Dose Conversion Factor for a target close to Semi Infinite Source of Gamma Radiation.

Absorbed dose rates in air have been calculated using the N-particle Monte Carlo simulation, MCNP version 5. The geometry assumed is a point target (receptor) at 1m above an infinite volume of soil containing uniform distribution of photon emitters. Photons of energies between 10KeV and 10MeV were considered, this range include all photons produced by natural occurring radionuclides. The constituents of soil and air and their compositions were adopted from the Federal Guidance Report (Los Alamos Laboratories, USA). Other data required for particle transport and simulation were obtained from the MCNP version 5 package.

The dose at receptor was recorded for a simulation equivalent to a measurement of a second and the result extrapolated to a whole year. Tabulated results were recorded for each of the twenty five energy values in the range between 10 KeV and 10MeV, forming the targeted conversion factors desired.


Air absorbed dose responses were successfully obtained for uniformly distributed photon sources in the soil. The Monte Carlo simulation in the current study predicted the results that agreed well to the previous calculations based on similar work. To use the dose conversion factors generated herein to predict dose resulting from a uniformly concentrated volume source, its only necessary to obtain source concentration, density of the contaminated medium and the initial energy of emitted photons.


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