| 1. |
- Nagy, Lajos, 1991, et al.
(författare)
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An extended theory of multiplicity counting from fission chamber signals in the current mode
- 2017
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M and C 2017.
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the derivation of the individual and joint statistics of the signals of up to threefission chambers operating in the current mode, detecting neutrons emitted from a sample containing fissioningmaterial. The purpose is to develop an alternative method to the traditional pulse detection based multiplicitycounting for the determination of the sample parameters. The underlying theory and corresponding method ofunfolding the parameters of the sample from such continuous signals was recently developed by the authors forthe case when multiple neutrons emitted simultaneously were assumed to be also detected simultaneously inthe same or different detectors. In the present paper the method is generalized by extending it to the case whenthe detection of the multiply emitted neutrons occurs with a random time delay individually for each neutron,such that the delays are independent, identically distributed random variables. It is seen that in the arisingformulas, in addition to the detector pulse shape and amplitude distribution, the properties (parameters) ofthe time delay distribution appear as well. At the same time it is also seen that, although at the expense of asomewhat more involved calibration procedure, the unfolding of the sample parameters from the three lowestorder auto- and cross-cumulants of the detector signals is still possible, in a procedure similar to using thesingles, doubles and triples count rates of traditional multiplicity counting. In contrast to this latter method, theprocedure proposed here is free from the dead time problem, and requires a somewhat simpler data processing.In particular, being free from the dead-time problem and by the relative insensitivity of the fission chambers togamma contributions, especially for the higher order cumulants, makes the method particularly suitable forthe multiplicity analysis of spent fuel.
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| 2. |
- Nagy, Lajos, 1991, et al.
(författare)
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Measurements and simulations to investigate the feasibility of neutron multiplicity counting in the current mode of fission chambers
- 2020
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 225
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Konferensbidrag (refereegranskat)abstract
- In two earlier papers [1], [2] we investigated the possibility of extracting traditional multiplicity count rates from the cumulants of fission chamber signals in current mode. It was shown that if all neutrons emitted from the sample simultaneously are also detected simultaneously, the multiplicity rates can be retrieved from the first three cumulants of the currents of up to three detectors, but the method breaks down if the detections of neutrons of common origin take place with a time delay spread wider than the pulse shape. To remedy these shortcomings, in this work we extended the theory to two- and three-point distributions (correlations). It was found thatthe integrals of suitably chosen two- and three-point moments with respect to the time differences become independent of the probability density of the time delays of detections. With this procedure, the multiplicity rates can be retrieved from the detector currents for arbitrary time delay distributions. To demonstrate the practical applicability of the proposed method, a measurement setup was designed and built. The statistics (shape and amplitude distribution) of the detector pulse were investigated as important parameters of the theoretical model. Simulations were performed to estimate the expected value of the multiplicity rates in the built setup. Measurements were performed and two types of moments (the mean and the covariance function) of the recorded detector signals were calculated. Values of singles rates were successfully recovered.
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| 3. |
- Pál, Lénárd, 1925, et al.
(författare)
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Comments on the stochastic characteristics of fission chamber signals
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents a theoretical investigation of the stochastic properties of the signal series of ionisation chambers, in particular fission chambers. The signals of the detector are assumed to be generated by incoming particles correspondig to an inhomogeneous Poisson distribution. Each incoming particle generates a current pulse with constant shape and random amplitude, and thedetector signal consists of the time series of such current signal pulses incurring also a pile-up effect in the case of high intensity of the primary events. Exact relationships are derived for the higher order moments of the detector signal, which constitute a generalisation of the so-called higher order Campbelling techniques. The probability distribution of the number of time points when the signal exceeds a certain level is also derived.Assuming that the incoming particles form a homogeneous Poisson process, explicit expressions are given for the higher order moments of the signal and the number of levelcrossings in a given time interval for a few selected pulse shapes.
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| 4. |
- Pazsit, Imre, 1948, et al.
(författare)
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Multiplicity counting from fission chamber signals in the current mode
- 2016
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 839, s. 92-101
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Tidskriftsartikel (refereegranskat)abstract
- In nuclear safeguards, estimation of sample parameters using neutron-based non-destructive assay methods is traditionally based on multiplicity counting with thermal neutron detectors in the pulse mode. These methods in general require multi-channel analysers and various dead time correction methods. This paper proposes and elaborates on an alternative method, which is based on fast neutron measurements with fission chambers in the current mode. A theory of “multiplicity counting” with fission chambers is developed by incorporating Böhnel's concept of superfission [1] into a master equation formalism, developed recently by the present authors for the statistical theory of fission chamber signals [2], [3]. Explicit expressions are derived for the first three central auto- and cross moments (cumulants) of the signals of up to three detectors. These constitute the generalisation of the traditional Campbell relationships for the case when the incoming events represent a compound Poisson distribution. Because now the expressions contain the factorial moments of the compound source, they contain the same information as the singles, doubles and triples rates of traditional multiplicity counting. The results show that in addition to the detector efficiency, the detector pulse shape also enters the formulas; hence, the method requires a more involved calibration than the traditional method of multiplicity counting. However, the method has some advantages by not needing dead time corrections, as well as having a simpler and more efficient data processing procedure, in particular for cross-correlations between different detectors, than the traditional multiplicity counting methods.
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