Radiation Attenuation Coefficients Research Articles

Spectral distribution of secondary gamma rays in fibre concrete shields / Spektrale Verteilung sekundärer Gammastrahlung in Abschirmungen aus Faserbeton.

When concrete is used for neutron and gamma shielding, its shielding effectiveness for gamma radiation can be improved by addition of iron. However, secondary gamma radiation will be produced as a result of inelastic scattering of fast neutrons and capture of thermal neutrons by iron nuclei. The spectral distribution of the secondary gamma radiation in ilmenite-limonite concrete with addition of steel fibres was investigated. It is shown that the linear attenuation coefficient for secondary gamma radiation has its maximum at a steel fibre concentration of 2 per cent

Gamma ray slush hydrogen monitor

Mass attenuation coefficients for 109Cd radiation have been measured in single phases and mixtures of phases of five chemical compounds. As expected, the mass attenuation coefficients are independent of the phases of the test chemicals. As a result of this study, it is recommended that a slush hydrogen monitoring system based on low energy gamma ray attenuation be developed for use on board the National Aerospace Plane.

Radiotherapy treatment planning of basal meningiomas: improved tumor localization by correlation of CT and MR imaging data

A localization technique, based on three-dimensional CT and MR imaging data for precision radiotherapy of basal meningiomas, is presented. Indications for radiotherapy included unresected tumors, gross disease remaining despite surgery, and recurrences. The patient's head was fixed in a stereotactic localization system which is usable at the CT, MR and the linear accelerator installations. The geometrical distortion of MR imaging data was evaluated in three dimensions by phantom measurements. The geometrical distortion was “corrected” (reducing displacements to the size of a pixel by calculations based on modelling the distortion as a fourth order two-dimensional polynomial. The target volume was defined in three-dimensional MR imaging data after application of 0.1 mmol/kg b.w. Gd-DTPA solution and transferred precisely from MR onto CT data to provide a map of the radiation attenuation coefficient for dose calculation. The superior soft tissue contrast of MR showed an excellent tumor delineation especially when the bony base of the skull obscured the target in CT images. Target volume, calculated dose distribution, and critical structures could be transferred between CT and MR imaging data and displayed as three-dimensional shaded structures for better assessment for matching of target volume and dose distribution. With the described planning system a more precise target definition of basal meningiomas was possible by integration of the superior tumor delineation in MR compared with CT.

Should 60Co tissue-air ratios be re-evaluated?

Taking mu p as the attenuation coefficient of the primary radiation and d is the depth in tissue, Bjarngard et al (1989) showed that plots of TAR (d, S) exp ( mu pd) against S, for given values of the ratio S/d, were approximately linear and converged to 1.00 at zero field size, using the unmodified values of published TAR data. This observation was used to support the proposition that the zero-field-size values of TAR, TAR(d, 0), should be reduced. Bjarngard and Petti (1988) also suggested that a normalized TAR(dm, 0) was inconsistent with the notion that TAR(d, 0) describes primary dose. The present author shows that there is another way to interpret Bjarngard's analysis, which is consistent with a normalized TAR(dm, 0). The consequence of this alternative analysis is that non-zero-field-size TAR should be increased.

The identification problem and image reconstruction of the exponential X‐ray transform

AbstractThe emission‐type CT which utilizes the radiation from the radioisotope (RI) injected into the body can reconstruct the biochemical information inside the body as an image. At present, the multicross‐sectional method is employed in reconstructing the three‐dimensional distribution of RI, as in the case of X‐ray CT.In this method, a spatial nonuniform resolution is produced in the reconstructed RI image. It should be noted, on the other hand, that RI injected into the body emits radiations in all directions in the space. By utilizing all those radiations, a three‐dimensional image can be reconstructed without a nonuniformity in the resolution.This paper shows that the three‐dimensional distribution of RI can directly be reconstructed from the radiations emitted spatially from inside the body. It is shown first that the problem to determine the three‐dimensional distribution of RI from the radiations is the inverse problem with the exponential line integral as the measured value. The relation between the Fourier transform of the projections by the exponential line integral and the Fourier transform of the original three‐dimensional image is analyzed. Then it is shown that the radiation attenuation coefficient of RI can be determined only from the projection data.Furthermore, based on the relation between the Fourier and Hankel transformations, a method is derived for the direct three‐dimensional image reconstruction from the radiation projection using the series expansion.

Design and experimental verification of a tubular multilamp reactor for water and wastewater treatment

A model for the design of a multilamp tubular photoreactor employed for water and wastewater treatment was developed. A test reaction was used to achieve an experimental corroboration of the model. It was shown that under normal conditions a two-dimensional mass balance is sufficient to describe the system and that the additional numerical complexity required by a three-dimensional model is not justified. Deviations between model predictions with constant and variable radiation attenuation coefficients were also studied. For low values of the flow rate (conversions higher than 10%), good predictions were obtained only with the second approach. By use of the well-known oxalic acid-uranyl sulfate actinometer, the reactor model was successfully verified, showing good agreement with the experimental data

Heat and mass transfer and energy transport of integral radiation in light-scattering materials during exposure to diffuse and directional fluxes

Regularities are established for changes in the layer of of integrated quantities of the resultant flux density, the spatial irradiance, and the absorbed energy for solar and IR-generator KGT-220-100 radiation. Dependences of the integrated radiation flux absorption, scattering, and attenuation coefficients on the coordinate are determined. The possibility is shown of approximating the complex integrated function of the internal heat sources due to radiation absorption by a simplified exponential dependence that permits solution of the heat transfer problem top be obtained.

The selection of stopping power and mass energy absorption coefficient data for the HPA Code of Practice for dosimetry

All the recent protocols for high-energy X-ray dosimetry, introduced by the AAPM (1983), NACP (1980) and the HPA (1983), result in absorbed dose conversion factors significantly different from those that have been in use since 1969 when ICRU Report 14 was published. Clearly for all protocols, general or specific, it is necessary to select appropriate stopping power and mass absorption coefficient ratios for a range of X-ray beam qualities. Cunningham and Shultz (1984) have recently described a method of selecting these ratios, taking into account differences in spectral properties of radiation beams rather than the peak accelerating voltage which is not an adequate index of radiation quality. A table is given showing quality of X-ray or gamma -ray radiation versus narrow beam attenuation coefficient in water.

Remotely sensing the surface dynamics of the Adriatic Sea

A set of images of the Adriatic Sea, collected by the Coastal Zone Color Scanner on board the satellite Nimbus-7, has been processed to obtain maps of the diffuse attenuation coefficient for visible radiation and of apparent temperature. Using the spatial variations of these properties as tracers of motion in the surface layer, a correlation between image patterns and water mass movements has been attempted. The majority of the large-scale features observed in the processed images has been directly related to known aspects of the surface circulation in the Adriatic Sea. Some small-scale phenomena, however, could not be explained in these terms and will require more detailed observations.

6-Methylprednisolon beim Hirntumor: Klinische Beobachtungen mit Kontrolle von EEG, CT und intrakraniellem Druck

In an acute preoperative study over seven days, the efficacy of 6-methylprednisolone was investigated in ten patients with solitary supratentorial tumors (five meningeomas and five tumors of the brain itself). Progress observations of EEG, ICP and CT were carried out poly-graphically to provide objective clinical neurological evidence for the improvement under steroid therapy of the functional disorders due to the tumors. Methylprednisolone was initially given i.v. at a dose of 1000 mg and subsequently 3 × 40 mg/day on five consecutive days. Visual and computer-assisted EEG analysis showed a favorable influence of methylprednisolone on brain function. This was reflected in a significant decrease in the intensity in the delta and in the slow intermediate wave bands as well as in an increase of the power in the rapid intermediate wave and in the alpha frequency range both on the side of the tumor and on the contralateral brain hemisphere. This alteration in power can be evaluated as manifestation of a direct favorable influence on the brain metabolism of mesencephalic and diencephalic-hypothalamic structures in the sense of a tendency to normalization or increase of vigilance. A direct correlation between the extent of the EEG alterations to observed and the localization and degree of peritumoral brain edema as well as the intracranial pressure could not be demonstrated. No patient showed a rise in ICP under 6-methylprednisolone. A cranial CT was carried out to determine the relative radiation-attenuation coefficient under methylprednisolone in the peritumoral edema (boundary region tumor/edema and edema/white matter) as well as a contralateral white matter reference area (ROD. A significant rise of the absolute values of the radiation attenuation coefficient was shown in the course of steroid medication on the second to fifth day both in the edema area adjacent to the tumor as well as contralaterally. A significant fall of the density values after discontinuation of the medication was found in the white matter area adjacent to the tumor as a manifestation of a steroid-induced alteration of the water content. Under high-dosage administration of 6-methylprednisolone. EEG and CT findings paralleled the improvement of the neurological and brain organic deficit phenomenon to be observed clinically.

Nonlinear propagation of laser radiation in a solid-particle aerosol

An experimental investigation was made of the nonlinear propagation of λ = 1.06 μ laser pulses in an aerosol formed from corundum particles. The radiation attenuation coefficient was found to increase beyond I1.600.1 MW/cm2 but fell in the range I1.0602 MW/cm2. This bleaching of the aerosol was accompanied by the motion of particles at velocities of 10–30 m/sec and by their luminescence. The effects were attributed to an anomalous increase in the absorption coefficient of corundum due to interaction of the particles with the laser radiation.

Permissible change in the ? flux when a filler is used in radiometric flaw detection

1. An analytic expression (2), has been found for δ1 for the permissible difference between the radiation attenuation coefficients of the article and filler materials. 2. An increase in the ratiol/dc beyond 8–10 offers no significant reduction of δ1. 3. In the quality control of thick articles, having μx = 5–10, the change in δ1 reaches 10% and can be reduced by discrimination to values satisfying condition (1). The dependence of δ1 on the discrimination threshold is nearly linear.

LIGHT ATTENUATION COEFFICIENT AND PRODUCTIVITY IN ’VERNAL’ ALFALFA

A field stand of ’Vernal’ alfalfa (Medicago sativa L.), cut three times during the growing season, was studied over two years. The attenuation coefficient for radiation of wavelength 300 nm to 400 nm, and the rate of dry matter accumulation, was greater in first growth than in both second and third growth. Percentage dry matter increment below ground was least during first growth.

Net and Spectral Radiation in Soybean Canopies1

AbstractNet and spectral radiation profiles were measured for two soybean varieties of different leaf shapes. Net radiation attenuation differences were found for varieties but not for row spacings. The attenuation coefficient for both spectral and net radiation was very high, indicating the principal use of radiation is in the outer periphery of the soybean canopy. Net radiation was found to deviate from a Beer's Law absorption in the lower region of the soybean canopy.

A New Variant to the Exponential Transformation Technique in Monte Carlo Shielding Calculations

Monte Carlo calculations of deeply penetrating radiation fields are improved by use of a transformation involving the factor e−cz. The optimum value of c generally appears to be at or near the value for total attenuation coefficient for the source radiation, but there are some difficulties in choosing such a value of c. This work describes and illustrates an approach that allows c to be made equal to µo, and the resulting transformed equation is handled in a simple fashion. The technique is encoded into a FORTRAN program called FETMOC, and illustrative problems are solved. Results are given in terms of buildup factors. Two-way energy spectrum and directional distribution at arbitrary points are obtained, also. All results are compared with previously reported calculations to the extent possible.

The thermal radiation theory for plane flame propagation in coal dust clouds

The Nusselt radiation theory of steady state propagation of a plane flame through a dust cloud has been extended to take into account: a finite temperature difference between the particles and air; and, a finite preignition zone (implying finite ignition time or distance). The dust cloud is assumed to be monodisperse, formed by the suspension of finely ground coal in air. As the ignition temperature of coal dust is believed to be the coal decomposition temperature, this is a constant, independent of the ambient conditions, and it therefore effectively decouples the preignition and flame zones; this means that the preignition zone can be treated independently of the flame. The dust in the preignition zone is assumed to be heated by radiation from the flame alone; conduction is neglected. Part of the radiant heat absorbed by the particles is then lost by conduction to the surrounding gas. The gas temperature therefore lags that of the particles. Because of this heating, however, the gas expands with the consequence that the gas density and the dust concentration (and therefore the radiation-attenuation coefficient) all drop. The system as specified is governed by two simultaneous ordinary differential equations, and analytical solutions for the respective rise of the particles and gas temperatures have been found. In the limiting case, when the particle temperature reaches ignition, the solution for the particle temperature provides an expression for the flame speed.