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This study aimed to develop and validate a Monte Carlo (MC) model for the Papillon+ contact x-ray brachytherapy (CXB) device, producing 50 kilovolt (kV) X-rays, specifically focusing on its application with a 25 mm diameter rectal applicator for contact therapy. The validation process involved depth dose and transverse dose profile measurements using EBT3 gafchromic films positioned in a plastic water low energy range phantom. The half-value layer (HVL) was further measured and derived from the simulated X-ray spectra. Excellent agreement within ±2% was achieved between the measured and simulated on-axis depth dose curves for the 25 mm rectal applicator. Transverse dose profile measurements showed a high level of agreement between the simulation and measurements, on average 3.1% in contact with the applicator at the surface of the phantom and on average 1.7% at 10 mm depth. A close agreement within 5.5% was noticed concerning the HVL between the measurement and simulation. The simulated gamma spectra and 2D-dose distribution demonstrated a soft X-ray energy spectrum and a uniform dose distribution in contact with the applicator. An MC model was successfully developed for the Papillon+ eBT device with a 25 mm diameter rectal applicator. The validated model, with its demonstrated accuracy in depth dose and transverse dose profile simulations, is a valuable tool for quality assurance and patient safety and, in a later phase, may be used for treatment planning, dose calculations and tissue inhomogeneity corrections. [ABSTRACT FROM AUTHOR]

The fragmentation of light relativistic nuclei can be studied in detail by the technique of nuclear track emulsions. The registration of all charged particles and their identification enable one to explore the isotopic composition of fragments and the projectile fragmentation channels. In the present paper results of an analysis of decay of the 7Be nucleus in dissociation of 8B nuclei are presented and a comparative analysis of the experimental data with the Monte Carlo model calculations is made. The paper is illustrated with characteristic images, obtained by means of a microscope, equipped with a CCD camera. [ABSTRACT FROM AUTHOR]

Sources of pulsed photon radiation are widely used in science and industry. In this regard, there is a growing demand for dosimetry instruments capable of operating in these pulsed photon radiation fields. Until now there is no comprehensive methodology that describes the characteristics of reference fields of pulsed photon radiation required for calibration and verification of dosimetry equipment. The aim of this paper was to study the possibility of using a medical linear electron accelerator as a generating source of a reference pulsed photon radiation field. The paper investigates main characteristics of photon radiation field (namely, spectrum and average energy) generated by CLINAC in two modes of operation: 6 MV and 18 MV. Additionally it researches the possibility of attenuation of the CLINAC photon radiation intensity by a lead filter. The spectrum and average energy of the CLINAC photon radiation were calculated by means of Monte Carlo simulation in the Fluka program. The validation of the calculation was determined by comparing the attenuation coefficients calculated by the model with ones obtained experimentally by using real CLINACs. Experimentally, the attenuation coefficients were obtained by measuring the air kerma rate generated by the photon radiation fields of Varian VitalBeam and Varian iX CLINACs at a given point of space. Based on the simulation results, the Ḣ*(10) ambient dose equivalent ratio generated by CLINACs were calculated. It was found that the lead filter effectively attenuates the CLINAC photon radiation in terms of both air kerma rate and ambient dose equivalent rate to levels suitable for calibration of dosimetry equipment designed to measure pulsed radiation. It is shown that the lead filter significantly affects both the photon spectrum of the CLINAC and its average energy.

This work presents comparisons between numerical simulations and secondary electron emission yield measurements. The impact on the secondary electron emission yield of a growing graphite layer deposited on copper substrates is analyzed. The numerical simulations confirm experimental observations showing that a very thin coating deposit, with a thickness of few nm, can affect significantly the emission yield of an irradiated material. Beyond 5 nm thickness, the surface material alone drives the secondary emission. [ABSTRACT FROM AUTHOR]

Plastic-fluidized bed interaction has been investigated by non-invasive X-ray imaging techniques in the temperature range of 500–650 °C and under pyrolysis conditions. Experiments were conducted by feeding a single polypropylene particle using either overbed or underbed feeding methods. The fluidized bed was operated from minimum fluidization conditions to bubbling regime, up to 2U mf. Interestingly, experimental observations show that the understanding of the mixing/segregation behaviour of polypropylene in a hot fluidized bed does not appear to be as straightforward as in the case of more conventional feedstocks, such as biomass. Further analysis and an alternative point of view to investigate the complex behaviour observed for plastic feedstock have been provided. The interaction between the fluidized bed and a single polypropylene particle was modelled by means of an axial segregation model, and a physics-assisted stochastic approach. In the second case, it was possible to simulate the formation of the sand-plastic agglomerate (incipient agglomeration stage) and the evolution of its density over time. The models were then validated by means of axial segregation data obtained via X-ray imaging techniques and by measuring the physical properties of real sand-polypropylene agglomerates produced within the bed operating at high temperatures. Results obtained in this study show that the unpredictable sinking-floating behaviour of the plastic particles is not related to the change in density associated to the formation of the sand-polypropylene agglomerates over time. [Display omitted] • The plastic-sand incipient agglomeration in a BFBR is investigated. • X-ray observations reveal the segregation behaviour of polypropylene particles. • Polypropylene particles settle at the bottom of the bed after under bed feeding. • A Monte Carlo-based agglomeration model is developed to predict agglomeration. • Surface tension forces may dominate over gravitational forces for molten plastics. [ABSTRACT FROM AUTHOR]

In recent decades, considerable research has been carried out both in measuring and modelling the brightness of the sky. Modelling is highly complex, as the properties of light emission (spatial and spectral distribution) are generally unknown, and the physical state of the atmosphere cannot be determined independently. The existing radiation transfer models lack the focus on light pollution and model only a narrow spectral range or do not consider realistic atmospheric circumstances. In this paper, we introduce a new Monte Carlo simulation for modelling light pollution, including the optical density of the atmosphere and multiple photon scattering, then we attempt to combine the available information of satellite and ground-based measurements to check the extent to which it is possible to verify our model. It is demonstrated that we need all the separate pieces of information to interpret the observations adequately.

This paper addresses the influence of land topography and cover on 3D radiative effects under cloudless skies in the Hornsund area, Spitsbergen, Svalbard. The authors used Monte Carlo simulations of solar radiation transfer over a heterogeneous surface to study the impact of a non-uniform surface on: (1) the spatial distribution of irradiance transmittance at the fjord surface under cloudless skies; (2) the spectral shortwave aerosol radiative forcing at the fjord surface; (3) normalized nadir radiance at the Top Of the Atmosphere (TOA) over the fjord. The modelled transmittances and radiances over the fjord are compared to the transmittances and radiances over the open ocean under the same conditions. The dependence of the 3D radiative effects on aerosol optical thickness, aerosol type, surface albedo distribution, solar azimuth and zenith angle and spectral channel is discussed. The analysis was done for channels 3 (459-479 nm) and 2 (841-876 nm) of the MODIS radiometer. In the simulations a flat water surface was assumed. The study shows that snow-covered land surrounding the fjord strongly modifies the radiation environment over the fjord surface. The enhancement of the mean irradiance transmittance over the fjord with respect to the open ocean is up to 0.06 for channel 3. The enhancement exceeds 0.11 in the vicinity of sunlit cliffs. The influence of the snow-covered land on the TOA radiance over the fjord in channel 3 is comparable to the impact of an increase in aerosol optical thickness of over 100%, and in lateral fjords of up to several hundred percent. The increase in TOA radiance is wavelength dependent. These effects may affect retrievals of aerosol optical thickness.

Risk assessment of debris flow is an uncertain problem involving randomness and fuzziness. The cloud model is used to distinguish for assessing the risk of debris flow scientifically and rationally. Firstly, the system standard of debris flow risk assessment is constructed; secondly, impact factor of each assessment system which belonging to cloud droplet of each risk level produced by normal cloud generator, the subjective weights and objective weights of the debris flow influence factors are coupled by using game theory, and consider the fuzziness of debris flow basic data, using the Monte Carlo modelling thought, and by generating large cloud droplets and statistics of the average value in a mini zone near the basic data for evaluating debris flow as the basic data belonging to some hierarchical average degree of certainty; finally, the proposed model is used for case research, and compared to several existing mature methods to prove the proposed model is feasible and reasonable. [ABSTRACT FROM AUTHOR]

Liquid water saturation of pores in the gas diffusion layer (GDL) and the catalyst layer (CL) of polymer electrolyte membrane fuel cells (PEMFC) hinders the transport of the reactant gases, leading to inhomogeneous current density distribution, reduced overall cell performance, and accelerated material degradation. This effect restricts the PEMFC operation, specifically at high current densities. In this study, the simulation results illustrate how the interplay of wettability and pore sizes influences the water distribution within the CL, microporous layer (MPL) of the GDL, and specifically their interface. The liquid water distribution within the porous material is studied employing a voxel-based Monte Carlo (MC) model reflecting the effect of local thermodynamic boundary conditions and inner surface characteristics. Real material structures obtained with a focused ion beam - scanning electron microscope (FIB-SEM) are employed. Local temperature and relative humidity values required as inputs are obtained from sophisticated computational fluid dynamics (CFD) simulations comprising all relevant effects, including the electrochemical reactions. The results show that avoiding drastic changes in wettability at the CL-MPL interface can help to mitigate the possible detrimental water accumulations. Further developing and exploiting this study will contribute to facilitate the systematic material development for better PEMFC performance and durability. [ABSTRACT FROM AUTHOR]

Paired cosmogenic nuclides are often used to constrain the exposure/burial history of landforms repeatedly covered by ice during the Quaternary, including tors, high-elevation surfaces, and steep alpine summits in the circum-Arctic regions. The approach generally exploits the different production rates and half-lives of 10 Be and 26 Al to infer past exposure/burial histories. However, the two-stage minimum-limiting exposure and burial model regularly used to interpret the nuclides ignores the effect of variable erosion rates, which potentially may bias the interpretation. In this study, we use a Monte Carlo model approach to investigate systematically how the exposure/burial and erosion history, including variable erosion and the timing of erosion events, influence concentrations of 10 Be and 26 Al. The results show that low 26 Al/ 10 Be ratios are not uniquely associated with prolonged burial under ice, but may as well reflect ice covers that were limited to the coldest part of the late Pleistocene combined with recent exhumation of the sample, e.g. due to glacial plucking during the last glacial period. As an example, we simulate published 26 Al/ 10 Be data from Svalbard and show that it is possible that the steep alpine summits experienced ice-free conditions during large parts of the late Pleistocene and varying amounts of glacial erosion. This scenario, which contrasts with the original interpretation of more-or-less continuous burial under non-erosive ice over the last ∼1 Myr, thus challenge the conventional interpretation of such data. On the other hand, high 26 Al/ 10 Be ratios do not necessarily reflect limited burial under ice, which is the common interpretation of high ratios. In fact, high 26 Al/ 10 Be ratios may also reflect extensive burial under ice, combined with a change from burial under erosive ice, which brought the sample close to the surface, to burial under non-erosive ice at some point during the mid-Pleistocene. Importantly, by allowing for variable erosion rates, the model results may reconcile spatially varying 26 Al/ 10 Be data from bedrock surfaces preserved over multiple glacial cycles, suggesting that samples from the same high-elevation surface or neighbouring alpine summits may have experienced similar long-term burial under ice, but varying amounts of glacial erosion. [ABSTRACT FROM AUTHOR]

Conducting polymer composites are attractive alternatives for applications such as electromagnetic shielding in which metals are conventionally used. They have unique advantages like light weight, ease of processing and good strength to weight ratio. This makes them economically viable especially in industries like avionics where weight is an important criterion. However, a major challenge in using conducting polymer composites in many of the applications is its limited conductivity. Even though many models exist to describe the conductivity of the composites at the macro level taking into account the interparticle conductivity, very few studies are conducted to understand the conductivity of the composites directly from basic principles. In this study, Monte Carlo (MC) simulations are carried out to study the conductivity in such composites. The results obtained using the MC model showed good agreement with the Mamunya model and the experimental measurements. The effect of various parameters like filler diameter and filler conductivity on the final composite conductivity is studied for spherical and fibrous carbon fillers in silicone rubber. The method can be easily adopted for any other filler–polymer combination and can also be used as a predictive tool for designing simple composites of required electrical properties. [ABSTRACT FROM AUTHOR]

The present case study compares transmission Kikuchi diffraction (TKD) with electron back-scattering diffraction (EBSD) on the same area of an electron transparent cross-section of a twinning induced plasticity steel. While TKD expectedly provides better clarity of internal defect substructures in the band contrast map, EBSD returns orientation data that approaches the quality of the TKD map. This was rationalised by Monte Carlo simulations of the electron energy spreads, which showed that due to the geometry-based compromises associated with adapting a conventional EBSD detector (which is off-axis with respect to the incident electron beam) to TKD, a broadening in the electron energy distribution of the forward-scattered electrons collected on the detector phosphor screen, is unavoidable. In this circumstance, the values of the full-widths at half-maximum of the energy distributions for TKD and EBSD are of the same order. It follows that EBSD on electron transparent cross-sections may be a viable alternative to TKD when: (i) conventional EBSD detectors are adapted to TKD and, (ii) sample microstructures comprise features whose sizes do not mandate the application of TKD. [ABSTRACT FROM AUTHOR]

Characterising the impact of lithium additions in the precipitation sequence in Al-Li-Cu alloys is important to control the strengthening of the final material. Since now, transmission electron microscopy (TEM) at high beam voltage has been the technique of choice to monitor the size and spatial distribution of δ' precipitates (Al3Li). Here we report on the imaging of the δ' phase in such alloys using backscattered electrons (BSE) and low accelerating voltage in a high-resolution field-emission scanning electron microscope. By applying low-energy Ar+ ion milling to the surface after mechanical polishing (MP), the MP-induced corroded layers were efficiently removed and permitted the δ's to be visible with a limited impact on the observed microstructure. The resulting BSE contrast between the δ's and the Al matrix was compared with that obtained using Monte Carlo modelling. The artefacts possibly resulting from the sample preparation procedure were reviewed and discussed and permitted to confirm that these precipitates were effectively the metastable δ's. The method described in this report necessitates less intensive sample preparation than that required for TEM and provides a much larger field of view and an easily interpretable contrast compared to the transmission techniques. [ABSTRACT FROM AUTHOR]

This paper estimates the influence of land topography and cover on 3D radiativeeffects under overcast skies in the Arctic coastal environment, in particular in theHornsund fjord region, Spitsbergen. The authors focus on the impact of anon-uniform surface on: (1) the spatial distribution of solar fluxesreaching the fjord surface, (2) spectral shortwave cloud radiative forcing atthe fjord surface, (3) the solar flux anomaly at the domain surface resultingfrom the assumption of a uniform surface, i.e. the error due to plane parallelassumptions in climate models, and (4) remote sensing of cloud opticalthickness over the fjord. Their dependence on spectral channel, cloud opticalthickness, cloud type, cloud base height, surface albedo and solar zenithangle is discussed. The analysis is based on Monte Carlo simulations of solarradiation transfer over a heterogeneous surface for selected channels of theMODIS radiometer. The simulations showed a considerable impact of the landsurrounding the fjord on the solar radiation over the fjord. The biggestdifferences between atmospheric transmittances over the fjord surface and over theocean were found for a cloud optical thickness τ = 12, low solar zenith angle θ, high cloud base and snow-covered land. For τ = 12, θ = 53°, cloud base height 1.8 km andwavelength λ = 469 nm, the enhancement in irradiance transmittanceover the fjord was 0.19 for the inner fjords and 0.10 for the whole fjord(λ = 469 nm). The land surrounding the Hornsund fjord also hada considerable impact on the spectral cloud radiative forcing on the fjordsurface and the solar flux anomaly at the domain surface due to the uniformsurface assumption. For the mouth and central part of the fjord the error dueto the use of channel 2 of the MODIS radiometer (λ = 858 nm) forcloud optical thickness retrieval was < 1 in the case of low-level clouds(cloud base height 1 km, nadir radiance, θ = 53°, cloudoptical thickness retrieved solely from MODIS channel 2). However, near theshoreline (up to 2 km from it), especially over the inner fjords, the cloudoptical thickness was then overestimated by > 3 for τ = 5 and by> 5 for τ = 20.

• 125 °C is a lower extraction temperature for PHB with dimethyl carbonate. • PHA solvent extraction temperatures from dried biomass can be evaluated by DSC. • PHA intrinsic viscosity can be measured in dimethyl carbonate solutions at 60 °C. • PHA scission kinetics can be followed with change of weight average molecular mass. • Thermal treatment of dry PHA-rich biomass lowers PHA molecular weight predictably. Past studies have repeatedly demonstrated the technical feasibility to produce polyhydroxyalkanoate (PHA) using bacterial biomass of mixed microbial cultures (MMCs). Commercial quality grades of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, can be produced with control of average monomer composition. However, demonstration of PHBV production and recovery with quality control of molecular weight (MW) distribution has been lacking in the research literature. Towards this goal, a workflow has been developed for characterizing molecular weight control by thermal treatment pre-processing of dried PHA-rich biomass before solvent extraction. Dimethyl carbonate (DMC) was a suitable solvent in this workflow in the routine evaluation of extractable PHA. From assessments of DMC extraction using differential scanning calorimetry, 125 °C was selected for nominally 100 percent extraction yield independent of polymer 3-hydroxyvalerate (3HV) content (2 to 41 wt.% 3HV) and molecular weight (100 to 1400 kDa). Intrinsic viscosity measurements of PHBV in DMC at 60 °C was used for molecular weight monitoring. Mark-Houwink constants, α (0.738 ± 0.010) and LogK (-2.016 ± 0.025), were estimated for a PHBV co-polymer blend having 36 wt.% 3HV. A model of random scission supported that weight average molecular weight (M w) was a more robust metric, compared to number average molecular weight (M n), for assessing the polymer scission rates. During isothermal heat treatment for a given biomass batch, interpreted scission rate was reproducible and commonly, but not always, constant in time. Scission rates between biomass batches were also variable. Measured properties of the polymer in the biomass (thermal stability, biomass PHA content, PHBV grade, initial moisture content) could not be correlated to this observed batch-to-batch variation of scission rate. Molecular weight loss before extraction did not influence the melting temperatures of the co-polymer blends of PHBV evaluated over a wide sub-eutectic range of average 3HV content. Molecular weight changes for these PHBV co-polymer blends were considered to have likely influenced the nature of blend 3HV distribution, and consequently, crystallization behaviour. Molecular weight loss effects on crystallization behaviour at constant PHBV average 3HV wt.% content could then have contributed to the observed variability for glass transition temperatures and melting enthalpies. However, a reproducible correlation between this variability and MW change was not observed. [ABSTRACT FROM AUTHOR]

Introduction: Osteoporosis is a bone disease in which there is a reduction in the amount of bone mineral content leading to an increase in the risk of bone fractures. The affected individuals not only have to go through lots of pain and suffering but this disease also results in high economic costs to the society due to a large number of fractures. A timely and accurate diagnosis of this disease makes it possible to start a treatment and thus preventing bone fractures as a result of osteoporosis. Radiographic methods are particularly well suited for in vivo determination of bone mineral density (BMD) due to the relatively high x-ray absorption properties of bone mineral compared to other tissues. Materials and Methods: Monte Carlo simulation has been conducted to explore the possibilities of triple photon energy absorptiometry (TPA) in the measurement of bone mineral content. The purpose of this technique is to correctly measure the bone mineral density in the presence of fatty and soft tissues. The same simulations have been done for a dual photon energy absorptiometry (DPA) system and an extended DPA system. Results: Using DPA with three components improves the accuracy of the obtained result while the simulation results show that TPA system is not accurate enough to be considered as an adequate method for the measurement of bone mineral density. Discussion: The reason for the improvement in the accuracy is the consideration of fatty tissue in TPA method while having attenuation coefficient as a function of energy makes TPA an inadequate method. Conclusion: Using TPA method is not a perfect solution to overcome the problem of non uniformity in the distribution of fatty tissue.

Hadron therapy allows for highly conformal dose distributions and better sparing of organs-at-risk, thanks to the characteristic dose deposition as function of depth. However, the quality of hadron therapy treatments is closely connected with the ability to predict and achieve a given beam range in the patient. Currently, uncertainties in particle range lead to the employment of safety margins, at the expense of treatment quality. Much research in particle therapy is therefore aimed at developing methods to verify the particle range in patients.Non-invasive in-vivo monitoring of the particle range can be performed by detecting secondary radiation, emitted from the patient as a result of nuclear interactions of charged hadrons with tissue, including beta+ emitters, prompt photons, and charged fragments. The correctness of the dose delivery can be verified by comparing measured and pre-calculated distributions of the secondary particles. The reliability of Monte Carlo (MC) predictions is a key issue. Correctly modelling the production of secondaries is a non-trivial task, because it involves nuclear physics interactions at energies, where no rigorous theories exist to describe them. The goal of this review is to provide a comprehensive overview of various aspects in modelling the physics processes for range verification with secondary particles produced in proton, carbon, and heavier ion irradiation. We discuss electromagnetic and nuclear interactions of charged hadrons in matter, which is followed by a summary of some widely used MC codes in hadron therapy. Then we describe selected examples of how these codes have been validated and used in three range verification techniques: PET, prompt gamma, and charged particle detection. We include research studies and clinically applied methods. For each of the techniques we point out advantages and disadvantages, as well as clinical challenges still to be addressed, focusing on MC simulation aspects.

Scintillator based coded-aperture imaging has proven to be effective when applied for X- and gamma-ray detection. Adaptation of the same method for neutron imaging has resulted in a number of propitious systems, which could be potentially employed for neutron detection in security and nuclear decommissioning applications. Recently developed scintillator based coded-aperture imagers reveal that localisation of neutron sources using this technique may be feasible, since pulse shape discrimination algorithms implemented in the digital domain can reliably separate gamma-rays from fast neutron interactions occurring within an organic scintillator. Moreover, recent advancements in the development of solid organic scintillators make them a viable solution for nuclear decommissioning applications as they present less hazardous characteristics than currently dominating liquid scintillation detectors. In this paper existing applications of coded-apertures for radiation detection are critically reviewed, highlighting potential improvements for coded-aperture based neutron source localisation. Further, the suitability of coded-apertures for neutron imaging in nuclear decommissioning is also assessed using Monte-Carlo modelling. [ABSTRACT FROM AUTHOR]

Optical interrogation of suspicious skin lesions is standard care in the management of skin cancer worldwide. Morphological and functional markers of malignancy are often combined to improve expert human diagnostic power. We propose the evaluation of the combination of two independent optical biomarkers of skin tumours concurrently. The morphological modality of reflectance confocal microscopy (RCM) is combined with the functional modality of laser Doppler flowmetry, which is capable of quantifying tissue perfusion. To realize the idea, we propose laser feedback interferometry as an implementation of RCM, which is able to detect the Doppler signal in addition to the confocal reflectance signal. Based on the proposed technique, we study numerical models of skin tissue incorporating two optical biomarkers of malignancy: (i) abnormal red blood cell velocities and concentrations and (ii) anomalous optical properties manifested through tissue confocal reflectance, using Monte Carlo simulation. We also conduct a laboratory experiment on a microfluidic channel containing a dynamic turbid medium, to validate the efficacy of the technique. We quantify the performance of the technique by examining a signal to background ratio (SBR) in both the numerical and experimental models, and it is shown that both simulated and experimental SBRs improve consistently using this technique. This work indicates the feasibility of an optical instrument, which may have a role in enhanced imaging of skin malignancies. [ABSTRACT FROM AUTHOR]

Computed Tomography (CT) high-resolution imaging have been used to investigate if there is a significant change in the crystal-to-window distance, i.e. the air gap thickness, in a small n-type detector cooled to 77 K, and in a medium sized p-type HPGe detector when cooled to 100 K. The findings were compared to detector dimension data made available by the manufacturer. The air gap thickness increased by (0.38±0.07) mm for the n-type detector and by (0.40±0.15) mm for the p-type detector when the detectors were cooled to 77 resp. 100 K compared to at room temperature. Monte Carlo calculations indicate that these differences have a significant impact on the efficiency in close geometries (<5 cm). In the energy range of 40–700 keV with a source placed directly on endcap, the change in detector efficiency with temperature is 1.9–2.9% for the n-type detector and 0.3–2.1% for the p-type detector. The measured air gap thickness when cooling the detector was 1.1 mm thicker than manufacturer data for the n-type detector and 0.2 mm thicker for the p-type detector. In the energy range of 40–700 keV and with a source on endcap, this result in a change in detector efficiency of 5.2–7.1% for the n-type detector and 0.2–1.0% for the p-type detector, i.e. the detector efficiency is overestimated using data available by the manufacturer. [ABSTRACT FROM AUTHOR]

A fast neutron generator with a tritium target can be used to generate d–d and d–t reaction products corresponding to thermonuclear reactions in tokamaks or stellarators. In this way, convenient laboratory conditions for tests of spectrometric detectors – prior to their installation at the big fusion devices – can be achieved. Distributions of the alpha particles, protons, deuterons, and tritons generated by the fast neutron generator operating at the Institute of Nuclear Physics PAN in Cracow, Poland, were calculated by means of the Monte Carlo (MC) codes. Results of this MC modelling are presented. [ABSTRACT FROM AUTHOR]

In this work, the influence of the internal concrete structure on linear attenuation coefficients was investigated. The attenuation coefficient of 15 different concrete samples, identical in mixing design, was measured with a narrow beam setup in an energy range of 609–2447 keV. Fluctuations of up to 16.8% in the measured attenuation coefficients were observed between the different samples. In order to attribute these fluctuations to the internal sample structure, Computer Tomography (CT) scans were made of each individual sample. The scans were incorporated into a Monte Carlo (MC) model of the attenuation setup. Results of the MC model closely match experimental values and the same fluctuating trend between the attenuation coefficients of the different samples was observed. The CT images revealed the presence of mortar at the beam location for samples with low linear attenuation coefficient values. Correspondingly, aggregates were found to be present at the beam location for samples with high attenuation coefficients. The impact of the internal concrete structure can play an important role in applications such as contamination depth profiling or activity determinations in nuclear decommissioning. Also for other applications in gamma-ray spectrometry, the proposed method of combining CT images with MC modelling can be a useful tool to improve the quantitative analysis of radionuclides. Especially for inhomogeneous samples or samples of irregular shape, the CT imaging can add value. • The influence of the concrete internal structure (aggregates, mortar and voids) on attenuation coefficients was studied. • A compact narrow-beam setup was used to measure the attenuation coefficient of different concrete samples. • Computed Tomography images of the concrete samples were made and incorporated in a Monte Carlo model. • Fluctuations in the attenuation coefficient of 16.8% were measured. [ABSTRACT FROM AUTHOR]

To develop an improved dosemeter to assess photon and beta exposures of the eye lens, and in response to issues surrounding the preferred values of H lens to be used for guiding operational radiation protection, a programme of re-optimization of the current PHE thermoluminescence dosemeter has been performed. In particular, refinements of the filter located in front of the sensitive 7 LiF:Mg,Cu,P element have been considered, so that the dose response characteristics of the device provide a better and more conservative estimate of risk. The investigation was performed using the Monte Carlo modelling software MCNP5, to produce a final design that featured a filter containing a 9.5 mm diameter polypropylene hemisphere truncated to a maximum thickness of 3.0 mm. The responses of this design in photon and electron fields are presented here, contrasted against those of the existing PHE eye dosemeter, with respect to the operational quantity H p (3, E , θ ) and both current and suggested values for the absorbed dose per fluence risk profile for the lens of the eye. [ABSTRACT FROM AUTHOR]

Abstract: To improve the photovoltaic power conversion efficiency of organic solar cells it is necessary to increase the open circuit voltage and short circuit current. Prior work has shown that both these device properties can be improved by using donor–acceptor systems composed of two polymers, which favors excitons dissociation and charge generation, and subsequent charge transport to the electrodes. However, device performance depends strongly on the experimental conditions under which the device was created, because they determine the molecular structure of the interface between the two polymers. Polymer chains can have different conformations relative to the interface, creating different arrangements of the conjugated segments whose disorder degree can affect energy and charge transfer. Thus, understanding this effect is of utmost importance to improve the efficiency of all-polymer excitonic solar cells. In this work, we present the results obtained using a Monte Carlo model that takes into account the arrangement of the polymer strands at polymer–polymer interfaces and considers the main physical processes mediating exciton and charge dynamics. Our results show that the amount of charge extracted from the interface is sensitive to the orientation of polymer strands at interfaces and on the diffusive layer width formed by the mixture of both polymers. [Copyright &y& Elsevier]

Purpose: On 1 July 2012, the Australian Clinical Dosimetry Service (ACDS) released its Optically Stimulated Luminescent Dosimeter (OSLD) Level I audit, replacing the previous TLD based audit. The aim of this work is to present the results from this new service and the complete uncertainty analysis on which the audit tolerances are based. Methods: The audit release was preceded by a rigorous evaluation of the InLight R nanoDot OSLD system from Landauer (Landauer, Inc., Glenwood, IL). Energy dependence, signal fading from multiple irradiations, batch variation, reader variation, and dose response factors were identified and quantified for each individual OSLD. The detectors are mailed to the facility in small PMMA blocks, based on the design of the existing Radiological Physics Centre audit. Modeling and measurement were used to determine a factor that could convert the dose measured in the PMMA block, to dose in water for the facility's reference conditions. This factor is dependent on the beam spectrum. The TPR20,10 was used as the beam quality index to determine the specific block factor for a beam being audited. The audit tolerance was defined using a rigorous uncertainty calculation. The audit outcome is then determined using a scientifically based two tiered action level approach. Audit outcomes within two standard deviations were defined as Pass (Optimal Level), within three standard deviations as Pass (Action Level), and outside of three standard deviations the outcome is Fail (Out of Tolerance). Results: To-date the ACDS has audited 108 photon beams with TLD and 162 photon beams with OSLD. The TLD audit results had an average deviation from ACDS of 0.0% and a standard deviation of 1.8%. The OSLD audit results had an average deviation of -0.2% and a standard deviation of 1.4%. The relative combined standard uncertainty was calculated to be 1.3% (1s). Pass (Optimal Level) was reduced to =2.6% (2s), and Fail (Out of Tolerance) was reduced to >3.9% (3s) for the new OSLD audit. Previously with the TLD audit the Pass (Optimal Level) and Fail (Out of Tolerance) were set at =4.0% (2s) and >6.0% (3s). Conclusions: The calculated standard uncertainty of 1.3% at one standard deviation is consistent with the measured standard deviation of 1.4% from the audits and confirming the suitability of the uncertainty budget derived audit tolerances. The OSLD audit shows greater accuracy than the previous TLD audit, justifying the reduction in audit tolerances. In the TLD audit, all outcomes were Pass (Optimal Level) suggesting that the tolerances were too conservative. In the OSLD audit 94% of the audits have resulted in Pass (Optimal level) and 6% of the audits have resulted in Pass (Action Level). All Pass (Action level) results have been resolved with a repeat OSLD audit, or an on-site ion chamber measurement. [ABSTRACT FROM AUTHOR]

Abstract: This paper extends the work presented in a previous publication (Hansford, 2011 , subsequently referred to as Paper 1) to optimise the performance of a simple reflection-mode X-ray diffraction instrument with respect to the geometrical configuration. Both papers focus on the maximisation or minimisation of quantifiable characteristics of the X-ray beam incident on the sample in order to optimise the peak heights and widths in the resulting diffractogram. The reason for this approach is mathematical tractability, and its success relies on the relationship between the incident beam characteristics and the diffractogram properties. Part of Paper 1 was devoted to the minimisation of the equatorial divergence angle of the X-ray beam, while keeping the total X-ray flux constant, in order to minimise the diffractogram peak widths. While equatorial divergence and peak widths are certainly linked, their relationship is complex and depends quite significantly on other geometric parameters. An alternative optimisation approach is taken in this paper, focusing on the maximisation of the X-ray flux and minimisation of the incident beam axial divergence, while equatorial divergence is kept constant to ensure at least reasonable resolution. The rationale for this approach is that the incident beam flux and the axial divergence angle are more directly linked to diffractogram peak heights and peak asymmetry, respectively. Families of candidate geometric solutions result from this approach which is regarded as advantageous because there is no unique optimised solution and it allows the parameter space to be fully explored. [Copyright &y& Elsevier]

Abstract: The pure and unperturbed (ideal, at birth) spectra of 241AmLi(α,n)10B sources were determined using Monte Carlo simulations, along with the neutron spectrum measured outside a source''s encapsulation. Various parameters that affect photon and neutron yields and energy distributions were investigated. The source''s microparticle size was deduced. Subsequently, the calculated theoretical neutron energy spectra of the 241AmLi(α,n) reaction were compared to both the ideal spectra and the calculation of Geiger and van der Zwan predominantly used since early 1970s. [Copyright &y& Elsevier]

Abstract: The infinite matrix assumption is commonly used to derive dose rates in the field of paleodosimetric dating methods. The update of nuclear data allowed calculating new dose rate conversion factors and attenuation factors for taking account of grain size. The relevance of the infinite matrix assumption was found to be limited to specific cases and a discussion of potential errors in estimating dose rates to natural dosimeters in sedimentary media is proposed. A new set of geometric features is shown to be of paramount importance for estimating dose rates in sedimentary media. To quantify these effects, Monte Carlo modelling was applied and the architecture of the programmes is described. It is also shown that proper characterization of sediment samples, coupled to the modelling of radioactivity in these sediments may provide more accurate dose rates to quartz grains, down to the single grain scale. [Copyright &y& Elsevier]

Abstract: This paper presents a detailed study of the RF and noise performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and noise figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the noise performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm , cut-off frequency fT , and non-quasistatic dynamic parameters. The drain and gate intrinsic noise sources show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT . Therefore, the deterioration of the intrinsic noise performance of the SB-MOSFET has no significant impact on high-frequency noise FoMs as NFmin , Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on Γopt , optimum noise reactance and susceptance has been also analyzed. [Copyright &y& Elsevier]

Abstract: Microbeam radiation therapy is an experimental technique utilising synchrotron X-rays collimated into a planar array of microbeams. Due to the complex structure of the radiation field and high dose rate, this introduces dosimetric challenges. Current dosimetric methods are inadequate in that they lack either real-time readout, or high spatial resolution. A detector system, consisting of the Silicon Multi-Strip Detector and associated readout system was developed at the University of Wollongong. This system performs online, real-time dosimetry, and is designed for placement upstream of the patient as a transmission detector. The interaction of synchrotron radiation with this detector, both in terms of perturbative effects on the beam and interactions within the detector are investigated with the Monte Carlo simulation toolkit, Geant4. The interaction percentage of the detector with the traversing beam was determined as being (1.97 ± 0.01) %. Energy deposition was found to be uniform across the depth of the detector, negating the most proximal and distal 5-μm region, a phenomenon that may be attributed to a lack of charged particle equilibrium. The effect that the detector has on a traversing beam’s macroscopic dose deposition was determined as being a mean reduction in dose of (1.44 ± 0.15) % for depths in water between 5 and 35 mm. [Copyright &y& Elsevier]

Abstract: Low energy X-ray radiation impact on the coated Si structures is discussed in this paper. Experimental sandwich structures consisting of amorphous hydrogenated a:C–H or SiO x -containing DLC films were synthesized on Si 〈111〉 wafers using direct ion deposition method and exposed to low energy (medical diagnostic range) X-ray photons. Irradiation of samples was performed continuously or in sequences and protective characteristics of the irradiated DLC films were investigated. Experimental data were used as the input data for Monte Carlo modelling of X-ray scattering effects in the coated silicon constructions, which affect significantly the “signal to noise ratio” in DLC-coated Si structures proposed for their application in medical radiation detectors. Modelling results obtained in the case of DLC coatings were compared to the results of calculations performed for other commonly used combinations coating–detector material. The evaluation method of coated structures for their possible application in medical radiation detector constructions has been proposed in this paper. It is based on the best achieved compatibility between the appropriate mechanical characteristics, coating’s resistance against the radiation damage and the lowest estimated scattering to total dose ratio in the coated radiation sensitive volume. [Copyright &y& Elsevier]

Abstract: Published survival data of V79 cells irradiated by 0.5–5.0MeV (7–) protons have been analyzed with a detailed radiobiological model to estimate the per-track yields of lethal lesions. Their correlations with distribution patterns of deposited energy, radical concentrations and with the yields of specific classes of DNA damage have been studied. The observed correlations indicate a potential interpretation of DNA damage lethal for the cell and the initial physical and chemical processes leading to such damage. [Copyright &y& Elsevier]

Abstract: This study simulates the combination of crystal growth by evaporation–condensation with the potential for a phase change once the crystals have reached a critical size. Crystal growth has been simulated as a two-dimensional Monte Carlo process in which the probability of accepting or rejecting an individual evaporation–condensation step is given by the Metropolis algorithm. Crystals, taken to be of the anatase form of TiO2, which have grown larger than a specified critical size may transform irreversibly to a second phase, taken to be rutile. The probability of conversion increases with increasing crystal size. For each critical size there exists a limited range over which the transformation kinetics follow the familiar relationship α =1−exp(−kt n ) (where α is the fractional conversion at time, t). The dependence of the mean size of the two polymorphs and of the rutile size-spread (rms) on critical size have been investigated. The most significant aspect of the plots of the normalized size-spread, rms/mean-size, is its gradual increase as the rutile fraction increases from 0.75 to 0.98. [Copyright &y& Elsevier]

Abstract: The Monte Carlo code MCNP-4C2 is used to design a new personal thermoluminescence dosemeter that assesses both and in mixed photon/electron fields. The new dosemeter utilizes two 7LiF:Mg,Cu,P elements contained within a Harshaw TLD-700H card, itself inside a polypropylene holder with walls 2mm thick. Several potential designs of holder are considered; the best incorporates a polytetrafluoroethylene cylinder of diameter 18mm and thickness 4.3mm that acts as a filter to provide the correct electron cut-off and an acceptably flat relative response to photons, with an open hole in front of the element. Response characteristics for both detectors in this final design are presented for irradiation from a variety of angles of interest, with source energies between 16 and 6174keV used. Comparison is made between modelled and measured data at normal incidence; the relative responses generally agree well. A new estimate for the relative light conversion efficiency relevant to the 7LiF:Mg,Cu,P is also derived and presented. [Copyright &y& Elsevier]

Electron beam welding is a well known process used where high precision, high reliability welds are needed, often in exotic materials. Recently, it has been proposed to apply the electron beam produced in a standard scanning electron microscope (SEM), with reversible modifications to increase beam current, for microscale welding. In addition to providing the clean environment associated with the column vacuum, the SEM in imaging mode provides exceptional capabilities in visualising extremely small parts. Furthermore, the standard stage and beam motion controls offer the possibility of flexible programming of beam path with relatively minor software additions. In order to better evaluate the requirements for and effects of μE-beam welding (μEBW) on typical microtechnologically important materials, a clear understanding of the characteristics of the SEM's beam and its interaction with possible target materials is needed. The penetration ability of electrons depends strongly upon their accelerating voltage and the target they are being directed at. Hence, in some circumstances the beam may interact as a surface heat source, while in others it may act as a volume heat source, with important consequences on weld schedule development for the parts and geometry being welded. In this work, the authors explore some of the factors involved and propose simple models for the electron beam heat source which depend on the parameters being used. [ABSTRACT FROM AUTHOR]

Abstract: Localisation of ion impacts with a resolution better than can be achieved with a focused ion beam microprobe may potentially be achieved by employing a high-aspect ratio nano-aperture mask. The present paper applies Monte Carlo methods to investigate the role of ion scattering and straggling through the aperture and the influence of these processes on the transmitted ion energy and intensity distribution. The objective of the investigation is to determine the potential of this method for delivering few or single ions to sub-100nm locations on substrates. Simulation of 2 and 4MeV He, 8MeV F and 71MeV Cu has indicated that the masking process is effective, with probabilities between 82% and 93% of obtaining single ions with full energy at the exit of the aperture. Possible applications include precision ion doping, single-ion machining and potentially ion beam analysis. [Copyright &y& Elsevier]

Abstract: A Monte Carlo-based algorithm for simulating the mass crystallisation process in a continuous adiabatic MSMPR crystallizer was presented. The algorithm is based on accurate, reciprocal interrelations among mass, heat, population balances and kinetic (nucleation, crystal growth) equations. The algorithm was successfully used to simulate the mass crystallisation process of the two inorganic salts—KNO3 and CuSO4·5H2O—where ΔL McCabe''s rule is fulfilled. The obtained results reflect physical nature of the mass crystallisation process correctly reproducing the periodical fluctuations of selected process parameters. [Copyright &y& Elsevier]

All available measured data for the response characteristics of the Leake counter have been gathered together. These data, augmented by previously unpublished work, have been compared to Monte Carlo simulations of the instrument''s response characteristics in the energy range from thermal to 20 MeV. A response function has been derived, which is recommended as the best currently available for the instrument. Folding this function with workplace energy distributions has enabled an assessment of the impact of this new response function to be made. Similar work, which will be published separately, has been carried out for the NM2 and the Studsvik 2202D neutron area survey instruments. [Copyright &y& Elsevier]

Device-tissue interface geometry influences both the intensity of detected fluorescence and the extent of tissue sampled. Previous modelling studies have often investigated fluorescent light propagation using generalised tissue and illumination-collection geometries. However, the implementation of approaches that incorporate a greater degree of realism may provide more accurate estimates of light propagation. In this study, Monte Carlo modelling was performed to predict how illumination-collection parameters affect signal detection in multilayer tissue. Using the geometry and optical properties of normal and atherosclerotic aortas, results for realistic probe designs and a semi-infinite source-detection scheme were generated and compared. As illumination-collection parameters, including single-fibre probe diameter and fibre separation distance in multifibre probes, were varied, the signal origin deviated significantly from that predicted using the semi-infinite geometry, The semi-infinite case under-predicted the fraction of fluorescence originating from the superficial layer by up to 23% for a 0.2mm diameter single-fibre probe and over-predicted by 10% for a multifibre probe. These results demonstrate the importance of specifying realistic illumination-collection parameters in theoretical studies and indicate that targeting of specific tissue regions may be achievable through customisation of the illumination-collection interface. The device- and tissue-specific approach presented has the potential to facilitate the optimisation of minimally invasive optical systems for a wide variety of applications. [ABSTRACT FROM AUTHOR]

Clear evidence (in the form of structured diffuse scattering) is found for short range ordering of metal ions and associated induced structural relaxation in two members of the cubic BZN pyrochlore (Bi1.5−αZn0.5−β)(Zn0.5−γNb1.5−δ)O(7−1.5α−β−γ−2.5δ) solid solution. An average neutron powder diffraction structure refinement is carried out for one of these. Electron probe micro-analysis suggests that the primary mechanism for non-stoichiometry in cubic BZN is the removal of ZnO from the nominally fully occupied (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 end-member. A detailed bond valence sum analysis of a recently reported average crystal structure is used to suggest possible local cation ordering schemes along with the induced displacive relaxation that is likely to accompany such local cation ordering. The observed diffuse distribution is qualitatively interpreted via Monte Carlo modelling. [Copyright &y& Elsevier]

The three-dimensional structure of a coniferous shoot gives rise to multiple scattering of light between the needles of the shoot, causing the shoot spectral reflectance to differ from that of a flat leaf. Forest reflectance models based on the radiative transfer equation handle shoot level clumping by correcting the radiation attenuation coefficient with a clumping index. The clumping index causes a reduction in the interception of radiation by the canopy at a fixed leaf area index (LAI). In this study, we show how within-shoot multiple scattering is related to shoot scale clumping and derive a similar, but wavelength dependent, correction to the scattering coefficient. The results provide a method for integrating shoot structure into current radiative transfer equation based forest reflectance models. The method was applied to explore the effect of shoot scale clumping on canopy spectral reflectance using simple model canopies with a homogeneous higher level structure. The clumping of needles into shoots caused a wavelength dependent reduction in canopy reflectance, as compared to that of a leaf canopy with similar interception. This is proposed to be one reason why coniferous and broad-leaved canopies occupy different regions in the spectral space and exhibit different dependency of spectral vegetation indices on LAI. [Copyright &y& Elsevier]

A custom fibre optic probe has been built for the assessment of light levels inside a mandarin (Citrus reticulata), which has been illuminated with 808 nm laser light. The probe has minimal effect on the light being measured and enables the direct measurement of light levels at any location in the fruit. Results show there is a rapid reduction in light level across the thick illuminated skin, a less rapid but still high reduction as the light continues to diffuse into the flesh, a generally exponential decay through the tissue regions (with some perturbation through the central pith and air) and finally a rapid drop across the distal skin. Measurements supported by Monte Carlo simulations show that the skin has significant internal reflective properties, which increases the light level measured inside the flesh. For subjects of this size and light transmission ability, boundary conditions are critical to the internal light distribution. We suggest that separate scattering and absorption parameters for skin, flesh, and air spaces of the core would enable the development of a more accurate model for the light levels in a mandarin. [Copyright &y& Elsevier]

Surface solar irradiance (ISFC) can be inferred from satellite-observed radiance with retrieval algorithms based on the independent pixel approximation (IPA). As the spatial resolution of satellite sensors increases, the effects from spatially inhomogeneous cloud fields become more important. Clouds affect the distribution of radiation in a region larger than the resolution of an individual pixel and IPA is no longer justified. The objective of this study is to identify effects of clouds and find corrections for IPA to compensate for these effects. For this purpose, cloud fields are generated with the mesoscale model MM5 at high resolution. A shallow and a convective cloud field are then used as input for a 3-D Monte Carlo radiation model that computes the radiance distribution at the top of the atmosphere and at the surface. Surface irradiance is computed from the upwelling radiance with a method that simulates IPA retrieval. The retrieved irradiance is compared against the one computed with the 3-D model. Two effects of clouds are related to the solar and viewing geometry, noted as a shift of the apparent position of clouds and their shadows. Another cloud effect is the diffusion of radiation: Scattering removes part of the radiation from an atmospheric column and distributes it to neighboring columns. Corrections for these effects are suggested, which can improve the IPA-based retrieval of ISFC. All corrections depend upon the cloud altitude, which may be difficult to obtain in operational applications. A sensitivity analysis suggests that a coarse estimate of the cloud top altitude is sufficient for the corrections. [Copyright &y& Elsevier]