Evaluation of a low-cost commercial mosfet as radiation dosimeter

Abstract

In this work, a low-power commercial MOS transistor was tested as a gamma radiation dosimeter. Due to the small size of its detector, low cost, reproducibility, minimal power requirements, signal conditioning and data processing, it offers excellent possibilities as a dose monitor in radiotherapy. Sensor irradiation in the unbiased mode was aimed at improving patient comfort and facilitating use. Uncertainties in the results were obtained from an exhaustive dosimetric study, following a full statistical study using Monte Carlo analysis techniques. A procedure to compensate for temperature effects was introduced in order to correct the dosimetric parameter extracted. Excellent linearity and good reproducibility were found in the accumulated threshold voltage shift as a function of the accumulated dose, up to 58 Gy (air equivalent). The uncertainty regarding sensor sensitivity was found to be less than 1% for individual device calibration. When collective calibration was carried out, the uncertainty was around 5%, accounting for a set of 31 devices. In this case, a mean value of 29.2 mV/Gy was obtained. In addition, the angular and dose rate dependencies showed good behaviour. These results suggest that the transistor studied would be an excellent candidate for use as the sensing device of a low-cost measurement system capable of in vivo dosimetry.

Electronic system for data acquisition to study radiation effects on operating MOSFET transistors

“…Several results for gamma-radiation were observed in Ref. [6], showing this kind of device present excellent linearity and good reproducibility as a calibrated radiation sensor.…”

“…This device is very sensible to detection of radiation due to low gate-substrate voltage before breakdown occurs, which indicates that it has the thicker gate oxide. Gate oxide thickness is the main parameter to the sensitivity of the transistor functioning as radiation sensor [6]. Specially, this DUT is very appropriate in studies of radiation effects, since after irradiation its I DS current always reduce, facilitating the observation of the relationship between the accumulated dose and the change of the characteristic parameters in the device [1][2][3].…”

“…and their operation mode for low power consumption, are found. References [4][5][6][7] present the theoretical and practical basis for mounting the experiment in which the electronic system used for data acquisition is prepared to study TID effects. In the performed experiments we have used 10 keV effective energy X-rays impinging directly into the MOSFET transistors, in operation mode, provoking degradation of their electrical parameters [2].…”

Application of pMOS Dosimeters in Radiotherapy

“…Asensio et al [50] show results of some most important dosimetric parameters (sensitivity, linearity, reproducibility and angular dependence) for power p-channel MOSFETs 3N163. These transistors were irradiated by gamma-rays originating from…”

Extension of the measurement range of MOS dosimeters using radiation induced charge neutralization

“…This dispersion introduces measurement error if the devices are not individually calibrated. Reported values of the dispersion between devices from the same batch or Si-wafer are of about 5% [16]- [19].…”