Characterisation and measurement of dosimetry x-ray beam in Kenya

The need for the specification of x-ray beam quality arises from the fact that several parameters required for the determination of absorbed dose depend on the x-Ray source energy. This includes calibration factors, tube potential, target material, window material, monitor chamber material, filtration material and thickness, shape of collimation, and the of x-ray source (Dosimetry) by indirectly specifying the radiation beam quality through measurement of half value layer (HVL), tube potential and air kerma. This involves determination of qualitative and quantitative of X-Ray beam, physical characteristic, energy deposition and calibration of photon. The quantity air kerma is used for calibrating the reference photon radiation fields and ionization chamber as reference instrument. The charge collected by the ionization chamber is measure with an electrometer, and corrections are applied to account for the effects of air temperature, air pressure, ionic recombination and other influence parameter. The measurements are carried out in Secondary Standard Dosimetry Laboratory (SSDL) that have X-ray beams generated from the tungsten anode at tube voltages of 40-250 kv. Different HVL increases with increasing filter thickness as the beam become increasingly harder because it contains a greater proportion of higher-energy photons. X-ray tube current voltage, filtration, target material and voltage waveform will be analyzed as factors that affect the emission spectrum and quality. (author)