Photon Penetration Depth Research Articles

Gamma-ray shielding features of Co1-xCuxFe2O4 ferrite: A combined experimental, theoretical and simulation investigation

This study describes a rapid synthesis of Co1-xCuxFe2O4 nanoparticles using sol–gel auto-ignition and the produced materials were examined using different techniques such as XRD (X-Ray Diffraction), UV–Vis (Ultraviolet–visible), (FTIR Fourier Transform Infrared Spectroscopy), FE-SEM (Field emission scanning electron microscopy), and EDS (Energy-dispersive X-ray spectroscopy) to explore their structural, optical, and functional group morphological properties, and elemental analysis. Additionally, utilizing several gamma-ray sources and a NaI (Tl) scintillation detector, we studied the gamma-ray shielding characteristics for the prepared materials. Experimental results were validated by the results of XCOM program and the Geant4 simulations. For four chosen ferrites, the gamma ray energy absorption build-up factor is investigated at 0.01–15 MeV incident photon energy and penetration depths of 1–40 mean free path, mfp, using the geometric progression fitting technique. Ferrite samples can be employed as radiation attenuators across a range of nuclear domains, as per the findings of this study. In comparison to the other spinel ferrites, the Co1-xCuxFe2O4 (x = 0.75) ferrite demonstrated superior shielding capabilities. Important details regarding the physio-chemical properties of spinel ferrites and their ability to shield against gamma radiation are provided in the present study.

Statistics of maximum photon penetration depth in a two-layer diffusive medium.

We present numerical results for the probability density function f(z) and for the mean value of photon maximum penetration depth ‹zmax› in a two-layer diffusive medium. Both time domain and continuous wave regime are considered with several combinations of the optical properties (absorption coefficient, reduced scattering coefficient) of the two layers, and with different geometrical configurations (source detector distance, thickness of the upper layer). Practical considerations on the design of time domain and continuous wave systems are derived. The methods and the results are of interest for many research fields such as biomedical optics and advanced microscopy.

Immobilizing graphitic carbon nitride on porous silica via hydrogen bonds for photocatalytic flow synthesis of azoxybenzene

Heterogeneous photocatalysis is an ideal method for eco-friendly synthesis of value-added chemicals. However, due to the limited penetration depth of photons and inefficient utilization of the catalytic active sites, the scalability of heterogeneous photocatalysis is restrained. Combining heterogeneous photocatalysis and flow system is a promising solution to optimize the light absorption and mass transfer; however, an affordable, practical design of the flow system and the immobilization method of the photocatalyst is still missing. Here, we report a flow system for heterogeneous photocatalytic synthesis of azoxybenzene and its derivatives from reductive coupling of nitrobenzene at a gram-scale using anchored graphitic carbon nitride (gCN) on porous silica (gCN-SiO2). The hydrogen bonds formed between the gCN and the tetramethoxysilane (TMOS) precursor during the dehydrative condensation process prevent unwanted leaching of catalyst, enabling photocatalytic flow synthesis of azoxybenzene with high selectivity, efficiency, and durability. Mechanistic studies reveals that the gCN-SiO2 regulates the photocatalytic reduction kinetics of nitrobenzene by facilitating the generation of nitrosobenzene and N-phenylhydroxylamine intermediates while preventing the formation of unwanted 4-phenylazophenol byproducts, resulting in efficient and selective synthesis of azoxybenzene. Our work provides an alternative path towards large scale heterogeneous photocatalysis.

Photochemistry sample sticks for inelastic neutron scattering.

Every material experiences atomic and molecular motions that are generally termed vibrations in gases and liquids or phonons in solid state materials. Optical spectroscopy techniques, such as Raman, infrared absorption spectroscopy, or inelastic neutron scattering (INS), can be used to measure the vibrational/phonon spectrum of ground state materials properties. A variety of optical pump probe spectroscopies enable the measurement of excited states or elucidate photochemical reaction pathways and kinetics. So far, it has not been possible to study photoactive materials or processes in situ using INS due to the mismatch between neutron and photon penetration depths, differences between the flux density of photons and neutrons, cryogenic temperatures for INS measurements, vacuum conditions, and a lack of optical access to the sample space. These experimental hurdles have resulted in very limited photochemistry studies using INS. Here we report on the design of two different photochemistry sample sticks that overcome these experimental hurdles to enable in situ photochemical studies using INS, specifically at the VISION instrument at Oak Ridge National Laboratory. We demonstrate the use of these new measurement capabilities through (1) the in situ photodimerization of anthracene and (2) the in situ photopolymerization of a 405nm photoresin using 405nm excitation as simple test cases. These new measurement apparatus broaden the science enabled by INS to include photoactive materials, optically excited states, and photoinitiated reactions.

Effect of down-shifting phosphor particles on crystalline silicon solar cells

Introducing down-shifting phosphor particles onto solar cells can improve their spectral response to short wavelength photons, but it also leads to the rise of reflection in middle and long wavelength range due to the scattering by phosphor particles. In this work, the down-shifting solar cells are fabricated by packaging crystalline silicon solar cells with ethylene vinyl acetate (EVA) films which include different concentration of down-shifting Ce-doped yttrium aluminum garnet (YAG:Ce) phosphor particles. Experimental result shows that the increasing concentration of YAG:Ce phosphors strengthens the down-shifting effect and makes the reflection rise. The competition between the down-shifting effect and the reflection results in the best improvement of the solar cells when the phosphor's concentration is 0.7%. The optical ray-tracing simulations clarify that the packaged solar cell with YAG:Ce absorbs less photons than those without YAG:Ce, but their conversion efficiency is higher than those without YAG:Ce. This indicates that the penetration depth of the short wavelength photons is responsible for the poorer spectral response of the solar cells in the short wavelength range.

Non-invasive optical monitoring of human lungs: Monte Carlo modeling of photon migration in Visible Chinese Human and an experimental test on a human.

The human lung was quantified and visualized by photon transport in this paper. A Monte Carlo (MC) simulation of voxelized media was used with the visible Chinese human (VCH). This study theoretically explored the feasibility of non-invasive optical detection of pulmonary hemodynamics, and investigated the optimal location of the light source in the lung photon migration and optimized the source-detector distance. The light fluence intensity showed that the photon penetration depth was 6-8.4 mm in the human lung. The optimal distance from the light source to the detector was 2.7-2.9 cm, but the optimal distance of the superior lobe of right lung was 3.3-3.5 cm. We then conducted experiments on diffuse light reflectance using NIRS on 14 volunteers. These measurements agree well with the simulation results. All the results demonstrated the great potential of non-invasive monitoring of pulmonary hemodynamics and contribute to the study of human lungs in the biomedical optics community.

Practical Ferrioxalate Actinometry for the Determination of Photon Fluxes in Production-Oriented Photoflow Reactors

Accurate determination of the photon flux is of major importance to evaluate and characterize photochemical reactor setups. Knowing the photon flux ensures reproducible reactor operation and facilitates predictable scale-up. Over the past years, flow reactors have proven to be the key enabling technology for photochemistry to become relevant on production scales. This is mainly due to the mitigation of the limited penetration depth of photons in typical batch reactors. However, due to the practical drawbacks of the widely accepted standard for photon flux determination (ferrioxalate actinometry) concerning precipitation and gas formation at higher conversion, reliable actinometry in flow reactors is still challenging. In this paper, three practical approaches for the ferrioxalate-based determination of the photon flux are presented, which address these problems. These “dimmed emitter,” “segment-based,” and “time-resolved” methods thus allow photon flux determination in flow reactors with higher irradiated volumes and more powerful light sources, which is of utmost importance in the context of future scale-up.

Engineering the gain and bandwidth in avalanche photodetectors.

Avalanche and Single-Photon Avalanche photodetectors (APDs and SPADs) rely on the probability of photogenerated carriers to trigger a multiplication process. Photon penetration depth plays a vital role in this process. In silicon APDs, a significant fraction of the short visible wavelengths is absorbed close to the device surface that is typically highly doped to serve as a contact. Most of the photogenerated carriers in this region can be lost by recombination, get slowly transported by diffusion, or multiplied with high excess noise. On the other hand, the extended penetration depth of near-infrared wavelengths requires thick semiconductors for efficient absorption. This diminishes the speed of the devices due to the long transit time in the thick absorption layer that is required for detecting most of these photons. Here, we demonstrate that it is possible to drive photons to a critical depth in a semiconductor film to maximize their gain-bandwidth performance and increase the absorption efficiency. This approach to engineering the penetration depth for different wavelengths in silicon is enabled by integrating photon-trapping nanoholes on the device surface. The penetration depth of short wavelengths such as 450 nm is increased from 0.25 µm to more than 0.62 µm. On the other hand, for a long-wavelength like 850 nm, the penetration depth is reduced from 18.3 µm to only 2.3 µm, decreasing the device transit time considerably. Such capabilities allow increasing the gain in APDs by almost 400× at 450 nm and by almost 9× at 850 nm. This engineering of the penetration depth in APDs would enable device designs requiring higher gain-bandwidth in emerging technologies such as Fluorescence Lifetime Microscopy (FLIM), Time-of-Flight Positron Emission Tomography (TOF-PET), quantum communications systems, and 3D imaging systems.

Binary contributions of Dy3+ ions on the mechanical and radiation resistance properties of oxyfluoroborotellurite Dyx-glasses

5CaF2–5BaF2 – 60B2O3–10TeO2 – (20-x)Na2O – xDy2O3: (0.5 ≤ x ≤ 2.5 mol percent) glasses were studied for their physical, mechanical, and gamma radiation resistance. The density of Dy0.5 and Dy2.5 glass samples containing 0.5 and 2.5 mol of Dy2O3 was changed from 2.98 to 3.09 g/cm3, respectively. The estimated values of longitudinal (LB-C) were altered from 171.085 to 165.390 GPa, bulk (KB–C) from 105.100 to 102.680 GPa, Young's (EB-C) from 128.602 to 122.674 GPa, and shear (SB–C) from 49.612 to 47.150 GPa for mechanical characteristics (GPa). The Poisson's ratio (σB-C) was varied between 0.296 and 0.300. The MCNPX code and Py-MLBUF online calculation platform were used to calculate mass attenuation coefficients for all Dyx-glasses. In terms of quantitative values, the acquired results are in good agreement. For all photon energies, the Dy2.5 glass sample exhibits the highest linear (μ) and mass (μm) attenuation coefficients. All analyzed Dyx-glasses exhibit a similar trend in half-value layer (T1/2) and mean free path (MFP), (T1/2, λ)Dy0.5 > (T1/2, λ)Dy1.0 > (T1/2, λ)Dy1.5 > (T1/2, λ)Dy2.0 > (T1/2, λ)Dy2.5. Over the whole gamma-ray energy range, the Dy2.5 sample has the highest effective atomic number (Zeff) values. Across the whole photon energy and penetration depth range, the Dy2.5 has the lowest EBF and EABF values. Because of the maximum contribution of Dysprosium (III)-oxide, the Dy2.5 sample can be deemed superior in terms of gamma-ray shielding qualities.

3-dimensional simulation of light transport in tissue using a steady state monte carlo method for photodynamic therapy application

Photodynamic therapy (PDT) is a developing treatment modality for cancer and surface carcinomas that uses a combination of non-ionizing light in the presence of a photosensitizing (PS) agent and oxygen to produce singlet oxygen that can be combined with other physiological factors to cause an organ cells death of the target area. This research simulates the propagation of light photons through normal tissue and tissue incubated with a PS agent (Metvix – Methyl Aminolevulinate (MAL)) and prepped for PDT procedure. Using the Hop/Drop/Spin nomenclature, the photons, after being allocated a weight, are allowed to take random step-size through the tissue as they are attenuated by the tissue and the presence of the photosensitizing agent while accounting for the degradation of the PS agent as the process proceeds. In each step, a fraction of the photon’s weight is deposited into allocated three-dimensional Cartesian bin. In comparison with normal tissue, the result from tissues prepped with the PS agent showed increased divergence of photon’s spatial trajectory, increment in photon penetration depths and overall attenuation. The introduction of the PS agents into tissue during PDT causes improvement in the overall attenuation of the tissue, and this improvement in attenuation can be used for accurate localization of treatment area during PDT procedures and, combined with other photodynamic factors, used for calculating the effective photon dose (PD).

Imaging deeper than the transport mean free path with multiphoton microscopy.

Multiphoton fluorescence microscopy enables deep in vivo imaging by using long excitation wavelengths to increase the penetration depth of ballistic photons and nonlinear excitation to suppress the out-of-focus fluorescence. However, the imaging depth of multiphoton microscopy is limited by tissue scattering and absorption. This fundamental depth limit for two-photon microscopy has been studied theoretically and experimentally. Long wavelength three-photon fluorescence microscopy was developed to image beyond the depth limit of two-photon microscopy and has achieved unprecedented in vivo imaging depth. Here we extend the theoretical framework for characterizing the depth limit of two-photon microscopy to three-photon microscopy. We further verify the theoretical predictions with experimental results from tissue phantoms. We demonstrate experimentally that high spatial resolution diffraction-limited imaging at a depth of 10 scattering mean free paths, which is nearly twice the transport mean free path, is possible with multiphoton microscopy. Our results indicate that the depth limit of three-photon microscopy is significantly beyond what has been achieved in biological tissues so far, and further technological development is required to reach the full potential of three-photon microscopy.

Enhancement of Gamma-ray Shielding Properties in Cobalt-Doped Heavy Metal Borate Glasses: The Role of Lanthanum Oxide Reinforcement.

The direct influence of La3+ ions on the gamma-ray shielding properties of cobalt-doped heavy metal borate glasses with the chemical formula 0.3CoO-(80-x)B2O3-19.7PbO-xLa2O3: x = 0, 0.5, 1, 1.5, and 2 mol% was examined herein. Several significant radiation shielding parameters were evaluated. The glass density was increased from 3.11 to 3.36 g/cm3 with increasing La3+ ion content from 0 to 2 mol%. The S5 glass sample, which contained the highest concentration of La3+ ions (2 mol%), had the maximum linear (μ) and mass (μm) attenuation coefficients for all photon energies entering, while the S1 glass sample free of La3+ ions possessed the minimum values of μ and μm. Both the half value layer (T1/2) and tenth value layer (TVL) of all investigated glasses showed a similar trend of (T1/2, TVL)S1 > (T1/2, TVL)S2 > (T1/2, TVL)S3 > (T1/2, TVL)S4 > (T1/2, TVL)S5. Our results revealed that the S5 sample had the highest effective atomic number (Zeff) values over the whole range of gamma-ray energy. S5 had the lowest exposure (EBF) and energy absorption (EABF) build-up factor values across the whole photon energy and penetration depth range. Our findings give a strong indication of the S5 sample’s superior gamma-ray shielding characteristics due to the highest contribution of lanthanum oxide.

Evaluation of radiation attenuation properties of some cancer drugs

The present study was conducted to estimate the radiation attenuation parameters of six different antineoplastic drugs used in the cure of cancer diseases. The effective atomic number and electron density of anastrozole, epirubicin, gemcitabine, ifosfamide, methotrexate and paclitaxel were computed theoretically in the energy region of 1keV to 100 GeV. The energy absorption buildup factors (EABF) and exposure buildup factors (EBF) for these chemotherapy drugs were also examined by applying GP-fitting method. The variation of EABF and EBF values with photon energy and penetration depth were presented graphically and discussed. The results obtain from this study pointed out that buildup factors rely on the chemical combination of the drugs, incident photon energy and penetration thickness. It was observed that ifosfamide had a significantly better radiation absorption effect compared to other drugs. The data obtained from this study are expected to be useful in the fields of radiation biology, radiation dosimetry and radiotherapy.

Optical crosstalk photon penetration depth in Silicon Photomultipliers

In recent years, many researchers have explored the application of Silicon Photomultipliers (SiPMs) in various weak light detection fields. Optical crosstalk probability (Pct) is one of the most important parameters of the SiPM, so the performance of the device may be optimized by further research on the Pct mechanism. The two-dimensional (2D) and 1D spatial distribution analysis of optical crosstalk probability in a typical SiPM were employed in this study via pulsed laser focusing and precision displacement methods in order to obtain the penetration depth of optical crosstalk photons in the SiPM. It was believed that there are five propagating modes of crosstalk photons in SiPM. One of the propagating modes is that the crosstalk photons generated by an avalanche photodiode (APD) cell passing through the substrate material and reflecting to other APD cells at the bottom interface of the substrate, thus causing other APD cells to avalanche. However, the probability of this crosstalk photon propagating mode appears to be negligible. By fitting the experimental results, the penetration depth of crosstalk photons in the SiPM was determined to be less than 22 micrometers. As the substrate thickness of most SiPMs is more than 300 micrometers, the probability of crosstalk photons passing through SiPM substrate material and reflecting to other APD is less than 1.4 E-12. Therefore, this crosstalk mode needs not be considered in the crosstalk mechanism analysis of SiPMs. A novel technique for measuring the effective propagating distance of the crosstalk photons in SiPMs was developed which can be used to characterize the effective action distance of the crosstalk photons in different structures and types of SiPMs. This work may provide a reference for the design and fabrication of SiPMs in the future.

Noninvasive Monitoring of Glucose Using Near-Infrared Reflection Spectroscopy of Skin-Constraints and Effective Novel Strategy in Multivariate Calibration.

For many years, successful noninvasive blood glucose monitoring assays have been announced, among which near-infrared (NIR) spectroscopy of skin is a promising analytical method. Owing to the tiny absorption bands of the glucose buried among a dominating variable spectral background, multivariate calibration is required to achieve applicability for blood glucose self-monitoring. The most useful spectral range with important analyte fingerprint signatures is the NIR spectral interval containing combination and overtone vibration band regions. A strategy called science-based calibration (SBC) has been developed that relies on a priori information of the glucose signal (“response spectrum”) and the spectral noise, i.e., estimates of the variance of a sample population with negligible glucose dynamics. For the SBC method using transcutaneous reflection skin spectra, the response spectrum requires scaling due to the wavelength-dependent photon penetration depth, as obtained by Monte Carlo simulations of photon migration based on estimates of optical tissue constants. Results for tissue glucose concentrations are presented using lip NIR-spectra of a type-1 diabetic subject recorded under modified oral glucose tolerance test (OGTT) conditions. The results from the SBC method are extremely promising, as statistical calibrations show limitations under the conditions of ill-posed equation systems as experienced for tissue measurements. The temporal profile differences between the glucose concentration in blood and skin tissue were discussed in detail but needed to be further evaluated.

Polymeric nanowrinkles: surface modification of polypropylene films in the VUV energy range

The development of strategies for shape-programming polymer materials has been considerably growing. This is due to the possibility of shifting two to three-dimensional shapes producing nanotexturing, such as nanowrinkles. In this work, nanowrinkle patterns were produced in polypropylene (PP) films using a broadband non-monochromatic radiation ranging from 3 to 21 eV by a synchrotron source. The superficial modification was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, X-ray photoelectron (XPS) and Raman spectroscopy were used to study the chemical modifications of the PP samples. The surface modifications became more evident as the exposure time increased, proving that the formation of nanowrinkles presents a time-dependent behavior, clearly proved by AFM and SEM analysis. Another important aspect is that nanowrinkles consist of a thin layer compatible with the photon penetration depth in this energy range with almost no change in bulk. The spectroscopic results show crosslinking and unsaturated bonds formation increase as a function of time, which corroborates nanowrinkle formation via stress creation on the surface plane, and the relief of this stress outside the plane.

Exposure buildup factor investigation of tungsten gadoliniumborate system

Abstract The gamma ray exposure buildup factors (EBF) of xWO3:(70-x)Gd2O3:30B2O3 system (where x=40, 45, 50, 55 and 60 mol%) have been calculated in the energy region 0.015–15 MeV up to a penetration depth of 40 mfp (mean free path). The five parameter geometric progressions (G-P) fitting method has been used to compute exposure buildup factor values. Variation of exposure buildup factors with incident photon energies and penetration depth have been studied. It was found that EBF values were higher in the intermediate energy region, for all glass system. Moreover, tungsten gadolinium borate glass of 40 mol% WO3, was found to present the lowest EBF values, hence it is excellent gamma ray shielding material. The obtained results in this paper show that these glasses can be used as radiation shielding materials

Short-Circuit Photocurrent Density Determination of Chalcopyrite Solar Cells and Study of Basic Parameters Under AM0, AM1, AM1.5 Spectra

In this work we present a method to evaluate the short-circuit photocurrent density delivered by a solar cell by and study basic parameters which are at the origin of the latter by considering the solar spectra AM0, AM1 and AM1.5. This photocurrent density is the greatest current density that the cell can supply according to the considered parameters for a given illumination. We apply this method to a 4-layer model composed of absorber materials based on chalcopyrite semiconductors (CuInSe₂ and CuInS₂) and based on a wide band gap window layers (ZnO and CdS) according to the model ZnO(n⁺)/CdS(n)/CuInS₂(p)/CuInSe₂ (p⁺) (model n⁺/n /p/p⁺). For this model the CuInS₂ and CuInSe₂ layers are named respectively base and substrate. We exploit continuity equation that governing charge carriers transport in semiconductor materials and use Newton's quadrature integration method over the entire solar spectrum ranging from 1 eV to 4 eV. For this calculation, we have found values of the short-circuit photocurrent density equal to 24.5 mA.cm^-2, 19.3 mA.cm^-2, 17.5 mAcm^-2 respectively for the spectra AM0, AM1 and AM1.5 for the used parameters. The same principle of calculation and reasoning is used to determine and study under a given solar spectrum some intrinsic basic parameters such as the generation rate of carriers, the densities of minority carriers generated and the resulting photocurrents versus the junction depth. The study of these parameters shows a low penetration depth of photons for the considered materials CuInS₂/CuInSe₂, losses of charge carriers due to recombination phenomena in surface and interface, bulk recombinations, and losses which are also due to the natural phenomenon of diffusion of carriers in the material under a concentration gradient. This study tries to show that the optimization of the growth conditions of layers, a good choice of material arrangement and a good geometric dimensioning are essential to improve collection efficiency of charge carriers and the short-circuit photocurrent of a photovoltaic cell.

Gamma-Ray Exposure Buildup-Factors Calculations for Some Radiation-Resistant and Radiation-Protective Glasses

In this article, we first calculate gamma-ray exposure buildup-factors of some radiation-resistant glasses and radiation-protective glasses by using the Geometric Progression (G-P) fitting method. And then we analyze variations of the exposure buildup-factor with the incident photon energy and penetration depth. The results show that exposure buildup-factors strongly associate with photon energy and penetration depth. Exposure buildup-factors calculated in this article are useful for the design of a peer window used in nuclear industry.

Photocured conductive PANI/acrylate composites for digital light processing. Influence of HDODA crosslinker in rheological and physicochemical properties

The design of novel photocurable conductive acrylic composites demands thorough research to find appropriate balance between the relative concentrations of monofunctional/ multifunctional monomers, photoinitiators and conductive filler, besides adjusting polymerization conditions. Likewise, when an intrinsically conductive polymer such as polyaniline (PANI) is selected as conductive filler, the homogeneous distribution of its nanometric aggregates is essential to prevent heterogeneous curing due to its strong UV absorption. In this work, the influence of PANI-HCl on the physical properties of acrylic composites based on Ethyleneglycolphenylether acrylate (EGPEA) and Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), photoinitiator, was examined in the frame-work of the percolation model. Rheological testing combined with Scanning Electron Microscopy (SEM) were used for efficient control of the filler dispersion in order to better understand the electrical conductivity-structure behaviour. Infrared Spectroscopy probed the degree of monomer conversion and the filler interaction with the polymer matrix, whereas the thermal properties were evaluated with the aim of establishing the maximum working temperatures. Above the percolation threshold, the formulation with 4.8 wt% PANI was selected as the most suitable composition achieving maximum conductivity (10-3 S cm−1) at the lowest PANI content. The problem of excessive aggregation of PANI clusters was tackled by the addition of a 15 wt% of the reactive diluent 1,6-hexanediol diacrylate (HDODA) to the previous formulation. The outcomes were improved dispersion and better integration of PANI nanorods within the acrylic matrix plus a smoother film surface, while retaining high electrical conductivity. The viscosity of the selected prepolymer formulations and penetration depth of UV photons gave encouraging results for the use of the developed compositions as anticorrosion coatings, digital light processing (DLP) or piezoelectric sensors. The high critical cure dosages obtained will be easily overcome by adjusting the type and/or amount of photoinitiator.