Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.

Synergistic effect of La2O3 on mass stopping power (MSP)/projected range (PR) and nuclear radiation shielding abilities of silicate glasses

Abstract: Photon and neutron attenuation properties of La2O3 based Li2O-SiO2-La2O3 glass system have been evaluated through MCNPX (2.6.0) Monte Carlo code at some photon energies of 0.256–1.33 MeV. In order to control the accuracy of the data, the estimated MCNPX of mass attenuation coefficients have been compared to those of WinXCOM software. The half value layer (HVL), tenth value layer (TVL) and mean free path (MFP) values of the selected glass system exhibited that the shielding performance of the gamma photons is related to the density of glass, thus, the inclusion of TeO2 to Li2O-SiO2 improves the capacity of the glass system to attenuate more photons. In addition, the effective removal cross-section (ΣR) calculations have been done. Further, Mass sopping power (MSP) and Projected range (PR) are calculated for proton particles (H1) and alpha particles (He+2). It may be deduced that La4 glass among the studied samples may be kept in view as a superior glass in terms of shielding for photon and neutron while La0 glass can be considered as a best shielding material against to alpha and proton particles. The results of this study may be useful for shielding optimization of medical and industrial facilities.

Plasma confinement in multiple‐mirror systems. I: Theory

Abstract: For an intermediate mean free path regime where λ ≪ L, the system length, but where λ ≫ lm, the scale length of the magnetic field variation, it is found that the confinement time τmm of ions in a multipole mirror system scales quadratically with the system length. When either inequality is not satisfied, a transition is found to a scaling which is more closely proportional to L. For the high density regime this corresponds to magnetohydrodynamic flow. By comparison with numerical and experimental results a criterion is found for the transition from the quadratic to the linear scaling. The value of τmm = ML2/(2lcν¯) found from diffusion theory is in good agreement with a more accurate analytic treatment which is valid in the limit of λ/M ≪ lc, where M is the mirror ratio, Lc is the cell length, and ν is the average ion velocity. Good agreement is also obtained with a self‐consistent numerical computation.

Electrical conduction mechanisms in thermally evaporated tungsten trioxide(WO3) thin films

Abstract: Thin films of amorphous tungsten trioxide, a-WO3, have been thermally evaporated onto glass substrate held at 350K. Annealing at 723K caused the formation of polycrystalline tungsten trioxide, c-WO3, with a monoclinic structure. The dark DC electrical conductivity of both a-WO 3 and c-WO3 was studied over a temperature range from 298 to 625K in two environmental conditions (air and vacuum). A simple Arrhenius law, a polaron model and a variable range hopping model have been used to explain the conduction mechanism for a-WO3 films. Using the variable range hopping model, the density of localized states at the Fermi level, N(EF), was found to be 1.08 × 1019eV -1cm-3. The mechanism of electrical conduction in c-WO3 films is explained by means of the Seto model. The Seto model parameters were determined as the energy barrier (Eb ≤ 0.15eV), the energy of trapping states with respect to the Fermi level (Et ≤ 0.9eV) and the impurity concentration (ND ≤ 4.05 × 1015eV-1cm-3). The thickness dependence of resistivity of c-WO3 films has been found to decrease markedly with increasing film thickness, which is explained on the basis of the effective mean free path model. Using this model, the mean free path of electrons in c-WO 3 films was evaluated. The temperature dependence of the thermoelectric power for a-WO3 films reveals that our samples are n-type semiconductors.

First-principles study of thermal transport properties in the two- and three-dimensional forms of Bi2O2Se.

Abstract: Recently, an air-stable layered semiconductor Bi2O2Se has been synthesized [Nat. Nanotechnol., 2017, 12, 530; Nano Lett. 2017, 17, 3021]. It possesses ultrahigh mobility, semiconductor properties, excellent environmental stability and easy accessibility. Here, we report on the thermal transport properties in monolayer (ML), bilayer (BL), and bulk forms of Bi2O2Se using density-functional theory and the Boltzmann transport approach. The results show that the ML exhibits better thermal transport properties than the BL and bulk. The intralayer opposite phonon vibrations greatly suppress the thermal transport and lead to an ultralow lattice thermal conductivity of ∼0.74 W m−1 K−1 in the ML, which has a large band gap of ∼2.12 eV, a low value of average acoustic group velocity of ∼0.76 km s−1, low-lying optical modes of ∼0.54 THz, strong optical-acoustic phonon coupling, and large Gruneisen parameters of ∼5.69. The size effect for all three forms is much less sensitive due to their short intrinsic phonon mean free path (MFP).