Neutron activation experiments for bremsstrahlung characterization studies

Activation experiments were conducted to assess the bremsstrahlung continuum produced from the activation of the ⁷Li isotope and the subsequent short-lived 13 MeV beta decay of ⁸Li (T _1/2 = 843 ms). The combination of the high energy beta-decay and the high atomic numbered metals used in piping for ⁷Li liquid metal coolants is a scenario in which bremsstrahlung production is a principal shielding concern. A series of fast pneumatic activation experiments have been performed to obtain the spectral distributions of bremsstrahlung gamma-rays transmitted through stainless steel shield samples. Detectors were used in both pulse-height and multichannel scaling analysis modes for energy spectra determination and half-life verification, respectively. Experimental results were utilized to validate the electron transport and bremsstrahlung production models used in the Monte Carlo MCNP code.     

Damage‐depth profiling of ion‐irradiated polyimide films with a variable‐energy positron beam

Various polyimide layers [2.2–2.6 μm of hexafluoroisopropylidene bis(phthalic anhydride‐oxydianiline), pyromellitic dianhydride‐oxydianiline, and 3,3′‐4,4′‐biphenyltetracarboxylic dianhydride‐p‐phenylenediamine] spin‐coated on silicon substrates were studied with a variable‐energy positron beam in combination with a Doppler‐broadened annihilation radiation technique. From the experiments, the thickness of the layers was estimated with the VEPFIT routine. These values corresponded well to the values determined from interferometry and ellipsometry. Irradiation of the polyimides with 1 × 10¹⁵ boron ions/cm² at an energy of 180 keV led to a strong chemical modification of the irradiated top layer. This caused the inhibition of positronium formation in the irradiated layer, which was observed as a lowering of the annihilation line S parameter. The thickness of the modified layer was estimated to be 700–800 nm. This value did not agree with the ellipsometric measurements but corresponded to the maximum implantation depth of boron ions calculated with TRIM (Transport of Ions in Matter) code. The positron results appeared somewhat larger than the TRIM estimates. Reasons for these relations are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3062–3069, 2000     

Enhancing Fluorescence of Shallow Nitrogen-Vacancy Centers in Diamond by Surface Coating with Titanium Oxide Layers

We present an enhancement of the fluorescence of shallow (<10 nm) nitrogen-vacancy (NV^-) centers by using atomic layer deposition to deposit titanium oxide layers on the diamond surface. In this way, the shallow NV^- center charge states were stabilized, leading to the increasing fluorescence intensity of about 2 times. This surface coating technique could produce a protective layer of controllable thickness without any damages to the solid-state quantum system surface, which might be an approach to the further passivation or packaging techniques for the solid-state quantum devices.     

Aluminum,copper, tin and lead as shielding materials in the treatment of cancer with high-energy electrons

During irradiation of lesions in cancer treatment with electrons, irregular field sizes are shaped by blocking off the areas to be protected usually with lead or Lepowitz metal of adequate thickness. Sometimes these blocks are placed directly on the skin. In such cases, the block should not only be of minimum weight (thickness), but also the residual dose received by the protected organs should be as small as possible. However, due to the production of bremsstrahlung, it is difficult to achieve a higher degree of attenuation unless a sufficient thickness of shielding material is used. Hence, a minimum or optimum thickness is needed to be measured. Transmission measurements are performed to determine suitable minimum thicknesses and to measure the transmission at this minimum thickness, for aluminum, copper, tin and lead for electron broad-beam field sizes 6×6, 10×10 and 20×20 cm² of energies 6, 12 and 20 MeV produced by a medical linear accelerator. The ratio of the measured ionization with and without the shielding material in percent is expressed as a measure of transmission. The minimum thickness is `knee' position of the transmission curves, where the dose received by the organs (residual dose) is mostly dominated by the bremsstrahlung component and any addition of shielding material is not of much advantage in achieving further appreciable shielding effect. It is noticed that at this minimum thickness the percentage dose received by the vital organs behind the shield varies from 1 to 14% of the original unshielded dose as the atomic number of the shielding material increases from 13 (aluminum) to 82 (lead) and as the electron energy of the beam increases from 6 to 20 MeV. In other words, the effectiveness of shielding decreases from 99 to 86% as the atomic number increases from 13 to 82. Depending on the treatment volume, its position and the clearance between the electron cone and the skin, the dose received by the vital organs surrounding the tumor can be minimized by choosing the optimum thickness of these elements.     

On the creation of high energy bremsstrahlung and intensity by a multitarget and repeated focusing of the scattered electrons by small-angle backscatter at the wall of a cone and magnetic fields—A possible way to improve linear accelerators in radiotherapy and to verify Heisenberg-Euler scatter

The yield of bremsstrahlung from collisions of fast electrons (energy at least 6 MeV) with a Tungsten target can be significantly improved by exploitation of Tungsten wall scatter in a multi-layered target. The Tungsten wall can serve to refocuse small angle scattered electrons. It is necessary that the thickness of one Tungsten layer does not exceed 0.02 mm. Further repeated focusing of electrons results from suitable magnetic fields with field strength between 0.5 T and 6 T (if the cone with multi-layered targets is rather narrow). Linear accelerators in radiation therapy only need repeated focusing by wall scatter without further magnetic fields (standard case: ca. 100-000 plates with 0.01 mm thickness and 1 mm distance between the plates). The construction of a very narrow bremsstrahlung beam with extremely high photon intensity requires an additional strong magnetic field (order 1-6 T), which provides the possibility to check Heisenberg-Euler scatter of high energy photons.     

Influence of the grain size on the quality of standardless WDXRF analysis of river Nile sediments

In multichannel wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) the fluorescence intensity might depend on grain size and heterogeneity of the sample. Six river Nile sediment samples were collected two meters below the water surface from different locations covering the greater Cairo, Egypt. Each sample was dried at 65 °C for 48 h and divided into four grain size fractions: < 32 μm, 32–63 μm, 63–125 μm and 125–200 μm using different sieves. The dry sediment samples were mixed with low contamination binder (Wax, C₆H₈O₃N₂) in a mass ratio of wax:sample = 4:0.9 g. Sample pellets were made using a hydraulic press at a pelletizing pressure of 120 KN cm^{− 2}. The results show that the XRF intensities of the K_α radiation might increase or decrease with decreasing grain size, depending on the atomic number of the analyte. In the present thick pelletized samples, the penetration depth of the characteristic radiation increases at low grain sizes, and consequently the probability of the grain-size effect on the characteristic radiation decreases. Depending on the experimental data, a general theoretical equation, relating fluorescence intensity, grain size and atomic number, was derived by using cubic spline interpolation. The fractions were identified by WDXRF using standardless quantitative analysis, depending on the fundamental parameter approach. According to the present statistical analysis and the Certified Reference Material (CRM) results, the quantitative analysis results were found acceptable when the grain size of the river Nile sediments less than 32 μm. At a grain size > 63 μm, standardless analysis using fundamental parameter approach was found to be useful for qualitative and semi-quantitative analysis only whereas there are a strong positive correlations.     

Determination of zinc in ammoniacal ore leaching solutions by X-ray fluorescence spectrometry using a radioactive source

A method was developed for the fast determination of zinc in leaching solutions by radioisotope energy-dispersive X-ray fluorescence (EDXRF) spectrometry. The measured intensities were used to develop regression models for estimating the zinc concentration. The primary radiation was provided by the ²⁴⁴Cm radioisotope. Several experimental parameters including the saturation thickness and detection limit were determined. The advantages of the utilization of conditioning agents with elements of low atomic number such as nitric acid were established.     

Motion of a Colloidal Sphere Covered by a Layer of Adsorbed Polymers Normal to a Plane Surface

A combined analytical–numerical study is presented for the slow motion of a spherical particle coated with a layer of adsorbed polymers perpendicular to an infinite plane, which can be either a solid wall or a free surface. The Reynolds number is assumed to be vanishingly small, and the thickness of the surface polymer layer is assumed to be much smaller than the particle radius and the spacing between the particle and the plane boundary. A method of matched asymptotic expansions in a small parameter λ incorporated with a boundary collocation technique is used to solve the creeping flow equations inside and outside the adsorbed polymer layer, where λ is the ratio of the characteristic thickness of the polymer layer to the particle radius. The results for the hydrodynamic force exerted on the particle in a resistance problem and for the particle velocity in a mobility problem are expressed in terms of the effective hydrodynamic thickness (L) of the polymer layer, which is accurate to O(λ²). The O(λ) term forLnormalized by its value in the absence of the plane boundary is found to be independent of the polymer segment distribution and the volume fraction of the segments. The O(λ²) term forL, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant.     

Permeation of oxygen dissolved in water through substituted polyacetylene membranes

The permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficients P in the range 10^?9?10^?8 cm³ (STP) cm cm^?2s^?1 cmHg^?1. The resistance r of the boundary layer and the permeability P_∞, at infinite membrane thickness were determined from the dependence of P on membrane thickness. The r values of Si-containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. The P_∞, values of Si-containing and aliphatic polyacetylenes agreed closely with the permeability coefficients P_g for gaseous oxygen. In contrast, P_∞ values for aromatic polyacetylenes were larger than P_g values.     

Die sekundäranregung bei der Röntgenfluoreszenzanalyse ebener dünner schichten

The characteristic radiation of thin element films is in certain cases excited by the characteristic radiation of the substrate material, or, on the contrary, the thin film radiation is able to excite the substrate radiation. Based on theoretical considerations a calculation of this effect is given.

For thin film radiation the amount reaches up to 25 per cent of the total intensity and for substrate radiation at maximum 5 per cent.

Thin alloy films show a secondary excitation as well as bulk materials, but the influence is comparably smaller. At film thicknesses of approximately 1000 Å maximum values of 2 per cent of the total intensity have been calculated.     

The oscillator strength in atomic absorption spectroscopy

The role of the oscillator strength, f, in the theory of atomic absorption is investigated. For a pure natural broadened absorption line, the peak absorption coefficient α_o is independent of the oscillator strength. The peak absorption coefficient becomes dependent on f only through additional broadening processes such as Doppler or collisional broadening. The peak cross section for resonance absorption, α₀/N₁, for a closed transition with equal statistical weights is given by σ₀ = 2πXXX² = ( )/[cn(ω₀)] (where XXX = and n(ω₀) is the spectral mode density of the radiation field at the resonance frequency ω₀) and physically represents the cross-sectional area per allowed mode of the radiation field per unit time per unit frequency interval, multiplied by a lineshape factor 2/π.A summary is presented of some recent determinations of oscillator strengths of atomic absorption lines, based on lifetime measurements made in this laboratory. The results are used to revise values of the theoretical characteristic mass for Ag, Al, Au, Ca, Cu, Mo, Na, Ti and V used in absolute analysis by graphite furnace atomic absorption spectroscopy.     

Sample geometry and efficiency determination of bremsstrahlung radiation of 90Sr on gamma detection systems

Summary The bremsstrahlung radiation energy spectra were produced by hard beta-emitters the ⁹⁰Sr-⁹⁰Y contaminated tea sample sources placed in a copper cylinder (cylinder counting geometry) and encapsulated in two Cu discs (sandwich counting geometry). These energy spectra were directly measured by using two separate gamma-ray spectrometers with a coaxial 110% efficient HpGe detector and a 110 cm³ HpGe well-type detector. The minimum detectable activity and the absolute efficiency of beta-activity for the sandwich and cylinder geometries were found to be 23 Bq ^. kg^-1 and (1.67±0.04)% and 55 Bq ^. kg^-1 and (2.61±0.05)%, respectively. These results indicate that the bremsstrahlung radiation counting method can be applied to some environmental studies when high efficient HpGe detectors, especially well-type HpGe are used.     

Electrophoretic mobility and stability of SiO2 nanoparticles in the solutions of AOT in n-hexadecane-chloroform mixtures

Electrophoretic mobility of SiO₂ nanoparticles in a n-hexadecane-chloroform mixture depending on AOT concentration and chloroform content was determined. It was shown that an increase in chloroform content and a decrease in AOT concentration cause a growth in electrophoretic mobility. The use of the values of Debye lengths (characteristic thickness) of the diffuse part of the electric double layer (EDL) that were determined previously allowed us to calculate the electrokinetic potential and to evaluate the stability of organosols. The obtained data were in good correlation with the dynamics of temporal changes of hydrodynamic radius and the intensity of light scattering. Organosols may be used for heteroaggregation (sorption) of Au and Ag nanoparticles on SiO₂.     

Measurement of A Two Layer Sample Using Pseudo Pulse Excited Photoacoustic Spectrometry

Abstract

To obtain surface layer thickness easily, a simple pseudo pulse excited photoacoustic spectrometric method was proposed. An argon ion laser was chopped mechanically to generate a pseudo pulse (pulse width; 6.6 ms, duty 1.67%), which was then led to a sample enclosed in photoacoustic cell. Two layer samples made of polymethyl methacrylate (PMMA) were used as model samples. The photoacoustic signal waveform observed showed a maximum from the negative edge of the pseudo pulse of the laser. The delay of the signal increased concomitant with the sample surface thickness. The delay time of the signal was calculated by a cross-correlation method. A linear relationship was obtained between the delay time of the photoacoustic signal from the input pseudo pulse and the surface transparent layer thickness in the range of 0–90 mm. The regression line between the film thickness x (cm) and the delay time was expressed with the thermal diffusivity of the film k, as follows; Δτ (s) = 1.16 × 10^?1 κ^?½ x + 0.006. Using this result, the method proposed was successfully applied to the measurement of the thickness for laminated polyethylene film on papers. The method proposed is simple and easy to perform without any modification of usual photoacoustic instrumentation.     

X-ray fluorescence spectrometry with synchrotron radiation

X-ray fluorescence spectrometry (x.r.f.) can be done through excitation with synchrotron radiation. This permits multi-element determinations in the trace region with improved detection limits compared to conventional x.r.f. Detection limits are evaluated and compared with theoretically calculated values. For a beam diameter of 0.5 mm and a sample of 1 mg cm^?2, absolute detection limits are between 0.1 and 0.4 pg. The dependence of the detection limit on the atomic number is reduced, when white synchrotron radiation is used for excitation instead of monochromatic radiation. The optimum of the limit of detection on the Z-scale can be shifted to higher atomic numbers and improved through filtration of the primary radiation by aluminium absorbers. Preparation of samples on different polymeric films is discussed in relation to blank values.     

Experimental study on the 3D‐printed plastic parts and predicting the mechanical properties using artificial neural networks

This study investigates the mechanical properties of 3D‐printed plastic parts fabricated using Fused Deposition Modeling (FDM). For this purpose, a 3D printer named KASAME was designed and built by the researchers. The test samples were fabricated using polylactic acid (PLA). The experiments were conducted using three melt temperatures (190°C, 205°C, and 220°C), four layer thickness values (0.06 mm, 0.10 mm, 0.19 mm, and 0.35 mm), and three raster pattern orientations (+45°/?45° [the crisscross pattern], horizontal and vertical). Tensile strength tests were performed to determine tensile strength values of the samples and fracture surfaces were also analyzed. Using artificial neural networks, a mathematical model for the tensile test results was generated corresponding to the raster pattern employed in 3D fabrication. Tensile strength tests indicated that melt temperature, layer thickness, and raster pattern orientation had a significant effect on the tensile strengths of the samples. According to the result of the experiment, the maximum average tensile strength values were observed for the samples fabricated using the crisscross raster pattern. The analysis of variance (ANOVA) table shows the raster pattern (PCR) value of 48.68% was obtained with the highest degree of influence. With respect to R ², the best performing artificial neural network model, with test and training values of 0.999199 and 0.999997, respectively, was observed to be the crisscross raster pattern. Copyright © 2016 John Wiley & Sons, Ltd.     

Bremsstrahlung emission in α-decay of210Po

Bremsstrahlung photons associated with the α-decay of²¹⁰Po were measured in α-γ coincidence measurements with Si and Ge detectors. Emission probabilities of the bremsstrahlung deduced for²¹⁰Po were 10⁻¹¹∼10⁻¹²/keV/sr/decay for 100≤E _γ≤600 keV. It was found that the bremsstrahlung yields are much smaller than those predicted by a Coulomb acceleration model. This suggests that α-particles also emit photons inside the barrier. The bremsstrahlung spectrum was compared with a quasi-classical calculation in which the bremsstrahlung emission in tunneling motion of α-particles is taken into account. It is shown that the data can be interpreted as a consequence of destructive interference of radiative amplitudes outside the Coulomb barrier with those in tunneling.     

Precise non-destructive X-ray fluorescence method for uranium and thorium concentration measurements

A precise non-destructive radioisotope X-ray fluorescence method for uranium and thorium concentration measurements was developed. A beta-emitting⁹⁰Sr−⁹⁰Y source was used for excitation of characteristic X-ray lines. It is proved that the beta-excited X-ray fluorescence method (in spite of the significant bremsstrahlung intensity) has essential advantages for analysis of high concentrations of U and Th, characteristic for nuclear power cycle materials, because of the higher sensitivity of the method. (3% changes of the intensity per 1% change of the concentration.) Portable semiconductor or scintillation detectors and multichannel analysers are used for detection of analytical lines. The accuracy achieved by this method is 0.2–0.3% for 15 minutes measurement and 0.1 mCi activity of the source. This work was performed under contract with the International Atomic Energy Agency, Vienna.