either the event is recorded as a partial or total sum of
two or more pulses, or one or more pulses are ignored altogether. The
phenomenon of chance summing of pulses is known as pulse pileup and
causes a distortion of the acquired spectrum which becomes more severe
as the incoming count rate increases. A computation algorithm was
described by Q. Bristow and R.G. Harrison (1991) for the correction of
spectral distortion due to pulse pileup. The author demonstrated the
application of the algorithm in the correction of high-count-rate
spectra acquired from a 10×10×40 cm scintillation crystal
for pulse pileup
Determination of the convolution function for calculating pile- up impulse spectra, (Bestimmung der faltungsfunktion zur berechnung von spektren aufgestockter impulse)
- WAIBEL E