Interest in safeguards verification measurements using passive thermal neutron counting to assay 235U content in large 30B UF6 canisters has grown in recent years. The prohibitively high cost and ...impracticality of using reference 30B calibration cylinders extensively will likely make accurate simulations of increasing interest. Accuracy of the simulated response will define the confidence in the predicted response and the extent to which simulations can reasonably be relied upon. With 234U driven 19F(α, n) reactions being the main neutron source in low enriched UF6 the uncertainties of the 19F(α, n) energy spectrum and the thick target yield of 234U in UF6 propagate into the uncertainty in the predicted response and represent a major influence of basic nuclear data. Here sensitivity of the simulated total (Singles) and coincidence (Doubles) count rates are assessed for the Passive Neutron Enrichment Meter using six potential 19F(α, n) neutron energy spectra over a range of enrichments and material distributions. The results indicate that variations in the Singles and Doubles due to simulated (α, n) neutron spectrum are less than 1.5% for this set of simulated neutron spectra, with dependence varying inversely with enrichment. Singles uncertainty is only slightly less than that of the thick target 19F(α, n) yield corresponding to the primary neutron source, whereas the 19F(α, n) yield dependence of the Doubles is reduced by the non-negligible 238U(SF) coincident neutron emissions. Based on available thick target 19F(α, n) yield estimates the uncertainty is on the order of 5%, establishing this as the main nuclear data limitation when simulating thermal neutron detectors response for 30B UF6 storage cylinders. Based on these findings, it appears that the measurement and evaluation of the thick target 19F(α, n) yield for uranium hexafluoride is due.
CR-39 SSNTD is used to measure the photoneutron spectrum produced by a medical linear accelerator in an intense γ-ray background. The spectroscopic resolution and the neutron detection threshold have ...been improved by introducing the event selection criteria, based on the track diameter-brightness correlation. The CR-39 detector’s efficiency is determined by adapting the 1H(n,el) cross section from the ENDF/B-VIII.0 evaluations. The measured spectrum was reproduced through Talys-1.96 calculations by implementing the Gogny-HFB microscopic level density model.
The Nuclear Physics Institute of the Czech Academy of Sciences (NPI CAS) operates several neutron sources, including a generator of a continuous spectrum of neutrons up to 33 MeV. Accelerated protons ...from the U-120M cyclotron are directed to an 8 mm thick beryllium target to produce the neutrons.
In this work, the neutron spectrum at distances of 3–8 m was directly measured with NE213 and stilbene scintillator detectors in the forward, diagonal and perpendicular directions. At a distance of 50 cm from the Be target, the neutron spectrum was validated with a gold activation detector. From previous work, the neutron spectra at close distances were characterized for use in high-intensity irradiation. Both the newly measured spectra at large distances and the previously measured spectrum were simulated using the Monte Carlo code, MCNP6.2, with ENDF7PROT and JENDL-4.0/HE nuclear data libraries. The comparison of the simulated and experimentally measured spectra revealed several limitations of both libraries.
Unfolding neutron spectra using splines Trunec, David; Mazánková, Věra; Mravec, Filip ...
Radiation measurements,
April 2024, 2024-04-00, Letnik:
173
Journal Article
Recenzirano
Organic scintillators detect neutrons by scattering reactions with hydrogen nuclei (protons) in organic compounds. The recoil protons then produce the light output from the scintillator. The energy ...spectrum of neutrons impinging on the scintillator has to be determined from this light output using a so-called unfolding algorithm. However, this problem is ill-posed and therefore difficult to solve. In this study, a new method for unfolding neutron spectra is presented. This method uses B-splines approximation of neutron energy spectrum. Results of this method are shown for test data and experimental data and compared to the results of the previously developed unfolding method.
•A new method for unfolding neutron spectra using B-splines is presented in this paper.•This unfolding method was tested on test and experimental data.•A good agreement was found between the results of the proposed method and Expectation Maximization algorithm.
The objective of this paper is to present the results of the neutron spectrum unfolding using a high-performance code that we have developed, which is based on genetic algorithm. This paper presents ...the methodology used for neutron spectrum unfolding and describes the general architecture of our developed code. It also includes results of neutron spectrum unfolding in the case of the ARC-700 reactor using our genetic algorithm-based code and using an iterative method. In order to evaluate and validate our code, a comparison between reference values and results obtained using the iterative and genetic algorithm methods was presented. The comparison is performed both at the spectra as well as at the reproduced activation scale. This comparison shows a very good agreement between the results obtained using our code and the reference values and also shows a clear distinction of the genetic algorithm method compared with the iterative method. This validation shows that our code can be successfully used for neutron spectra unfolding in nuclear reactors using the activation detectors approach.
•Unfolding of the neutron spectrum using genetic algorithms method.•Neutron spectrum unfolding in the case of the ARC-700 nuclear reactor.•Genetic algorithms methodology for neutron spectra unfolding•Unfolding of the neutron spectrum using iterative method.
Neutron irradiation to single crystal pure tungsten was performed in the mixed spectrum High Flux Isotope Reactor (HFIR). To investigate the influences of neutron energy spectrum, the microstructure ...and irradiation hardening were compared with previous data obtained from the irradiation campaigns in the mixed spectrum Japan Material Testing Reactor (JMTR) and the sodium-cooled fast reactor Joyo. The irradiation temperatures were in the range of ∼90–∼800 °C and fast neutron fluences were 0.02–9.00 × 1025 n/m2 (E > 0.1 MeV). Post irradiation evaluation included Vickers hardness measurements and transmission electron microscopy. The hardness and microstructure changes exhibited a clear dependence on the neutron energy spectrum. The hardness appeared to increase with increasing thermal neutron flux when fast fluence exceeds 1 × 1025 n/m2 (E > 0.1 MeV). Irradiation induced precipitates considered to be χ- and σ-phases were observed in samples irradiated to >1 × 1025 n/m2 (E > 0.1 MeV), which were pronounced at high dose and due to the very high thermal neutron flux of HFIR. Although the irradiation hardening mainly caused by defects clusters in a low dose regime, the transmutation-induced precipitation appeared to impose additional significant hardening of the tungsten.
•The microstructure and irradiation hardening of single crystal pure W irradiated in HFIR was investigated.•The neutron energy spectrum influence was evaluated by comparing the HFIR results with previous work in Joyo and JMTR.•In the dose range up to ∼1 dpa, the neutron energy spectrum influence of irradiation hardening was not clear.•In the dose range above 1 dpa, the neutron energy influence on irradiation hardening and microstructural development was clearly observed.•The irradiation induced precipitates caused significant irradiation hardening of pure W irradiated in HFIR.
Fast neutron leakage spectra from the light and heavy water sphere of 30cm in diameter with neutron source in its centre were measured by a stilbene scintillation detector in the region of 1–10MeV in ...the distance of 85cm from the spheres surface. We use the light and heavy water to eliminate the effect of hydrogen. 252Cf with the approximate emission rate of 5.5E8 n/s was used as a neutron source for all measurements involved and was placed in the centres of the spheres. The measured neutron spectra are compared with MCNP transport code calculations in ENDF/B-VII.0, ENDF/B-VIII.b4 and JENDL-4 nuclear data libraries. Experimental results for both cases follows similar trend. The best agreement is achieved with ENDF/B-VIII.b4 library in both cases. All libraries underestimate experimental measurement in the region of 3–4MeV. Furthermore, JENDL-4 library overestimates experiment in the region of 4–6.5MeV. In addition, we performed cross section sensitivity analysis for elastic, inelastic and (n,α) reaction in JENDL-4 and ENDF/B-VIII.b4 libraries since they have almost independent evaluations of 16O.
•Measurement of fast neutron flux penetrating through heavy and light water spheres.•Effect of different data libraries on calculations.•Sensitivity analysis of 16O elastic, inelastic and (n, alpha) cross sections.
•Neutron spectrum emitted by Sodern Genie 16C sealed tube generator reconstruction.•Indication of tritium amount decrease due to radioactivity in neutron generator.•Consideration the compatibility of ...the results obtained by different methods.•The combination of different methods in neutron spectrum reconstruction.
The presented paper is a continuation of the Tikhonov Regularisation, Minimum Fisher Information, Maximum Entropy, and Maximum Likelihood methods application to unfolding the neutron spectra emitted by the fusion devices from activation measurement. The aim of the analysis is the evaluation of the possible uncertainty improvement. The developed algorithms and methodology were validated with 14 MeV portable neutron generators before application to the analysis of the neutron spectrum emitted from tokamak. The analysis concerns plasma-target generator did not provide satisfactory uncertainty of the results. The modification of the irradiation foils’ set and the improvement in the activity measurement precision progress the results. The sealed tube portable neutron generator irradiated the Al, Fe, Ni, Zr, Au, Mg, and Nb foils. The HPGe spectrometer measured the induced activity with an uncertainty of about 10 %. The synthetic data analysis was made to establish the ratio between the error of the spectrum reconstruction and the discrepancy between the input data and activities reconstructed for this spectrum by the FISPACT-II inventory code. Two bin structures were considered. One was compatible with the FISPACT-II code, but the energy resolution was not regular. The second was characterised by constant bin spacing connected with the modification requirement before simulation and additional uncertainty of about 5 %. The best results were obtained by calculation of the mean value from all methods. The corresponding reconstruction uncertainty is equal to 11 %. The reconstructed spectrum has a dominant deuterium tritium peak slightly shifted to the higher energies due to the beam-target reaction kinematics. The evaluation of the impact of the deuterium-deuterium reaction due to the long-term operation was not reachable due to the measured high intensity from scattered neutrons.
•The pressure tube geometry in PHWR changes as the reactor ages.•The neutron spectrum in the pressure tube contributes to these changes.•The impact of changing various operational parameters on the ...spectrum has been investigated.•Coolant temperature and diametral creep have the most impact on the spectrum.
The fuel bundles in the pressurized heavy water reactor design (PHWR), such as the CANDU (Canada Deuterium Uranium), are placed inside horizontal fuel channels. Each fuel channel consists of concentric tubes called the pressure tube (PT) and the calandria tube (CT). Due to continuous exposure to extreme neutronics and thermal hydraulics conditions, the PTs undergo physical deformations in both the axial and radial directions, as the reactor ages. The deformations include diametral creep, wall thinning, sag, and axial elongation. One of the contributing factors to these deformations is the neutron spectrum in the PT, especially neutrons with energy greater than 1 MeV. In this paper, the sensitivity of the neutron spectrum in the PT to various operating conditions of a PHWR is evaluated. Sensitivity assessments have been completed on several parameters namely the coolant purity, coolant temperature, moderator purity, moderator temperature, and pressure tube diametral creep (PTDC). Since the deformations are inevitable, identifying parameters that have the greatest impact on the population of neutrons with energy greater than 1 MeV in the PTs would be important for fine-tuning the operational conditions which are conducive to reducing the rate of deformation. From this study, it is concluded that the coolant temperature and PTDC are the two variables having the most impact on the fast energy neutron population in the pressure tubes.
Activation analysis is used in this work to measure the flux of a fast neutron beamline at a spallation source over a wide energy spectrum, extending from thermal to hundreds of MeV. The experimental ...method is based on the irradiation of multiple elements and measurements of activation γ-lines using a High Purity Germanium detector. The method for data analysis is then described in detail, with particular attention to the evaluation of uncertainties. The reactions have been chosen so to cover the whole energy range, using mainly (n, γ) for thermal and epithermal neutrons, and threshold reactions for the fast region. The variety of these reactions allowed for the unfolding of the neutron spectrum, using an algorithm based on a Bayesian statistical model, and limited correlations have been found between the energy groups.
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