Photon Energy Region Research Articles

Thick target total bremsstrahlung spectra of lead compounds in the photon energy region 1–10 keV by 90Sr beta particles

Total bremsstrahlung spectral photon distribution generated in thick targets of lead compounds Pb(CH3COO)2·3H2O, Pb(NO3)2 and PbCl2 by 90Sr beta particles has been investigated theoretically and experimentally in the photon energy region 1–10keV. The experimental results are compared with the theoretical models describing ordinary bremsstrahlung and the theoretical model which includes polarization bremsstrahlung into ordinary bremsstrahlung, in stripped approximation. It is observed that the experimental results show better agreement with the model which describes bremsstrahlung in stripped approximation in the energy range 3–10keV. However, the results show positive deviation in the photon energy region of 1–3keV. Further, it has been found that there is a continuous decrease of polarization bremsstrahlung contribution into ordinary bremsstrahlung in the formation of total bremsstrahlung spectra with increase in photon energy. The suppression of polarization bremsstrahlung has been observed due to the presence of large fraction of low Z elements in the compounds. The results clearly indicate that polarization bremsstrahlung plays an important role in the formation of total bremsstrahlung spectra in compounds in the studied energy region.

Modern status of photonuclear data

The reliability of experimental cross sections obtained for (γ, 1n), (γ, 2n), and (γ, 3n) partial photoneutron reactions using beams of quasimonoenergetic annihilation photons and bremsstrahlung is analyzed by employing data for a large number of medium-heavy and heavy nuclei, including those of 63,65Cu, 80Se, 90,91,94Zr, 115In, 112−124Sn, 133Cs, 138Ba, 159Tb, 181Ta, 186−192Os, 197Au, 208Pb, and 209Bi. The ratios of the cross sections of definite partial reactions to the cross section of the neutron-yield reaction, F i = σ(γ, in)/σ(γ, xn), are used as criteria of experimental-data reliability. By definition, positive values of these ratios should not exceed the upper limits of 1.00, 0.50, 0.33,... for i = 1, 2, 3,..., respectively. For many nuclei, unreliable values of the above ratios were found to correlate clearly in various photon-energy regions F i with physically forbidden negative values of cross sections of partial reactions. On this basis, one can conclude that correspondent experimental data are unreliable. Significant systematic uncertainties of the methods used to determine photoneutron multiplicity are shown to be the main reason for this. New partial-reaction cross sections that satisfy the above data-reliability criteria were evaluated within an experimental–theoretical method [σ eval(γ, in) = F i theor (γ, in) × σ expt(γ, xn)] by employing the ratios F i theor (γ, in) calculated on the basis of a combined photonuclear-reaction model. It was obtained that cross sections evaluated in this way deviate substantially from the results of many experiments performed via neutron-multiplicity sorting, but, at the same time, agree with the results of alternative activation experiments. Prospects of employing methods that would provide, without recourse to photoneutron-multiplicity sorting, reliable data on cross sections of partial photoneutron reactions are discussed.

Optical And Thermoelectric Properties Of Nanocrystalline Bi2(Se1-xTex)3 Films

ABSTRACTGranular nanocrystalline Bi2(Se1-xTex)3 films were prepared from highly crystalline bulk alloys used as source materials by means of thermal evaporation under vacuum (2 × 10−6 mbar). The nanofilms were deposited onto highly cleaned glass substrates of BK7 type. The structural characteristics, including surface morphology, roughness, and crystallite size, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis. Perfect crystallinity and nanoscalability of the prepared samples were asserted. Transmittance and reflectance spectra of the prepared nanofilms were investigated over the wavelength range of 400–2,700 nm. In the visible light region, all of the films showed an opaque behavior; however, as the wavelength increased into the infrared region, a growing transparency was observed. Based on the measured transmission and reflection spectra, the coefficients of absorbance and extinction as well as the optical band gap were determined. The refractive index was deduced from the reflectance measurements using the determined extinction coefficient. Direct allowed band transitions were confirmed in all films with a band gap energy of 0.85–1.05 eV, depending on the Te content. The possibility of an indirect band gap in the lower photon energy region was discussed. The Seebeck coefficient and electrical conductivity were measured in the temperature range of 300–500 K. Very large values of the power factor of 80 and 131 were obtained for Be2Se3 films at room temperature and 473 K, respectively; the latter is three times larger than best previously reported values for similar film systems.

Studies of total bremsstrahlung spectra in the oxides of lanthanides

Total bremsstrahlung spectral photon distribution generated in thick targets of oxides of lanthanides (Pr6O11, Gd2O3, Tb4O7 and Er2O3) by 89Sr beta particles has been investigated in the photon energy region 1–100keV. The experimental results are compared with the theory describing ordinary bremsstrahlung and the theory which includes polarization bremsstrahlung into ordinary bremsstrahlung in stripped approximation. It has been found that contribution of polarization bremsstrahlung into total bremsstrahlung in a target is limited to a low energy region only and also varies with the effective atomic number (Zeff) of target material. Further, it has been found that the suppression of polarization bremsstrahlung has been observed due to the presence of large fraction of low Z element oxygen in the compounds.

Synthesis of Polymer Nanocomposites Based on [Methyl Cellulose](1-x):(CuS)x (0.02 M ≤ x ≤ 0.08 M) with Desired Optical Band Gaps.

In this paper, the sample preparation of polymer nanocomposites based on methyl cellulose (MC) with small optical bandgaps has been discussed. Copper monosulfide (CuS) nanoparticles have been synthesized from the sodium sulphide (Na2S) and copper chloride (CuCl2) salts. Distinguishable localized surface resonance plasmon (LSRP) absorption peaks for CuS nanoparticles within the 680–1090 nm scanned wavelength range were observed for the samples. An absorption edge (Ed) was found to be widely shifted to a lower photon energy region. A linear relationship between the refractive index of the samples and the CuS fraction was utilized to describe the distribution of the particle. The optical bandgap of MC was reduced from 6.2 to 2.3 eV upon the incorporation of 0.08 M of CuS nanoparticles. The optical dielectric loss, as an alternative method, was used successfully to estimate the optical bandgap. Moreover, the electronic transition type was identified by using Tauc’s extrapolation method. The plots of the optical dielectric constant and energy bandgap as a function of the CuS concentration were utilized to examine the validity of the Penn model. For the nanocomposite samples, the Urbach energy was found to be increased, which can be evidence for a large possible number of bands-to-tail and tail-to-tail transitions. However, from the X-ray diffraction (XRD) analysis, it was also found that the synthesized CuS nanoparticles disrupted the crystallinity phase of the MC polymer. Finally, fourier transform infrared (FTIR) spectroscopy for the samples was also performed. Significant decreases of transmittance intensity as well as band shifting in the FTIR spectra were observed for the doped samples.

Spectroscopic planar diffraction ellipsometry of Si‐based multilayer structure with subwavelength grating

Spectroscopic ellipsometry has been applied at room temperature to a multilayer device structure with plain and nanograting‐embedded Si layer on the top. In both cases, the real and imaginary parts of the complex dielectric function of the top layer have been retrieved. In nanograting case, ellipsometric data were collected in planar diffraction geometry. A profound change in dielectric function in the photon energy region between 1.5 and 3.5 eV is established for nanograting‐embedded Si layer compared to plain Si layer. Both real and imaginary parts of the former are no longer Si‐like and resemble more those for metals. The maximum of interband density‐of‐states for optical transitions is positioned at 2.1 eV and coincides with the energy of optical transitions from the main irradiative eigenstate. The obtained results are discussed in terms of geometry‐induced doping changes in interband density of states.

Merging of X-Ray photons in the field of a light atomic ion

The process of merging of three X-ray photons into one photon in the field of a light atomic ion is theoretically studied. A pronounced resonance structure and a strong angular anisotropy of the differential cross section for merging are predicted in the region of the incident photon energy ħω ≅ I 1s /2 (I 1s is the threshold energy of ionization of the -shell of the ion). The magnitude of the observed merging cross section is estimated.

Total bremsstrahlung spectra of thick lead compounds produced by 90Sr beta emitter in photon energy region of 10–100 keV

The total bremsstrahlung spectra in the thick targets of lead acetate trihydrate (Pb(CH3COO)2·3H2O), lead nitrate Pb(NO3)2 and lead chloride (PbCl2) produced by 90Sr beta particles have been investigated in the photon energy region of 10–100keV. The experimental bremsstrahlung spectra have been compared with the theoretical models Elwert corrected (non relativistic) Bethe Heitler theory, modified Elwert factor (relativistic) Bethe Heitler theory for ordinary bremsstrahlung and modified Elwert factor (relativistic) Bethe Heitler theory which includes polarization bremsstrahlung in the stripped atom approximation. The experimental results show better agreement with theoretical model that includes polarization bremsstrahlung in stripped approximation in the photon energy region below 30keV. However, at higher photon energy region 30–100keV, the theoretical model which describes ordinary bremsstrahlung is more accurate to describe the experimental bremsstrahlung spectra. The experimental results show positive deviations from the entire theoretical models at higher energy end of the spectrum. The results indicate that polarization bremsstrahlung plays important role in the formation of total bremsstrahlung spectra in lead compounds produced by continuous beta particles at low photon energy region of 10–30keV.

FinEstBeaMS – A wide-range Finnish-Estonian Beamline for Materials Science at the 1.5 GeV storage ring at the MAX IV Laboratory

The FinEstBeaMS beamline is under construction at the 1.5GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3eV) to soft X-rays (1000eV) but experiments will also be possible at the Mg and Al Kα energies. Instead of having two different insertion devices and optical schemes for low and high photon energy regions, we have based our design on a single long-period, elliptically polarizing undulator and a plane grating monochromator. This solution will provide very good conditions for planned experiments in the whole photon energy region. The beamline will have two branches: one will mainly be used to investigate free atoms, molecules and clusters with photoelectron/photoion coincidence spectroscopy as well as solids with photoluminescence spectroscopy whereas the other one will be dedicated to ultra-high vacuum studies of surfaces and interfaces, utilizing X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. This paper focuses on the optical design of the beamline and general design concepts of the gas phase and solid state end stations.

Investigation of radiological properties of some shielding materials on charged and uncharged radiation interaction for neutron generator

ABSTRACTRadiation interaction parameters such as total stopping power, projected range (longitudinal and lateral) straggling, mass attenuation coefficient, effective atomic number (Zeff) and electron density (Neff) of some shielding materials were investigated for photon and heavy charged particle interactions. The ranges, stragglings and mass attenuation coefficients were calculated for the high-density polyethylene(HDPE), borated polyethylene (BPE), brick (common silica), concrete (regular), wood, water, stainless steel (304), aluminum (alloy 6061-O), lead and bismuth using SRIM Monte Carlo software and WinXCom program. In addition, effective atomic numbers (Zeff) and electron densities (Neff) of HDPE, BPE, brick (common silica), concrete (regular), wood, water, stainless steel (304) and aluminum (alloy 6061-O) were calculated in the energy region 10 keV–100 MeV using mass stopping powers and mass attenuation coefficients. Two different methods namely direct and interpolation procedures were used to calculate Zeff for comparison and significant differences were determined between the methods. Variations of the ranges, longitudinal and lateral stragglings of water, concrete and stainless steel (304) were compared with each other in the continuous kinetic energy region and discussed with respect to their Zeffs. Moreover, energy absorption buildup factors (EABF) and exposure buildup factors (EBF) of the materials were determined for gamma rays as well and were compared with each other for different photon energies and different mfps in the photon energy region 0.015–15 MeV.

Study of the Few Nucleon Systems at CLAS

The study of few nucleon systems with electromagnetic probes is an essential component of the scientific program carried out at the Thomas Jefferson National Accelerator Facility (JLab). Here we present measurements of exclusive reactions on light nuclei using real photon beams with energies up to 3 GeV and the CEBAF Large Acceptance Spectrometer (CLAS), a nearly 4pi magnetic spectrometer, in order to study the properties of strongly interacting matter and the transition from hadronic (i.e in terms of nucleons and mesons) to partonic (in terms of quark and gluons) degrees of freedom in nuclear interactions. We discuss the progress made in understanding the relevant degrees of freedom using polarisation observables and cross sections of deuteron and ^3He photodisintegration in the few-GeV photon-energy region. In addition, recent high-statistics experiments with the CLAS detector have provided us with sufficient counting rates to study the effects of initial- and final-state interactions in reactions off the deuteron. Such data allow us to extract a large set of polarisation observables for final-state interactions in hyperon photoproduction and to study the properties of the hyperon–nucleon interaction. Initial-state effects are studied by mapping the dependence of experimental observables on the spectator-nucleon momentum. We also present recent results for polarisation observables for quasi-free K^+varLambda off the bound proton in a deuteron as well as for final-state interactions in the reaction gamma drightarrow K^+varLambda n, and will discuss their impact on hyperon–nucleon studies.

Doubly-polarised pion photoproduction on the nucleon at MAMI

The A2 Collaboration at MAMI (Mainz) carried out new measurements of the helicity dependence of the total inclusive photo-absorption cross section and of the partial cross sections for several reaction channels on the proton and on the neutron in the photon energy region 200 He targets. Hadronic reaction products were detected by the large acceptance Crystal Ball-TAPS spectrometer, complemented by plastic scintillators and vertex detectors for charged particle tracking and identification.These new, high-quality doubly-polarised pion-photoproduction data sets provide a valuable input to the study of the nucleon structure and excitation spectrum by significantly constraining the electromagnetic multipole evaluation performed by the different available partial wave analysis models. Furthermore, the helicity dependent observables provide the main ingredient for the verification of the well-known Gerasimov-Drell-Hearn (GDH) sum rule, which relates the helicity-dependent photoasborption process to the main static nucleon properties (mass, charge, spin).

Effect of incident electron energy of beta emitter on the formation of bremsstrahlung spectra in the photon energy region of 1–5 keV

The effect of incident electron energy of beta emitter 204Tl (end-point energy=765keV) and 90Sr (end-point energy=546keV), on the formation of total bremsstrahlung spectra in thick targets, was investigated in the photon energy region of 1–5keV. Theoretical bremsstrahlung spectra were obtained from theory that describes ordinary bremsstrahlung (OB) and the theoretical model, which includes the contribution of polarization bremsstrahlung (PB) in OB in stripping approximation. The theoretical and experimental bremsstrahlung spectra were modified by applying corrections due to the range of beta particles, self-absorption of photons in target, absorption of photons in detector compounds, and backscattering of beta particle. It was observed that the experimental results were 10–15% higher than that of the theoretical model, which includes the contribution of PB in OB in stripping approximation, particularly for medium and high Z elements. The contribution of PB in OB was suppressed with the increase in the end-point energy of the beta emitters. The results reported here clearly indicate the inadequacy of stripping approximation and the need to include the term of interference of OB and PB while describing the total bremsstrahlung spectra.

Performance of the undulator based ultraviolet and soft x-ray beamline for catalysis and surface science at National Synchrotron Radiation Laboratory

The undulator based ultraviolet and soft x-ray beamline BL11U for catalysis and surface science at National Synchrotron Radiation Laboratory (NSRL) has been under opteration for months and the present performance is described. This beamline utilizes radiation from an in-vacuum undulator, which has 30 magnetic periods with the period length of 40mm. A varied-line-spacing plane grating monochromator is employed tto cover the photon energy region of 20–600eV by two gratings with nominal groove densities of 400llmm and 1200l/mm respectively. The energy resolution power E/ΔE is measured with a gas ionization chamber and the photon flux is measured by a photodiode. Results show that the resolution power is better than 10,000 at a photon energy of 29.2eV. And the flux is higher than 1×1010phs/s under 300mA ring beam current for most of the covered photon energy.

Structural, morphological and optical characterizations of ZnO:Al thin films grown on silicon substrates by pulsed laser deposition

The pulsed laser deposition (PLD) technique is used to grow Al-doped ZnO (AZO) thin films at 500 ° C on silicon substrates under vacuum or oxygen gas background from ablating AZO nanoparticle targets synthesized via the sol-gel process. The structural, morphological and optical properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. XRD and TEM images show that AZO powder has a wurtzite-type structure and is composed of small prismatic-like shape nanoparticles with an average size of 30nm. The structural properties of the AZO films grown under oxygen show no significant changes compared to those of the film grown under vacuum. However, the optical properties show a dependence on the growth conditions of the AZO films. Highly c -axis-oriented AZO thin films were obtained with grain size ∼ 15 nm. The stress in the AZO films is tensile as measured from the c -parameter. The dielectric function, the refractive index and the extinction coefficient as a function of the photon energy for the AZO films were determined by using spectroscopic ellipsometry measurements in the photon energy region from 1 to 6eV. The band gap energy was observed to slightly decrease in the presence of the O2 gas background and this may be attributed to the stress. The surface and volume energy loss functions are calculated and exhibit different behaviors in the energy range 1-6eV. Refractive indices of 1.9-2.1 in the visible region were obtained for the AZO films. Also, the electronic carrier concentration appears to be related to the presence of O2 during the growth process.

A data-based photonuclear simulation algorithm for determining specific activity of medical radioisotopes

For simulating more accurately neutron or proton production from photonuclear reactions, a data-based photonuclear reaction simulation algorithm has been developed. Reliable photonuclear cross sections from evaluated or experimental database are chosen as input data. For checking the validity of the use of the data-based photonuclear algorithm, benchmarking simulations are presented in detail. We calculate photonuclear cross sections or reaction yield for 9Be, 48Ti, 133Cs, and 197Au and compare them with experimental data in the region of incident photon energy below ~30 MeV. While Geant4 can hardly reproduce photonuclear experimental data, results obtained from the data-based photonuclear algorithm are found in good agreement with experimental measurements. Potential application in estimation of specific activity of radioisotopes is further discussed. We conclude that the developed data-based photonuclear algorithm is suitable for an accurate prediction of photon-induced neutron or proton productions.

Polarization operator of a photon in a magnetic field

In the first order of the fine structer constant, the polarization operator of a photon is investigated in a constant and homogeneous magnetic field at arbitrary photon energies. For weak and strong fields H, compared with the Schwinger critical field, approximate expressions have been found. We consider the pure quantum region of photon energy near the threshold of pair creation, as well as the region of high energy levels where the quasiclassical approximation is valid. The general formula has been obtained for the effective mass of photon with given polarization. It is useful for an analysis of the problem under consideration on the whole and at a numerical work

Investigation of Coulombic bremsstrahlung spectra of metallic targets for the photon energy region of 1–100 keV

In the present paper, the formation of bremsstrahlung spectra by ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB) in metallic targets by 35S beta particles has been investigated in the photon energy region of 1–100keV. From the experimental measurements and the theoretical results obtained from Elwert corrected (non-relativistic) Bethe Heitler (EBH) theory, modified Elwert factor (relativistic) (FmodBH) theories for OB and Avdonina and Pratt (FmodBH+PB) theory for total bremsstrahlung (BS) having the contribution of PB into OB, it has been found that the contribution of PB into BS in a target is limited to a low energy region only and also varies with the atomic number of target material. The FmodBH+PB theory is in agreement with the experimental results in low energy regions of the target, whereas at high energy region FmodBH is found to give better agreement. Further, the present experimental results indicate that the screening effects in the Coulombic bremsstrahlung process cannot be neglected in the high energy region, and the multiple scattering and secondary electron emissions effects in thick target are required to be taken into account in describing the bremsstrahlung process.

Near-infrared photoluminescence and thermally stimulated current in Cu3Ga5Se9 layered crystals: A comparative study

Near-infrared photoluminescence (PL) and thermally stimulated current (TSC) spectra of Cu3Ga5Se9 layered crystals grown by Bridgman method have been studied in the photon energy region of 1.35–1.46eV and the temperature range of 15–115K (PL) and 10–170K (TSC). An infrared PL band centered at 1.42eV was revealed at T=15K. Radiative transitions from shallow donor level placed at 20meV to moderately deep acceptor level at 310meV were suggested to be the reason of the observed PL band. TSC curve of Cu3Ga5Se9 crystal exhibited one broad peak at nearly 88K. The thermal activation energy of traps was found to be 22meV. An energy level diagram demonstrating the transitions in the crystal band gap was plotted taking account of results of PL and TSC experiments conducted below room temperature.

Combined low-temperature photoluminescence and thermally stimulated current studies in Cu3In5S9 layered single crystals

Photoluminescence (PL) and thermally stimulated current (TSC) spectra of Cu3In5S9 layered crystals grown by Bridgman method have been studied in the photon energy region of 1.20–1.65eV and the temperature range of 15–70K (PL) and in the temperature region of 10–130K (TSC). A broad PL band centered at 1.484eV was observed at T=15K. Radiative transitions from shallow donor level located at 16meV to moderately deep acceptor level located at 120meV were suggested to be responsible for the observed PL band. TSC curve of Cu3In5S9 crystal exhibited one broad peak at about 60K. The activation energy of trap level was found to be 17meV. An energy level diagram showing transitions in the band gap of the crystal was plotted taking into account the results of PL and TSC measurements carried out below room temperature. Moreover, the absorption edge of Cu3In5S9 crystals have been studied through transmission and reflection measurements in the photon energy range 1.13–1.85eV. The band gap energy was determined as 1.61eV.