Gamma-ray buildup factor and radiation absorbed dose enhancement at tissue-bone interfaces.

During superficial radiotherapy, and for cases where bony structures lie relatively close to the surface behind the tissue region being treated, perturbations to delivered dose are expected due to the change in tissue scattering conditions and the value of buildup factor near the tissue/bone interface. The absorbed dose distribution within bone, muscle, and muscle-bone-muscle interfaces was estimated for photons within the energy range 0.05 to 1.333 MeV. The energy absorption buildup factor is computed using the (GP) fitting method for a geometry of adjacent layers within a multilayer tissue matrix where a thick slab of solid bone is located in-between slabs of muscles of the same thickness. It was observed that dose enhancement was limited only to a few millimeters close to the interface. Also, variations in dose at the interface were found significant only for low photon energies and relatively insignificant at photon energies higher than 0.06 MeV.

Measurement of natural radioactivity in Jordanian building materials and their contribution to the public indoor gamma dose rate.

This study is undertaken to determine the activity concentration of (226)Ra, (232)Th and (40)K in samples of commonly used building materials in Jordan. Samples of seven different materials were collected from construction sites and local agencies supplying raw construction materials and analyzed using a HPGe gamma-ray spectrometer, taking into account self-attenuation in bulk samples. The average specific activity concentrations of (226)Ra, (232)Th, and (40)K ranged from 2.84 to 41.52, 0.78 to 58.42. and 3.74 to 897 Bq/kg, respectively. All the samples had radium equivalent activities well below the limit of 370 Bq/kg set by the Organization for Economic Cooperation and Development (OECD, 1979). External and internal hazard indices, absorbed dose and annual effective dose rate associated with the radionuclides of interest were calculated and compared with the international legislation and guidance. In general, most of the activities did not exceed the recommended international limits, except for granite and ceramic samples which are usually used as secondary building materials in Jordan.

Radioactive point source localization in one, two, and three dimensions within a bulky medium.

The major objective of this study has been to investigate methods of radioactive point source localization within an object. Count rate ratios from two opposite detectors around an object are used for localization. Potentially useful mathematical non-linear equations are derived and solved by MATHEMATICA-based program to identify activity position in multidimensions.

Nondestructive inspection of low atomic number media using inelastic photon scattering.

The purpose of this study was to examine the potential of using scatter information to evaluate tissue density at selected sites. A method for non-invasively generating profiles of density distribution within an object using Compton scattered X-rays is presented. The Compton scatter method is modified to scan longitudinal sections of composite phantoms and samples of tissue substitute materials. Line scan data are used to describe how the detected count rate changes in response to localized density variations within an extended object. The physical limitations of quantification are discussed, including the effect of attenuation, multiple scatter, and limited spatial resolution. Further, the theory of the method, its performance and results of experimental phantom studies are described. The results presented indicate that the suggested method has the potential for measuring physical density distribution within an object with a spatial resolution of 2mm and an accuracy of approximately 4% under the circumstances in which attenuation correction is avoided.

Practical aspects of Compton scatter densitometry.

A technique for determining the physical density distribution within an object using Compton scattered radiation is described. The technique is based on measuring the variation with the depth of 90 scattered radiation flux from an external monoenergetic photon source using a high-resolution solid-state detector. The measured scattered signal from an isolated volume element of the interrogated object is proportional to its electron density. For a definite region within the scanned object, the variation of the scattered yield with depth, along the direction of the incident beam, will give a counting curve with slope proportional to the density of the examined region. The spatial resolution of the system, determined by the collimator width, is 2 mm. The mathematical aspects of the technique are presented and the experimental data obtained in line scans of representative tissue equivalent materials are also shown to demonstrate the validity of the method.

Developments in tomographic methods for biological trace element research.

Neutron-induced gamma-ray emission tomography for quantitative determination of concentration and distribution of elements in a selected plane through a biological specimen is briefly explained and applied by way of illustration to the analysis of gallstones. A system capable of carrying out studies of the binding site of 75Se is different matrices using time differential perturbed angular correlation spectroscopy is also briefly described. Developments in the detector technology of positron emission tomography have allowed small-diameter imaging devices to be built for in vivo preclinical evaluation of new tracers in small animals and are discussed in the context of a proposed experiment combining the techniques mentioned above.