RESUMO
Electrons generated in matter by photons could be a fundamental basis for an adequate analysis of radiation effects and damage. We have studied separately the 'primary electrons' generated directly by photons from the 'secondary electrons' (SE) produced by electron-electron interactions. In this work, track-average linear energy transfer, [Formula: see text], of SE in LiF:Mg,Ti and liquid water produced by twelve photon energy beams from 20 kV x-ray to 60Co gamma rays have been investigated using the EGSnrc Monte Carlo Code. The exposure of LiF:Mg,Ti in different phantom materials has been considered. Depending on the photon energy, SE represent 40%-90% of the total electron fluence (TEF) between 1 keV and 10 keV, being higher when the photon energy increases. Independent of the medium, [Formula: see text] versus mean photon energy displays a local minimum at around 40 keV, followed by a local maximum at ~80 keV-100 keV. The [Formula: see text] of SE generated by the x-ray beams are of order of 11 keV µm-1 to 19 keV µm-1 in LiF:Mg,Ti and 5 keV µm-1 to 9 keV µm-1 in liquid water which represent 3-5 times those produced by 60Co gamma rays in both media. These values were considerably greater than those of TEF, by factors of 3-8. Furthermore, [Formula: see text] of SE generated in liquid water by 20 kV-200 kV x-rays are similar to those of 76 MeV-120 MeV 3He ions. Contrary to the TEF, where [Formula: see text] were independent of the phantom material, at low photon energies [Formula: see text] of SE was found to be sensitive to the surrounding medium showing higher values within the phantom than in air. This result, which agrees with published experimental results, implies the importance of the SE ionization density for an understanding of dosimeter response induced by photon beams.
Assuntos
Elétrons , Transferência Linear de Energia , Imagens de Fantasmas , Monitoramento de Radiação/instrumentação , Água/química , Radioisótopos de Césio/química , Radioisótopos de Cobalto/química , Fluoretos/química , Raios gama , Humanos , Compostos de Lítio/química , Magnésio/química , Método de Monte Carlo , Titânio/química , Raios XRESUMO
The correlation of Cs-137 specific activity profiles with the historical fallout sequence in the study region is essential in sediment cores dating using this technique. The authors of the referenced article considered 1965 the end of Cs-137 fallout in the study region, omitting the South Pacific nuclear test from 1966 to 1974, proved that generated the most intense Cs-137 fallout.
Assuntos
Amerício/química , Radioisótopos de Césio/química , Sedimentos Geológicos/química , Radioisótopos de Chumbo/química , Monitoramento de Radiação , Cinza Radioativa , Argentina , Meia-VidaRESUMO
In this work, an experimental study of the radiation beam characteristics of the photon beams produced by commercial irradiator that uses a single collimated 137Cs source is performed. A set of lead attenuators are placed at the exit window of the irradiator to vary the air Kerma that is required to cover the instrument scales at a particular calibration distance. The results strongly enhance the findings of previous studies that a single source with appropriate attenuation and collimation is a practical solution for calibration laboratories with an acceptable overall accuracy.