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Experimental Study of Anisotropic Light Scattering and Polarization Effects of EBT3-Films

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A Schoenfeld

A Schoenfeld1,2*, D Poppinga1,2, D Harder3, B Poppe1,2, (1) WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, Germany (2) Pius Hospital, Oldenburg, Germany (3) University of Goettingen, Goettingen, Germany

SU-E-I-87 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Further experiments are needed to understand the underlying optical properties of flat-bed scanned EBT3-films.

Methods:
EBT3-films, arranged in landscape orientation and irradiated with different doses, were illuminated with a homogeneous spot of unpolarized white light. Polarizer foils could be added in front of and behind the EBT3-film. The light scattered by the film was collected by a plano-convex lens and focused onto a diffusing glass plate placed at focal length distance. Thereby, the scattering angle was transformed into an offset from the optical axis, forming a characteristic corona. This image was digitized with a DSLR-camera and the red color channel used for analysis.
The effect of incident light polarization was investigated by stepwise rotating the electrical vector of a polarizer in front of the film, with 0° parallel to the preferred direction of the polymer fibres. The polarization of the scattered light was investigated by a second polarizer behind the lens.

Results:
With an unpolarized light source, anisotropic scattering is preferently propagated orthogonal to the direction of the active polymers, for both landscape and portrait orientation, and the amount of scattered light increases with dose. Scattering by the EBT3-film varies from almost zero to a maximum when the electrical vector of the light source varies from parallel to orthogonal with the direction of the active polymers. The electrical vector of the scattered light is rotated by 90° compared with the incident light.

Conclusion: By experimental separation between scattered and unscattered transmitted light it was proved that incident light polarization only affects the scattered component. This effect hints upon a role of the magnetic component in the excitation of anisotropic scattering. The effect may be utilized to enhance or suppress scattering influences in EBT-3 film dosimetry.


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