Nima Ghal-Eh

A prototype moisture measurement system was designed and constructed, based on neutron scattering, for preforming measurements in the laboratory. The system consisted of a rectangular soil container, an 241Am/Be neutron source and two parallel 10BF3 detectors (one near the source and the other far from it). Neutrons from the source are moderated and backscattered within the soil sample before being detected by two parallel counters, whose count ratios are shown to be linearly related to the soil moisture even within short measurement times. The system's performance was demonstrated using the Monte Carlo simulations, and a series of measurements on soil samples made of clay (40 wt%) and sand (60 wt%), mixed with different percentages of water. The results showed that the detectors response ratio is linear, up to about 25% of water content. © 2018 Elsevier Ltd

The sensitivities of both time and energy resolutions of a typical scintillation detector to major optical parameters (i.e. paint reflectivity, quantum efficiency of photomultiplier tube and attenuation coefficient) have been estimated using a dedicated Monte Carlo (MC) optical photon transport (OPT) simulation code, PHOTRACK, and the OPT capabilities of general-purpose code, FLUKA. Both cylindrical and parallelepiped geometries have been considered for the scintillator cell and lightguide. The results determine the scintillation light wavelength regions that the energy and time resolution represent enhanced sensitivities to small change/uncertainty in optical parameters. © 2018 World Scientific Publishing Company.

Prompt gamma neutron activation analysis (PGNAA) is frequently used in on–line analysis of raw materials in cement and coal industries which normally incorporates bismuth germanate (BGO) or sodium iodide (NaI(Tl)) scintillators. The quantitative results are basically undertaken through full–spectrum analysis method which requires an efficient noise reduction procedure to optimize PGNAA data. Here in this study, the empirical mode decomposition (EMD) technique has been used to reduce the noise level of PGNAA spectra of a neutron–irradiated NaCl·H2O solution and then the results have been compared with those of wavelet technique. The mean square errors (MSEs) comparisons confirm that both EMD and wavelet techniques can be efficiently used for noise reduction purposes, however, this study recommends the EMD technique for its independency of basic functions, simplicity and spectrum data-based operation. © 2018 Elsevier Ltd

A variety of formulations was investigated for the fabrication of an appropriate shielding rubber to be used in neutron–gamma mixed fields. Having considered the required mechanical properties together with tungsten as the gamma-ray absorbing element, calculations with MCNPX 2.6 code confirmed that the incorporation of 5 weight percentage (wt%) of boron carbide exhibited the best performance as a thermal neutron absorber. A series of both experimental and simulation results are provided for comparison. © 2018, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Chinese Nuclear Society, Science Press China and Springer Nature Singapore Pte Ltd.

The Monte Carlo simulation code, FLUKA version 2011.2c.5, has been used to estimate the in–phantom dosimetric parameters for use in BNCT studies. The in–phantom parameters of a typical Snyder head, which are necessary information prior to any clinical treatment, have been calculated with both FLUKA and MCNPX codes, which exhibit a promising agreement. The results confirm that FLUKA can be regarded as a good alternative for the MCNPX in BNCT dosimetry simulations. © 2017 Elsevier Ltd

In this study, a conventional Bonner sphere spectrometer, together with 6LiI(Eu) inorganic scintillator used as the central detector, was used to obtain the neutron energy spectrum of an 241Am–Be source. To achieve this, we calculated the response matrices corresponding to eight different sizes of polyethylene spheres for the neutron energies ranging from about 10-7 to 15 MeV in 54 energy groups by using the MCNPX2.6 code, and the 241Am–Be neutron spectrum was obtained using a modified version of the neutron spectrum unfolding code, AFITBUNKI. In a feasibility study, similar calculations were performed with different sizes of polyethylene cylinders. A comparison between the unfolded spectra of a typical 241Am–Be neutron source with those of Bonner spheres, cylinders of similar sizes, and standard 241Am–Be neutron energy spectra shows that the spectrometer with polyethylene cylinders can be used as a potential alternative for conventional Bonner spheres. © 2017 Elsevier Ltd

In this study, a scintillator-based measurement instrument is proposed which is capable of measuring a two-dimensional map of thermal neutrons within a phantom based on the detection of 2.22 MeV gamma rays generated via nth+H→D+γ reaction. The proposed instrument locates around a small rectangular water phantom (14 cm×15 cm×20 cm) used in Birmingham BNCT facility. The whole system has been simulated using MCNPX 2.6. The results confirm that the thermal flux peaks somewhere between 2 cm and 4 cm distance from the system entrance which is in agreement with previous studies. © 2016 Elsevier Ltd.

The appropriate gamma-ray detector shielding configuration is critical for a precise prompt gamma neutron activation analysis (PGNAA) measurement. The shielding material has to prevent the radiation damage to the detector crystal and it must produce less activation gamma rays, whether prompt or delayed, which may interfere the gamma ray spectrum of the sample. In this research, using common shielding materials, a number of combinations have been studies to form a 50 cm long shield for portable PGNAA system against both fast and slow neutrons as well as gamma rays emitted by 20Ci Am-Be source. The measurement results show that in contrast with conventional shadow cone in which the shielding material starts with 20 cm heavy metals such as iron and ends with 30. cm polymer materials, in portable PGNAA systems, the shielding material gives better results if it starts with about 40 cm borated polymer material and ends with an appropriate thickness (7 cm to 10 cm) of heavy metal such as tungsten. © 2015 Elsevier Ltd.

A prompt gamma neutron activation analysis (PGNAA) system including an Am-Be neutron source and BGO scintillation detector are used for quantitative analysis of bulk samples. Both Monte Carlo-simulated and experimental data are considered as input data libraries for two different procedures based on neural network and least squares methods. The results confirm the feasibility and precision of the proposed methods. © 2015 Elsevier B.V.

The manganese sulfate bath technique is a standard tool for neutron source strength measurement (Park et al., 2005). However, the dominate Compton continuum of most sodium iodide scintillators used in manganese bath systems (MBSs) does not allow the precise identification of induced gamma rays required for such measurements. In this research, to resolve this problem, a Compton-suppression system has been proposed which consists of a 2in. by 2in. NaI(Tl) right cylindrical scintillator as the main and a set of eight rectangular NE102 plastic scintillators of 12×12×15cm3 dimensions as suppression detectors. Both detectors operate in anti-coincidence circuit to suppress the Compton continuum. The proposed system has been simulated with the MCNPX code with two different approaches and the corresponding measurements with 137Cs gamma-ray source and neutron-activated MnSO4 solution have been undertaken that give rise to a promising agreement. © 2015 Elsevier Ltd.

The NE102 plastic scintillator response to 137Cs gamma rays and NE213 liquid scintillator response to both mono-energetic and 241Am-Be neutrons have been modeled using FLUKA's EVENTBIN and MCNPX's PTRAC cards. The comparison made in different energy regions confirms that the overall difference is less than 6%. © 2015 Elsevier B.V.

In this research, based on pulse reconstruction method, digital storage oscilloscopes with an 8-bit digital-to-analog convertor was used to successfully perform the neutron-gamma discrimination with NE213 (or its equivalent BC501A) scintillator anode pulses at minimum discrimination bias value of 95keVee (or keV electron equivalent). Also, a 100mCi 241Am-Be source and micro-Curie gamma ray sources (137Cs and 22Na) were used for the system calibration and discrimination studies. The results confirm the feasibility and simplicity of the proposed method. © 2014 Elsevier Ltd.

Silver-activated Geiger counters together with a polyethylene layer as neutron moderator are frequently used in pulsed neutron flux measurements in research studies with plasma focus (PF) devices. In this study, an array of seven counters was used at seven different angles (0°, ±30°, ±60° and ±90°) to the PF-axis for which a software and a 10-channel data acquisition hardware (PCT2660) compatible with NIM standards have been designed and fabricated. In the proposed PCT2660, the preset timing algorithms are considered as general and they can be programmed for required detector calibrations and neutron flux measurements. The calibration constant measurement has been undertaken with a 16.5 Ci Am–Be source of 35 mm diameter by 70 mm cylindrical active volume located at anode top whilst the neutron flux at zero degree of PF device axis at 13.5 kV operating voltage and 13.54 × 10−2 PSI pressure is measured as (2.88 ± 0.29) × 108 neutrons per shot. Accordingly, the studies on the angular distribution of the PF neutron emission within the pressure range of 7.73 × 10−2–15.47 × 10−2 PSI confirm an anisotropy ranging from 1.53 ± 0.09 to 2.95 ± 0.24 and a symmetry of angular distribution around the anode axis. © 2014, Springer Science+Business Media New York.

The response of an NE213 (or its BICRON equivalent, BC501A) scintillator attached to different sizes of polished/painted lightguides when exposed to 241Am-Be neutrons has been simulated. This kind of simulation basically needs both particle and light transports: the transport of neutrons and neutron-induced charged particles such as alphas, protons, carbon nuclei and so on has been undertaken using MCNPX whilst the scintillation light transport has been performed with PHOTRACK codes. The comparison between simulated and experimental response functions of NE213 attached to different sizes of polished/painted lightguides and also the influence of length/covering of lightguide on the detection efficiency and uniformity of the scintillator-lightguide assembly response have been studied. © 2013 Elsevier Ltd.

The paper reports on the capabilities of Monte Carlo scintillation light transport code Optix, which is an extended version of previously introduced code Optics. Optix provides the user a variety of both numerical and graphical outputs with a very simple and user-friendly input structure. A benchmarking strategy has been adopted based on the comparison with experimental results, semi-analytical solutions, and other Monte Carlo simulation codes to verify various aspects of the developed code. Besides, some extensive comparisons have been made against the tracking abilities of general-purpose MCNPX and FLUKA codes. The presented benchmark results for the Optix code exhibit promising agreements. © 2013 Elsevier B.V.

Scintillation of the photomultiplier glass window and its effects on the detector response were studied. It was proved that effects could have a considerable contribution to the pulse-height spectrum, especially when low-efficiency scintillators were used. © 2014.

A 5cm diameter by 6cm height NE213 scintillator attached to two XP2282 PHOTONIS photomultiplier tubes (PMTs) exposed to 241Americium-Berylium (Am-Be) neutron-gamma source has been used for timing response studies. The neutron-gamma discrimination (NGD) measurements based on a modified zero-crossing (ZC) method show that the discrimination quality, usually expressed in figure-of-merit (FoM) and peak-to-valley (P/V) values, has been improved. The timing response evaluated with Monte Carlo light transport code, PHOTRACK, also verifies this improvement. © 2013 Elsevier Ltd.

The detailed Monte Carlo simulation of a boron-lined proportional counter response to a neutron source has been presented. The MCNP4C and experimental data on different source-moderator geometries have been given for comparison. The influence of different irradiation geometries and boron-lining thicknesses on the detector response has been studied. © The Author 2013. Published by Oxford University Press. All rights reserved.

In this paper, three different radiation detectors (BF3 counter, NE213 and BGO scintillators) and an 241Am-Be isotopic neutron-gamma source have been used for a typical liquid levelmetry. The study shows that the use of the Am-Be source together with an NE213 scintillator has the best performance. © The Author 2013. Published by Oxford University Press. All rights reserved.

This paper reports on how to generate the response function of an NE213 scintillator when exposed to mono-energetic neutrons using the PTRAC card of the MCNPX code. The light transport part of the simulation has been undertaken with the Monte Carlo PHOTRACK code. The comparison confirms that the simulated response function represents a promising agreement with the previously published simulations and experiments. © 2012 Elsevier B.V.

The new-type scintillator, Ultima Gold Alpha-Beta (UGAB), was studied for its neutron-gamma discrimination capability. The figure-of-merit and peak-to-valley values for the neutron-gamma discrimination spectra of UGAB scintillator when exposed to 241Am-Be neutron source were presented. The results show that this new-type scintillator can efficiently be used in neutron-gamma discrimination experiments. ©The Author 2012. Published by Oxford University Press.

In this paper, using zero-crossing method, the neutron-gamma discrimination has been discussed to estimate the contribution of light transport on the timing characteristics of scintillation detectors. Both experimental and simulation verifications for the influence of lightguide length on the neutron-gamma discrimination quality of a 2×2 in. NE213 scintillator have been presented. © 2012 Elsevier Ltd.

A couple of 2-inch by 2-inch right cylinder sodium iodide scintillators and an Am-Be radioisotope neutron source have been used in a neutron porosity well-logging tool to explore the variation of hydrogen contents in a prototype formation. Both Monte Carlo N-particle transport code simulation and experimental results of the near- to far-detector responses confirm the reliable sensitivity of proposed tool to the formation porosity. © The Author 2012. Published by Oxford University Press. All rights reserved.

The response function of NE102 plastic scintillator to gamma rays has been simulated using a joint FLUKA+PHOTRACK Monte Carlo code. The multi-purpose particle transport code, FLUKA, has been responsible for gamma transport whilst the light transport code, PHOTRACK, has simulated the transport of scintillation photons through scintillator and lightguide. The simulation results of plastic scintillator with/without light guides of different surface coverings have been successfully verified with experiments. © 2012 Elsevier Ltd.

The neutron-gamma discrimination capability of the new-type UGLLT liquid scintillator has been compared with NE213 (or its Bicron equivalent, BC501A). An Am-Be combined neutron-gamma isotopic source and a zero-crossing circuitry were used to explore various biases resulting the optimum figure of merits (FOMs) of 1.52 and 1.18 for NE213 and UGLLT at 170. keVee bias, respectively. The study shows that the UGLLT scintillator can be a good alternative for NE213 in pulse-shape discrimination experiments. © 2011 Elsevier Ltd.

In this paper, a novel iterative method is proposed to obtain approximate-analytical solutions for the linear systems of first-order fuzzy differential equations (FDEs) with fuzzy constant coefficients (FCCs) while avoiding the complexities of eigen-value computations. A theorem for the convergence and the validity of the approach is also presented in detail. Numerical experiments and comparisons with exact solutions reveal that the proposed method is capable of generating accurate results. © 2011 Elsevier Inc. All rights reserved.

A Monte Carlo simulation of the light transit time in scintillation detectors is described, with the wavelength dependencies of different interaction processes being taken into account. The simulation results presented give an estimate of the contribution of light transport to the timing resolution of scintillation detectors. © 2010 Elsevier Ltd.

The silver activated Geiger counters are frequently used for measuring pulsed neutron fluxes especially in plasma focus devices. These counters basically utilize a Geiger-Mueller (GM) counter surrounded by a silver layer as an activation medium and also a polyethylene layer as a neutron moderator. Neutrons are slowed down in polyethylene prior to activating the silver layer. The neutron flux can be estimated through measuring the silver activity by Geiger-Mueller counter. In this paper, the construction of an activation counter is explained and the Monte Carlo MCNP4C code is used to calculate the calibration constant. Finally, the calculated calibration constant is compared with the measurement undertaken with an Am-Be neutron source, based on the saturation count rate method. The comparison represents a good agreement between simulation and experimental values of calibration constant. The Amir Kabir Plasma Focus (APF) device is used as a fast neutron source. © Springer Science+Business Media, LLC 2010.

This paper introduces the basics of the light transport simulation in scintillators and the wavelength-dependencies in the process. The non-uniformity measurement of the photocathode surface is undertaken, showing that for the photocathode used in this study the quantum efficiency falls to about 4 % of its maximum value, especially in areas far from the centre. The wavelength-and position-dependent quantum efficiency is implemented in the Monte Carlo light transport code, showing that, the contribution of the photocathode non-uniformity to the energy resolution is estimated to be around 18 %, when all position-and wavelength-dependencies are included. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org.

In this study, the light transport simulation in scintillators is introduced, the wavelength-dependencies in the process are taken into account, the effect of different shapes/lengths of lightguides on the response of the scintillation detectors are investigated and finally the need for such a simulation in addition to the particle transport simulation in a perfect response function predicting code is explained. © 2008 Elsevier B.V. All rights reserved.

An extended version of the scintillator response function prediction code SCINFUL has been developed by incorporating PHOTRACK, a Monte Carlo light transport code. Comparisons of calculated and experimental results for organic scintillators exposed to neutrons show that the extended code improves the predictive capability of SCINFUL. © 2007 Elsevier Ltd. All rights reserved.

In this study, an extended version of the Monte Carlo light transport code, PHOTRACK, has been used for a sensitivity analysis to estimate the importance of different wavelength-dependent parameters in the modelling of light collection process in scintillators. © 2007 Elsevier B.V. All rights reserved.

The resonance absorption filter technique has been used to determine the thermal/epithermal neutron flux. The main idea in this technique is to use an element with a high and essentially singular resonance in the neutron absorption cross section as a filter surrounding a miniature-type lithium glass scintillator. The count with and without the filter surrounding the detector gives the number of resonance-energy neutrons. Some preliminary results and a comparison with the MCNP code are shown. © 2007 Elsevier Ltd. All rights reserved.

A simple Monte Carlo procedure is described for simulating the multiple scattering and absorption of electrons with a definite incident energy in the range of keV up to 20 MeV, moving perpendicular or at a definite angle through one slab, or two adjacent slabs of uniformly-distributed material of given atomic number, density and thickness. The simulation is based on a Screened Rutherford cross section and Bethe continuous energy-loss equation. Programs were written in FORTRAN to determine: scattering, backscattering, transmission and absorption coefficients, providing the user with a graphical output of the electron trajectories. The results of several simulations are presented by using various numbers of electrons. The program is used to analyze the relation between the energy and the range of electron in the slab, the scattering, backscattering, absorption, transmission coefficients and the angular distribution. The technique has been applied to the transport properties of the electron through body tissue, bone and water slab by dividing media into several parts of different materials. Comparisons show that the results are in good agreement with the MCNP code within the range of energy considered and with the experimental data of Linear Electron Accelerator of Imam-Reza Hospital in Mashhad, Iran. © 2006 IACS.

The effect of different surface coverings of scintillation counters on the light collection efficiency and the detection resolution is investigated using an extended version of PHOTRACK, a Monte Carlo light transport code, which has been verified by reproducing other workers' experimental and theoretical results. The underlying wavelength dependencies in light collection process are also presented. © 2005 Elsevier Ltd. All rights reserved.