Using RADFET for the real-time measurement of gamma radiation dose rate

Abstract

RADFETs (RADiation sensitive Field Effect Transistors) are integrating ionizing radiation dosimeters operating on the principle of conversion of radiation-induced threshold voltage shift into absorbed dose. However, one of the major drawbacks of RADFETs is the inability to provide the information on the dose rate in real-time using the conventional absorbed dose measurement technique. The real-time monitoring of dose rate and absorbed dose can be achieved with the current mode dosimeters such as PN and PIN diodes/photodiodes, but these dosimeters have some limitations as absorbed dose meters and hence they are often not a suitable replacement for RADFETs. In that sense, this paper investigates the possibility of using the RADFET as a real-time dose rate meter so that it could be applied for simultaneous online measurement of the dose rate and absorbed dose. A RADFET sample, manufactured by Tyndall National Institute, Cork, Ireland, was tested as a dose rate meter under gamma irradiation from a Co-60 source. The RADFET was configured as a PN junction, such that the drain, gate and source terminals were grounded, while the radiation-induced current was measured at the bulk terminal, whereby the bulk was successively biased with 0 , 10 , 20 and 30 V. In zero-bias mode the radiation-induced current was unstable, but in the biased mode the current response was stable for the investigated dose rates from 0.65 to 32.1 Gy h−1 and up to the total absorbed dose of 25 Gy. The current increased with the dose rate in accordance with the power law, whereas the sensitivity of the current read-out was linear with respect to the applied bias voltage. Comparison with previously analyzed PIN photodiodes has shown that the investigated RADFET is competitive with PIN photodiodes as a gamma radiation dose rate meter and therefore has the potential to be employed for the real-time monitoring of the dose rate and absorbed dose.

Use of High-Field Electron Injection into Dielectrics to Enhance Functional Capabilities of Radiation MOS Sensors

“…Nowadays in the field of medicine, space devices, nuclear power, etc., metal-oxide-semiconductor (MOS) sensors of a radiation are widely utilized [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Most frequently, these sensors are based on p-channel MOSFET (radiation sensitive field effect transistors (RADFET) sensors).…”

“…As a result, one observes a change of threshold voltage of RADFET sensors. Using reference dependencies acquired at earlier stage, one calculates an absorbed dose on the basis of threshold voltage shift [1,[9][10][11][12][13][14][15]. One of the main techniques to raise the sensitivity of RADFET sensors is an applying of positive voltage to the transistor gate [1,4,9,14].…”

Application of p-Channel Power VDMOSFET as a High Radiation Doses Sensor

“…Experimental results of dependence for components irradiated without gate bias can be very well described by exponential growth function. The results regarding the fixed traps and switching traps densities obtained by the midgap technique [40] proved that the dominant role in increase is played by fixed traps and their density is larger in power IRF9520 than in RAD-FETs for the same value of radiation dose. The results also show that 24 h fading is larger in IRF9520 than in RADFETs.…”

“…Tyndall produces other RADFET types (with 400 nm and 1000 nm gate oxide thickness) which are more sensitive and hence suitable for lower dose range [16], [18]. RADFETs production procedure, cross-section and pin arrangement are given in [40]. According to datasheet, IRF9520 breakdown voltage is V, conduction resistivity is and maximum drain current is 6.8 A.…”

Dose verification system based on MOS transistor for real-time measurement

“…The main limitations in the unbiased mode are low sensitivity and reduced linearity at high doses. Efforts to increase the sensitivity of MOSFET dosimeters have involved fabricating them with a special technological process to achieve a thick gate oxide (more than 200 nm), with the resulting devices being known as RADFETs (RADiation Field Effect Transistor) [8- [10].…”