Study of neutron response for two hybrid RPC setups using the GEANT4 MC simulation approach

The present article describes a detailed neutron simulation study in the energy range 10^-10 MeV to 1.0 GeV for two different RPC configurations. The simulation studies were taken by using the GEANT4 MC code. Aluminum was utilized on the GND and readout strips for the （a） Bakelite-based and （b） glass-based RPCs. For the former type of RPC setup the neutron sensitivity for the isotropic source was Sn = 2.702 × 10^-2 at En = 1.0 GeV, while for the latter type of RPC, the neutron sensitivity for the same source was evaluated as Sn = 4.049 × 10^-2 at En = 1.0 GeV. These results were further compared with the previous RPC configuration in which copper was used for ground and pickup pads. Additionally A1 was employed at （GND＋strips） of the phosphate glass RPC setup and compared with the copper-based phosphate glass RPC. Good agreement with sensitivity values was obtained with the current and previous simulation results.     

First neutron spectrometry measurement at the HL-2A Tokamak

A compact neutron spectrometer based on the liquid scintillator is presented for neutron energy spectrum measurements at the HL-2A Tokamak. The spectrometer was well characterized and a fast digital pulse shape discrimination software was developed using the charge comparison method. A digitizer data acquisition system with a maximum frequency of 1 MHz can work under an environment with a high count rate at HL-2A Tokamak. Specific radiation and magnetic shielding for the spectrometer were designed for the neutron spectrum measurement at the HL-2A Tokamak. For pulse height spectrum analysis, dedicated numerical simulation utilizing NUBEAM combined with GENESIS was performed to obtain the neutron energy spectrum. Subsequently, the transportation process from the plasma to the detector was evaluated with Monte Carlo calculations. The distorted neutron energy spectrum was folded with the response matrix of the liquid scintillation spectrometer, and good consistency was found between the simulated and measured pulse height spectra. This neutron spectrometer based on a digital acquisition system could be well adopted for the investigation of the auxiliary heating behavior and the fast-ion related phenomenon on different tokamak devices.     

Effects of Δ-Isobars on Neutron Stars

We have investigated the possibility of the presence of the deltas in neutron star matter and their effects on neutron stars. Δ-meson couplings of the theoretical predictions are only restricted in a region where the deltas can be present and even a first-order phase transition may take place, making the EOS sorer and the maximum mass of neutron stars smaller. The presence of the deltas leads to the rapid decrease of neutrino mean free paths.     

Design and simulations for the detector based on DSSSD

The present paper describes the design and simulation results of a position-sensitive charged particle detector based on the Double Sided Silicon Strip Detector （DSSSD）. Also, the characteristics of the DSSSD and its testing result were are discussed. With the application of the DSSSD, the position-sensitive charged particle detector can not only give particle flux and energy spectra information and identify different types of charged particles, but also measure the location and angle of incident particles. As the detector can make multi-parameter measurements of charged particles, it is widely used in space detection and exploration missions, such as charged particle detection related to earthquakes, space environment monitoring and solar activity inspection.     

A higher-dimensional model of the nucleon-nucleon central potential

Based on a theory of extra dimensional confinement of quantum particles [E. R. Hedin, Physics Essays, 2012, 25（2）： 177], a simple model of a nucleon nucleon （NN） central potential is derived which quantitatively reproduces tile radial profile of other models, without adjusting any free pa- rameters. It is postulated that a higher-dimensional simple harmonic oscillator confining potential localizes particles into three-dimensional （3D） space, but allows for an ewmescent penetration of the particles into two higtmr spatial dimensions. Producing an effect identical with the relativistic quan- tum phenolnenon of zitterbewegung, the higher-dimensional oscillations of amplitude h（mc） call be alternatively viewed as a localized curvature of 3D space back and forth into the higher dimensions. The overall spatial curvature is proportional to the particle＇s extra-dimensional ground state wave function in tile higher-dimensional harmonic confining potential well. Minimizing the overlapping curvature （proportional to the energy） of two particles in proximity to each other, subject to the constraint that for the two particles to occupy the same spatial location one of them must be excited into the 1st excited state of the harmonic potential well, gives the desired NN potential. Specifying only the imcleon masses, the resulting potential well and repulsive core reproduces the radial profile of several published NN central potential models. In addition, the predicted height of the repulsive core, when used to estimate the maximum neutron star mass, matches well with the best estimates from relativistic theory incorporating standard nuclear matter equations of state. Nucleon spin, Coulomb interactions, and internal nucleon structure are not considered in the theory as presented in this article.     

Progress on the construction of the 100 MeV/100 kW electron linac for the NSC KIPT neutron source

IHEP, China is constructing a 100 MeV/100 kW electron Linac for NSC KIPT, Ukraine. This linac will be used as the driver of a neutron source based on a subcritical assembly. In 2012, the injector part of the accelerator was pre-installed as a testing facility in the experimental hall #2 of IHEP. The injector beam and key hardware testing results met the design goal. Recently, the injector testing facility was disassembled and all of the components for the whole accelerator have been shipped to Ukraine from China by the ocean shipping. The installation of the whole machine in KIPT will be started in June, 2013. The construction progress, the design and testing results of the injector beam and key hardware are presented.     

Speckle intensity images of target based on Monte Carlo method

Speckle intensity in the detector plane is deduced in the free-space optical system and imaging system based on Van Cittert-Zemike theorem. The speckle intensity images of plane target and conical target are obtained by using the Monte Carlo method and measured experimentally. The results show that when the range extent of target is smaller, the speckle size along the same direction become longer, and the speckle size increase with increasing incident light wavelengths. The speckle size increases and the speckle intensity images of target is closer to the actual object when the aperture scale augments. These findings are useful to access the target information by speckle in laser radar systems.     

Theoretical study of molecular hydrogen and spiltover hydrogen storage on two-dimensional covalent-organic frameworks

Molecular hydrogen and spiltover hydrogen storages on five two-dimensional （2D） covalent-organic frameworks （COFs） （PPy-COF, TP-COF, BTP-COF, COF-18 A, and HHTP-DPB COF） are investigated using the grand canonical Monte Carlo （GCMC） simulations and the density functional theory （DFT）, respectively. The GCMC simulated results show that HHTP-DPB COF has the best performance for hydrogen storage, followed by BTP-COF, TP-COF, COF-18 A, and PPy-COE However, their adsorption amounts at room temperature are all too low to meet the uptake target set by US Department of Energy （US-DOE） and enable practical applications. The effects of pore size, surface area, and isosteric heat of hydrogen on adsorption amount are considered, which indicate that these three factors are all the important factors for determining the H2 adsorption amount. The chemisorptions of spiltover hydrogen atoms on these five COFs represented by the cluster models are investigated using the DFT method. The saturation cluster models are constructed by considering all possible adsorption sites for these cluster models. The average binding energy of a hydrogen atom and the saturation hydrogen storage density are calculated. The large average binding energy indicates that the spillover process may pro- ceed smoothly and reversibly. The saturation hydrogen storage density is much larger than the physisorption uptake of H2 molecules at 298 K and 100 bar （1 bar = 105 Pa）, and is close to or exceeds the 2010 US-DOE target of 6 wt% for hydrogen storage. This suggests that the hydrogen storage capacities of these COFs by spillover may be significantly enhanced. Thus 2D COFs studied in this paper are suitable hydrogen storage media by spillover.     

A Study of Surfactant-Induced Growth of Ag on Ag （111）

A new growth model is introduced to describe surfactant-induced growth of Ag on Ag （111） with realistic physical parameters. In this model, the A-S exchange mechanism is considered for the first time. Using the Monte Carlo simulations, the influence of exchange mechanism, surface temperature T, the exchange barrier Eεx, and the coverage of surfactant θM on the growth mode and morphology during multilayer film growth of Ag/Ag （111） are studied in detail Both the referenced value of surfactant coverage and the method to obtain perfect layer-by-layer film in surfactantinduced Ag/Ag （111） system are provided. Our simulation results are consistent with many experimental observations for surfactant-induced growth of Ag on Ag （111）.     

Coverage Dependence of Growth Mode in Heteroepitaxy of Ni on Cu（100） Surface

A realistic kinetic Monte Carlo （KMC） simulation model with physical parameters is developed, which well reproduces the heteroepitaxial growth of multilayered Ni thin film on Cu（100） surfaces at room temperature. The effects of mass transport between interlayers and edge diffusion of atoms along the islands are included in the simulation model, and the surface roughness and the layer distribution versus total coverage are calculated. Speeially, the simulation model reveals the transition of growth mode with coverage and the difference between the Ni heteroepitaxy on Cu（100） and the Ni homoepitaxy on Ni（100）. Through comparison of KMC simulation with the real scanning tunneling microscopy （STM） experiments, the Ehrlich-Schwoebel （ES） barrier Ees is estimated to be 0.18±0.02 eV for Ni/Cu（100） system while 0.28 eV for Ni/Ni（100）. The simulation also shows that the growth mode depends strongly on the thickness of thin film and the surface temperature, and the critical thickness of growth mode transition is dependent on the growth condition such as surface temperature and deposition flux as well.     

Energy of Long-Lifetime Configurations in Zero-Temperature Dynamics

Using Monte Carlo method with zero-temperature dynamics, we investigate energy evolution of Ising spin configuration on a square lattice. The energies of some configurations exhibit long duration before those configurations reach the final state -- ground state or frozen stripe state. For ground-state dynamical realization, the duration occurs when the energy per spin is 4/L, where L is the lattice size. For stripe-state dynamical realization, the energy is slightly higher than 2/L when the duration appears in the last evolution stage. In addition, it is found that the average energy per spin in final state is approximately 2/3L.     

Finite Size Effect in Path Integral Monte Carlo Simulations of ^4He Systems

Path integral Monte Carlo （PIMC） simulations are a powerful computational method to study interacting quantum systems at finite temperatures. In this work, PIMC has been applied to study the finite size effect of the simulated systems of ^4He. We determine the energy as a function of temperature at saturated-vapor-pressure （SVP） conditions in the temperature range of T ∈ [1.0 K,4.0 K], and the equation of state （EOS） in the grmmd state For systems consisted of 32, 64 and 128 ^4He atoms, respectively, We find that the energy at SVP is influenced significantly by the size of the simulated system in the temperature range of T ∈ [2.1 K, 3.0 K] and the larger the system is, the better results are obtained in comparison with the experimental values; while the EOS appeared to be unrelated to it.     

Reverse electric field Monte Carlo simulation for vector radiative transfer in the atmosphere

In this paper, a reverse electric field Monte Carlo （REMC） method is proposed to study the vector radiation transfer in the atmosphere. The REMC is based on tracing the multiply scattered electric field to simulate the vector transmitted radiance. The reflected intensities with different total optical depth values are obtained, which accord well with the results in the previous research. Stokes vector and the degree of polarization are numerically investigated. The simulation result shows that when the solar zenith angle is determined, the zenith angle of detector has two points, of which the degree of polarization does not change with the ground albedo and the optical depth. The two points change regularly with the solar zenith angle. Moreover, our REMC method can be applied to the vector radiative transfer in the atmosphere-ocean system.     

Status and accuracy of the Monte Carlo generators for luminosity measurements

The status and accuracy of the precision Monte Carlo generators used for luminosity measurements at flavour factories is reviewed. It is shown that, thanks to a considerable, long-term effort in tuned comparisons between the predictions of independent programs, as well as in the validation of the generators against the presently available calculations of the next-to-next-to-leading order QED corrections to Bhabha scattering, the theoretical accuracy reached by the most precise tools is of about one per mille. This error estimate is valid for realistic experimental cuts, appears to be quite robust and is already sufficient for very accurate luminosity measurements. However, recent progress and possible advances to further improve it are also discussed.     

Large energy-loss straggling of swift heavy ions in ultra-thin active silicon layers

Monte Carlo simulations reveal considerable straggling of energy loss by the same ions with the same energy in fully-depleted silicon-on-insulator (FDSOI) devices with ultra-thin sensitive silicon layers down to 2.5 nm. The absolute straggling of deposited energy decreases with decreasing thickness of the active silicon layer. While the relative straggling increases gradually with decreasing thickness of silicon films and exhibits a sharp rise as the thickness of the silicon film descends below a threshold value of 50 nm, with the dispersion of deposited energy ascending above ±10%. Ion species and energy dependence of the energy-loss straggling are also investigated. For a given beam, the dispersion of deposited energy results in large uncertainty on the actual linear energy transfer (LET) of incident ions, and thus single event effect (SEE) responses, which pose great challenges for traditional error rate prediction methods.     

Microwave propagation with the gas breakdown

By combining the microwave propagation theory and the gas breakdown theory, the microwave propagation with the gas breakdown is analyzed theoretically. Particle-in-cell/Monte Carlo collision （PIC/MCC） simulations are carried out to verify the theoretical results. Based on this theoretical method, the breakdown phenomenon of the pulse microwave is analyzed. The results show that the product values of the initial electron density and the propagation length are the criterion to distinguish the pulse peak decline breakdown and the pulse width reduction breakdown. Furthermore, the energy transmission is also studied, which shows that the total output energy is approximately independent of the input electric field if the electric field is not extremely large.     

Strong and electromagnetic J/ψ and ψ（2S） decays into pion and kaon pairs

We discuss interference effects important for the form factors extraction in the vicinity of J/ψ and ψ（2S） resonances in combination with resonance parameters determination. The implementation to the Monte Carlo event generator PHOKHARA of the J/ψ and ψ（2S） contributions to the muon, pion and kaon pairs production associated with a photon at next-to-leading order is also described.     

A pressure calibration method for a portable wide-access ＂panoramic＂ cell

A simple and convenient pressure calibration method is developed for a newly designed portable wide-access ＇panoramic＇ cell. This cell is adapted to angle-dispersive-mode high-pressure in situ neutron diffraction of reactor neutron sources. This pressure calibration method has established a relationship between the cell pressure and the anvil displace- ment （gasket compression） based on the fixed-point calibration technique. By employing TiZr gasket with a thickness of 3 mm and WC anvil with a culet of 4 mm diameter, the average anvil displacements are 1.31 mm and 2.22 mm for Bi phase transitions （2.55 GPa and 7.7 GPa）, and 1.85 mm for Ba phase transitions （5.5 GPa）, respectively. In this pressure range, the pressure increases quickly with decreasing gasket thickness, and undergoes a linear increase with the anvil displacement. By extrapolating the calibration curve, the cell pressure will achieve 10 GPa when the anvil displacement is around 2.5 ram.     

High efficiency event-counting thermal neutron imaging using a Gd-doped micro-channel plate

An event-counting thermal neutron imaging detector based on 3 mol % nattGd2O3-doped micro-channel plate （MCP） has been developed and tested. A thermal neutron imaging experiment was carried out with a low flux neutron beam. Detection efficiency of 33% was achieved with only one doped MCP. The spatial resolution of 72μ m RMS is currently limited by the readout anode. A detector with larger area and improved readout method is now being developed.     

Effect of Strong Magnetic Field on Gamow-Teller Transition Electron Capture of Iron Group Nuclei at Crusts of Neutron Stars

The electron capture of Gamow--Teller transition on iron group nuclei is investigated in a strong magnetic. field at the crusts of neutron stars. The results show that the magnetic field has only a slight effect on the electron capture rates with the range of the magnetic fields （10^9 - 10^13 G） on surfaces of most neutron stars, whereas for some magnetars whose range of the magnetic field is 10^13 - 10^18 G, the electron capture rates of most iron group nuclei would be debased greatly and may be even decreased overrun 3 orders of magnitude by the strong magnetic field.