Roberto Cesareo

A new tomographic device based on the detection of fluorescent x-rays

Fluorescent X-rays emitted by a small volume (voxel) of an irradiated sample can be employed for obtaining tomographic images. A finely collimated beam from an X-ray tube has been employed, and the X-rays emitted at 90° by the elements in a voxel have been analyzed with a highly collimated detector. Moving the sample in the x−y plane, the elemental distribution can be determined in the slice of the object crossed by the radiation. The intensities of the measured peaks have been corrected for absorption effects in the object. The distribution of iodine in test objects has been determined.

X- and gamma -rays computerized minitomograph scanner for soil science

A computerized tomograph scanner system that uses X- and gamma -rays for applications in soil science is described. Use of the apparatus in measuring volumetric water content to an accuracy of +or-3% and soil bulk density to +or-2% (in grams per cubic centimeters) is discussed. The system features translation and rotation scanning modes, a 200-mm effective field of view, signal processing by pulse counting, and 1.0-mm spatial resolution. The systems advantages over classical methods are listed, principles of the tomographic method and physical considerations are presented, and the systems design is described. >

ATTENUATION COEFFICIENTS AND TOMOGRAPHIC MEASUREMENTS FOR SOIL IN THE ENERGY RANGE 10-300 KEV

Abstract The relationship between soil parameters such as density, atomic number of the components and electron density, and mass attenuation and effective atomic number of the soil are presented. The theoretical and experimental attenuation coefficient values are compared, for Brazilian and Italian soils. The best conditions for tomographic imaging of soil, are also shown, and an example of soil tomography is given.

Coherent and incoherent scattering of 14.93, 17.44 and 21.12 keV photons from Al, Cu, Sr, Cd, Ce, Pr, Sm, Pt, Au and Pb

Coherent and incoherent scattering cross sections for the elements Al, Cu, Sr, Cd, Pr, Ce, Sm, Pt, Au and Pb have been measured at 14.93, 17.44 and 21.12 keV Kα x-ray energies. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source instead of radioisotopes. Bremsstrahlung radiation from the x-ray tube has been used to excite nearly monoenergetic x-rays in secondary targets. In order to improve the efficiency of the detection system the excitation source detector and the target assembly were placed in a vacuum chamber and a pressure of 10−2 mbar is maintained throughout the measurements. The coherently and incoherently scattered intensity by the sample into the detector has been detected at an angle of 90° using low energy HP Ge and Si (Li) photon detectors. The present system considerably reduced the scattering and background effects and improved the monochromacy. Experimental scattering cross sections are compared with the normalised integrated cross section based on form factor and incoherent scattering approximations. The present experimental results do not strongly support any set of theoretical values. More accurate experimental results and extended exact calculations of atomic form factors at more closely spaced values of incident x-ray energies and scattering angles are clearly needed if more meaningful comparison between experiment and theory are to be possible.

L X-ray fluorescence cross sections of heavy elements excited by 15.20, 16.02, 23.62 and 24.68 keV photons

Abstract L X-ray fluorescence cross sections have been measured for the elements La, Ce, Gd, Er and Au using photon energies of 15.20, 16.02, 23.62 and 24.68 keV. Measurements have been performed using an X-ray tube with a secondary exciter system as the excitation source. The X-ray tube with a secondary target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an X-ray tube it is possible to measure X-ray fluorescence cross sections even for low-intensity X-rays (L 1 ). Experimental results have been compared with the theoretically calculated values of L X-ray fluorescence cross sections. A fairly good correspondence is observed between experimental and calculated values.

Increased plasma levels of endothelin-1 in patients with hyperthyroidism.

Plasma concentrations of endothelin-1 (ET-1) were measured in 25 hyperthyroid subjects, 15 hypothyroid subjects, and 21 age-matched normal controls. In hyperthyroid patients, plasma concentrations of ET-1 were significantly higher than in the control group (P < .0001) and in hypothyroid patients (P < .0001). In contrast, no differences were found between hypothyroid patients and controls. Plasma levels of ET-1 were similarly elevated as in patients with Graves disease and those with toxic adenoma. No correlations were found between plasma ET-1 levels, thyroid hormones, and thyrotropin (TSH) in hyperthyroid, hypothyroid, and euthyroid groups. The results of our study clearly indicate that in hyperthyroidism, circulating levels of ET-1 are strongly increased, although the pathogenesis of the increase is unclear.

Total M X-ray fluorescence cross sections and fluorescence yields for Pt, Au and Pb in the energy region 5.47 ≤ E ≤ 9.36 keV

Abstract Total M X-ray fluorescence cross sections for the elements Pt, Au and Pb have been measured at incident photon energies 5.47, 5.96, 7.04, 8.14, 8.74 and 9.36 keV. Average M-shell fluorescence yield at each incident photon energy has been deduced, using the experimental total M X-ray fluorescence cross section and theoretical M-shell photoionisation cross sections. Experimental total M X-ray fluorescence cross sections and M-shell fluorescence yields are found to be in good agreement with the theoretical estimates based on relativistic Dirac-Hartree-Slater theory.

Principles and applications of differential tomography

Abstract A new tomographic method is described: the differential tomography. In this method, selective isolation of an element in the scanned sample is realized, when two X-ray beams are employed, which energies straddle a photoelectric discontinuity of the element. The CT-map exalts the presence of this element with respect to the matrix. The differential tomography can be employed in each case in which the presence of an element has to be enhanced, naturally present in the sample, or used as tracer, for medical and nonmedical applications.

M X-ray fluorescence cross sections and yields in the atomic region 78 ⪕ Z ⪕ 82 excited by 6.47 and 7.57 keV photons

Abstract Experimental M X-ray fluorescence cross sections for the elements Pt, Au and Pb have been measured at incident photon energies 6.47 and 7.57 keV. Theoretical M X-ray fluorescence cross sections for the elements Yb, W, Hg, Tl, Bi and Ra at 6.47 and 7.57 keV are also calculated. Experimental results are compared with the theoretical values based on relativistic Dirac-Hartree-Slater calculations of Chen et al. and non-relativistic calculations of McGuire. The average M shell fluorescence yields ω M have been deduced using experimental cross section values and the theoretical M shell photoionization cross sections. Results are compared with the available theoretical values.

L-shell X-ray intensity ratios for Au and Pb at excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV

The L-shell x-ray intensity ratios I(L1)/I(Lα), I(Lβ)/I(Lα) and I(Lγ)/I(Lα) for Au and Pb have been measured at the excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV with a HP Ge(Li) detector. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source. The x-ray tube with a secondary target arrangement was used to obtain high intensity with high degree of monochromatisation. A comparison is made of the experimental results with the calculated values obtained by using theoretical x-ray emission rates, sub shell ionisation cross-sections sub shell fluorescence yields and Coster-Kronig transition probabilities. A fairly good agreement is observed between experimental and theoretical values. The intensity ratios for intense transitions ILβ/ILα are in good agreement with the theoretical values.