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Pileup recovery algorithms for digital gamma ray spectroscopy

JOURNAL OF INSTRUMENTATION 2012年第09期7卷 P09013-P09013页

作者： Mahmoud, I. I. El Tokhy, M. S. Konber, H. A. Atom Energy Author NRC Dept Engn Cairo Egypt Al Azhar Univ Dept Elect Engn Cairo Egypt

This paper presents algorithms for overcoming a common problem of gamma ray spectroscopy, namely the peak pileup recovery problem. Three different approaches are studied and evaluated within a spectroscopy system. The algorithms are evaluated by the means of parameters error and fitting error calculations. The first approach is a direct search based on Nelder-Mead technique without any derivatives in order to find the local minimum points. A Gaussian shape in conjunction with the peak height and its position of each pulse are used to construct the pulse. So, the main pulse parameters such as peak amplitude, position and width can be determined. The second algorithm is based on the nonlinear least square method. In this paper another technique is tried. This technique which is proposed as third algorithm is based on a maximum peak search method combined with the first derivative method to determine peak position of each pulse. Comparison among these approaches is conducted in terms of parameters errors. The pulse parameters have been calculated and compared with the actual one. The second approach shows the best accuracy, for determining peak height and position, but the width parameter scored the highest error.

关键词： Radiation calculations data processing methods Models and simulations Simulation methods and programs

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Neutron measurements in ITER using the Radial Neutron Camera

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JOURNAL OF INSTRUMENTATION 2012年第03期7卷 C03033-C03033页

作者： Marocco, D. Esposito, B. Moro, F. Assoc Euratom ENEA Fus I-00044 Frascati Roma Italy

The Radial Neutron Camera (RNC) is one of the key diagnostic systems of the ITER international fusion experiment. It is designed to measure the uncollided 14MeV and 2.5MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions taking place in the ITER plasma through an array of 45 detectors positioned along collimated lines of sight. Scintillators and diamonds coupled to fast digital acquisition electronics are among the detectors presently considered for the RNC. The RNC will provide spatially resolved measurements of several plasma parameters needed for fusion power estimation, plasma control and plasma physics studies. The line-integrated RNC neutron fluxes are used to evaluate the local profile of the neutron emission (neutron emissivity, s(-1)m(-3)) and therefore the total neutron yield and the birth profile of the alpha particles. The temperature profile of the bulk ions can be derived from the Doppler broadened widths of the RNC line-integrated spectra, that also provide insight on the supra-thermal ions produced by the injection in the plasma of electromagnetic waves and neutral particles. The RNC emissivity and temperature measurements can be employed to estimate the composition of the ITER fuel, namely the ratio between the tritium and deuterium densities. data processing techniques involving spatial inversion and spectra unfolding are necessary to deduce the profile quantities from the line-integrated RNC measurements. The expected performances of the RNC as a diagnostic for the neutron emissivity/ion temperature/fuel ratio profile (measurement range, time resolution, accuracy, precision) have been estimated by means of synthetic data simulating actual RNC measurements. The results of the simulations, together with an overall description of the diagnostic and of the measurement techniques, are presented.

关键词： Simulation methods and programs Nuclear instruments and methods for hot plasma diagnostics data processing methods Plasma diagnostics - interferometry, spectroscopy and imaging

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Study and optimization of positioning algorithms for monolithic PET detectors blocks

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JOURNAL OF INSTRUMENTATION 2012年第06期7卷 C06010-C06010页

作者： Garcia de Acilu, P. Sarasola, I. Canadas, M. Cuerdo, R. Rato Mendes, P. Romero, L. Willmott, C. CIEMAT E-28040 Madrid Spain

We are developing a PET insert for existing MRI equipment to be used in clinical PET/MR studies of the human brain. The proposed scanner is based on annihilation gamma detection with monolithic blocks of cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) coupled to magnetically-compatible avalanche photodiodes (APD) matrices. The light distribution generated on the LYSO: Ce block provides the impinging position of the 511 keV photons by means of a positioning algorithm. Several positioning methods, from the simplest Anger Logic to more sophisticate supervised-learning Neural Networks (NN), can be implemented to extract the incidence position of gammas directly from the APD signals. Finally, an optimal method based on a two-step Feed-Forward Neural Network has been selected. It allows us to reach a resolution at detector level of 2 mm, and acquire images of point sources using a first BrainPET prototype consisting of two monolithic blocks working in coincidence. Neural networks provide a straightforward positioning of the acquired data once they have been trained, however the training process is usually time-consuming. In order to obtain an efficient positioning method for the complete scanner it was necessary to find a training procedure that reduces the data acquisition and processing time without introducing a noticeable degradation of the spatial resolution. A grouping process and posterior selection of the training data have been done regarding the similitude of the light distribution of events which have one common incident coordinate (transversal or longitudinal). By doing this, the amount of training data can be reduced to about 5% of the initial number with a degradation of spatial resolution lower than 10%.

关键词： data reduction methods data processing methods Gamma camera, SPECT, PET PET/CT, coronary CT angiography (CTA)

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A non-linear algorithm for current signal filtering and peak detection in SiPM

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JOURNAL OF INSTRUMENTATION 2012年第08期7卷 P08014-P08014页

作者： Putignano, M. Intermite, A. Welsch, C. P. Cockcroft Inst Daresbury England Univ Liverpool Liverpool L69 3BX Merseyside England

Read-out of Silicon Photomultipliers is commonly achieved by means of charge integration, a method particularly susceptible to after-pulsing noise and not efficient for low level light signals. Current signal monitoring, characterized by easier electronic implementation and intrinsically faster than charge integration, is also more suitable for low level light signals and can potentially result in much decreased after-pulsing noise effects. However, its use is to date limited by the need of developing a suitable read-out algorithm for signal analysis and filtering able to achieve current peak detection and measurement with the needed precision and accuracy. In this paper we present an original algorithm, based on a piecewise linear-fitting approach, to filter the noise of the current signal and hence efficiently identifying and measuring current peaks. The proposed algorithm is then compared with the optimal linear filtering algorithm for time-encoded peak detection, based on a moving average routine, and assessed in terms of accuracy, precision, and peak detection efficiency, demonstrating improvements of 1 divided by 2 orders of magnitude in all these quality factors.

关键词： Pattern recognition, cluster finding, calibration and fitting methods data processing methods data reduction methods

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Measuring field multipoles in accelerator magnets with small-apertures by an oscillating wire moved on a circular trajectory

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JOURNAL OF INSTRUMENTATION 2012年第05期7卷 P05003-P05003页

作者： Arpaia, P. Buzio, M. Perez, J. Garcia Petrone, C. Russenschuck, S. Walckiers, L. Univ Sannio Dept Engn I-82100 Benevento Italy CERN Dept Technol Grp Magnets Superconductors & Cryostats MSC Sect Magnet Measurements CH-1211 Geneva 23 Switzerland

A method based on an oscillating wire for measuring the field quality in accelerator magnets with small apertures of the order of 10 mm is proposed. The wire is positioned step-by-step on the generators of a cylindrical domain inside the magnet aperture, i.e. its end-points at the stages are moved on a circular trajectory. The amplitudes of the wire's forced oscillations are measured and related to field harmonics by a suitable analytical model. In this paper, the analytical model, the measurement procedure, and the measurement system architecture of the oscillating wire method are presented. The method is validated by comparison with the standard rotating-coil system. A case study on small-aperture, permanent-magnet quadrupoles constructed for the Linac4 injector at CERN is illustrated.

关键词： Instrumentation for particle accelerators and storage rings - high energy (linear accelerators, synchrotrons) Acceleration cavities and magnets superconducting (high-temperature superconductor radiation hardened magnets normal-conducting permanent magnet devices wigglers and undulators) data processing methods Accelerator Subsystems and Technologies

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Time-resolved spectrometry for the characterization of a reference field for pulsed radiation

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JOURNAL OF INSTRUMENTATION 2012年第10期7卷 T10002-T10002页

作者： Sievers, P. Klammer, J. Hupe, O. Michel, T. Anton, G. PTB D-38116 Braunschweig Germany Univ Erlangen Nurnberg ECAP D-91058 Erlangen Germany

The investigation of the spectral change during a radiation pulse is of high interest. The aim of the work presented is to prove that the emitted X-ray spectrum of a novel X-ray tube [1], developed at PTB as a reference field for pulsed photon radiation, has no time dependency of the spectral distribution during the pulse. Nowadays X-ray tubes are pulsed by switching on and off the HV generator. Therefore, they have a rising edge of about 600 mu s until the pre-set acceleration voltage (e.g. 60kV) is reached. In contrast, the newly developed X-ray tube reduces the rise and fall time by up to a factor of 10 or 60, respectively. This was achieved by designing the X-ray tube as a triode. The X-ray emission of this tube can be switched on and off by switching only the quite low voltage of the additional grid while the high voltage remains constantly on. For the measurements we used a Timepix detector [2] operated in Time of Arrival (ToA) mode. Additionally, the adjustable analogue threshold was swept through. With such a measurement over multiple X-ray pulses we obtained information about the timing and the energy distribution of the emitted photons during the rise time of the HV generator. The real impinging spectrum was gained by the deconvolution of the time-resolved measured threshold scan. Such a deconvolution is necessary due to the blurring of the energy information in the pixelated sensor by effects like charge sharing or Compton scattering. For the deconvolution the Bayesian approach [3] was chosen as it turned out to be very stable even for low statistics in the measurements. For the novel X-ray tube it is now possible to confirm that the full acceleration voltage is reached quite instantaneously and therefore no spectral change can be observed.

关键词： data processing methods X-ray detectors Spectrometers Timing detectors

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Reference analysis of the signal plus background model in counting experiments

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JOURNAL OF INSTRUMENTATION 2012年第01期7卷 P01012-P01012页

作者： Casadei, D. NYU New York NY 10003 USA

The model representing two independent Poisson processes, labelled as "signal" and "background" and both contributing additively to the total number of counted events, is considered from a Bayesian point of view. This is a widely used model for the searches of rare or exotic events in presence of a background source, as for example in the searches performed by high-energy physics experiments. In the assumption of prior knowledge about the background yield, a reference prior is obtained for the signal alone and its properties are studied. Finally, the properties of the full solution, the marginal reference posterior, are illustrated with few examples.

关键词： Analysis and statistical methods data processing methods

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Comprehensive track reconstruction tool "NETSCAN 2.0" for the analysis of the OPERA Emulsion Cloud Chamber

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JOURNAL OF INSTRUMENTATION 2012年第07期7卷 P07001-P07001页

作者： Hamada, K. Fukuda, T. Ishiguro, K. Kitagawa, N. Kodama, K. Komatsu, M. Morishima, K. Nakano, T. Nakatsuka, Y. Nonoyama, Y. Sato, O. Yoshida, J. Nagoya Univ Nagoya Aichi 4648602 Japan Toho Univ Funabashi Chiba 2748510 Japan Aichi Univ Educ Kariya Aichi 4488542 Japan

NETSCAN is a track reconstruction algorithm used in Emulsion Cloud Chambers (ECC). NETSCAN and Emulsion Cloud Chambers were used in the DONUT experiment to detect Tau-neutrinos interactions. The algorithm has been revised in order to cope with the OPERA event analysis performed in Japan. A new version of NETSCAN was necessary to effectively analyze the most massive emulsion experiment in history with limited resources.

关键词： data processing methods Particle tracking detectors

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data reduction and uncertainty propagation of time-of-flight spectra with AGS

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JOURNAL OF INSTRUMENTATION 2012年第11期7卷 P11002-P11002页

作者： Becker, B. Bastian, C. Emiliani, F. Gunsing, F. Heyse, J. Kauwenberghs, K. Kopecky, S. Lampoudis, C. Massimi, C. Otuka, N. Schillebeeckx, P. Sirakov, I. EC JRC IRMM B-2440 Geel Belgium CEA Saclay DSM Irfu SPhN F-91191 Gif Sur Yvette France Univ Bologna Dept Phys I-40126 Bologna Italy Sez INFN Bologna I-40126 Bologna Italy IAEA Nucl Data Sect A-1400 Vienna Austria Inst Nucl Energy Res BG-1784 Sofia Bulgaria

Results of neutron time-of-flight measurements are commonly used to parameterize neutron induced reaction cross sections in the resonance region based on the R-matrix reaction theory. Reaction yields or transmission as well as their covariance information are derived starting from measured counting spectra. They are then used in a least squares adjustment for obtaining model parameters. In this paper, a compact formalism is presented to propagate both the correlated and uncorrelated uncertainty components. Full information on the origin of each correlated component of the covariance matrix is maintained. This is particularly important in order to avoid a bias on the model parameters through a phenomenon known as Peelle's Pertinent Puzzle (PPP). This compact formalism was implemented into the data reduction code AGS (Analysis of Geel Spectra).

关键词： data processing methods Instrumentation and methods for time-of-flight (TOF) spectroscopy data reduction methods

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Pulse pile-up recovery for the front-end electronics of the PANDA Electromagnetic Calorimeter

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JOURNAL OF INSTRUMENTATION 2012年第11期7卷 P11001-P11001页

作者： Tambave, G. Kavatsyuk, M. Guliyev, E. Schreuder, F. Moeini, H. Lohner, H. Univ Groningen Kernfys Versneller Inst NL-9747 AA Groningen Netherlands Ecole Polytech Lab Leprince Ringuet F-91128 Palaiseau France

At the future Facility for Antiproton and Ion Research near Darmstadt in Germany the PANDA detector will be employed to study the charmonium spectrum and to search for narrow exotic hadronic states, predicted by Quantum Chromodynamics. In the PANDA experiment, 1.5 to 15GeV/c anti-protons will annihilate with a hydrogen target at an average rate of 20 MHz. Among the sub-detectors of PANDA is the Electromagnetic Calorimeter (EMC) planned for the studies of electromagnetic transitions and neutral meson decays. Due to the high annihilation rates, the EMC will be exposed to single-detector hit rates up to 500 kHz, which may lead to pulse overlap. Hence, to recover the energy and time information of the overlapping pulses, a pulse pile-up recovery method is developed. The method is easy to implement in FPGA for online data processing. The Constant Fraction Timing algorithm is applied at the trailing edge to determine the time stamp of pile-up pulses. The energy and the time information of pile-up pulses can be recovered up to time differences of 50 ns, equal to the pulse rise-time, in a large dynamic energy range.

关键词： data processing methods Digital signal processing (DSP) Calorimeters

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