J.M. Sharaf

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.

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.

Application of Geant4 in routine close geometry gamma spectroscopy for environmental samples.

This work examines the utilization of Geant4 to practically achieve crucial corrections, in close geometry, for self-absorption and true coincidence summing in gamma-ray spectrometry of environmental samples, namely soil and water. After validation, different simulation options have been explored and compared. The simulation was used to correct for self-absorption effects, and to establish a summing-free efficiency curve, thus overcoming limitations and uncertainties imposed by conventional calibration standards. To be applicable in busy laboratories, simulation results were introduced into the conventional software Genie 2000 in order to be reliably used in everyday routine measurements.

Developments in Tomographic Methods for Biological Trace Element Research

Neutron-induced γ-ray emission tomography for quantitative determination of the 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 of75Se in 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.

Determination of the elemental distribution in a sample using neutron induced gamma-ray emission tomography

The factors that affect accurate, quantitative results to be obtained by neutron induced gamma-ray emission tomography are stated. The technique, which is a combination of neutron activation analysis with computerised gamma-ray emission tomography, would be enhanced by the use of multiple detector assemblies, in geometrical configurations, which simultaneously record the gamma-rays emitted and improve detection efficiency. Developments in the past few years in positron emission tomography (PET) where scanners made of single scintillation block detectors, cut into smaller segments, to form individual crystal detector elements and packed in ring around the radioactive object, are discussed. The coincident detection efficiency for annihilation photons and cascade gamma-rays for such systems are considered and the possibilities of carrying out NIGET with coincident gamma-ray tomography are explored whilst indicating some of the limitations. This is an area which requires further, intense investigation and has an impact on a wide range of applications, particularly in the biomedical field.

Elemental analysis of biological matrices using tomographic techniques

Gamma-ray transmission tomography and neutron induced gamma-ray emission tomography (NIGET) where delayed gamma-rays from an activated sample are detected in a tomographic mode, were used to investigate the elemental composition and distribution of a salivary gland stone, nondestructively. Transmission tomography provided information about the distribution of the linear photon attenuation coefficient in the object and showed clearly the two regions of inorganic and organic material in a number of sections through it. In addition it was possible to derive from the data the concentration of Ca and the ratio of Ca to P in the stone. By using NIGET it was shown that the concentration of Ca and Na in the object can be mapped and quantitative measurements of these elements could be obtained in any particular location within the salivary gland stone. The spatial resolution which depends on detector collimation was 1 mm for transimission and 2 mm for emission measurements. Instrumental neutron activation analysis was also used to determine the concentration of five elements in the stone, as a whole.

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.