Increasing Photon Energy Research Articles

Photocatalytic Assessment of Selective Distribution of Product Arising from Methanol Oxidation on Platinum-deposited TiO2 Mesoporous Layer in a Fixed-film UV Reactor

The photocatalytic assessment of methanol conversion through cross-coupling reaction of methanol with its products was studied in a UV reactor consisting of platinum nanoparticles deposited onto a mesoporous TiO2 film. The temperature-programmed desorption (TPD) analysis showed excess methanol can affect the selective formation of formaldehyde, formic acid, and methyl formate (MF). The TPD results showed the methanol surface coverage, UV photon energy and irradiation time have mutual effects on the oxidation products. At saturated fraction of methanol coverage, formaldehyde was converted to MF and the desorption temperature of MF shifts to lower value. At 266 nm, the photooxidation reaction was more than two orders of magnitude faster than at 355 nm, suggesting that the selectivity of MF increases by the saturated fraction of methanol and increasing photon energy, while the formation of formaldehyde decreases at the same conditions. The formaldehyde conversion to formic acid gradually increases with increasing irradiation time.

Determination of absolute photoionization cross-sections of some aromatic hydrocarbons.

Aromatic hydrocarbons play an important role in the formation and growth of polycyclic aromatic hydrocarbon (PAH) and soot particles. Measurements of their absolute photoionization cross-sections (PICSs), that benefit the quantitative investigation of mass spectrometry, are still lacking, however. PICSs of some aromatic hydrocarbons were measured with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Nitric oxide and benzene were chosen as standard references for PICS calibration, since their photoionization cross-sections are well documented in the literature. Binary liquid mixtures of the investigated molecules and their specific solvents were used in the measurements. The investigated aromatics include naphthalene, phenanthrene, 1-methylnaphthalene, indene, 2-/3-/4-methylphenylacetylene, 2-methylindene, diphenylacetylene, 1-/2-ethynylnaphthalene and acenaphthylene. Photo-induced fragments from the molecules were also observed with increasing photon energy. Based on our measurements and literature data, PICSs of most aromatic molecules have very similar values beyond their ionization energies. However, molecules that contain the phenylacetylene structure have PICSs higher than other aromatics.

Combined experimental and theoretical study on the ultraviolet photodissociation dynamics of 1-bromo-2,6-difluorobenzene in 267 nm-234 nm.

Thanks to their specific molecular symmetry, aromatic molecules and their derivatives represent ideal model systems in understanding photo-induced chemistry of small molecules. Herein, ultraviolet photodissociation dynamics of the 1-bromo-2,6-difluorobenzene molecule has been visualized via imaging the recoiling velocity distributions of photofragments. The measured recoiling angular distributions of the Br(2P3/2) product vary significantly with the increasing photon energy, arguing against the simple bond-fission mechanism within the C2v symmetry. Ab initio calculations reveal that in addition to the C-Br bond cleavage, two additional internal molecular coordinates that break the molecular symmetry are likely involved. The Br out-of-plane bending opens a direct dissociation pathway on the S1-1A″ (S1-1ππ*) state, while the asymmetric C-F stretching significantly changes the orientation of the transition dipole moment. The present study sheds new light on the effect of symmetry breaking in the photodissociation dynamics of symmetric aryl halides, highlighting the multi-dimensional feature of excited state potential energy surfaces.

Improvement of the thermal stability and optical properties for poly (ortho phenylene diamine) using soft templates

A crystalline protonated-poly (ortho phenylenediamine) microrods [POPDA] with ladder-type structure was elaborated at room temperature in an acidic medium. The synthesis method was based on an oxidative polymerization, including sodium dodecyl sulphate [POPDA-SDS] and glycine [POPDA-Gly]. In case of absence or soft template presence, thin films from the considered polymers were fabricated by physical vapor deposition (PVD). Both the resulting polymer flakes and prepared thin films were studied via different techniques such as XRD, FTIR, TGA, SEM, UV–Vis, while optical properties are discussed in detail. The optimization of the samples was performed using Cambridge Serial Total Energy Package (CASTEP) program and density functional theory (DFT) by DMol3. Structural properties of resulting polymers were determined by XRD and FT-IR analysis. XRD results of thin films showed (Monoclinic 2) crystal structure and showed an increase in crystallite size for the polymer, prepared in the presence of SDS surfactants. The surface morphology study revealed the existence of a smooth surface with a significant number of uniform microrods. The optical calculation showed that absorption index k, refractive index n, dielectric constants, and optical conductivity decrease with photon energy increase. The optical properties of simulated FTIR, XRD, and CATSTEP of the considered polymers present a respectable level of experimental study agreement. The polymer thin films present a promising case to be the right candidate for optoelectronics and solar cell applications.

Generalizable density functional theory based photoemission model for the accelerated development of photocathodes and other photoemissive devices

In this work, we have developed an ab initio photoemission model that accurately describes the photoemission process for the most diverse range of photocathode materials to date. Compared to previous photoemission models, this is accomplished by considerably reducing the number of approximations and assumptions used in representing the photoemission process and the photoemitting material itself. Notably, our model directly includes the full electronic structure of the material, photoexcitation probabilities for all direct optical transitions, and an improved surface-vacuum barrier transmission probability. To test the performance of our model, we perform validations with experimental measurements for all photocathode materials studied in this work. Whereas previous models have often qualitatively disagreed with the measured photoemission properties of some materials, our model is found to provide quantitative agreement with experimental measurements for all tested materials. As an example, our method predicts the root-mean-square transverse momentum of electrons emitted from PbTe up to an excess energy of 1.0 eV with a mean absolute error that is \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{} less than from previously derived expressions. Perhaps more importantly, our model is able to match experimentally observed decreases in intrinsic emittance with increasing photon energy---a feat that current analytical models are unable to achieve. We expect that the broad applicability of our model will greatly accelerate the rate of discovery, characterization, and scientific understanding of photocathodes and other photonic devices.

Electronic cross-sections and Compton attenuation and transfer coefficients of 82Pb208, 29Cu64, 27Co59, 20Ca40 and 13Al27 for applications in radiation shielding and dose

Characterizing various materials for radiation shielding and dose calculation is very important. The purpose of the present work is to use Klein-Nishina formula to calculate the electronic cross-sections, atomic cross-section, transfer cross-sections, Compton mass attenuation coefficients and mass-energy transfer cross sections of 82Pb208, 29Cu64, 27Co59, 20Ca40 and 13Al27 when γ-ray photons of various energies interact with these elements. The results reveal that all these cross-sections and coefficients are strongly dependent on the energy of photon and the charge number of the material used. The cross-sections and coefficients decrease with increasing photon energy and increase with increasing charge number to mass number ratio Z/A. It also observed that neutron to proton ratio must support the elements’ stability conditions when calculating these coefficients. The conclusion describes that fundamental quantities and parameters like charge number, energy of interacting photon and Z/A of these elements can be used and controlled to make them very useful for radiation shielding and protection, radiation dose measurements and imaging.

Application of experimental measurements, Monte Carlo simulation and theoretical calculation to estimate the gamma ray shielding capacity of various natural rocks

Experimental measurements and Monte Carlo simulation were applied to simulate the mass attenuation coefficient (MAC) for five various rock samples collected from southwestern Sinai, Egypt. Also, for the same rocks we determined the MAC and exposure buildup factors (EBF and EABF) theoretically using Phy-X/PSD software. The results show that there is adequate agreement between experimental and simulated results as well as with the Phy-X/PSD data. The linear attenuation coefficient (μ) decreases as the photon energy increases. The decrease is dramatically steep for energies bellow 0.3445 MeV and then gradually decreases with further increasing in the energy. Basalt-2 has slightly higher μ than basalt-1 and both rocks have higher μ than limestone (Dike), Basalt sill, and Rhyolite. We also calculated the effective atomic number (Zeff) for the investigated rocks and the Zeff values are in the range of 18.80–23.68, 18.52–23.57, 13.98–20.49, 19.15–23.89 and 22.32–26.68 for baslat-1, basalt-2, dike, basalt-sill and rhyolite respectively. The result showed that basalt-2 possesses the lowest half value layer at all energies followed by basalt-1. The radiation protection efficiency (RPE) at 122 keV is found to be in the range of 34.295–38.982%, while at 662 keV in the range of 17.402–22.886. The obtained results of EBF and EABF showed that limestone (Dike) possess the highest EBF and EABF while samples Basalt-1 and Basalt-2 possess the lowest EBF and EABF among the studied rocks.

Optical Absorption and Tsallis Entropy of Polaron in Monolayer Graphene

We studied the effect of polar vibration modes on optical absorption of polaron and the rate of disorder in a graphene monolayer. Our investigation focused more particularly on the role played by phonons. We found that the amplitude of optical absorption decreases with increasing photon energy and with increasing magnetic field. We also found that the rate of local disorder in the system increases with increasing temperature and with increasing graphene-substrate distance. However, it decreases with the increase in magnetic field. These observations show that the absorption of a polaron by the photon creates a relative disorder in the graphene lattice. It is also shown that entropy and optical absorption of polaron strongly depend on the type of substrates.

Simulation of dose enhancement in radiotherapy caused by cisplatin

This research considers potential dose increase in a target due to cisplatin (Pt) concentration and radiation type. Dose changes were calculated with cisplatin concentrations from 0.003 to 120 mM. Monte-Carlo simulation of Linear accelerator (Elekta Synergy) and X-ray tube (Xstrahl300) was carried out using Geant4 and PClab. At the first stage of this research, we performed a simulation of energy spectrum from radiotherapy units (spectrum model). The next stage was the modeling of a linear accelerator head and an X-ray tube, and the dose distribution in the water phantom (PDD model). At the second stage, dose changes were investigated in the presence of cisplatin in the target (CIS model). The simulation results showed that the dose escalation can be caused by photon-capture therapy (PCT). There is a dose enhancement in the volume where cisplatin is accumulated. However, the photon energy increase from 60 to 250 kV and the increase of the target depth reduces the effect of PCT due to the decrease of the photoelectric effect cross-section. It should be noticed, that the orthovoltage X-rays energy, listed in the table with results, shows higher dose enhancement, than the megavoltage photon beam generated from linear acceleration sources. In addition, the dose enhancement factors (DEF) are higher in a linac without a flattening filter, than in a linac with a flattening filter.

Investigation of Photon Attenuation Properties of CR-39 Lens

The purpose of this study is to investigate photon attenuation parameters of Colombia Resin-39 (CR-39) lens, which are linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), half value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Zeff) and effective electron density (Neff). MACs were determined theoretically and with simulation in the energy range from 0.01 to 105 MeV. Also, obtained MACs of CR-39 lens were compared with MACs of pure aluminum and lead. Theoretically obtained Zeff values were compared with Zeff results obtained by the computer software.The results of this study are; a) the theoretically obtained MACs values are in agreement with MACs obtained results from simulation software, b) the theoretically obtained Zeff values are in agreement with Zeff obtained by the computer software c) the MACs of CR-39 lens are much lower than MACs of pure lead whereas there is not too much differences between MACs of CR-39 and pure aluminium d) the HVLs, TVLs and MFPs rise with increasing photon energy while the LACs and MACs reduce with increasing photon energy.

Gamma-ray shielding properties of phosphate glasses containing Bi2O3, PbO, and BaO in different rates

Glass-based materials are one of the most common shielding materials. Phosphate glasses have unique properties that make them useful for some technical and industrial applications. The mass attenuation coefficients (μm), effective atomic cross sections (σa), effective atomic numbers and electron densities (Zeff and Neff) of phosphate glasses containing different concentrations of Bi2O3, PbO, and BaO (30–70% by weight) have been determined in the energy range of 10 keV–10 MeV. To calculate these parameters, XCOM and XMuDat computer programs and also the Auto-Zeff software and interpolation method have been used. The results of XCOM, XMuDat and Auto-Zeff programs were in good agreement. It was found that the μm and σa parameters decrease as the photon energy increase. Also, the σa and Zeff values improve by increasing the Bi2O3, PbO and BaO contents, while increasing these contents to the same fraction has no significant effect on μm in the energy range of 0.4–4 MeV, where the Compton Effect takes over as dominant process. Furthermore, the Neff is approximately independent of metal oxides concentrations. Wherever possible, the calculated values were compared with the experimental data.

Method of spatial size measurement of relativistic electrons beams with small bunch length

We investigate the practical implementation of a previously proposed method for determining the transverse dimensions of an electron beam on a target by measuring the two-dimensional angular distributions of diffracted transition radiation of relativistic electrons for two distances between the crystal where the radiation is generated and the coordinate detector for femtosecond bunches. We show that determining electron microbunches with small longitudinal sizes requires an increased photon energy, achieved by decreasing the observation angle. The sensitivity limits of the method and the influence of the emission of secondary electrons and photons from the detector pixels are discussed.

Experimental measurement of effective atomic numbers and albedo factors for some alloys using the backscattering technique

Alloys of the type Pb60Sn20ZnxCd(20-x) where x = 0, 5, 10, 15 or 20 were prepared by a conventional melt quench technique. The intensity distribution of backscattered photons from the radioactive isotopes 22Na and 137Cs (with photon energies of 511 keV and 662 keV, respectively) were recorded for different thicknesses of alloy samples and some metallic samples (Al, Zn, Sn and Pb) with use of a GAMMA-RAD5 spectrometer (76 mm × 76 mm NaI(Tl) scintillation detector). Backscattered photon intensities were plotted as a function of both the atomic number and the target thickness. A best fit curve was drawn between backscattered photon counts and the atomic number of the metallic samples, from which the effective atomic numbers (Zeff) of the alloys were obtained at a particular photon energy as well as thickness. The experimentally obtained Zeff values are in good agreement with the theoretical ones (based on mass attenuation coefficients from the WinXCom database). The plot of intensity versus thickness shows that the intensity of backscattered photons increases with sample thickness. The albedo factors (energy albedo, number albedo and dose albedo) were also determined experimentally at these photon energies for the alloys and metallic samples. In the Compton scattering dominant region, the albedo factors decrease with an increase in atomic number as well as with an increase in photon energy.

Study on gamma-ray attenuation characteristics of some amino acids for 133Ba, 137Cs, and 60Co sources

Amino acids are the building blocks of proteins, which are the most abundant macromolecules in living cells. From the standpoint of the photon interaction cross sections of amino acids, the mass attenuation coefficients, half and tenth value layers, mean free path, effective atomic and electronic cross sections, effective atomic number, and effective electron density of fifteen essential amino acids have been determined for 133Ba, 137Cs, and 60Co gamma-ray sources. The MCNP-4C code and the XCOM program have been used to calculate these parameters. The results have been compared to the available experimental and theoretical data. The theoretical results agreed with the experimental data, with RD values of ≤ ± 7%. In the energy region of 81–1332.5 keV, it was found that the µm, σa, and σe values of the amino acids decreased as the photon energy increased, and the increasing density of amino acids had no steady effect on these quantities. Additionally, results demonstrated that the HVL, TVL, and MFP values increased with the increase in photon energy. The µm, σa, and Zeff values of aspartic acid were the highest among those of all amino acids, and they were the lowest for isoleucine. The Zeff value of each sample containing H, C, N, and O atoms was nearly constant in the studied energy region. The Neff values of the studied amino acids varied in the range of 3.14 × 1023–3.44 × 1023 electron/g. Furthermore, the Neff values were approximately independent of the amino acid type in this energy region.

Study of Structural and Optical Properties of Non-Oxide Se90Cd10–xSbx(2 ≤ x ≤ 8) Chalcogenide Thin Films

Thin films of Se90Cd10–xSbx (2 ≤ x ≤ 8) of thickness 0.4 microns were prepared on ultra-clean glass substrate by thermal evaporation technique. The vacuum level was 10–6 torr. This paper intends to investigate the impact of Sb concentration on the optical characterization. XRD measurement has been done to investigate the Structural characterization of the prepared thin films. XRD result indicates the prepared thin have amorphous nature. To analyze the optical characterization of the thin films the absorption spectra were recorded over 400–1100 nm wavelength range. In the present study the optical absorption follows direct allowed transition. An increase in photon energy causes an increase in absorption coefficient while extinction coefficient has been found to increase with an increase in frequency of the photons i.e., deceases with increase of wavelength. Optical bandgap (Eg) of thin films have been studied and an increase in it has been recorded with increasing Sb concentration.

Structural and optical characterization of aluminum zinc co-doped tin oxide grown by sol-gel spin coating techniques

Aluminum Zinc co-doped Tin Oxide (AZSO) thin film was grown by sol-gel spin coating techniques onto a glass substrate using various doping concentrations (0, 2, 4, 6, and 8 wt%) and the effect of doping on each sample were studied using structural analysis; X-ray Diffraction (XRD) pattern, gravimetric method; thin film thickness and UV photo-spectrometer; optical properties. The results of the XRD were revealed that all the peaks have a tetragonal phase of SnO2, which were oriented at the 110, 101, and 211 planes. The film thickness was observed to vary with doping concentration. In the visible region, all the film samples were exhibited at average transmittance. The coefficient of absorption was gradually increased with an increase in photon energy at a certain level with a decrease in the absorption coefficient as the photon energy increases further. At 550-800 nm range of wavelength, a high extinction coefficient (k) was recorded and the refractive index curves show regular dispersion behavior. The optical conductivity of the films followed a similar pattern, which showed that conductivity increased to a peak at 3.60 eV. The energy bandgap of the film samples (AZSO1 - AZSO5) is 4.095 eV, 4.103 eV, 4.087 eV, 4.114 eV, and 4.106 eV, respectively. The studies show that the properties of Al-Zn co-doped SnO2 films can be explored for optoelectronic applications.

Hot electron transfer in Zn-Ag-In-Te nanocrystal-methyl viologen complexes enhanced with higher-energy photon excitation.

The dynamics of hot electron transfer from Zn–Ag–In–Te (ZAITe) nanocrystals (NCs) to adsorbed methyl viologen (MV2+) were investigated by transient absorption spectroscopy. The bleaching of the exciton peak in the ZAITe NC–MV2+ complexes evolved faster than that of ZAITe NCs. The hot electron transfer efficiency increased from 45% to 72% with increasing excitation photon energy.

Electronic and Optical Properties of Indium Selenide Nanosheet Using First-Principle Calculations

Density functional theory (DFT) have been used to examine the electronic and optical, properties of two-dimensional (2D) indium selenide (InSe) nanosheet. Our calculations indicate that the energy band gap of InSe is indirect and equal to 1.53 eV. It can be seen that for the pristine case, the majority and minority density of state (DOS) are fully symmetric. The optical properties are considered up to 36 eV. Our results established that the absorption starts in the visible region, while the peaks in the ultraviolet region. The refractive index value is 1.84 at zero photon energy limit and increase to 2.31. The high refractive index allows this nanosheet to be utilized as an internal layer coating between the substrate and the ultraviolet absorbing layer. Additionally, we observed that the gained optical properties of InSe nanosheet are in the ultraviolet range and the results are significant. It is expected that from these calculations to provide useful information for further experimental investigations of InSe nanosheet.

Erbium oxide and Cerium oxide-doped borosilicate glasses as radiation shielding material

ABSTRACTIn this paper, the radiation shielding parameters such as linear attenuation coefficients (LAC, µ), mass attenuation coefficients (MAC, µ/ρ), effective atomic numbers (Zeff), effective electron densities (Neff), half value of layers (HVL) and mean free paths (MFP) were investigated for rare earth metal oxides (CeO2 and Er2O3) doped borosilicate (BS) glasses. The glass samples were manufactured by the mechanical alloying process CeO2, Er2O3, and BS powders. The radiation shielding parameters of the BS glass samples were determined at photon energies in the energy region of 22.16–59.54 keV using a high purity germanium detector. The theoretical results for MAC were obtained from WinXCom program. It was observed that theoretical and experimental results are compatible with each other. The radiation absorption increased with increasing the concentration of CeO2 and Er2O3 in the BS samples due to high density increasing with the concentration of CeO2 and Er2O3, which are high atomic mass. Furthermore, LAC, MAC, Zeff, and Neff values for CeO2 and Er2O3 doped BS glass decreased with increasing photon energy. While the MAC value at 59.54 keV energy level for pure BS sample was 0.242 cm2/g, it increased to 0.624 cm2/g with CeO2 addition and 0.838 cm2/g with the addition of Er2O3. The and values of glass samples with Er2O3 were bigger than CeO2 doped glass samples owing to high atomic number. Consequently, it was determined that BS-Er2O3 glasses had better the radiation shielding capacity than BS-CeO2 glasses.

Optical response of Te-based monolayer materials from first principles

Using density functional theory combined with nonequilibrium Green's function, the photocurrent induced by the photogalvanic effect of two phases of Te-based monolayer materials is calculated along both their zigzag and armchair directions under the irradiation of the linearly polarized light. Results show that the photocurrent has a sinusoidal shape with regard to the polarization angle of the light at all simulated bias voltages for different photon energies. A photocurrent peak for α-Te and β-Te is at the photon energy of around 1.4 and 1.8 eV, respectively. Furthermore, for α-Te the phase of the photocurrent vs the polarization angle curve reserves when the photon energy increases, while for β-Te the phase remains unchanged in our simulated photon energy range. The different optical responses of the two phases of Te-based monolayer materials along different directions make them have potential applications in various aspects of optoelectronics.