Performance of a thin epitaxial diode as a relative dosimeter in radiation protection
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2024
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SIMPOSIO REPROLAM, 1st
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Silicon diodes have been used as relative dosimeters in radiation protection, medical imaging, and
radiation therapy. Usually, the diode operates in the short-circuit current mode and remains unbiased to
minimize the dark current contribution to the radiation-induced current signal. The dosimetric parameter is
the net output current linearly dependent on the dose rate within certain limits. The corresponding
collected charge (obtained as the integral of the current signal) is proportional to the dose.
Many articles in the literature report several advantages of diode-based dosimeters despite a key drawback
regarding their sensitivity decay with increasing accumulated doses. This issue has been tackled by
developing devices with different geometries or tailoring the impurity density in the silicon bulk grown
through distinct techniques. A combined approach of these strategies outcomes the epitaxial diode under
investigation in this work. It has a thin n-type epitaxial layer (50 μm, 25 mm2) grown on a 300 μm Cz Si
substrate. The p+-n junction is provided by a highly doped p-type silicon layer (@ 1 μm) on the front side
of the diode. This structure, which keeps the active volume constant with a tiny entrance window and
negligible dark current, opens up potential applications for radiation protection dosimetry.
The diode is housed in a light-tight polymethylmethacrylate probe with an entrance window covered by a thin (8.3 mg/cm2)
black paperboard. The planar pad (p+) signal electrode is directly connected to the input of a Keithley® 6517B electrometer
with the backplane n+ grounded and the guard ring structure floating. The current measurements are performed in the shortcircuit
mode without externally applied voltage to the diode.
The sensitivity, repeatability, reproducibility, dose-response linearity, and directional response are evaluated for N60, N80,
N100, and N150 beam qualities [1]. Irradiations are performed with a Pantak-Seifert 160HS Isovolt X-ray generator
previously standardized by a Radcal 10X5-180 ionization chamber calibrated at the PTB. The probe is positioned at the
center of a circular irradiation field of 42 cm diameter, with 99% homogeneity, at 250 cm from the X-ray tube (focal spot).
The current signals produced by photon beams of different qualities (60 -150 kV) are stable and
characterized by repeatabilities better than 5%. The dose-responses curves are also linear but slightly
dependent on the photon energy. The angular dependence and long-term stability parameters remain to be
investigated. To give theoretical support to the data sensitivity calculations, assuming the diode is a thin
abrupt junction, are underway.
Como referenciar
GONCALVES, JOSEMARY A.C.; ANTONIO, PATRICIA de L.; SANTOS, LEONARDO C. dos; POTIENS, MARIA da P.A.; CALDAS, LINDA V.E.; BUENO, CARMEN C. Performance of a thin epitaxial diode as a relative dosimeter in radiation protection. In: SIMPOSIO REPROLAM, 1st, November 5-8, 2024, Recife, PE. Abstract... Disponível em: https://repositorio.ipen.br/handle/123456789/48884. Acesso em: 30 Dec 2025.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.