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Now showing items 1 - 5 of 5

  • High count rate gamma-ray spectroscopy with LaBr3:Ce scintillation detectors

    Loeher, B.   Savran, D.   Fiori, E.   Miklavec, M.   Pietralla, N.   Vencelj, M.  

    The applicability of LaBr3:Ce detectors for high count rate gamma-ray spectroscopy is investigated. A 3 in. x 3 in. LaBr3:Ce detector is used in a test setup with radioactive sources to study the dependence of energy resolution and photo peak efficiency on the overall count rate in the detector. Digitized traces were recorded using a 500 MHz FADC and analysed with digital signal processing methods. Good performance is obtained using standard techniques up to about 500 kHz counting rate. A pile-up correction method is applied to the data in order to further improve the capabilities at even higher rates with a focus on recovering the losses in efficiency due to signal pile-up. It is shown that gamma-ray spectroscopy can be performed with only moderate lossen in efficiency and high resolution at count rates even above 1 MHz and that the performance can be enhanced in the region between 500 kHz and 10 MHz by using the applied pile-up correction techniques. (C) 2012 Elsevier B.V. All rights reserved.
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  • Event by event pile-up compensation in digital timestamped calorimetry

    Vencelj, M.   Bucar, K.   Novak, R.   Wortche, H. J.  

    In digital nuclear calorimetry, the effect on measured pulse amplitudes by piling up of pulses can be compensated based on the pulses' respective timestamps, making use of the fact that, for stable pulse shapes, the amount of pile-up induced error at each pulse amplitude measurement is completely determined by the amplitudes and precise occurrences in time of the neighboring pulses. We propose here a compensation method, based on the above observation, suitable for real-time as well as off-line implementation. Successful tests performed off-line both on synthetic and experimental data are shown as a proof of principle. We further propose a draft architectural approach to real-time compensation schemes of this functionality and the corresponding interaction with the experimental controls. (C) 2009 Elsevier B.V. All rights reserved.
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  • Pulse shape classification in liquid scintillators using the fuzzy c-means algorithm

    Savran, D.   Loher, B.   Miklavec, M.   Vencelj, M.  

    A new approach to pulse shape classification for neutron detectors of type BC501A has been investigated The method is based on the fuzzy c-means (FCM) algorithm which allows finding clusters of similar shapes in a set of digitized detector pulses The aim of the method is to provide principal pulse shapes which further can be used to apply a pulse shape based particle identification Since the method is not adapted to the case of liquid scintillator signals it is of general use and can also be applied to signals of other detector types A detailed study of the quality of the FCM method for the search of principal pulse shapes in BC501A liquid scintillators is presented using a 500 Msample/s 12 bit digitizer and a Cf-252 neutron source A comparison to principal pulse shapes extracted using time-of-flight information proves the applicability of the method Finally an example of a pulse shape discrimination method based on the extracted principal pulse shapes is presented and compared to the well-known integration method (C) 2010 Elsevier B V All rights reserved
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  • Pile-up Reconstruction Algorithm for High Count Rate Gamma-Ray Spectrometry

    Petrovic, T.   Vencelj, M.   Lipoglavsek, M.   Novak, R.   Savran, D.  

    In high count rate gamma-ray spectrometry, the pile-up phenomenon turns out to be an important problem with respect to energy resolution and detection efficiency. Pile-up effects occur when two events are detected so close in time that instrumentation cannot properly extract information from both of them. Because this kind of data is incorrect and marginally useful, such data had to be rejected in traditional pulse processors. In times of digital pulse processing however, one can reconstruct piled-up pulse amplitudes by special algebraic approaches. In fully digital signal acquisition, the moving window deconvolution (MWD) method is commonly used. This method requires two parameters to be carefully set, namely the flattop time (dictated by the maximum rise time of the signal) and the shaping time, to accomplish the best possible energy resolution. In this way, the maximum energy resolution is accomplished, but a lot of piled-up events are rejected, reducing detection efficiency. We propose a method that restores some of the pile-up events, using a parallel block MWD implementation where the shaping time parameter differs for every MWD block. Careful detection of as many true events as possible, as well as determining their exact occurrence in time (their respective timestamps) is the key in getting the most out of the measured signal. With proper analysis logic we get more experimental information through reduced dead time, at the cost of controlled and selectively worsened energy resolution, on an event-by-event basis, achieving better overall detection efficiency. This method was tested on real experimental data where the detection efficiency of our method is higher, by a factor of 4.4(9), than the efficiency of a standard method with pile-up rejection at 500 kcps count rate.
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  • Real-Time Algorithm For Robust Coincidence Search

    Petrovic, T.   Vencelj, M.   Lipoglavsek, M.   Gajevic, J.   Pelicon, P.  

    In in-beam gamma-ray spectroscopy experiments, we often look for coincident detection events. Among every N events detected, coincidence search is naively of principal complexity O(N-2). When we limit the approximate width of the coincidence search window, the complexity can be reduced to O(N), permitting the implementation of the algorithm into real-time measurements, carried out indefinitely. We have built an algorithm to find simultaneous events between two detection channels. The algorithm was tested in an experiment where coincidences between X and gamma rays detected in two HPGe detectors were observed in the decay of Cu-61. Functioning of the algorithm was validated by comparing calculated experimental branching ratio for EC decay and theoretical calculation for 3 selected gamma-ray energies for Cu-61 decay. Our research opened a question on the validity of the adopted value of total angular momentum of the 656 keV state (J(pi)=1/2(-)) in Ni-61.
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