We considered the main passive and active neutron methods for detecting fissile material in a sample which are used, for example, in inspection installations and in the control of waste from the ...nuclear fuel cycle. Calculations are presented to assess the possibilities of using these methods to detect enriched uranium. The differential die-away analysis (DDAA) is considered in detail. A model has been developed for detecting the presence of
235
U in a sample by using DDAA with the Geant4 software package. In the developed model, a criterion for determining the mass of
235
U is proposed and verified. The proposed model and criterion can significantly simplify the process of developing and optimizing the parameters of expensive devices for detecting fissile substances by creating a digital model.
The work describes features of the procedure for obtaining a response matrix to neutron radiation with energies from 1 to 19 MeV for a single-crystal stilbene scintillation detector. This response ...matrix is subsequently used in solving the problem of unfolding the neutron energy distribution at the detector location. The procedure for obtaining the matrix includes both experimental work and simulations of nuclear physics processes. In order to carry out the simulations, the Geant4 library package with the connected optical physics accounting module was used. The resulting matrix can be used as part of the amplitude method for unfolding the spectra of neutrons with energies in the range of 1–19 MeV with a step of 0.1 MeV. The obtained response matrix takes into account the main physical processes and instrumental effects of detectors based on organic scintillators, including the dependence of the light yield in the scintillator on the type and energy of charged particles, as well as the energy resolution of the detector depending on the energy of detected particles. In comparison with earlier results obtained using response matrices that do not take into account the above formation features of hardware spectra, it was possible to reduce the lower limit of the detected neutron energy from 1.5 to 1.0 MeV, as well as to increase the reliability of unfolded neutron energy distributions at the measurement point. The error in determining the neutron energy in the range of 1–15 MeV was not more than 200 keV.
The paper considers and compares methods for obtaining spectra of fast neutrons using detectors based on a diamond sensor, an organic (plastic) scintillator for separating neutrons and γ-quants, and ...a spectrometric set of threshold activation detectors. The neutron spectrum was unfolded using the methods of least squares, Tikhonov regularization, neural networks, and maximum entropy, implemented in the MAXED code, as well as the GRAVEL iterative algorithm. In order to form detector response matrices, mathematical simulation methods and analytical calculations were used followed by verification using experimental data. The unfolding quality criteria, according to which the best method is selected, are given.
The article discusses the question of obtaining energy spectra of neutron and γ-quantum sources using a spectrometer based on a stilbene monocrystal for separation according to the pulse shape. A ...procedure for calibrating the spectrometric path is described. Mathematical modeling implementing the Monte Carlo method in the Geant4 environment was used to calculate the matrices of responses to neutrons and γ-quanta detected using this instrument confi guration. The spectra of the neutron and associated γ-radiation from the generators of 2.5 and 14 MeV neutrons are unfolded with the aid of the GRAVEL iterative algorithm. The relative width of peaks in unfolded neutron spectra (unfolding uncertainty) comprises 19 ± 0.3 and 7.2 ± 0.7% for D–T- and D–D-neutrons, respectively.
The paper presents the experimental assessment for the characteristics of a fast neutron spectrometer based on a diamond sensor detector. The presented characteristics include the energy range of ...detected neutrons, energy resolution, the effect of associated radiation (γ-quants and scattered neutrons) on the measurement results, as well as the range of the measured neutron flux density. Some effects typical to diamond-based detectors, e.g., the effect of polarization on the measurement results, are considered. The possibility of performing spectrometry of neutrons with an energy of 14 MeV at a resolution of less than 1% is demonstrated, including the influence of electronics, as well as the absence of a polarization effect on the detector operation during measurement at points where the fast neutron flux density is up to 10
7
s
−1
∙ cm
−2
.
A high-time resolution Neutron Monitor Database (NMDB) has started to be realized in the frame of the Seventh Framework Programme of the European Commission. This database will include cosmic ray ...data from at least 18 neutron monitors distributed around the world and operated in real-time. The implementation of the NMDB will provide the opportunity for several research applications most of which will be realized in real-time mode. An important one will be the establishment of an Alert signal when dangerous solar cosmic ray particles are heading to the Earth, resulting into ground level enhancements effects registered by neutron monitors. Furthermore, on the basis of these events analysis, the mapping of all ground level enhancement features in near real-time mode will provide an overall picture of these phenomena and will be used as an input for the calculation of the ionization of the atmosphere. The latter will be useful together with other contributions to radiation dose calculations within the atmosphere at several altitudes and will reveal the absorbed doses during flights. Moreover, special algorithms for anisotropy and pitch angle distribution of solar cosmic rays, which have been developed over the years, will also be set online offering the advantage to give information about the conditions of the interplanetary space. All of the applications will serve the needs of the modern world which relies at space environment and will use the extensive network of neutron monitors as a multi-directional spectrographic detector. On top of which, the decreases of the cosmic ray intensity – known as Forbush decreases – will also be analyzed and a number of important parameters such as galactic cosmic ray anisotropy will be made available to the users of NMDB. A part of the NMDB project is also dedicated to the creation of a public outreach website with the scope to inform about cosmic rays and their possible effects on humans, technological systems and space-terrestrial environment. Therefore, NMDB will also stand as an informative gate on space research through neutron monitor’s data usage.
Calibration of the scintillator detector based on a plastic scintillator EJ-276 for neutron–gamma pulse shape discrimination (PSD) experiments was carried out. Optical characteristics of electrons as ...the function of their deposited energy were experimentally studied. The calibration was implemented by comparing the experimental response from gamma sources with that obtained by means of GEANT4 simulation. It is shown that a similar relationship for protons built on the basis of the published data on EJ-299-33, is also applicable to EJ-276 which confirms the information about the equivalence of these scintillators. The experimental response of the EJ-276 to 14 MeV neutrons is compared with Geant4 simulation data. The experimental and simulated data were also presented as the function of light output in electronic equivalent (MeVee) obtained by both exponential and Birks’ laws.
An experimental setup was constructed with Ø51 × 51 mm EJ-276 scintillator. The CAEN DT5730B digitizer was used for PSD signal discrimination. Based on the current experiments and the earlier published data a calibration relation between the setup channels and the light output was obtained in electronic equivalent (MeVee).
The boundary-domain integral method with the analytical integrals over the individual boundaries and internal cells for the solving the boundary value problems of fluid flow problems is developed. ...The axisymmetric potential flow of an incompressible fluid around a sphere, the fluid flow in a porous medium with spatially inhomogeneous permeability and the problem of convective-diffusive transport of a gas suspension in a periodic cell are calculated The comparison of the numerical results with analytical solutions show the efficiency and good accuracy of the developed boundary-domain integral method.
This article demonstrates the performance of the EJ-276 plastic scintillator-based neutron radiation spectrometer with neutron–gamma separation capability. This work continues the earlier research ...devoted to the demonstration of the EJ-276 spectrometric capabilities. An NG-150M generator located at RFNC-VNIIEF (Sarov) was used as a neutron source. Neutron energy distribution was unfolded for several angles between neutron generator and the target-scintillator direction using a Geant4 simulated response matrix and a set of experimental response spectra. The experimental neutron spectra are compared with the calculated ones. DT neutron unfolded energy uncertainty is 2%. The accompanying gamma radiation spectra were unfolded with the same uncertainty.
The present work is devoted to implementation of the stilbene-based neutron spectrometer energy calibration method. The results of experiments with portable neutron generators and 238PuBe source and ...scattering materials with known cross sections are used for this method. It is shown that the submitted method makes it possible to carry out fast neutron spectrometry in the energy range from 1 to 15 MeV with the uncertainty of the unfolded neutron energy no more than 200 keV. Neutron spectra unfolding was carried out based on the measured spectra and a Geant4 simulated response matrix. Unfolded spectra were compared with the literature data and reference spectra.
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