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ST 3.2 –
Protección radiológica en radiodiagnóstico
(orientada a la tomografía computada)
DETERMINATION OF THE EFFECTIVE VOLUME OF AN EXTRAPOLATION
CHAMBER FOR X-RAY DOSIMETRY
Tanuri de Figueiredo, Marcus Tadeu*; Da Silva, Teógenes Augusto
Centro de Desenvolvimento da Tecnologia Nuclear. Brasil.
* Responsible author, email: mttf@cdtn.br
Determination of the effective volume of an extrapolation chamber for x-ray Dosimetry M.T.T.
Figueiredo1; T.A. da Silva1,2 1 Post graduation Course on Science and Technology of
Radiation, Minerals and Materials, CDTN/CNEN, Belo Horizonte, Brazil 2Development Center
of Nuclear Technology, CDTN/CNEN, Belo Horizonte, Brazil Keywords: Extrapolation chamber,
low energy x-ray, chamber effective volume The measurement of air kerma in low energy x-rays
is performed at primary calibration laboratories with free-in-air ionization chamber. Although an
extrapolation chamber is designed to be used for beta radiation dosimetry it may also be
feasible for low energy x-ray since its small changeable volume makes possible to comply the
Bragg-Gray cavity principle. An inherent capacitance is associated with any parallel-plate
ionization chamber; therefore, there should be a well-defined relationship among the
capacitance, the effective colleting area and the electrode spacing of an extrapolation chamber.
In this work, a critical analysis of the methodology for determining the air sensitive volume of an
extrapolation chamber through its capacitance in standardized condition was done. Low energy
filtered x-rays were used with different tube currents and potentials; the relationship between the
capacitance and the effective volume of a 23392 Böhm model PTW ionization chamber was
analyzed within 0.4 to 5.0 mm electrode distances.