| 1. |
- Chernikova, Dina, 1982, et al.
(author)
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Testing a direct method for evaluating the concentration of boron in a fuel pool using scintillation detectors, and a 252Cf and an 241Am-Be source
- 2013
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In: Proceeding of ESARDA meeting 2013.
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Conference paper (peer-reviewed)abstract
- The present investigations are aimed at the development and testing of a direct non-destructive method for evaluating the concentration of boron in a fuel pool using scintillation detectors. The method uses a modified ratio between two gamma lines with energy of 480 keV and 2.23 MeV. These lines belong to the capture of a thermal neutron in boron and hydrogen, respectively. The relation between them can reveal the concentration of boron in the fuel pond.The method proposed was tested in a laboratory experiment with a 252Cf and an 241Am-Be source. EJ-309 liquid scintillation detectors were used for measurements of gamma spectra. The concentration of boron in water varied from 1550 ppm to 4200 ppm. The optimization and test studies were performed via MCNPX simulations.The results of these tests are provided in the present paper and they show that the boron content in water can be determined through using the characteristics of gamma lines with energy of 480 keV and 2.23 MeV.
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| 2. |
- Kitamura, Yasunori, et al.
(author)
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Calculation of higher moments of the neutron multiplication process in a time-varying medium
- 2007
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In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 34:5, s. 385-395
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Journal article (peer-reviewed)abstract
- The zero-power reactor noise theory in a steady neutron multiplying medium was extended recently to a medium randomly varying in time to bridge the fields of the zero-power and the power reactor noise. For a time-varying medium in which the transition probability randomly fluctuates, only the use of the probability generating function technique based on the forward master equation approach is practical. However, with the forward master equation approach, the treatment of the joint moments of the neutron number and the medium state leads to a closure problem. Recently, the capability of the moment calculation technique for such cases was extended such that the closure problem could be solved exactly. The present paper describes and demonstrates this closure-free moment calculation technique in a time-varying binary multiplying medium, in which the medium state has two possible realizations. In addition to the first two moments of the neutron number N alone (irrespective of the medium state η), the joint moments of Nn and ηm, i.e., , were also obtained in a compact form for n = 1, 2 and arbitrary values of m, without a closure assumption. It was found that, for even m values, the asymptotic values of Nn and ηm are uncorrelated, whereas, for odd m values, they are negatively correlated, namely, their covariance is less than zero. The first two moments of the neutron number theoretically obtained were verified by the Monte Carlo technique. A perfect agreement was found between the Monte Carlo and the theoretical solutions. The closure-free moment calculation technique demonstrated in the present paper is expected to be applicable to various other problems related to the birth-and-death process with fluctuations of the transition probability, in which a closure problem occurs.
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| 3. |
- Anderson, Johan, 1973, et al.
(author)
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Derivation and quantitative analysis of the differential self-interrogation Feynman-alpha method
- 2011
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In: Proceedings 52nd INMM Conference 17-21 July, Palm Desert, CA, USA (2011).
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Conference paper (peer-reviewed)abstract
- A stochastic theory for a branching process in a neutronpopulation with two energy levels is used to assess theapplicability of the differential self-interrogation Feynman-alpha method by numerically estimated reaction intensities from Monte Carlo simulations. More specifically, the variance to mean or Feynman-alpha formula is applied to investigate the appearing exponentials using the numerically obtained reaction intensities.
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| 4. |
- Anderson, Johan, 1973, et al.
(author)
-
On the Feynman-alpha formula for fast neutrons
- 2011
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In: Proceedings 33rd ESARDA 16-20 May, Budapest, Hungary (2011).
-
Conference paper (peer-reviewed)abstract
- In this contribution, a stochastic theory for a branching process in a neutron population with two energy levels is investigated. In particular, a variance to mean or Feynman-alpha formula is derived in this generalized scenario using the Kolmogorov forward or master equation theory for the probabilities in a system with a compound Poisson source.
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| 5. |
- Avdic, Senada, et al.
(author)
-
Unfolding sample parameters from neutron and gamma multiplicities using artificial neural networks.
- 2009
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In: ESARDA Bulletin. - 0392-3029. ; :43, s. 21-29
-
Journal article (peer-reviewed)abstract
- Expressions for neutron and gamma factorial momentshave been known in the literature. The neutronfactorial moments have served as the basis of constructinganalytic expressions for the detection ratesof singles, doubles and triples, which can be used tounfold sample parameters from the measured neutronmultiplicity rates. The gamma factorial momentscan also be extended into detection rates of multiplets,as well as the combined use of joint neutronand gamma multiplicities and the corresponding detectionrates. Counting up to third order, there arenine auto- and cross factorial moments.Adding the gamma counting to the neutrons introducesnew unknowns, related to gamma generation,leakage, and detection. Despite of having more unknowns,the total number of independent measurablemoments exceeds the number of unknowns. On theother hand, the structure of the additional equationsis substantially more complicated than that of theneutron moments, hence the analytical inversion ofthe gamma moments alone is not possible.We suggest therefore to invert the non-linear systemof over-determined equations by using artificialneural networks (ANN), which can handle both thenon-linearity and the redundancies in the measuredquantities in an effective and accurate way. The useof ANN is successfully demonstrated on the unfoldingof neutron multiplicity rates for the sample fissionrate, the leakage multiplication and the ratio.The analysis is further extended to unfold also thegamma related parameters. The stability and robustnessof the ANNs is further investigated to verify theapplicability of the method. The ANN approach enablesextraction of additional important informationon the fissile sample compared to the application ofthe analytical method.
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| 6. |
- Chernikova, Dina, 1982, et al.
(author)
-
A direct method for evaluating the concentration of boric acid in a fuel pool using scintillation detectors for joint-multiplicity measurements
- 2013
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In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 714, s. 90-97
-
Journal article (peer-reviewed)abstract
- The present investigations are aimed at the development of a direct passive non-intrusive method for determining the concentration of boric acid in a spent fuel pool using scintillation detectors with the purpose of correcting joint-multiplicity measurement results. The method utilizes a modified relation between two gamma lines with energy of 480 keV and 2.23 MeV, respectively. The gamma line at 480 keV belongs to the thermal neutron capture in boron. The 2.23 MeV gamma line characterizes the capture of thermal neutrons in hydrogen. Thus, the relation between them can reveal the concentration of the boron in the fuel pool. In order to test this method, first MCNPX and MCNP-PoliMi simulations were performed. Then, based on the results of Monte Carlo simulations, the method was verified by an experimental study with a 241Am-Be source and EJ-309 scintillation detectors. The concentration of boron in water varied from 1550 ppm to 4000 ppm. The results of these tests are provided in the paper and they show that the spectral ratio between these two lines can in principle be used to determine the boron content.
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| 7. |
- Chernikova, Dina, 1982, et al.
(author)
-
Testing of small detectors with glass rod light guides for multiplicity measurement purposes
- 2012
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In: Proceedings of The 53nd Annual Meeting of the Institute of Nuclear Materials Management.
-
Conference paper (other academic/artistic)abstract
- In this paper we investigate the applicability of small scintillators with glass rod lightguides to measure both neutrons and gamma rays from the sample. Experimental test ofthese detectors and their suitability for the task can be performed at Lund University usingnatural uranium rods, therefore the MCNPX simulation set-up corresponds to the Lund con-figuration. The long-term goal of this research is to develop a method of joint-multiplicitycounting for fuel evaluation into a technology capable of quantifying plutonium in the fuelpool, where a lot of factors, such as presence of neutron absorbers (boron acid), can affect al-most all parameters, such as multiplication etc. Therefore, part of the present investigationswas devoted to the development of a direct method for determination of the concentrationof boron acid in the fuel pool using scintillation detectors with further correction of mea-surement results. For this purpose we suggest a method which utilizes a relation betweengamma lines with energy of 480 keV and 2.23 MeV for the direct evaluation of concentrationof boron acid in water. Test results of the new method, and an answer to questions regardingthe ability to measure both neutron and gamma rays using small scintillation detectors withglass rod light guides are provided in this paper.
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| 8. |
- Degweker, Shashikant, 1956, et al.
(author)
-
Stochastic equations in the invariant imbedding formulation of particle transport
- 2009
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In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 36:8, s. 1108-1119
-
Journal article (peer-reviewed)abstract
- Invariant imbedding theory is an alternative formulation of particle transport theory. Although stochasticfoundations of invariant imbedding have been known from the beginnings, the method itself has so farexclusively been used for calculating first moments, i.e. expectations. The present paper attempts toset up a probability balance equation in the invariant imbedding approach from which equations forthe first and second order densities are derived. It is shown that only the equations for the first order densitiesare non-linear, while subsequent order densities obey linear equations. This is expected to considerablysimplify solution to those problems which involve second order density calculations whereinvariant imbedding techniques may be profitably used. Examples of such quantities are the varianceor correlations between particles detected at two different energies or angles or the higher momentsof the emitted multiplicity distribution such as the variance from a target bombarded by incident particles.One possible area of application of our equations is non-destructive estimation of fissile material bythe active neutron assay technique. Another area is the study of particle cascade development in sputteringand positron backscattering from surfaces. The approach is illustrated by a simple forward–backwardscattering model for these two problems.
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| 9. |
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