The defect formation in neutron irradiated SiC was investigated by means of Rutherford backscattering spectrometry in channelling mode (RBS), optical absorption and Raman spectroscopy. The relative defect concentration determined by RBS increases linearly with the neutron fluence without any saturation in the investigated fluence region. The spectral dependence of the absorption coefficient  at photon energies below 3.2 eV is independent of the neutron fluence and corresponds to that observed in low-fluence ion implanted SiC. An increase of the defect concentration exhibits only in an increase of the absolute value of .For photon energies above 3.3 eV again an exponential increase of the absorption coefficient is found but with a slope increasing with rising defect concentration. This absorption is assumed to be of the Urbach type. Around 1.56 eV a broad absorption band is observed which is most probably caused by divacancies V Si V C . The defects produced by the neutron irradiation of SiC result in a decrease of the peak intensity and a shift of the position of TO and LO Raman peaks towards lower wave numbers. The latter can be explained by tensile stress due to defects and mass increase of lattice atoms due to neutron capturing. Keywords:Silicon carbide, neutron irradiation, optical spectroscopy, Raman spectroscopy 2 IntroductionRadiation damage by energetic ions or neutrons in crystals disturbs the periodic arrangements of atoms and thus is connected with significant changes of the optical properties of the corresponding material. Although these effects can be observed also in the infrared reflectance (see e.g. [1, 2]), it is especially significant at photon energies below the fundamental absorption edge because the sharp edges of valence and conduction band are directly related to the perfect periodic lattice structure. Consequently, the optical absorption at photon energies within the region of transparency of the perfect crystal, i.e. below the fundamental absorption edge, is a sensitive tool to detect radiation damage. This was The optical absorption coefficient  was calculated from the transmission spectra measured using an UV-VIS spectrometer Cary 5000 operating in the range of spectroscopic wave numbers  between 3000 and 30000 cm -1 corresponding to photon energies E between 0.37 and 3.7 eV (in the following text both units will be used). It is assumed that the samples are homogeneously damaged over the whole thickness, which allows a direct calculation of  basing on the Beer-Lambert law. In all cases the refractive index was assumed to be unchanged and the data for crystalline SiC were taken from Ref. Olympus microscope was used to focus the laser beam (spot size  2µm) on the samples and also collected the backscattering Raman signal. An integrated triple spectrometer was used in the double subtractive mode to reject Rayleigh scattering and dispersed the light onto a liquid nitrogen cooled Symphony CCD detector. The spectrometer was calibrated with the silicon phonon mode at 520 cm -1 ....

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The purpose of this study is to evaluate technical feasibility based on image capturing conditions (film-focus distance (FFD), film sensitivity, film brand, exposure level and tube voltage) that potentially alter radiographs and consequently may influence the semi-automated measurement of joint space distance (JSD) by computer-aided joint space analysis (CAJSA) in rheumatoid arthritis and osteoarthritis. The radiographs of a left hand (deceased man) were acquired under systematically changing image capturing conditions (exposure level: 4-8 mAs; FFD: 90-130 cm; film sensitivity: 200/400 and tube voltage: 40-52 kV with different image modalities: conventional radiographs, original digital radiographs, digital print-outs). All JSD-measurements were performed with the CAJSA-technology (Radiogrammetry Kit, Version 1.3.6; Sectra; Sweden) at the metacarpal-phalangeal articulation. JSD-analysis was not influenced by changes of FFD, exposure level, film sensitivity or film brand. JSD showed significant variation caused by tube voltage (conventional: CV = 1.913% for Agfa and CV = 2.448% for Kodak; digital: CV = 0.741% for Philips print-outs and CV = 0.620% with original digital images versus CV = 2.185% for Siemens print-outs and 0.951% with original digital images). Computer-aided joint space analysis for JSD-measurements is unaffected by the following image capturing parameters: film-focus distance, film sensitivity, film brand and exposure level. An influence of tube voltage was detected in a lesser extent for original digital images compared to the printed digital as well as conventional versions. Consequently, a standardized tube voltage is essential for accurate reproductions of CAJSA-measurements in rheumatoid arthritis and osteoarthritis.

The study revealed no significant influence of metacarpal rotation on the measurements of metacarpal bone mineral density as estimated by DXR. DXR measurements are not optimal when cast material is used. DXR can accurately quantify periarticular cortical bone mass. This is significant especially for rheumatoid arthritis and related conditions where X-ray imaging of arthritic hands with varying degrees of deformity is performed.

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