Energy Of Incident Radiation Research Articles

Thermoluminescence and kinetic parameters of synthesised BaAl2O4(Dy) phosphor irradiated with gamma and mega-voltage radiation

Dy doped BaAl2O4 powder sample was successfully synthesised by urea assisted combustion synthesis route. Post preparation calcination was done at 700°C for 1h. The formation of compound was confirmed by powder X-ray diffraction (PXRD).The estimated particle size was found to be ∼30.51nm by using Debye Scherer's formula. The high-resolution scanning electron microscope (SEM) micrograph shows the presence of several micro and nano-particles within the grain. Thermal behaviour of prepared powder sample was studied using thermogravimetric analysis (TGA). It has been confirmed that the prepared phosphor was thermally stable up to 800°C. Thermoluminescence (TL) analysis of prepared sample was carried out after the irradiation with Co-60 gamma rays, 6-mega voltage (MV) and 16MV photon beams. Glow curves of the prepared BaAl2O4 (Dy:1%) sample were similar in shape irrespective of incident energy and radiation type. The low and high intensity peak in each curve was appeared at around 108°C and 305°C, respectively. No appreciable shift in peak positions has been observed. The trapping parameters, namely activation energy (E), order of kinetics (b) and frequency factor (s) have been determined using glow curve shape (Chen's) method. The activation energy as well as frequency factor increases with increase in the energy of incident radiation. Energy dependence has been observed in the present phosphor due to Compton's scattering, dominates at this energy range. It has been observed that peak of each glow curves of the sample irradiated with gamma and mega-voltage photons, lies within ±5°C. This phosphor can be utilised for display technology as well as radiation dosimetry, especially where the need for tissue equivalent material is not a constraint. Low cost, less time consuming and high yield are some important key factors of this method over other synthesis techniques.

Effects of ultraviolet radiation on mercury isotope fractionation during photo-reduction for inorganic and organic mercury species

Photo-reduction of mercury (Hg) is an important mechanism for removal of both Hg2+ species and monomethylmercury (MMHg) from surface waters. Large mass independent fractionation (MIF) signatures of Hg isotopes preserved in natural samples are thought to reflect MIF produced during aqueous photo-reduction by the magnetic isotope effect (MIE). Recently, Hg MIF signatures in natural samples are being used to quantify photochemical reduction in aquatic systems. However, the fractionation factors used are from laboratory experiments that did not investigate many of the environmental parameters that may affect MIF during photo-reduction. In this study, the effects of different regions of the solar spectrum on the expression of MIF caused by the MIE during Hg2+ and MMHg photo-reduction were investigated to assess how the type of radiation affects the extent and signature of MIF. Photo-reduction in the presence of DOM was carried out through exposure to the full natural solar spectrum unfiltered, with the ultraviolet B (UVB; 290–320nm) portion removed and with both the UVB and the ultraviolet A (UVA; 320–400nm) removed. There is a clear relationship between the expression and magnitude of MIF and the energy of incident radiation for both Hg2+ and MMHg photo-reduction. The experiments indicate that MIF produced during photo-reduction of Hg2+ is significantly influenced by both UVB and UVA radiation. For MMHg photodemethylation, however, UVB radiation is mostly responsible for the MIF with minor contributions from UVA. Overall, there is a lack of correlation between the observed MIF and total photo-reduction in the experiments conducted in this study, which indicates that indirect and other non-MIF producing pathways of photo-reduction are the dominant pathways by which Hg species are being photo-reduced. Extrapolating these experimental results to natural systems is difficult as the experiments were not performed at realistic Hg/DOM ratios and the distribution of ligands that Hg is bound to in the experiments likely differs from natural systems. However, the strong relationship between MIF and energy of incident radiation in this study supports Hg MIF signatures as promising tools for helping to quantify photochemical cycling of mercury, but this study also highlights the need to understand the link between MIF and total photo-reduction before this tool can be fully utilized.

Environmental control of canopy stomatal conductance in a tropical deciduous forest in northern Thailand

Tropical seasonal forests in Southeast Asia are among the most important biomes in terms of global and local hydrologic and carbon fluxes, and their vulnerability to climate change. We conducted eddy flux measurements in a teak (Tectona grandis Linn. f.) plantation in northern Thailand over a 6-year period; this forest undergoes a drastic seasonal change in foliage with somewhat constant incident radiative energy. We used a combination of actual evapotranspiration (ET) flux data and an inversed version of a simple two-layer ET model for estimating the mean canopy stomatal conductance (gs). The main novelty of this analysis is that canopy conductance can be extracted from total surface conductance (including the canopy and forest floor effects), and thus environmental and biological controls of gs are explicitly compared among seasons and years. The relationship between seasonal variations in the leaf area index (LAI) and gs revealed an apparent effect of leaf age on leaf gas exchange capacity: within a year, gs peaked earlier than full-leaf expansion and abruptly declined after the peak of LAI. We used this result to classify three leaf age stages: leaf-out, mid-growing, and leaf-senescence seasons. Then, two ecophysiological parameters, the reference value of gs (gsref), and the sensitivity of gs to atmospheric demand (m), as well as their proportion (m/gsref), were derived from the logarithmic response curve of gs to vapor pressure deficit (VPD) for each season. We showed seasonal variation in gsref as follows: leaf-out season≈mid-growing season>leaf-senescence season. m demonstrated little seasonality and little interannual variation was observed in either parameter. This resulted in a value of almost 0.6 for m/gsref during the leaf-senescence season and of less than 0.6 in the leaf-out and mid-growing seasons, which suggests that the teak trees had strict stomatal regulation to prevent excessive xylem cavitation during the leaf-senescence season (i.e., under drought conditions) and less strict stomatal regulation during the leaf-out and mid-growing seasons (i.e., under moist conditions) when little risk of water stress-induced hydraulic failure would occur. In addition, we obtained a simple linear relationship between soil moisture and gsref, which can be a powerful tool for further research of land–atmosphere interactions using global climate and vegetation dynamics models.

GaN Radiation Detection Research Based on Monte Carlo Method

Gallium nitride (GaN) is the third generation of semiconductor material; it has a large band gap, high thermal conductivity, low dielectric constant, high drift speed, etc. Radiation detectors based on GaN material have small volume, high radiation resistance, and fast response, can be used to replace the existing Large Hadron Collider vertex detector and track detector. Energy deposition characteristic of GaN detectors to radiation beam is an important factor for detection efficiency, and there are many factors that affect the energy deposition characteristics of the detector, like the detection mechanism, the impact of material properties, the type of incident ray, radiation energy, and many other factors. This paper studies the physical properties of GaN detector by calculation based on Monte Carlo simulation. Energy deposition characteristics are discussed respectively for incident γ-ray with different energy, in the front-end and back-end add PTFE material. The results of our study present the theoretical properties of GaN radiation detectors.

Investigating the aerosol optical and radiative characteristics of heavy haze episodes in Beijing during January of 2013

AbstractSeveral heavy atmospheric haze pollution episodes occurred over eastern and northern China during January of 2013. The pollution covered more than 100 km2 and caused serious impacts on environmental quality, human health, and transportation. In this study, we characterize aerosol microphysical, optical, and radiative characteristics using a combination of ground‐based Sun/sky radiometer retrievals and a radiative transfer model. Our results show that during about half of the total number of days, daily PM2.5 and PM10 concentrations are larger than 100 µg/m3, with maxima of 462 and 433 µg/m3, respectively, during the haze events. Fine‐mode (PM2.5) particles dominated the aerosol size during the episodes. The volume size distribution and median radius of fine‐mode particles generally increase as aerosol optical depth at 440 nm (AOD440) increases. The median effective radius of fine‐mode particles increases from 0.15 µm at low AOD value (AOD440 ~ 0.3) to a radius of 0.25–0.30 µm at high AOD value (AOD440 ≥ 1.0). The daily mean single‐scattering albedo (SSA), imaginary part of refractive index (RI), and asymmetry factor display pronounced spectral behaviors. The overall mean SSA440 and SSA675 are 0.892 and 0.905, respectively. The corresponding RI440 and RI675 are 0.016 and 0.011, respectively. This indicates that a significant amount of absorption occurred under the haze event in Beijing during January 2013. Approximately half of the incident solar radiation energy went into heating the atmosphere as a result of strong aerosol loading and absorption. The daily averaged heating rate in the haze particle layer (0–3.2 km) varies from 0.12 to 0.81 K/day in Beijing, which might exert profound impact on the atmospheric thermodynamic and dynamical structures and cloud development, which should be further studied.

Thermoluminescence properties of Mn-doped CaYAl3O7 phosphor irradiated with ultra-violet, mega-voltage and gamma radiation

Low temperature combustion synthesis was employed for the preparation of CaYAl3O7(Mn2+) phosphor. X-Ray diffraction (XRD) patterns were recorded to confirm the phase formation. Estimated particle size was found to be ~19.9nm by using the Debye Scherrer׳s formula. FTIR study confirms the formation of CaYAl3O7 compound, escape of nitrates and other organic products. Thermoluminescence (TL) glow curves of the prepared phosphor were recorded after exposing the sample with Ultra-violet (UV), 6-Mega-voltage (MV), 16-MV and Co-60(Cobalt-60, 1.25-MeV average gamma energy) radiation. Trapping parameters namely activation energy (E), order of kinetics (b) and frequency factor(s) of main peak, centered around 186°C in the sample irradiated with UV source for 20min, were determined using glow curve shape (Chen׳s) method. It has been observed that the TL peak intensity increases with increasing the exposure from UV source. Also with increases the energy of incident radiation a decrease in TL peak intensity were observed. This could be due to higher penetration power and less absorbance of incident beam in the phosphor material. Analysis suggests that possibility of utilizing this phosphor in futuristic low and high energy dosimetric applications as well as in solid state lighting devices.

Borman effect in resonant diffraction of X-rays

A dynamic theory of resonant diffraction (occurring when the energy of incident radiation is close to the energy of the absorption edge of an element in the composition of a given substance) of synchronous X-rays is developed in the two-wave approximation in the coplanar Laue geometry for large grazing angles in perfect crystals. A sharp decrease in the absorption coefficient in the substance with simultaneously satisfied diffraction conditions (Borman effect) is demonstrated, and the theoretical and first experimental results are compared. The calculations reveal the possibility of applying this approach in analyzing the quadrupole-quadrupole contribution to the absorption coefficient.

Optical and transport properties of GaGeTe single crystals

GaGeTe single crystals were grown using a modified Bridgman method. The prepared samples were characterized by X-ray diffraction and investigated using measurements of the reflectance in the plasma-resonance-frequency region and measurements of the transmittance spectra in the MIR, NIR and VIS regions. An analysis of the plasma resonance indicates a near-degenerate state in the GaGeTe single crystal. The variation of the square of the absorption coefficient, α2, as a function of incident radiation energy showed two distinct minima of α located at ≈0.5 and ≈1.0eV. The free carrier scattering mechanism was estimated from the slope of the long-wavelength edge. The transport measurement evidence of single-crystalline GaGeTe is a degenerate p-type semiconductor with a concentration of holes of p≅5.1019cm−3. The mobility of the holes is rather low.

광도전체 물질의 치료 방사선 선량계 적용을 위한 가능성 연구

The use of the dosimetry have been increasingly recognized as high radiation energy and radiation treatment planning(RTP) have rapidly developed in radiotherapy. There are many types of detectors for the dosimetry such as ionization chamber, film, TLD, diode, and etc. Among such detectors, the diode detector uses a photoconductor materials that generate electrical signals by the incident radiation energy. Though many research groups are recently interested in such materials, there is few experimental results except for silicon in the radiation therapy field. In this study, the feasibility of photoconductor materials was verified as a dosimeter through the evaluation of response properties at a high radiation energy. For the fabricated detectors based on HgI2 and PbI2, reproducibility, linearity, and pulse-rate response were analyzed. Such evaluations are essential factors for the use of dosimeter. From results, linearity and reproducibility of the fabricated HgI2 detector indicated about 7% error. The fabricated PbI2 detector showed 1.7% error in linearity, and 12.2% error in reproducibility.

Kinetics of water disinfection using UV-C radiation

The current work is concerned with the development of a kinetic model for UV disinfection process at 254nm. The micro-organism was Escherichia coli (E. coli). The inactivation of E. coli active cells, suspended in sterile double-distilled water, free-of solids, nutrient and any trace of broth, was carried out in a bench-scale annular photoreactor, designed specifically for developing kinetic studies. The UV-C light source used was a tubular low pressure Philips lamp, model TUV-36W. The reactor model was based on the conservation principles. The radiation field was modelled according to the radial incidence model. The incident radiation energy at the photoreactor optical entrance was measured by homogeneous potassium ferrioxalte actinometry (1.4×10−9Einsteincm−2s−1). The Naperian absorption coefficient of the E. coli active cells was obtained (1.05×10−8cm2MPN−1). The kinetic model proposed was a simple phenomenological equation relating the reaction rate to both the concentration of microbial active cells and the radiation energy absorbed by these cells. A term related to the rate of growth of microbial cells was added to the kinetic model. The experimental runs were carried out for conditions where the initial concentration of E. coli active cells varied from 2.0×104MPNcm−3 to 2.0×106MPNcm−3, pH7 and temperature 25°C. Disinfection efficacies of 4.3-Log and 6.3-Log were achieved for both conditions and the respective required UV doses were 23.4mWcm−2 and 31.2mWscm−2. The kinetic model fitted the data well (to 95%). The kinetic parameters, n and K, were estimated in 0.5 and 2.9×10−2s−1(cm3Einstein−1)0.5, respectively.

Influences of diurnal rainfall cycle on CO2 exchange over Bornean tropical rainforests

In the Southeast Asian tropics, distinct peaks of the diurnal precipitation cycle at specific times of the day are among the dominant features of environmental factors. Although the characteristics of rainfall timing during the day are anticipated to affect the ecosystem CO2 flux (NE), no attempt has been made to quantify the impact. To address this issue, the potential alteration of NE corresponding to a change in the diurnal rainfall regime was investigated using a combination of detailed field measurements conducted at an eddy flux observation site, computation with a multilayer soil–vegetation–atmosphere transfer model, and rainfall time series constructed from rainfall statistics of observation-site data and published data of long-term diurnal precipitation cycles over Borneo. The results showed that there was little difference in the mean diurnal NE pattern between “wet” and “dry” days (days with and without rainfall, respectively) and the diurnal rainfall regime little affected NE on a whole-year scale. Similar NE values for wet and dry days might be attributed to (1) a minor contribution of lower NE during rainfall events to total NE in wet conditions, because of constant cloud cover on both wet and dry days and (2) the light saturation of NE at relatively low incident radiative energy (≈500Wm−2 of solar radiation) in this forest ecosystem.

Energy dependence of the relative light output of YAlO3:Ce, Y2SiO5:Ce, and YPO4:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO3:Ce (YAP:Ce), Y2SiO5:Ce (YSO:Ce), and YPO4:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.

A molecular theory for the effect of light on liquid crystals

The response of liquid crystals to light is very important in applications of liquid crystals in display and memory devices. Experiments have been conducted on liquid crystals doped with photoactive azo compounds, and has been shown that under incident UV radiation such systems can lower the nematic isotropic transition temperature, T NI. In addition, in some mixtures a photo-induced smectic phase is observed, attributable to the change from the trans (longer) isomer to the cis (shorter) isomer in the photoactive dopant. We have previously developed a molecular mean field model, on the assumption that the medium consists of interconverting anti-parallel and parallel pairs, to explain the molecular origin of ‘two lengths’. The model was used to explain double re-entrance, the effect of electric field on T NI, etc. This model has now been modified to include the change between the trans and cis isomer, which is equivalent to an increase in the fraction of parallel (shorter) pairs. The phase diagram calculated for incident UV radiation energy shows an induced smectic phase. This is in qualitative agreement with the experimental trends.

Linear and nonlinear intraband optical properties of ZnO quantum dots embedded in SiO2 matrix

In this work we investigate some optical properties of semiconductor ZnO spherical quantum dot embedded in an amorphous SiO2 dielectric matrix. Using the framework of effective mass approximation, we have studied intraband S-P, and P-D transitions in a singly charged spherical ZnO quantum dot. The optical properties are investigated in terms of the linear and nonlinear photoabsorption coefficient, the change in refractive index, and the third order nonlinear susceptibility and oscillator strengths. Using the parabolic confinement potential of electron in the dot these parameters are studied with the variation of the dot size, and the energy and intensity of incident radiation. The photoionization cross sections are also obtained for the different dot radii from the initial ground state of the dot. It is found that dot size, confinement potential, and incident radiation intensity affects intraband optical properties of the dot significantly.

An efficient directional fast neutron sensor for a mixed radiation field

Abstract Dual beam radiation transmission systems are often used to non-invasively distinguish binary materials in security, industrial and medical applications. Material discrimination is based on detecting changes in hydrogen content and effective atomic number. We propose use of a dual beam technology in the reverse sense, as a sensitive directional sensor for fast neutrons in a mixed radiation field. The system uses retractable filter elements aligned with an organic scintillation detector and displays a distinctive digital-like response. Detected events are processed with a discriminator and basic counting system. We discuss the detection principle, the fast neutron detection threshold, the basic operational algorithm used and the response to different incident radiation energies. We propose work to extend the capabilities. This direction-sensitive detection concept may improve the sensitivity for detecting special nuclear materials such as in stacks of sea containers.

Determining the parameters of the laser radiation intensity limiter based on a time-dependent equation of radiative transfer in a nonlinear medium

The effect of the radiation intensity limitation is described using the time-dependent radiative transfer equation taking into account the nonlinearity of the working material of the limiter, which makes it possible to abstract from specific microscopic mechanisms of interaction of radiation with matter. An expression is presented which describes both the deformation of the shape of the laser pulse propagating through a nonlinear medium and the output characteristic (dependence of the output energy on the energy of incident radiation) of the limiter at a known dependence of the absorption coefficient on the laser pulsed radiation intensity with a given pulse shape. A functional equation is derived to determine the dependence of the absorption coefficient on the intensity from the experimental output characteristic, which allows one to predict the limiter properties for different thicknesses of the working medium, as well as to effectively compare limiters of different types.

Numerical simulation of the resonant forbidden bragg reflection in germanium

“Forbidden” reflections are observed in synchrotron radiation diffraction when the energy of incident radiation is close to the absorption edges in crystals. In the present paper, a new method for calculating the intensity of thermal-motion-induced forbidden reflections is proposed. It includes two steps: simulation of the temporary atomic displacements with the help of the ab initio molecular dynamics followed by quantum-mechanical calculations of the resonant scattering amplitude for various configurations. This technique is applied to the calculation of the 600 reflection thermal behavior in Ge and gives an adequate quantitative fitting of experimental data. The proposed simulation method of the thermal-motion-induced forbidden reflections is suitable for any crystal structure and promises to explain many results obtained up to now in synchrotrons.

Real-Time In Vivo Dosimetry With MOSFET Detectors in Serial Tomotherapy for Head and Neck Cancer Patients

A real-time dose verification method using a recently designed metal oxide semiconductor field effect transistor (MOSFET) dosimetry system was evaluated for quality assurance (QA) of intensity-modulated radiation therapy (IMRT). Following the investigation of key parameters that might affect the accuracy of MOSFET measurements (i.e., source surface distance [SSD], field size, beam incident angles and radiation energy spectrum), the feasibility of this detector in IMRT dose verification was demonstrated by comparison with ion chamber measurements taken in an IMRT QA phantom. Real-time in vivo measurements were also performed with the MOSFET system during serial tomotherapy treatments administered to 8 head and neck cancer patients. MOSFET sensitivity did not change with SSD. For field sizes smaller than 20 × 20 cm(2), MOFET sensitivity varied within 1.0%. The detector angular response was isotropic within 2% over 360°, and the observed sensitivity variation due to changes in the energy spectrum was negligible in 6-MV photons. MOSFET system measurements and ion chamber measurements agreed at all points in IMRT phantom plan verification, within 5%. The mean difference between 48 IMRT MOSFET-measured doses and calculated values in 8 patients was 3.33% and ranged from -2.20% to 7.89%. More than 90% of the total measurements had deviations of less than 5% from the planned doses. The MOSFET dosimetry system has been proven to be an effective tool in evaluating the actual dose within individual patients during IMRT treatment.

Ab initio study of structural, electronic and optical properties of the Bi 12TiO 20 sillenite crystal

It is presented an analysis of some important structural, electronic and optical characteristics of the pure Bi 12TiO 20 sillenite crystal, based on the ab initio calculations of its electronic structure and complex dielectric tensor. The band gap is calculated to be 2.3 eV and found to be direct. The contributions to the valence band top and conduction band bottom come predominantly from O 2p- and Bi 6p-states, respectively. The optical absorption spectrum is calculated and interpreted in terms of electronic band structure for incident radiation energy up to 40 eV. The principal absorption occurs within the energy range from 2.5 to 10 eV, originating manly from the electronic transitions from the O 2p- to the Bi 6p-states.

Terahertz transmission of NbN superconductor thin film

Transmission of terahertz waves through a thin layer of the NbN superconductor deposited on a sapphire substrate was studied as a function of temperature in zero field as well as in magnetic field perpendicular to the sample. For photon energies lower than optical gap, detailed temperature measurements in zero field provide BCS-like curves with a pronounced peak below the critical temperature. In accordance with the BCS model, the temperature peak disappears as the energy of incident radiation is increased above the gap. In non-zero field, the temperature behavior of transmission is modified because the gap is suppressed and vanishes at upper critical field. In addition, the presence of quantized vortices in the superconducting film substantially changes shape of the temperature curves.