Characteristic Line Radiation Research Articles

A PHANTOM TEST OF PROTON-INDUCED DUAL-ENERGY X-RAY ANGIOGRAPHY USING IODINATED CONTRAST MEDIA

Characteristic-line radiation from heavy metal targets bombarded by MeV proton beams has been tested as an X-ray source for dual-energy K-edge subtraction imaging for human angiography (blood vessel imaging) based on iodinated contrast media. To utilize the strong absorption by iodine (Z = 53) at its K-absorption edge (33.2 keV), we used K α-line of La (lanthanum, Z = 57) at 33.4 keV. As a reference, also K α X emission of Sn (tin, Z = 50) at 25.2 keV was employed. Metallic plates of La and Sn were irradiated by 7-MeV protons to produce these characteristic X-rays. Energy-subtraction method was tested using Lucite phantoms which contain aqueous solutions of KI (potassium iodide) with different concentrations. Also Ca ( H 2 PO 4)2 powder was stuffed in these phantoms to simulate bones. The transmission images of the phantoms were recorded on imaging plates. During the exposure, the energy spectra of the X-rays were monitored by a CdTe detector. We found that the contrast of images of iodide solutions taken with La X-rays was higher than that with Sn X-rays. Also the energy subtraction procedure was successfully applied to reduce the graphical noise due to the bones and inhomogeneity of the soft tissue. However, to apply the present method to actual clinical use, the X-ray intensity must be increased by several orders of magnitude. Also the transmission of the “lower-energy” photons has to be a few orders higher for imaging of objects as thick as human chest.

Vacuum Ultraviolet Spectroscopy at TEXTOR

Spectroscopy in fusion experiments is an important tool to identify impurities in the plasma and to analyze their properties based on the measurement of their characteristic line radiation. For the temperature range typical in fusion plasmas, the dominant part of each impurity in the plasma is highly ionized, and its most intense spectral lines radiate in the vacuum ultraviolet (VUV) wavelength range (10 to 200 nm). The VUV overview spectrometers installed at TEXTOR working at moderate resolution allow one to identify intrinsic plasma impurities such as B (Z = 5), C (Z = 6), Fe (Z = 26), and Cu (Z = 29) as well as seeded impurities such as Ne (Z = 10) and Ar (Z = 18) and to derive information on their relative densities in the plasma. Optimizing these spectrometers for high time resolution provides a tool to analyze transient phenomena like impurity transport processes. In combination with impurity transport modeling and atomic data, the radial distribution of the radial diffusion coefficient is determined from the experimental data. For the case of ohmic discharges, the effective radial diffusion coefficient is found to be anomalously enhanced by more than one order of magnitude as compared to neoclassical predictions.

Monte Carlo simulation of a miniature, radiosurgery x-ray tube using the ITS 3.0 coupled electron-photon transport code.

A miniature, interstitial x-ray generator has recently been developed and is currently undergoing clinical trials for the treatment of brain tumors. The maximum photon energy from this x-ray tube is 50 keV, although most of the initial testing has been carried out at 40 keV. Dose rates of up to 2 Gy/min in a water phantom at a distance of 10 mm from the tube tip are produced. In this paper we describe the modeling and simulation of x-ray production from this device using the ITS 3.0 Monte Carlo code. Verification of the simulation of x-ray production in the device was carried out by comparing predictions of spatial photon distribution, energy spectrum, and dose versus depth in water with experimentally obtained measurements. Agreement between the simulated results and experimental measurements was fairly good when comparing the angular distribution of photons emitted from the x-ray tube and very good when comparing dose rate versus depth in a water phantom. Discrepancies observed when comparing the calculated and measured estimates of characteristic line radiation were reduced by incorporation of a modification to the ITS code. Possible causes of the remaining discrepancy in bremsstrahlung intensity are discussed.

Photographic observation of aluminum micropellet ablation in the MT-1M tokamak plasma

Laser beam accelerated aluminum micropellets were injected into the MT-1M tokamak plasma, and the distribution of characteristic line radiation of aluminum atoms and ions of different charge state was detected. The investigations are focused on the visualization of the pellet cloud, on the bending of the pellet path, and on the striation occurring in the radiation of different charge state along the pellet path in the plasma.

Beam emission spectroscopy as a comprehensive plasma diagnostic tool

A beam of injected fast atomic hydrogen presents a superb probe for hot fusion plasmas. The neutral particles experience excitation and ionization by collisions with electrons and ions as they penetrate into a plasma. The emitted characteristic line radiation is Doppler shifted and the spectral lines are split due to motional Stark fields. Measurements of wavelength, intensity and polarization of the Balmer- alpha emission reveal information about the neutral beam, such as beam attenuation, beam-geometry, beam-divergence and species mix. Local pitch angles and toroidal fields can be derived from the simultaneous measurement of the polarization pattern and the wavelength separation of the Stark multiplet. The implementation and application of beam emission spectroscopy as a quantitative diagnostic tool on the Joint European Torus (JET) experiment is reviewed.

Measurement of beam properties and reproducibility on recent PBFA II target shots

Recent proton experiments on Particle Beam Fusion Accelerator II used a 2 μm gold foil cone to characterize the ion beam. Using the ion beam images obtained by viewing beam-induced characteristic line radiation emitted by such foils with time-integrated x-ray pinhole cameras, the beam centroid axial location and azimuthal symmetry have been analyzed for a recent series of target shots. Azimuthal symmetry on the target midplane on individual shots varied from 6% to 29%. Averaged over the entire series of shots, inferred intensities on the target midplane varied by 24% to 37% from quadrant to quadrant. The beam profiles and beam reproducibility are vital to the interpretation of the results of these target experiments.

Transmission grating efficiencies for wavelengths between 54 Å and 448 Å

Diffraction efficiencies of 44.8-5.4-A x rays by a free-standing gold transmission grating of 1.0-microm period have been measured, using characteristic line radiation. Partial transparency of the grating affects the efficiency at the shorter wavelengths and causes an increase in the efficiencies for orders m>/=1 over the longwavelength values. Model calculations for a trapezoidal wire cross section are in good agreement with the measured efficiencies and allow the wire cross section to be determined. Gratings of this type have a high efficiency for wavelengths as short as 5 A and are, therefore, well suited for applications both in x-ray and extreme uv astronomy.

Efficiency Measurements of X-Ray Transmission Gratings

Diffraction efficiencies of 44.8 Å to 5.4 Å X-rays by a freestanding gold transmission grating of 1.0µm period have been measured, using characteristic-line radiation. Partial transparency of the grating affects the efficiency at the shorter wavelength and causes an increase in the efficiencies for orders m≥1 over the long-wavelength values. Model calculations for a trapezoidal wire cross section are in good agreement with the measured efficiencies and allow the wire cross section to be determined. Gratings of this type have a high efficiency for wavelengths as short as 5 Å and are, therefore, well suited for applications both in X-ray and XUV-astronomy.

The Absorption of X-Rays of Wave-Length1.5≤λ≤8.3A

The mass absorption coefficients for Be (4), C (6), Al (13), Cu (29), Ag (47) and Au (79) have been determined in the wave-length region $1.5\ensuremath{\le}\ensuremath{\lambda}\ensuremath{\le}8.3$ A. Only characteristic line radiation obtained with a vacuum spectrometer was used. Because of the presence of about 1 percent of heavier impurities in the Be (4), the apparent absorption coefficients for Be (4) may be as much as 100 percent higher than for the pure element. This large effect of a small amount of impurity on the apparent absorption coefficient of Be (4) leads to a suggested method of microanalysis for heavy impurities in elements of low atomic number. Following J\"onsson's procedure, a universal absorption curve is plotted.