WILLIAM DE SOUZA SANTOS

WILLIAM DE SOUZA SANTOS

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Monte Carlo approach for the determination of the angular dependence of an extrapolation chamber response
2019 - POLO, IVON O.; CALDAS, LINDA V.E.; SANTOS, WILLIAM S.
The angular dependence of an extrapolation chamber response is reported. The determination of the angular factors were carried out using the MCNP Monte Carlo Method. To determine the angular dependence, the PTW type 23392 extrapolation chamber of the Laboratory for Calibration of Instruments (LCI/IPEN) was simulated. The experiments were performed for the radiation fields of beta secondary standard BSS2 system sources. For the 90Sr/90Y source, the calibration distance of 11 cm without the beam flattening filter was used. For the 85Kr and 147Pm sources, the distances of 30 cm and 20 cm with the filter were used, respectively. The simulations were carried out by rotating the extrapolation chamber around the reference axis for angles between -90º and 90º, in steps of 5º. For the 90Sr/90Y source the angular dependence factor is greater than 1, predominating the dose build-up effect up to 60º and -60º, and the factor is less than 1 for the other angles, prevailing the absorption of beta particles. For the 85Kr and 147Pm sources, the angular dependence factor is less than 1 for all angles, predominating the absorption of beta particles too. The determined angular factors are in good agreement with the international report ISO 6980.
Characterization of an extrapolation chamber in beta radiation beams and Monte Carlo modelling
2020 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of a standard composed by the beta radiation sources for the dosimetry and calibration for personal monitoring in Brazil. For this purpose is used the Böhm extrapolation chamber (PTW model 23392). This chamber was already characterized at LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of PET (polyethylene terephthalate) known as Hostaphan. In this work, this extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparison purposes. The Monte Carlo code MCNP5 code was used to obtain an extrapolation chamber and the BSS2 system sources computational model, based on the determination of the absorbed dose rate. Saturation curves, ion collection efficiency, ion recombination, polarity effect, stability of response, null depth, linearity of response, variation of response as a function of source-detector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The difference between the experimental absorbed dose rates and those obtained using the Monte Carlo model, compared to those from the calibration certificates, was less than 1.9% for the 108 histories for each BSS2 system source. All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in good agreement with previous works performed at LCI. These results are suitable for the establishment of a standard instrument for the dosimetry and calibration of beta radiation sources and detectors in the LCI/IPEN. This standard will allow the calibration of detectors in beta radiation beams in dosimetry services in Brazil.
An extrapolation chamber for the establishment of a primary radiation standard in 85Kr and 147Pm beta radiation beams
2019 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
Introduction At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of the Böhm extrapolation chamber model 23392 as a primary standard system for the dosimetry and calibration of beta-radiation sources and detectors. This chamber was already characterized at the LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of Hostaphan. This extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparative purposes. Methods A Keithley model 6517B electrometer was used for the measurements. The utilized radiation sources are part of the Beta Secondary Standard BSS2. Moreover, the Monte Carlo code MCNP5 was used to determine the absorbed dose rates and to compare them with the experimentally determined dose rates and with those from the PTB calibration certifi cate. Results Saturation curves, ion collection effi ciency, ion recombination, polarity effect, response stability, real null depth, linearity of response, variation of response as a function of sourcedetector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The ion collection effi ciency was greater than 99%; the ionic recombination was less than 1%, and the polarity effect was greater than 1%. The stability of the response was lower than 0.15% for the repeatability test, and it was less than 0.36% for the reproducibility test. The difference between the experimental absorbed dose rates and those from the Monte Carlo model, compared to those from the calibration certifi cate, was less than 1.9% for all sources. Conclusions All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in the good agreement with previous works performed at LCI. These results are suitable for the establishment of a primary standard for beta radiation.
Monte Carlo modeling of a holder for irradiation of dosimeters in beta radiation beams
2019 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
A study of the influence of a dosimetric holder and its cover for the irradiation of the dosimeters in the Beta Secondary Standard BSS2 radiation fields is reported. The correction factors for attenuation or scattering were calculated taking into account the BSS2 beta source energy, as well as the detector source distance. The study and the determination of these factors were carried out using the Monte Carlo Method. The results of the correction factors showed that the absorption and scattering of the electrons depend greatly on the energy of beta radionuclides. The determined correction factors are in agreement with the international report ISO 6980.
Modelling the absorbed dose rate of the beta standard BSS2 147Pm source
2018 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
The dosimetric measurements of 147Pm beta radiation beams have limitations due to their low energy, low dose rate, great dispersion and attenuation in air or tissue. In this work, the Monte Carlo model was developed for a 147Pm absorbed dose rate determination. This model consists of an extrapolation chamber and a 147Pm beta radiation source. Moreover, the absorbed dose rate was determined by experimental measurements and the MCNP Monte Carlo code was used. The relative number of particles that crossed the radioactive source window and the particles that crossed the extrapolation chamber entrance window were determined. The source fluence spectrum was also determined. The results of the simulation and the experimental calculations are in agreement with the absorbed dose rate from the PTB calibration certificate. The results obtained are considered acceptable, and they agree within the uncertainties. The difference between the experimental result and that from the Monte Carlo model, compared to that from the calibration certificate, was only 0.8% in both cases.
Determination of correction factors in beta radiation beams using Monte Carlo method
2018 - POLO, IVON O.; SANTOS, WILLIAM de S.; CALDAS, LINDA V.E.
The absorbed dose rate is the main characterization quantity for beta radiation. The extrapolation chamber is considered the primary standard instrument. To determine absorbed dose rates in beta radiation beams, it is necessary to establish several correction factors. In this work, the correction factors for the backscatter due to the collecting electrode and to the guard ring, and the correction factor for Bremsstrahlung in beta secondary standard radiation beams are presented. For this purpose, the Monte Carlo method was applied. The results obtained are considered acceptable, and they agree within the uncertainties. The differences between the backscatter factors determined by the Monte Carlo method and those of the ISO standard were 0.6%, 0.9% and 2.04% for 90Sr/90Y, 85Kr and 147Pm sources respectively. The differences between the Bremsstrahlung factors determined by the Monte Carlo method and those of the ISO were 0.25%, 0.6% and 1% for 90Sr/90Y, 85Kr and 147Pm sources respectively.