Characterisation of micro-sized and nano-sized tungsten oxide-epoxy composites for radiation shielding of diagnostic X-rays

Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2–10 vol% WO₃ loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10–40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO₃-epoxy composites in the energy range of 10–25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30–40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO₃-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25–49 kV) were in the range of 15–25 keV. Similarly, for a radiology unit operating at 40–60 kV, the equivalent energy range was 25–40 keV, and for operating voltages greater than 60 kV (i.e., 70–100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO₃ loading resulted in deterioration of flexural strength, modulus and hardness.     

Crystal growth and scintillation properties of potassium strontium bromide

In this work, potassium strontium bromide activated with divalent europium, (KSr₂Br₅:Eu) has been studied. It has a monoclinic crystal structure and a density of 3.98 g/cm³. Two single crystals of KSr₂Br₅ doped with 5% Eu²⁺, with diameters of 13 mm and 22 mm, were grown in a two zone transparent furnace via the Bridgman technique. The X-ray excited emission spectrum consisted of a single peak at ∼427 nm due to the 5d–4f transition in Eu²⁺. The measured light yield and energy resolution at 662 keV was 75,000 ph/MeV and 3.5%. At low energies KSr₂Br₅:Eu 5% also displays good energy resolution, 6.7% at 122 keV and 7.9% at 59.5 keV.     

SEM and SIMS study of the buried SixNy layer formed in silicon

Standard 20 Ωcm boron doped Cz Si wafers were subjected to 100 keV hydrogen ion implantation at room temperature to fluences of 1 × 10¹⁶ or 4 × 10¹⁶ at/cm². Subsequently, nitrogen was incorporated in silicon from a DC plasma source at a temperature of 300 °C. Finally, all samples were annealed at 700 °C for 2 h in vacuum. Structural properties of samples were studied by SIMS and SEM. The SEM study was carried out both in the secondary electrons (SE) and the Surface-Electron-Beam-Induced-Voltage (SEBIV) modes. The experiments have demonstrated that incorporated from plasma nitrogen atoms were accumulated in the buried damage layer and the formed nitrogen-containing layer has an island-like structure.     

A 20 keV electron gun system for the electron irradiation experiments

An electron gun consisting of cathode, focusing electrode, control electrode and anode has been designed and fabricated for the electron irradiation experiments. This electron gun can provide electrons of any energy over the range 1–20 keV, with current upto 50 μA. This electron gun and a Faraday cup are mounted in the cylindrical chamber. The samples are fixed on the Faraday cup and irradiated with electrons at a pressure ∼10⁻⁷ mbar. The special features of this electron gun system are that, at any electron energy above 1 keV, the electron beam diameter can be varied from 5 to 120 mm on the Faraday cup mounted at a distance of 200 mm from the anode in the chamber. The variation in the electron current over the beam spot of 120 mm diameter is less than 15% and the beam current stability is better than 5%. This system is being used for studying the irradiation effects of 1–20 keV energy electrons on the space quality materials in which the irradiation time may vary from a few tens of seconds to hours.     

Low energy implantation to inhibit wear in N+ ions implanted WC–Co composite

This work discusses the influence of nitrogen ion (N⁺) implantation on wear resistance of WC–Co composite. The WC–Co samples were bombarded at low N⁺ ions energies of 20 and 30 keV and doses of 10¹⁷ and 2 × 10¹⁷ ions cm⁻². Tribological tests were conducted against cylindrical 100Cr6 pin at 200 N load and 180 mm s⁻¹ speed. The tests use water lubrication and four sample types with Co binder content ranging in 6.5–25%. The X-ray spectra reveal that implantation is able to transform the original [CFC] Co structure of virgin surface to harder amorphous phase. However, it was found that excessive low binder content alters the wear behavior on non-implanted samples since it causes wear rate transition from 0.59 × 10⁻⁷ to 2.1 × 10⁻⁷ mm³/(mm² s) imposing hence instable wear regime. The SEM micrographs confirm the formation of transferred film within the implanted worn surface owing to (i) an enhancement in Co flow and (ii) a generation of oxides (Fe₂O₃, Fe₃O₄, Co₂O₃, WO₂). While the formed film acts to inhibit severe abrasion, the material removal process combining cobalt flow and carbide grains pull-out seems to be associated with oxidation mechanisms to be accentuated with energy increase. The most improvements in wear resistance were observed on samples with the highest Co content and the results were found more sensitive to N⁺ ions implantation energy than dose.     

Structural characterization of TiN coatings on Si substrates irradiated with Ar ions

The present study deals with TiN/Si bilayers irradiated at room temperature (RT) with 120 keV Ar ions. The TiN layers were deposited by d.c. reactive sputtering on Si(100) wafers to a thickness of ～ 240 nm. After deposition the TiN/Si bilayers were irradiated to the fluences of 1 × 10¹⁵ ions/cm² and 1 × 10¹⁶ ions/cm². Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), grazing angle X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that the variation of the lattice constants, mean grain size and micro-strain can be attributed to the formation of the high density damage region in the TiN film structure. It has been found that this damage region is mainly distributed within ～ 100 nm at surface of the TiN layers.     

Comparative study of NiFe2−xAlxO4 ferrite nanoparticles synthesized by chemical co-precipitation and sol–gel combustion techniques

A series of aluminum substituted Ni-ferrite nanoparticles have been synthesized by chemical co-precipitation and sol–gel techniques. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), DC electrical resistivity and dielectric properties. Analysis of the X-ray diffraction pattern of all the samples confirmed the formation of spinel structure. The crystallite sizes remain within the range 25–41 ± 3 nm. FTIR measurements show two fundamental absorption bands, assigned to the vibration of tetrahedral and octahedral sites. DC electrical resistivity increases from 6.60 × 10⁷ to 6.9 × 10¹⁰ Ω cm as the Al³⁺ concentration increases from 0.00 to 0.50. The dielectric constant and loss tangent decreases with increasing Al³⁺ concentration from 22 to 14, 0.354 to 0.27 respectively at 5 MHz for all the samples. Impedance measurements as a function of frequency (1 kHz–5 MHz) at room temperature further helped in analyzing the electrical properties of the prepared samples.     

Characterization of Yb:YAG and Yb:YAP scintillators by means of LAAPD at temperature around 100 K

A new class of scintillators based on charge-transfer luminescence of the Yb³⁺ ion is being investigated for the last few years. The main prospect for these scintillators is in neutrino physics. The crystals manifest maximum light output at temperatures 100 K<T<150 K. In this range Large Area Avalanche Photodiodes (LAAPD) are the best photodetectors. In this work Yb(25%):YAG and Yb(5%):YAP scintillators were characterized by means of a 16 mm diameter API LAAPD at temperatures around 100 K. Light yield and energy resolution were determined. Light yield non-proportionality was detected for all the crystals comparing light output at 661.6 and 59.6 keV peaks.     

Crystal growth and characterization of europium doped KCaI3, a high light yield scintillator

The presented study reports on the spectroscopic characteristics of a new high performance scintillation material KCaI₃:Eu. The growth of ∅ 17 mm boules using the Bridgman–Stockbarger method in fused silica ampoules is demonstrated to produce yellow tinted, yet transparent single crystals suitable for use in spectroscopic applications due to very promising performance. Scintillation light yield of 72,000 ± 3000 ph/MeV and energy resolution of 3% (FWHM) at 662 keV and 6.1% at 122 keV was obtained from small single crystals of approximately 15 mm³. For a much larger 3.8 cm³ detector, 4.4% and 7.3% for the same energy. Proportionality of the scintillation response to the energy of ionizing radiation is within 96% of the ideal response over an energy range of 14–662 keV. The high light yield and energy resolution of KCaI₃:Eu make it suitable for potential use in domestic security applications requiring radionuclide identification.     

Anomalous activation of shallow B+ implants in Ge

The electrical activation of B⁺ implantation at 2 keV to doses of 5.0 × 10¹³–5.0 × 10¹⁵ cm^?2 in crystalline and pre-amorphized Ge following annealing at 400 °C for 1.0 h was studied using micro Hall effect measurements. Preamorphization improved activation for all samples with the samples implanted to a dose of 5.0 × 10¹⁵ cm^?2 displaying an estimated maximum active B concentration of 4.0 × 10²⁰ cm^?3 as compared to 2.0 × 10²⁰ cm^?3 for the crystalline sample. However, incomplete activation was observed for all samples across the investigated dose range. For the sample implanted to a dose of 5.0 × 10¹³ cm^?2, activation values were 7% and 30%, for c-Ge and PA-Ge, respectively. The results suggest the presence of an anomalous clustering phenomenon of shallow B⁺ implants in Ge.     

The thermal behaviour of the tritium source in KATRIN

The tritium source in the Karlsruhe Tritium Neutrino Experiment (KATRIN) will deliver 10¹¹ β decay electrons per second, in order to determine the mass of the electron antineutrino through analysing the tritium β spectrum. The source is built of a 10 m long beam tube of 90 mm inner diameter, which is operated at 30 K. Gaseous tritium is injected through a central injection chamber and diffuses towards the tube ends, where it is pumped by large turbomolecular pumps and further processed in a closed tritium loop. In order to achieve the KATRIN sensitivity of 0.2 eV/c², the decay rate in the source (and hence the tritium density profile) must be stable to a level of ±0.1%. As the density profile is influenced by the beam tube conductance, both the temperature stability and the temperature homogeneity must be within a range of ±0.03 K at 30 K. A thermosiphon with saturated neon was developed for this purpose, with horizontal evaporator tubes connected all along the 10 m beam tube. The system behaviour was tested in a 12 m long test cryostat, containing the original beam tube with the adjacent pumping chambers, as well as the cooling circuits and the thermal shields. The so-called “Demonstrator” was operated in the Tritium Laboratory Karlsruhe (TLK) being connected to the cryogenic infrastructure of KATRIN. The temperature stability was found a factor 20 better than specified, achieving a standard deviation of only 1.5 mK/h, which corresponds to ΔT/T = 5 × 10⁻⁵ h⁻¹ relative stability at 30 K. The ±0.03 K temperature homogeneity along the 10 m beam tube was not yet reached, because of an increased heat load through the pump ports. The repeatability of the temperature measurement with vapour pressure sensors was within ± 0.004 K.     

Analysis of layer splitting in x and z-cut KTiOPO4 implanted by H+ ions

H⁺ ions with various fluences are implanted into x and z-cut KTP crystals to achieve KTP film. Post-implantation annealing under different temperature is imposed on the samples to induce layer splitting and surface morphology modification. Layer exfoliation is observed in freestanding z-cut samples. Layer splitting is obtained using bonding method in x-cut sample implanted with 117 keV H⁺ ions at ion fluence of 6 × 10¹⁶ ions/cm². Optical microscopy, scanning electron microscope and atomic force microscopy are used to observe splitting phenomenon. Rutherford backscattering spectroscopy/channeling method is employed to measure lattice damage and to investigate the relationship between implantation-induced defects and layer splitting.     

Fabrication and testing of sputtered-sliced kinoform style Fresnel zone plate

The Fresnel zone plate (FZP) is a type of lens for focusing X-rays. We have fabricated a kinoform style FZP with a 30-step structure composed of concentric multilayer of alternating Cu layer, Al layer, and 28 composite material (Cu, Al) layers. The multilayer was deposited using a magnetron sputtering apparatus with two DC-sputtering guns. The focusing characteristics were evaluated at the synchrotron radiation beamline of SPring-8, and the focused beam size measured by knife-edge scanning was 0.8 μm at 40 keV. The peak diffraction efficiencies measured using ion chambers for 1st- and 2nd-order diffraction were 42% and 12% at 40 keV and 20 keV, respectively. High-order X-ray diffraction was also examined using the data obtained from a CCD camera.     

Commissioning and performance of X-ray absorption spectroscopy beamline at the Siam Photon Laboratory

We report commissioning results and performance of X-ray absorption spectroscopy (XAS) beamline, BL-8, at the Siam Photon Laboratory. BL-8 has been opened for users since the year 2006. It is tunable by a fixed-exit double crystal monochromator equipped with InSb(1 1 1), Si(1 1 1), and Ge(2 2 0) crystals covering photon energy from 1830 to 9000 eV. Thus elemental absorption K-edges of silicon up to copper can be investigated. Other heavier elements may be studied via their L or M edges. The front end is windowless and the beamline is terminated with a Kapton window followed by the XAS station equipped with ionization chambers for transmission-mode measurements. The measured photon flux at sample is approximately 10⁸–10¹⁰ photons/s/100 mA for the 1 mm×10 mm beam size. The commissioning XANES spectra of sulfur standards and EXAFS spectra of copper are presented.     

Hydrothermal synthesis and 121Sb Mössbauer characterization of perovskite-type oxides: Ba2SbLnO6 (Ln = Pr,Nd, Sm,Eu)

A mild hydrothermal process to prepare Ba₂SbLnO₆ (Ln = Pr, Nd, Sm, Eu) perovskite-type oxides are presented. These perovskites were characterized on the basis of X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), inductively-coupled plasma spectra (ICP) techniques. Primary structure was confirmed using Rietveld method based on XRD data shows that the likely space groups of Ba₂SbLnO₆ are R-3 for Ln = Pr and Nd and F_m-3_m for Ln = Sm and Eu, respectively. The measurement of Mössbauer effect of the 37.2 keV γ transition of ¹²¹Sb indicates that the isomer shift of these perovskites falls in the region of the Sb⁵⁺ and reflects some hybridized-orbital behavior in Sb–O bonds.     

Characterization of nitrogen-implanted TiO2 nanostructured films

Nanostructured tanium dioxide (TiO₂) films were implanted with N⁺ at 40 keV and ion dose range of 10¹⁶/cm² to 4 × 10¹⁶/cm², and annealed at temperatures between 673 and 973 K. From XRD and TEM analyses it was found that the anatase phase of TiO₂ remained stable up to annealing temperature of 973 K. The samples showed narrower XRD peaks corresponding to larger mean-grain sizes comparing to the un-implanted TiO₂ samples. The SIMS depth profile showed a peak of nitrogen concentration at about 60 nm beneath the film surface and this was confirmed using the SRIM-2003 program for simulating ion beam interactions with matter. The absorption spectra of the films as measured using spectrophotometer were found to shift toward longer wavelengths with the increase of ion dose.     

Formation of nanotubes in Cz Si wafers using He+ implantation and subsequent O+- or N+-plasma treatment

Standard 4.5 Ω cm n-type and 12 Ω cm p-type Cz Si wafers were implanted with helium ions of 300 keV energy and the fluences of 1 × 10¹⁵, 5 × 10¹⁵, 1 × 10¹⁶ or 2 × 10¹⁶ at/cm² at room temperature. The implanted wafers were then annealed in vacuum at 650, 700, 750 or 800 °C. Then oxygen or nitrogen ions of the fluence of 2 × 10¹⁷ cm^?2 were introduced to the silicon wafers from a plasma source followed by annealing the samples in vacuum at 900 °C.The structural properties of the samples were investigated using SEM. To control the treatment's influence on the electrical properties of the wafers, the measurements of charge carriers' lifetime were carried out.1D defects (nanotubes) normal to the sample surface with defect's length equal to the projected range of the implanted ions were formed in the Cz Si wafers following He⁺ implantation with subsequent vacuum annealing and plasma treatment. The surfaces of wafers contained a small density of defects.     

Modification of UHMWPE by ion,electron and γ-ray irradiation

Due to good wear resistance Ultrahigh Molecular Weight Polyethylene (UHMWPE) is the material of choice for the load bearing surfaces of total joint implants. In order to improve its performance polymer parts are often modified by the use of ionizing radiation. Here we report on the use of electron and ion beams and γ-rays for the purpose. UHMWPE samples were irradiated with 600 keV and 1.5 MeV electron beam with doses ranging from 50 to 500 kGy and bombarded with 1–10 MeV He- and 9 MeV Cl-ions to fluences ranging from 10¹² to 5 × 10¹⁶ ions/cm². Co-bomb was used for γ-ray irradiation. Polymer radiolysis due to the irradiations was studied by means of nuclear reaction analysis (NRA) using the ¹H(¹⁵N, αγ)¹²C reaction. Hydrogen release increases with the applied dose and was correlated to the linear energy transfer (LET). Irradiated polymers oxidize rapidly when exposed to the air. Oxygen uptake profiles were determined using RBS. Correlation between radiolysis and oxidation has been revealed. Enriched in oxygen region extends to the depth at which radiation induced hydrogen release took place. Once started oxidation proceeds until the saturation concentration of about 10 at.% was attained.     

Surface structural changes,surface energy and antiwear properties of polytetrafluoroethylene induced by proton irradiation

In this work, the polytetrafluoroethylene (PTFE) surface was modified with 25 keV proton beam irradiation in vacuum condition. Multiple characterization techniques including X-ray photoelectron spectroscopy, Raman spectroscopy and infrared spectroscopy were employed for research on microstructure changes in the PTFE surface. The changes in the surface energy and antiwear properties of PTFE were evaluated using contact angle analysis and a ball-on-disk tribometer, respectively. Experimental results showed that the surface energy of PTFE obviously increased from 13.17 mJ/m² to 33.73 mJ/m² and the wear rate decreased from 8.9 × 10^− 3 mm³/Nm to 5.8 × 10^− 4 mm³/Nm after proton irradiation for 15 min. Moreover, TRIM simulation indicated that the H⁺ ions cannot penetrate through the PTFE block and only stop at a depth of about 730 nm from the material surface. Proton irradiation has been proved to be a simple, rapid and effective measure for the surface modification of PTFE with distinctly improved surface energy and antiwear properties, and the possible reaction mechanism taking place in PTFE was also discussed in this paper.     

Thermal behaviour of helium in silicon carbide: Influence of microstructure

We have studied the microstructure dependence of He bubble formation in silicon carbide. Helium accumulation in SiC was performed by 500 keV ³He implantation at room temperature with a fluence of 5 × 10¹⁵ cm^?2. Depth concentration profiles have been investigated in 6H-SiC single crystals and α-SiC polycrystals by NRA spectrometry. Cross-sectional TEM samples have been imaged to study bubble formation. After annealing at 1300 °C, results clearly demonstrate an influence of grain boundaries on He retention yield in α-SiC polycrystals while helium is totally released from single crystals. Polycrystals also display the formation of intragranular overpressurized bubbles while no bubbles are observed in single crystals. Interpretations are proposed on the basis of the nature of He traps.