Gurmel S. Mudahar

A study of energy and effective atomic number dependence of the exposure build-up factors in biological samples

A theoretical method is presented to determine the gamma-radiation build-up factors in various biological materials. The gamma energy range is 0.015-15.0 MeV, with penetration depths up to 40 mean free paths considered. The dependence of the exposure build-up factor on incident photon energy and the effective atomic number (Zeff) has also been assessed. In a practical analysis of dose burden to gamma-irradiated biological materials, the sophistication of Monte Carlo computer techniques would be applied, with associated detailed modelling. However, a feature of the theoretical method presented is its ability to make the consequences of the physics of the scattering process in biological materials more transparent. In addition, it can be quickly employed to give a first-pass dose estimate prior to a more detailed computer study.

Effect of collimator size and absorber thickness on gamma ray attenuation measurements

Mass attenuation coefficients have been measured in extended media of soil and water for 662 keV gamma rays under different collimation conditions. A correlation effect due to absorber thickness and collimator size has been observed.

Total and partial mass attenuation coefficients of soil as a function of chemical composition

Abstract The mass attenuation coefficient ( μ s ) of soil for total and partial photon interaction processes has been calculated for five different elemental compositions of soils, in the energy range from 10 keV to 100 GeV, to study the influence of chemical composition. For the total photon interaction coefficient, appreciable variations in μ s due to chemical composition (soil type) are seen only below 300 keV and above 3 MeV photon energy. For partial interaction processes significant variations in μ s are seen for photoeffect, coherent scattering and pair production in the nuclear field at all energies. No significant variations were noted in μ s due to soil chemical composition for incoherent scattering and pair production in the electron field. We present graphs of the variations in μ s for total and partial photon interaction processes in soil due to the Z -dependences of the interaction processes.

Energy dependence of total photon attenuation coefficients of composite materials

Abstract Total photon attenuation coefficients of several composite materials (alloys, compounds, plastics, biological materials and soils) have been calculated over a wide energy range from 10 keV to 100 GeV. In the intermediate energy region, where incoherent scattering is the most dominant process, the attenuation coefficient (cm 2 /g) is found to be constant for all types of materials at a particular energy, whereas significant variation in the value μ/ρ is observed in the low and high energy regions. The variations of total photon attenuation coefficients for several composite materials in different energy regions, indicating Z -dependence of the interaction processes, are presented in the form of graphs.

Effective atomic number studies in different soils for total photon interaction in the energy region 10–5000 keV

Abstract Effective atomic numbers (Zeff) of 12 different soil samples were computed for total photon interaction cross sections using theoretical data over a wide energy region from 10 to 5000 keV. It is seen that Zeff of a composite material, like soil, changes with a change in energy. With an increase in energy from 10 to 20 keV, Zeff increases, then remains nearly constant up to 40 keV but decreases sharply from 40 to 400 or 500 keV, and a further comparatively small rate of decrease up to 1500 keV. However, there is a small but continuous increase in Zeff with photon energy increases of 1500–5000 keV. This significant change in Zeff of soil is due to variations in the domination of different interaction processes in different energy regions as well as to the large number of elements present in the soil.

Energy dependence of the effective atomic number of alloys

Abstract To investigate the variation of effective atomic number ( Z eff) of alloys with photon energy, the Z eff of eight different alloys (tungsten steel, monel metal, solder, bell metal, bronze aluminium, bronze ordinary, platinum-rhodium-I and platinum-rhodium-II) have been studied for the total and partial photon interaction processes over a wide energy range from 10 keV to 100 GeV using a recent theoretical compilation by Berger and Hubbell (1987). For the total photon interaction, in all the alloys Z eff initially increases to the maximum value with increase in energy and then decreases to the minimum value with further increase in energy, after which Z eff again starts increasing with further increase in energy. The maximum and minimum value of Z eff is at different energies for different alloys depending upon the relative proportion and the range of atomic numbers of constituent elements of the alloy. For photo-electric absorption, Z eff increases in the low energy region and becomes independent of energy, whereas in Compton scattering, except below 200 keV, Z eff is constant up to 100 MeV. In the case of pair production, Z eff decreases with the increase in energy up to 10–12 MeV, after which it is noted to be independent of photon energy.

Soil: A radiation shielding material

Abstract To support the use of soil as a suitable radiation protection material, the effects of soil grain size and pressure on γ-ray attenuation have been tested in the energy region from 279 to 1250 keV. The variation in linear—and mass—attenuation coefficients, μ and μ m , with soil grain diameter is found appreciable and independent of soil chemical composition. The increase of μ with pressure is only up to 10 4 kg/cm 2 pressure for soil particles of uniform grain size d = 0.12 ± 0.03 mm. However, no significant change is seen in μ m with pressure. The half-thickness values for attenuation were calculated from present data have also been discussed for different γ radiations.

A new method for simultaneous measurement of soil bulk density and water content

Abstract A new idea is given for the dual-energy method of measuring the soil-water characteristics in which two different energies are taken from a single source. Compared with the previous dual-energy as well as the single-energy methods, this proposed single-source dual-energy method is more accurate and convenient, for the simultaneous measurement of bulk density and water content of soil.

VARIATION OF BUILDUP FACTORS OF SOILS WITH WEIGHT FRACTIONS OF IRON AND SILICON

Abstract The effect of weight fractions of Fe and Si on buildup factors has been studied in five different soils. The chemical composition is seen to influence the buildup factors at lower energies only. At energies greater than 0.40 MeV, the buildup factor values are more or less independent of chemical composition of soils.

Energy absorption buildup factor studies in water, air and concrete up to 100 mfp using G-P fitting formula

Abstract The energy absorption buildup factors for water, air and concrete have been calculated up to a penetration depth of 100 mean free paths using 5-parameter Geometric Progression formula, in the energy range of 0.015–15.0 MeV. The results up to 40 mfp have been compared with the available standard data, whereas the buildup factors of these materials beyond 40 mfp and up to 100 mfp are new to the available literature.