A novel instrumentation for wavelength-and time-resolved plasma emission tomography in the range 0.1-4 keV has been demonstrated on the Torus Experiment for Technology Oriented Research ͑TEXTOR͒. The technique is intended for reconstruction of distributions of local emission coefficients ͑LEC͒ for selected spectral lines of impurity ions. Further determination ͑with additional data on electron density and temperature͒ of spatial distributions of impurity ions at particular ionization stages will become feasible. Spectrally selective plasma images at several viewpoints around plasma are obtained with miniature pinhole cameras supplemented with multilayer mirrors as dispersion elements. The x-ray image is converted to a visible image and transported by a fiber bundle to a gain enhanced recording camera with an electron bombarded charge coupled device tube. A part of the system has been installed on temporary TEXTOR ports. First demonstration results have been obtained on plasma imaging and on subsequent LEC reconstruction using a modified iterative sinogram restoration tomography algorithm. The complete diagnostics will be operational after the TEXTOR shutdown in 2001.
This work describes the set-up of an experimental system for micro-tomography developed in the framework of a collaboration between the Physics Department of the University of Bologna (Italy) and the Geosphaera Research Center of Moscow (Russia). The main goal of this inspection system is to carry out high-resolution analysis in vitro of biomedical samples † as well as nondestructive testing (NDT) of industrial components.The detection system consists of a 30x15 mm 2 rectangular fiber-optic taper (ratio 2:1) optically coupled to a cooled 12-bits CCD camera (1024x512 pixels). On the entrance window of the taper is deposited a thin layer of Gd 2 O 2 S:Tb phosphor which provides the X-light conversion. The image readout is carried out by means of a commercial frame grabber installed on a personal computer and specific software is used for data acquisition and control of the tomographic process.The object under investigation is arranged on a 3-degrees micro-positioning system (x-y translation and rotation) and irradiated by an X-ray microfocus beam (up to 200 kVp). The sample can be positioned easily along the source-detector axis in order to obtain a large magnification of details of interest.The X-ray detector has been intensively tested in order to determine its performance in terms of MTF, NPS, and DQE. Moreover, preliminary tests have been carried out on several samples in order to evaluate the performance of the micro-CT system.
A h ybrid image-intensier tube, suitable for extremely low-light imaging, has been tested. This device is based on an Electron-Bombarded CCD chip (EBCCD) with 1024 1024 sensitive pixels. The tube, which has a photocathode diameter of 40 mm, is gateable and zoomable, with an image magnication varying from 0.62 to 1.3. The high gain (about 4000 collected electrons per photoelectron at the operational voltage of 15 kV) and the relatively low noise (180 electrons per pixel at 10 MHz pixelreadout frequency), allows single-photoelectron signals to be separated from noise with a signal-to-noise ratio greater than 10. By applying an appropriate threshold on the signal amplitude, the background can almost be eliminated, with a loss of few percent in single-photoelectron counting. High inner gain, low noise, single-photoelectron sensitivity, and high spatial resolution make the EBCCD imaging tube a unique device, attractive for many applications in high-energy physics, astrophysics, biomedical diagnostics.
The decay K − → µ − νπ 0 has been studied using in-flight decays detected with "ISTRA+" setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The λ + and λ 0 slope parameters of the decay formfactors f + (t), f 0 (t) have been measured : λ + = 0.0321 ± 0.004(stat) ±0.002(syst) λ 0 = 0.0209 ± 0.004(stat) ±0.002(syst); the correlation dλ 0 /dλ + = −0.46 The limits on the possible tensor and scalar couplings have been derived: f T /f + (0) = −0.021 ± 0.028(stat) ±0.014(theory); f S /f + (0) = 0.004 ± 0.005(stat) ±0.005(theory)
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