Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Fluorescence “Turn‐On” Patterning With Polymers Having Pendant Triphenylmethane Groups as Fluorophore Precursors

A new methodology for creating patterned fluorescence images was developed based on acrylate polymers that have pendant triphenylmethane derivatives as precursor fluorophores. Photoinduced oxidation of the substituted nonfluorescent triphenylmethane substituents on the polymers results in the generation of fluorescent cationic species. Patterned fluorescence images were obtained when the polymer film was subjected to photomasked UV‐irradiation. The rate of formation and quality of the patterned images were found to be dependent on the nature of substituents on the methane carbon of the triphenylmethane group. Inefficient image formation takes place with the polymer derived from the H‐substituted derivative owing to the inefficient oxidation of the triphenylmethane group. In contrast, photomasked UV‐irradiation of a thin polymer film derived from the CN‐substituted triphenylmethane derivative leads to fast (1 s irradiation, 12 mW · cm⁻²) and finely resolved patterned fluorescence images.

     

Measurement of Inherent Material Density of Nanoparticle Agglomerates

We describe a new technique to measure the size dependent inherent material density of chain agglomerate particles. Measurements were carried out for diesel soot and aluminum/alumina agglomerate particles in the nanometer size range. Transmission electron microscopy was used to measure the volumes of agglomerate particles that were preselected by mass using an aerosol particle mass analyzer. We found that the density of diesel exhaust particles increased from 1.27 to 1.78g/cm³ as particle mobility size increased from 50 to 220nm. When particles are preheated to remove volatile components, the density was 1.77±0.07g/cm³, independent of particle size. The densities measured after heating correspond to the inherent material density of diesel soot. Measurements with aluminum nanoparticles were made downstream of a furnace where aluminum (Al) was converted to alumina (Al₂O₃). From measurements of inherent material density we were able to infer the extent of reaction, which varied with furnace temperature.     

Anomalously suppressed localization in the two-channel Anderson model

We study numerically the localization properties of a two-channel quasi-one-dimensional Anderson model with uncorrelated diagonal disorder within the nearest-neighbor tight-binding approximation. We calculate and analyze the disorder-averaged transmittance and the Lyapunov exponent. We find that the localization of the entire system is enhanced by increasing the interchain hopping strength t?. From the numerical investigation of the energy dependence of the Lyapunov exponent for many different interchain hopping strengths, we find that apart from the band center anomaly, which usually occurs in strictly one-dimensional disordered systems, additional anomalies appear at special spectral points. They are found to be associated with the interchain hopping strength and occur at E = ± t?/2 and ± t?. We find that the anomalies at E = ± t? are associated with the π-coupling occurring within one energy band and those at E = ± t?/2 are associated with the π-coupling occurring between two different energy bands. Despite having a similar origin, these two anomalies have distinct characteristics in their dependence on the strength of disorder. We also show that for a suitable range of parameter values, effectively delocalized states are observed in finite-size systems.     

Antireflection film in one-dimensional metallo-dielectric photonic crystals

We calculated the transmittance of a one-dimensional (1D) metallo-dielectric photonic crystal (MDPC) in the optical region including the absorption losses in metal layers. The structure consists of five Ag and four GaN layers stacked alternately. When we add an antireflection coating to each end of the stack, the transmittance of the MDPC is increased twice as much and the oscillations in the transmission spectrum are also smoothed out compared with the case without them. The transmittance for oblique incident angles is also increased by the addition of two antireflection layers at the ends of the 1D MDPC.     

Two‐Dimensional Fullerene Assembly from an Exfoliated van der Waals Template

Two‐dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom‐up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C₆₀ as a polymerizable monomer. The C₆₀ building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C₆₀ monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C₆₀. The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid.     

High-quality, large-area monolayer graphene for efficient bulk laser mode-locking near 1.25 μm

High-quality monolayer graphene as large as 1.2×1.2?cm² was synthesized by chemical vapor deposition and used as a transmitting saturable absorber for efficient passive mode-locking of a femtosecond bulk solid-state laser. The monolayer graphene mode-locked Cr:forsterite laser was tunable around 1.25?μm and delivered sub-100?fs pulses with output powers up to 230?mW. The nonlinear optical characteristics of the monolayer graphene saturable absorber and the mode-locked operation were then compared with the case of the bilayer graphene saturable absorber.     

Effect of mixing structure on the hygroscopic behavior of ultrafine ammonium sulfate particles mixed with succinic acid and levoglucosan

Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine(100 nm)ammonium sulfate particles internally mixed with either succinic acid〔slightly soluble) or levoglucosan(soluble) in different mixing structures(core-shell vs. well-mixed) were measured using a hygroscopicity tandem differential mobility analyzer(HTDMA). During the hydration process(6-92% relative humidity(RH)), the size of core-shell particles(ammonium sulfate and succinic acid) remained unchanged until a s|ow increase in particle size occurred at 79% RH; however, an abrupt increase in size(i.e., a clear deliquescence) was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles(80:20 by volume). This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan's higher solubility relative to succinic acid. The growth factor(GF) of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.     

A study on effects of size and structure on hygroscopicity of nanoparticles using a tandem differential mobility analyzer and TEM

A hygroscopicity tandem differential mobility analyzer (HTDMA) technique is used to determine size-effect of nanoparticles (NaCl, (NH₄)₂SO₄, KCl, NH₄NO₃, MgCl₂, CaCl₂) on their hygroscopic properties (deliquescence relative humidity (DRH) and hygroscopic growth factor (GF)). The HTDMA system uses a combination of two nano DMAs and two regular DMAs to measure particle size change in a wide dynamic particle size range. Particles are subsequently analyzed with a transmission electron microscopy to investigate the potential effect of particle structure or morphology on the hygroscopic properties. We found that structural properties of NaCl and (NH₄)₂SO₄ particles also play an important role in determination of the DRH and GF and are more pronounced at smaller diameters. Data show that the DRH of NaCl nanoparticles increased from ~75% up to ~83% RH at 8 nm and that their GF decreased with decreasing size. The extent to which the GF of NaCl nanoparticles decreased with decreasing size was greater than theoretically predicted with the Kelvin correction. The GF of furnace-generated NaCl nanoparticles that have pores and aggregate shape was found to be smaller than that of atomizer-generated particles that are close to perfectly cubic. For the case of atomizer-generated (NH₄)₂SO₄ nanoparticles, we observed no significant size-effect on their DRH, and the measured GF agreed well with predicted values using the Kelvin correction. For furnace-generated (NH₄)₂SO₄ nanoparticles, a gradual growth at moderate RH without noticeable deliquescence behavior occurred. Their TEM images showed that contrary to atomizer-generated (NH₄)₂SO₄ nanoparticles the furnace-generated (NH₄)₂SO₄ nanoparticles are not perfectly spherical and are often aggregates having pores and holes, which may favor holding residual water even in the dried condition. For atomizer-generated KCl, MgCl₂, and CaCl₂ nanoparticles, we observed no significant size-effects on their DRH and GF for the mobility size as small as 20 nm.