Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications.

We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

Vertically Well-Aligned ZnO Nanoscintillator Arrays with Improved Photoluminescence and Scintillation Properties.

ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm. To obtain high-quality nanostructures, samples were annealed in a 10% H2 + 90% N2 atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained.

A Monte Carlo investigation of some important radiation parameters and tissue equivalency for photons below 1 keV in human tissues.

The attenuation coefficients are important input values in estimating not only the dose and exposure in radiotherapy and medical imaging, but also in the proper design of photon shields. While studies are widely available above 1 keV, the attenuation coefficients of human tissues for photon energies less than 1 keV have not been studied yet. In this study, the attenuation coefficients of water and some human tissues were estimated for low energy photons using the MCNP6.1 code in the energy region 0.1 keV-1 keV. Mass attenuation coefficients were estimated at photon energies of 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000 eV for water and ten human tissues (Soft, Breast, Lung, Bone, Brain, Eye lens, Ovary, Skin, Thyroid and Prostate). Results were compared with those available in literature and a fairly good agreement has been obtained. These data were then used to calculate the mean free path, half value layer, tenth value layer, effective atomic number and specific gamma-ray constant (useful for calculation of dose rate) as well. Moreover, for comparison the effective atomic number of the water has been obtained using the results of this work and using the data available in NIST database from 0.1 to 1 keV. In addition, the human tissues were compared with some tissue equivalent materials in terms of effective atomic number and specific gamma-ray constant to study the tissue equivalency from the results, the muscle-equivalent liquid with sucrose has been found to be the best tissue equivalent material for soft tissue, eye lens and brain with relative difference below 4.1%.

Study of environment friendly bismuth incorporated lithium borate glass system for structural, gamma-ray and fast neutron shielding properties.

The present work is aimed at incorporating the heavy metal oxide 'bismuth oxide' in lithium-borate glass system and studying its effect on the glass structure, durability, gamma-ray and neutron shielding ability. The density, XRD, Raman, FTIR, and UV-Visible spectroscopic techniques assisted in understanding the structure of ternary bismuth­lithium-borate glass system. It has been found that the glass samples are of amorphous nature and structure is mainly built up of BO4, BO3, BiO6, BiO3 units and non-bridging oxygens (NBOs). Bismuth-incorporated glasses possess improved water resistance ability. The gamma-ray shielding ability was evaluated from mass attenuation coefficient, mean free path, tenth value layer and effective atomic number and it was found to be improved with the addition of bismuth oxide content. The exposure build up factor was also computed to account for the secondary photons and multiple Compton scattering. The removal cross section for fast neutrons (∑R) was also evaluated to study the neutron shielding ability of our prepared glasses. The glasses were also compared with barite concrete and commercial shielding glass RS 360 for gamma-rays and, with H2O, graphite, ordinary and hematite-serpentine concrete for checking neutrons shielding ability. It was observed that our glasses have better radiation shielding properties than the compared materials. In the light of these obtained results, it was concluded that the prepared bismuth­lithium-borate glass system can be utilised for radiation shielding applications.

Radiological properties of healthy, carcinoma and equivalent breast tissues for photon and charged particle interactions.

PURPOSE: In this paper, the effective atomic numbers (Zeff), electron densities (Neff), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) of healthy (H), carcinoma (C) and equivalent (E) breast tissues were investigated to quantify differences in radiological parameters between the tissues in the continuous energy region. For these purposes, Zeffs and Neffs, of healthy, carcinoma and equivalent (H-C-E) breast tissues were calculated for interaction of gamma rays and charged particles with selected tissues. EBFs and EABFs of the tissues were also calculated for gamma rays as well and were compared to each other for different photon energies (0.015-15 MeV) up to 40 mfp. METHOD: A well-known interpolation procedure has been used for the calculation of Zeff using the mass stopping powers and mass attenuation coefficients for charged and uncharged radiations in the continuous energy region. And the buildup factors of the tissues were calculated by the well-known G-P fitting method based on the interpolation from the equivalent atomic number (Zeq). RESULTS: The variation of Zeffs, Neffs with energy and differences (%) in the Zeffs between the tissues were determined for photon, electron, proton and C ion, which is commonly used in hadron therapy in the relevant energy region 1 keV-400 MeV. Differences (%) between healthy and carcinoma tissues in Zeff were around 9%, >4%, >5%, >2.5% for C ion, photon, electron and proton interaction, respectively. The relative differences (RD %) in Zeff between healthy and equivalent tissues in the energy range 0.02-1 MeV were found to be less than 1% for photons and C ions. In addition differences (%) between healthy and carcinoma tissues in EABF and EBF were around 25%, but differences (%) between healthy and equivalent tissues were <6% and <4% (at 40 mfp) in the continuous energy region. CONCLUSIONS: From the results, BR12 was found the be available for an equivalent to healthy breast tissue in 0.02-1 MeV for photons and C ions due to RD (%) in Zeff between healthy and equivalent tissues (less than 1%). However, for electron interaction, the RD (%) in Zeff between healthy and equivalent tissues was always greater than 4% in the entire energy range, thus BR12 was found the worse an equivalent to healthy breast tissue in in the entire energy range for electron. Also the reported data in the study should be useful to choose best equivalence for photon, electron, proton and Carbon ion interactions.

Effective atomic number of soft tissue, water and air for interaction of various hadrons, leptons and isotopes of hydrogen.

PURPOSE: Characterization of soft tissue, water and air in terms of effective atomic number (Zeff) with respect to the interactions of hadrons, leptons and isotopes of hydrogen. METHOD: Mass collision stopping powers (MCSPs) were calculated first using Bethe formula. Then, these values were used to estimate Zeff using linear-logarithmic interpolation. A scale equation was also used to calculate MCSP. RESULTS: Variation in Zeff, over the 0.5-50 MeV energy range considered, is minimum for muon and pion (π meson) interactions (relative difference [RD] ≤ 7%), while maximum variation has been noticed in Zefffor heavy charged particles, i.e. alpha particle (RD ≤ 26%). The highest values of Zeff were obtained for muon particle, the lightest particle while the minimum values of Zeff were obtained for alpha particle interaction. Except for very low kinetic energies, water equivalence of soft tissue is very satisfactory (RD ≤ 3%). The Zeff of water relative to air was found to be almost constant at high energies. The present results should be valid for especially high energies where the Bethe formula can be applied. This applies to relatively higher energies (>2 MeV) for heavier particles such as alpha particles and applies to relatively lower energies (>0.5 MeV) for lighter particles such as protons. CONCLUSIONS: In view of the importance of water equivalence in particle therapy, new data on Zeff in soft tissue, water and air for fundamental particle interaction should be important. Results revealed that soft tissue could be considered as water equivalent for interaction of various fundamental particles.

A study of effective atomic number and electron density of gel dosimeters and human tissues for scattering of gamma rays: momentum transfer, energy and scattering angle dependence.

The objective of this work was to study water- and tissue-equivalent properties of some gel dosimeters, human tissues and water, for scattering of photons using the effective atomic number (Z eff). The Rayleigh to Compton scattering ratio (R/C) was used to obtain Z eff and electron density (N e ) of gel dosimeters, human tissues and water considering a 10-2-109 momentum transfer, q (Å-1). In the present work, a logarithmic interpolation procedure was used to estimate R/C as well as Z eff of the chosen materials in a wide scattering angle (1°-180°) and energy range (0.001-100 MeV). The Z eff of the chosen materials was found to increase as momentum transfer increases, for q > ~1 Å-1. At fixed scattering angle and energy, Z eff of the material first increases and then becomes constant for high momentum transfers (q ≥ 3 Å-1), which indicates that Z eff is almost independent of energy and scattering angle for the chosen materials. Based on the Z eff data and the continuous momentum transfer range (10-2-109 Å-1), MAGIC, PAGAT and soft tissue were found to be water-equivalent materials, since their differences (%) relative to water are significantly low (≤3.2 % for MAGIC up to 103 Å-1, ≤2.9 % for PAGAT up to 109 Å-1, and ≤3.8 % for soft tissue up to 109 Å-1), while the Fricke gel was not found to be water equivalent. PAGAT was found to be a soft tissue-equivalent material in the entire momentum transfer range (<4.3 %), while MAGAT has shown to be tissue equivalent for brain (≤8.1 % up to 10 Å-1) and lung (<8.2 % up to 10 Å-1) tissues. The Fricke gel dosimeter has shown to be adipose tissue equivalent for most of the momentum range considered (<10 %).

Water and tissue equivalence properties of biological materials for photons, electrons, protons and alpha particles in the energy region 10 keV-1 GeV: a comparative study.

PURPOSE: To compare some biological materials in respect to the water and tissue equivalence properties for photon, electron, proton and alpha particle interactions as means of the effective atomic number (Zeff) and electron density (Ne). METHODS: A Z-wise interpolation procedure has been adopted for calculation of Zeff using the mass attenuation coefficients for photons and the mass stopping powers for charged particles. RESULTS: At relatively low energies (100 keV-3 MeV), Zeff and Ne for photons and electrons were found to be constant while they vary much more for protons and alpha particles. In contrast, Zeff and Ne for protons and alpha particles were found to be constant after 3 MeV whereas for photons and electrons they were found to increase with the increasing energy. Also, muscle eq. liquid (with sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) within low relative differences below 9%. Muscle eq. liquid (without sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) with difference below 10%. CONCLUSIONS: The reported data should be useful in determining best water as well as tissue equivalent materials for photon, electron, proton and alpha particle interactions.

Investigation of the effective atomic numbers of dosimetric materials for electrons, protons and alpha particles using a direct method in the energy region 10 keV-1 GeV: a comparative study.

A direct method has been used for the first time, to compute effective atomic numbers (Z eff) of water, air, human tissues, and some organic and inorganic compounds, for total electron proton and alpha particle interaction in the energy region 10 keV-1 GeV. The obtained values for Z eff were then compared to those obtained using an interpolation procedure. In general, good agreement has been observed for electrons, and the difference (%) in Z eff between the results of the direct and the interpolation method was found to be <10 % for all materials, in the energy range from 10 keV to 1 MeV. More specifically, results of the two methods were found to agree well (Dif. <10 %) for air, calcium fluoride, kapton polyimide film, paraffin wax and plastic scintillator in the entire energy region with respect to the total electron interaction. On the other hand, values for Z eff calculated using both methods for protons and alpha particles generally agree with each other in the high-energy region above 10 MeV.

Collisional, radiative and total electron interaction in compound semiconductor detectors and solid state nuclear track detectors: effective atomic number and electron density.

Effective atomic numbers, Zeff and electron densities, Ne are widely used for characterization of interaction processes in radiation related studies. A variety of detectors are employed to detect different types of radiations i.e. photons and charged particles. In the present work, some compound semiconductor detectors (CSCD) and solid state nuclear track detectors (SSNTD) were investigated with respect to the partial as well as total electron interactions. Zeff and Ne of the given detectors were calculated for collisional, radiative and total electron interactions in the kinetic energy region 10keV-1GeV. Maximum values of Zeff and Ne were observed at higher kinetic energies of electrons. Significant variations in Zeff and Ne up to ≈20-25% were noticed for the detectors, GaN, ZnO, Amber and CR-39 for total electron interaction. Moreover, the obtained Zeff and Ne for electrons were compared to those obtained for photons in the entire energy region. Significant variations in Zeff were also noted not only for photons (up to ≈40% for GaN) but also between photons and electrons (up to ≈60% for CR-39) especially at lower energies. Except for the lower energies, Zeff and Ne keep more or less constant values for the given materials. The energy regions where Zeff and Ne keep constant clearly show the availability of using these parameters for characterization of the materials with respect to the radiation interaction processes.

Effective atomic numbers, water and tissue equivalence properties of human tissues, tissue equivalents and dosimetric materials for total electron interaction in the energy region 10 keV-1 GeV.

Effective atomic numbers (Zeff) of 107 different materials of dosimetric interest have been calculated for total electron interactions in the wide energy region 10keV-1GeV. The stopping cross sections of elements and dosimetric materials were used to calculate Zeff of the materials. Differences (%) in Zeff relative to water have been calculated in the entire energy region to evaluate the water equivalency of the used materials. Moreover, the tissue equivalent materials have been compared with the tissues and dosimetric materials in terms of Zeff to reveal their ability to use as tissue substitutes. Possible conclusions were drawn based on the variation of Zeff through the entire energy region and water and tissue equivalency comparisons in terms of Zeff.

Photon buildup factors in some dosimetric materials for heterogeneous radiation sources.

Effective photon energy absorption (EABF(eff)) and exposure buildup factors (EBF(eff)) have been calculated based on the effective energy concept, for some dosimetric materials such as water, polymethyl methacrylate (PMMA), polystyrene, solid water (WT1), RW3 (Goettingen Water 3), and ABS (acrylonitrile butadiene styrene), for MV X-rays and (60)Co gamma rays. Firstly, the equivalent atomic numbers (Z(eq)) of the given materials have been determined using the effective photon energies (E eff). Then, the five-parameter geometric progression (G-P) fitting approximation has been used to calculate both EABF(eff) and EBF(eff) values. Since the G-P fitting parameters are not available for the E eff values of the given materials, a linear interpolation in which a function of the logarithm of the variable is used has been performed, in order to calculate the parameters in each E eff, which will be further used for the determination of EABF(eff) and EBF(eff). In the present paper, water equivalence properties of the given materials are also discussed based on the effective buildup factors. In this study, special emphasis is placed on the calculation of EABF(eff) and EBF(eff) values of different materials for photons that are not monoenergetic but heterogeneous in energy, to obtain an initial and prior knowledge of the probable energy and buildup of photons at locations of interest, i.e., to understand whether the real absorbed dose occurs at the surface or somewhere inside the medium of interest.

Verification of dosimetric materials to be used as tissue-substitutes in radiological diagnosis.

Dosimetric materials have been investigated in terms of calculated mass energy absorption coefficient, equivalent atomic number and KERMA (kinetic energy released per unit mass) in the energy range 0.015-15 MeV. Using analytical methodology it has verified that nylon is the best substitute dosimetric material for skin, muscle, bone and soft-tissues. Relative energy absorption buildup factors calculated by G-P fitting method confirm the findings. Nylon has been found to be good tissue substitute material for making tissue-phantoms of the biological tissues investigated.

Energy absorption and exposure buildup factors for some polymers and tissue substitute materials: photon energy, penetration depth and chemical composition dependence.

The gamma ray energy absorption and exposure buildup factors have been calculated by using the five parameter geometric progression (GP) fitting formula for some polymers and tissue substitute materials in the energy region 0.015-15 MeV up to a penetration depth of 40 mean free paths. From the results, it is worth noting that significant variations occur in gamma ray buildup factors for the given polymers and tissue substitute materials depending on photon energy, penetration depth and chemical composition of the materials. Also, it was observed that there are significant variations between energy absorption (EABF) and exposure (EBF) buildup factors which may be due to the variations in chemical composition of the materials used. Finally, it is expected that the presented buildup factor data may be helpful in (a) estimating the effective dose to be given to patients in radiation therapy and diagnostics, hence allowing corrections to be made to the intensity of radiation, as it is somewhat problematic to evaluate the real absorbed dose in critical organs due to the probability of photon buildup somewhere inside the medium; (b) estimating the health hazards arising from the exposure of the human body to radiation, thus it will be helpful in controlling the exposure of the human body to radiation.

Gamma-ray energy absorption and exposure buildup factor studies in some human tissues with endometriosis.

Human tissues with endometriosis have been analyzed in terms of energy absorption (EABF) and exposure (EBF) buildup factors using the five-parameter geometric progression (G-P) fitting formula in the energy region 0.015-15 MeV up to a penetration depth of 40 mfp (mean free path). Chemical compositions of the tissue samples were determined using a wavelength dispersive X-ray fluorescence spectrometer (WDXRFS). Possible conclusions were drawn due to significant variations in EABF and EBF for the selected tissues when photon energy, penetration depth and chemical composition changed. Buildup factors so obtained may be of use when the method of choice for treatment of endometriosis is radiotherapy.

Determination of effective atomic numbers in some compounds for photoelectric process at 59.54 keV by using different methods.

The total photoelectric cross sections, sigma(pe), of some compounds have been determined from the measured total attenuation cross sections by subtracting the scattering contributions at 59.54 keV. The values of sigma(pe) were then used to compute effective atomic numbers, Z(eff) for photoelectric process at 59.54 keV. Different methods such as a direct method, an interpolation procedure and an empirical relation were employed to calculate effective atomic numbers for different compounds wherever possible. Merits and demerits of the used methods were also discussed. The obtained values of sigma(pe) and Z(eff) from the measurements were compared with the calculated ones from theory.

Chemical composition, effective atomic number and electron density study of trommel sieve waste (TSW), Portland cement, lime, pointing and their admixtures with TSW in different proportions.

The trommel sieve waste (TSW) which forms during the boron ore production is considered to be a promising building material with its use as an admixture with Portland cement and is considered to be an alternative radiation shielding material, also. Thus, having knowledge on the chemical composition and radiation interaction properties of TSW as compared to other building materials is of importance. In the present study, chemical compositions of the materials used have been determined using a wavelength dispersive X-ray fluorescence spectrometer (WDXRFS). Also, TSW, some commonly used building materials (Portland cement, lime and pointing) and their admixtures with TSW have been investigated in terms of total mass attenuation coefficients (mu/rho), photon interaction cross sections (sigma(t)), effective atomic numbers (Z(eff)) and effective electron densities (N(e)) by using X-rays at 22.1, 25keV and gamma-rays at 88keV photon energies. Possible conclusions were drawn with respect to the variations in photon energy and chemical composition.

Assessment of trace element concentration distribution in human placenta by wavelength dispersive X-ray fluorescence: effect of neonate weight and maternal age.

Trace element status in human placenta is dependent on maternal-neonatal characteristics. This work was undertaken to investigate the correlation between essential trace element concentrations in the placenta and maternal-neonatal characteristics. Placenta samples were collected from total 61 healthy mothers at gestation between 37 and 41 weeks. These samples were investigated with the restriction that the mother's age was 20-40 years old and the neonate's weight was 1-4kg. Percent concentrations of trace elements were determined using wavelength dispersive X-ray fluorescence (WDXRF). The placenta samples were prepared and analyzed without exposure to any chemical treatment. Concentrations of Fe, Cu and Zn in placenta tissues were found statistically to vary corresponding to the age of the mother and weight of the neonate. In the subjects, the concentration of Fe and Cu were increased in heavier neonates (p<0.05) and the concentration of Zn was increased with increasing mother age (p<0.05). Consequently, the Fe, Cu and Zn elements appear to have interactive connections in human placenta.

Evaluation of root canal dentin after Nd:YAG laser irradiation and treatment with five different irrigation solutions: a preliminary study.

This study evaluated in vitro any changes in the morphology and mineral content of root canal dentin after treatments with Nd:YAG laser irradiation and 5 different irrigation solutions. The groups of extracted single-rooted human teeth were exposed to sterile saline solution, 5.25% NaOCl, 3% H2O2, 15% ethylenediaminetetraacetic acid, 2% chlorhexidine gluconate, and Nd:YAG laser irradiation. All prepared teeth were bisected longitudinally; half of each tooth was used for wavelength dispersive x-ray fluorescence spectrometry analysis to assess the mineral content. The other half was studied by using scanning electron microscopy to analyze the surface of the dentin. The results showed that the calcium level and calcium/phosphorus ratio decreased significantly with the NaOCl irrigation solutions (p < .05), suggesting the presence of changes at molecular level. Significant differences among the test groups were also observed in the scanning electron microscopy evaluation (p < .05). The lowest scores for root cleaning were obtained by using ethylenediaminetetraacetic acid followed by Nd:YAG laser treatment.