Vol.28,

Geant4 based Monte-Carlo study has been carried out to assess the improvement in efficiency of the planar structure of Silicon Carbide (SiC) based semiconductor fast neutron detector with the stacked structure. A proton recoil detector was simulated, which consists of hydrogenous converter i.e. High Density Polyethylene (HDPE) for generating recoil protons by means of neutron elastic scattering (n, p) reaction and semiconductor material SiC, for generating a detectable electrical signal upon transport of recoil protons through it. SiC is considered in order to overcome the various factors associated with conventional Si-based devices such as operability in harsh radiation environment, as often encountered in nuclear facilities. Converter layer thickness is optimized by considering 10⁹ neutron events of different monoenergetic neutron sources as well as ²⁴¹Am-Be neutron spectrum. It is found that the optimized thickness for neutron energy range of 1 - 10 MeV is ~ 400 μmm. However, the efficiency of fast neutron detection is estimated to be only 0.112 %, which is considered very low for meaningful and reliable detection of neutrons. To overcome this problem, a stacked juxtaposition of converter layer between SiC layers has been analyzed in order to achieve high efficiency. It is noted that a tenfold efficiency improvement has been obtained – 1.04 % for 10 layer stacked configuration vis-à-vis 0.112 % of single converter layer detector. Further simulation of stacked detector with respect to variable converter thickness has been performed to achieve the efficiency as high as ~ 3.85 % with up to 50 stacks.

492

For accurate counting of alpha tracks on the polyallyl diglycol carbonate (PADC) of CR-39 type track detectors, the size distributions of both artifact tracks and alpha tracks were investigated with an automatic counting system. At the same temperature and etchant concentration, the numbers and sizes of alpha tracks changed significantly with the etching time, and the artifact track changes were smaller. At the etching time of 5 h, the sizes of alpha tracks were evidently larger than those of the artifact tracks, and the deviation of its size distribution was much smaller than those of longer etching time. Based on the size distribution of alpha tracks etched for 5 h, the overlap effect and uncertainty of overlap correction were studied by the Monte Carlo simulations for different track densities. It was found that the counting uncertainty of the system could be less than 6% in a density range of 10–160 tracks·mm⁻² after taking the overlap correction into account.

480

This paper describes a method for energy calibration of laterally segmented electromagnetic calorimeters based on the detection of two-photon decays of π⁰ mesons. The calibration procedure performs a χ² function minimization between the measured π⁰ energy in the calorimeter and its expected energy deduced from the π⁰ momentum direction. The performance of this technique is demonstrated with a Monte Carlo simulation of an experimental case where biased calibration coefficients are employed. The real calibration coefficients are restored with less than 1% relative accuracy when a sufficient number of π⁰ is detected. This technique is applied to monitor daily the calibration coefficients of the calorimeter used in the Jefferson Lab Hall A DVCS experiments.

473

Fast reactors (FRs) based on thorium fuel has enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper, we present a reference core for a large fluoride-salt-cooled solid-fuel fast reactor (LSFR) using thorium-uranium fuel cycle. Neutronics physics of the LSFR reference core is investigated with 2D and 3D in-core fuel management strategy. The design parameters analyzed include the fuel volume fraction, power density level and continuous removal of fission products with 3D fuel shuffling that obtains better equilibrium core performance than 2D shuffling. A self-sustained core is achieved for all cases, and the core of 60% fuel volume fraction at 50 MW/m³ power density is of the best breeding performance (average breeding ratio 1.134). The LSFR core based on thorium fuel is advantageous in its high discharge burn-up of 20%–30% FIMA (Fissions per Initial heavy Metal Atom), small reactivity swing over the whole lifetime (to simplify the reactivity control system), the negative reactivity temperature coefficient (intrinsically safe for all cases), and accepted cladding peak radiation damage. The LSFR reactor is a good alternative option for deployment of a self-sustained thorium-based nuclear system.

706

Nuclear facility aging is one of the biggest problems encountered in nuclear engineering. Radiation damage is among one of the aging causes. This kind of damage is an important factor of mechanical proprieties deterioration. The interest of this study is on the Es-Salam research reactor aluminum vessel aging due to neutron radiation. Monte Carlo (MC) simulations were performed by MCNP6 and SRIM codes to estimate the defects created by neutrons in the vessel. MC simulations by MCNP6 have been performed to determine the distribution of neutron fluence and primary knock-on-atom (PKA) creation. Considering our boundary conditions of the calculations, the helium and hydrogen gas production in the model at a normalized total neutron flux of 6.62x10¹² n/cm².s were determined to be 2.86 x 10⁸ and 1.33 x 10⁹ atoms/cm³.s, respectively. The SRIM code was used for the simulation of defects creation (vacancies, voids) in the aluminum alloy of the Es-Salem vessel (EsAl) by helium and hydrogen with an approximate energy of 11 MeV each. The coupling between the two codes is based upon post-processing of the particle track (PTRAC) output file generated by the MCNP6. A small program based on the MatLab language is performed to condition the output file MCNP6 in the format of a SRIM input file. The concentration of silicon was determined for the vessel by the calculation of the total rate of ²⁷Al(n,γ)²⁸Si reaction. The DPA (displacement per atom) was calculated in SRIM according to R.E. Stoller recommendations; the calculated value is 0.02 at a fast neutron fluence 1.89 x10¹⁹ n/cm². RCC-MRx standard for 6061-T6 aluminum was used for the simulation of the evolution of mechanical properties for high fluence. The calculated values of nuclear parameters and DPA obtained were in agreement with the experimental results from the Oak Ridge High Flux Isotope Reactor (HFIR) reported by Farrell and coworkers.

700

As temperature changes constantly in nuclear reactor operation, on-the-fly Doppler broadening methods are commonly adopted for generating nuclear cross sections at various temperatures in neutron transport simulation. Among the existing methods, the widely-used SIGMA1 approach is inefficient because it involves error function and Taylor series expansion. In this paper, we present a new on-the-fly Doppler broadening with optimal double-exponential formula based on SuperMC to improve efficiency with given accuracy. In this method, double-exponential formula in 1/16 steps is used for broadening cross section at low energy, with both accuracy and efficiency. Meanwhile, the Gauss-Hermite quadrature of different orders is used for broadening cross section at resonance energy. The method can generate neutron cross section rapidly and precisely at the desired temperature. Typical nuclide cross sections and benchmarking tests are presented in detail.

512

Poly(vinyl acetate) (PVAc) was grafted onto wheat straw by γ-irradiation to improve the compatibility between wheat straw and high density polyethelene (PE). The grafting was proved by Fourier transform infrared (FTIR) spectroscopy. The compact structure of wheat straw was loosened because the chemical bonds and crystalline structure were destructed by the γ-rays. The modified wheat straw needed less energy for thermal transition, as revealed by differential scanning calorimetry (DSC). Thermal analysis revealed that grafted PVAc acted as a protective barrier for the wheat straw, and leads to an increase in maximum pyrolysis temperature. The crystallite size of grafted wheat straw decreased to 5.33 nm from 5.63 before irradiation. There were holes in melted form appeared on the surface of the grafted wheat straws. Both the grafted PVAc and irradiation are beneficial to lower the torque of wheat straw/PE melts and improve its mechanical properties by 36%. Possible mechanism of irradiation grafting was proposed.

859

Mass attenuation coefficient (μ_m) for polyethylene glycol (PEG) of different molecular weights are determined by using NaI(Tl) scintillator and WinXCOM mixture rule at gamma energies of 59.5, 302.9, 356.0, 661.7, 1173.2 and 1332.5 keV. The total atomic, molecular and electronic cross-sections, half-value layer, effective atomic and electron numbers, mass energy-absorption coefficients, and kermas relative to air, are calculated. The energy and compositional dependence of μ_m values, and the related radiation absorption parameters, are evaluated and discussed. The experimental results agree well with the theoretical ones, within an uncertainty of 1% in the effective atomic number for all PEG samples at the designated energies.

557

In this study, using the constant rate of supply model (CRS), sedimentation rates of Izmir Bay were calculated and discussed. For this purpose, eight sediment cores were collected from inner part of the bay and sedimentation rates were calculated from vertical distribution of ²¹⁰Pb. ²¹⁰Pb activities were determined indirectly from ²¹⁰Po activities. Sedimentation rates ranged from 0.10 to 0.52 cm·y⁻¹. The highest sedimentation rates were determined in stations close to the Poligon Stream. It was concluded that main transporting mechanism for sediments is river and streams in the area. In addition, sediment cores taken from the harbor were mixed due to bioturbation, water circulation and/or other factors.

454

Based on finite element analysis (FEA) of thermal mechanical behavior, structural optimization design was proposed for a side cooling collimating mirror subjected to high heat load for a beam-line at SSRF (Shanghai Synchrotron Radiation Facility). The temperature distribution, stress concentration effect, maximum equivalent (von-Mises) stress, and slope error of the mirror, were analyzed. In particular, the cooling water channels of the traditional structural design were optimized, and the modified designs were further optimized. Although the traditional structural and the improved designs could meet requirements for the temperature and thermal stress, the deformation gradients were relatively large for several structural designs, and this led to larger slope error. The further improved structural designs could be of better performance.

493

A synchrotron radiation source called TURKAY is proposed as a sub project of the Turkish Accelerator Center Project (TAC). The storage ring of TURKAY is a low emittance synchrotron and the radiation ranges between 0.01–60 keV and can be generated from the insertion devices and bending magnets placed on it. The injector system of the facility will mainly consist of a 150 MeV linac and full energy booster. In this study, we present design considerations and beam dynamics studies of the preinjector linac and booster ring for TURKAY.

467

In this paper we presents the design and optimization of a side-coupled accelerating structure with an energy switch. The beam parameters are optimized, and the electric field asymmetry in the first cell is analyzed. The new structure we designed has an improvement of 10 times in the accelerating field symmetry. Thermo-mechanical analysis is performed based on the electromagnetic results. The highest temperature is 72.5°C at the nose cone and the maximal deformation is 73 μm at the outer edge of the coupling cavity.

490

This study was to assess quantitatively the accuracy of ¹⁸F-FDG PET/CT images reconstructed by TOF+PSF and TOF only, considering the noise matching concept to minimize probable bias in evaluating algorithm performance caused by noise. PET images of similar noise level were considered. Measurements were made on an in-house phantom with hot inserts of Φ10–37 mm, and oncological images of 14 patients were analyzed. The PET images were reconstructed using the OSEM, OSEM+TOF and OSEM+TOF+PSF algorithms. Optimal reconstruction parameters including iteration, subset, and FWHM of post-smoothing filter were chosen for both the phantom and patient data. In terms of quantitative accuracy, the recovery coefficient (RC) was calculated for the phantom PET images. The signal-to-noise ratio (SNR), lesion-to-background ratio (LBR) and SUV_max were evaluated from the phantom and clinical data. The smallest hot insert (Φ10 mm) with 2:1 activity concentration ratio could be detected in the PET image reconstructed using the TOF and TOF+PSF algorithms, but not the OSEM algorithm. The relative difference for SNR between the TOF+PSF and OSEM showed significantly higher values for smaller sizes, while SNR change was smaller for Φ22–37 mm inserts both 2:1 and 4:1 activity concentration ratio. In the clinical study, SNR gains were 1.6±0.53 and 2.7±0.74 for the TOF and TOF+PSF, while the relative difference of contrast was 17%±1.05% and 41.5%±1.85 % for the TOF only and TOF+PSF, respectively. The impact of TOF+PSF is more significant than that of TOF reconstruction, in smaller inserts with low activity concentration ratio. In the clinical PET/CT images, the use of the TOF+PSF algorithm resulted in better SNR and contrast for lesions, and the highest SUV_max was also seen for images reconstructed with the TOF+PSF algorithm.

655

The ability to precisely estimate the void fraction of multiphase flow in a pipe is very important in petroleum industry. In this paper, an approach based on our previous works is proposed for predicting the void fraction independent of flow regime and liquid phase density changes in gas-liquid two phase flows. Implemented technique is a combination of dual modality densitometry and multi beam gamma ray attenuation techniques. The detection system is comprised of a single energy fan beam, two transmission detectors and one scattering detector. In this work, artificial neural network (ANN) was also implemented to predict the void fraction percentage independent of the flow regime and liquid phase density changes. Registered counts in three detectors and void fraction percentage were utilized as the inputs and output of ANN, respectively. By applying the proposed methodology, the void fraction was estimated with a mean relative error of less than just 1.2480 %.

637

Microstructure of shale formation is the key to understanding its petrophysical and chemical properties. Optical microscopy, scanning electron microscopy (SEM) and micro-computed tomography (μ-CT) have been combined for characterization of microstructure of Longmaxi (LMX) shale from Shizhu area, Sichan Basin. The results indicate that laminated LMX shale consists of mineral matrix-rich layers and organic matter(OM)-rich layers at micrometer scale in two and three dimensions. Mineral matrix layers, mainly consisting of interparticle pore and intraplatelet pores, are approximately parallel to the bedding plane. Pyrite-rich layer, mainly containing intercrystalline pores, shows a strong preferred orientation parallel to the bedding plane. OM-rich layer, mainly containing OM pores, seems to be discontinuous. In addition, intercrystalline pores are enriched in some layers while OM pores are distributed irregularly in matrix layers. This vertical heterogeneity of pore microscopic structures in LMX shale is of great inportance to understand its petrophysical and chemical properties.

588

Nuclear fusion is one of the world’s primary energy sources. Studies on the structural fusion materials are very important in terms of the development of fusion technology. Chromium, nickel, zinc, scandium, titanium, and yttrium are important structural fusion materials. In this paper, for use in nuclear science and technology applications, the excitation functions of the ⁵⁰Cr(d,n) ⁵¹Mn, ⁵⁸Ni(d,n) ⁵⁹Cu, ⁶⁴Zn(d,n)⁶⁵Ga, ⁶⁶Zn(d,n)⁶⁷Ga, ⁴⁵Sc(d,2n) ⁴⁵Ti, ⁴⁷Ti(d,2n) ⁴⁷V, ⁴⁸Ti(d,2n) ⁴⁸V, and ⁸⁹Y(d,2n) ⁸⁹Zr nuclear reactions were investigated. The calculations that are based on the pre-equilibrium and equilibrium reaction processes were performed using ALICE–ASH computer code. A comparison with Geometry dependent hybrid model has been made using the initial exciton numbers n₀=4 to 6, and level density parameters α=A/5; A/8; A/11. Also, the present model-based calculations were compared with the cross sections obtained using the formulae suggested from our previous studies. Furthermore, the cross section results have been compared with TENDL data based on TALYS computer code and the measured data in literature.

544