RESUMEN
A high-fidelity synthetic diagnostic has been developed for the ITER core x-ray crystal spectrometer diagnostic based on x-ray ray tracing. This synthetic diagnostic has been used to model expected performance of the diagnostic, to aid in diagnostic design, and to develop engineering tolerances. The synthetic model is based on x-ray ray tracing using the recently developed xicsrt ray tracing code and includes a fully three-dimensional representation of the diagnostic based on the computer aided design. The modeled components are: plasma geometry and emission profiles, highly oriented pyrolytic graphite pre-reflectors, spherically bent crystals, and pixelated x-ray detectors. Plasma emission profiles have been calculated for Xe44+, Xe47+, and Xe51+, based on an ITER operational scenario available through the Integrated Modelling & Analysis Suite database, and modeled within the ray tracing code as a volumetric x-ray source; the shape of the plasma source is determined by equilibrium geometry and an appropriate wavelength distribution to match the expected ion temperature profile. All individual components of the x-ray optical system have been modeled with high-fidelity producing a synthetic detector image that is expected to closely match what will be seen in the final as-built system. Particular care is taken to maintain preservation of photon statistics throughout the ray tracing allowing for quantitative estimates of diagnostic performance.
RESUMEN
It is well established that exposure of oxyhaemoglobin to ionizing radiation results in remarkably selective electron addition to the (FeO2) unit, giving a novel species, (FeO2)-, in which the extra electron is largely localized on iron and dioxygen. This work has now been extended to haemoglobin (Hb.) Iwate. The haemoglobin M. Iwate used is a mutant haemoglobin having only Fe(III) alpha-chains by oxy beta-chains (alpha 2 Met beta 2 oxy). The haem iron atoms in the alpha-chains are coordinated in the fifth site by a proximal tyrosine in place of histidine. This unit is a high-spin Fe(III) with axial symmetry and prominent electron spin resonance (ESR) features in the g = 6 and g = 2 regions. On exposure to 60Co gamma-rays at 77 K, efficient electron addition occurred at both types of iron centre, giving Fe(II) and (FeO2)- units. The former was monitored by the decrease of the g = 6 feature for Fe(III) and the latter by the growth of g-features at 2.254 (gx), 2.149 (gy) and 1.967 (gz). These values are close to those for the FeO2- centre formed in the beta-chains of normal oxyhaemoglobin. On annealing above 77 K, two changes occurred: first there was a small but clear increase in gx and gy, followed by a marked reduction in gx and gy giving g-values close to those for the centre formed directly in the alpha-chains of the normal protein. Finally, this intermediate species gave a centre having gx = 2.310, gy = 2.180 and gz = 1.935. These values are typical of low-spin Fe(III) haemoglobin and are assigned to the protonated complex, Fe(III)O2H. Ultimately at ca. room temperature, this was converted into the high-spin, met-form, with a gain in the g = 6 feature. These results established that the beta-chain centre in Hb. Iwate behave in the same way as isolated beta-chains. They also confirm that electron addition to the oxy-units is facile, even in the presence of Fe(III) units in each tetramer. The results also confirm that electron capture to give (FeO2)- units is not followed by internal electron-transfer to give Fe(II) from the Fe(III) centres in the alpha-chains.
