MOSFET Dosimeter

An electronic personal dosimeter is a modern dosimeter that can give a continuous read-out of cumulative dose and current dose rate and warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high-dose areas where the residence time of the wearer is limited due to dose constraints.

MOSFET dosimeter is a small portable device for monitoring and direct reading radiation dose rate. Since it is based on the MOSFET transistor, the metal-oxide-semiconductor field-effect transistor (MOSFET), the principle of operation is similar to semiconductor detectors. MOSFET dosimeters are now used as clinical dosimeters for radiotherapy radiation beams. Their main advantage is their physical size, which is less than 4 mm². In radiation therapy dosimetry, MOSFET dosimeters often replace TLD dosimeters since they offer immediate read-out.

Principle of Operation of MOSFET Detectors

The operation of MOSFET detectors is summarized in the following points:

Ionizing radiation enters the sensitive volume of the detector and interacts with the semiconductor material.
Particle passing through the detector ionizes the atoms of the semiconductor, producing the electron-hole pairs. Electron-hole pairs are generated within the silicon dioxide by the incident radiation. Electrons, whose mobility in SiO₂ at room temperature is about 4 orders of magnitude greater than holes, quickly move out of the gate electrode. In contrast, holes move in a stochastic fashion towards the Si/SiO₂ interface, where they become trapped in long-term sites, causing a negative threshold voltage shift (∆V_TH), which can persist for years.
The difference in voltage shift before and after exposure can be measured and is proportional to dose.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages

EPDs can display a direct reading of the detected dose and dose rate in real-time.
EPDs have a dose rate alarm and a dose alarm, which warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
EPDs can measure a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision.

Disadvantages

EPDs are generally the most expensive dosimeters.
EPDs are generally large.
EPDs measure and record radiation exposure due to gamma rays, X-rays, and sometimes beta particles. For neutrons, TLDs are more capable.

References:

Radiation Protection:

Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8/2010. ISBN-13: 978-0470131480.
Stabin, Michael G., Radiation Protection, and Dosimetry: An Introduction to Health Physics, Springer, 10/2010. ISBN-13: 978-1441923912.
Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4/2013. ISBN-13: 978-3527411764.
U.S.NRC, NUCLEAR REACTOR CONCEPTS
U.S. Department of Energy, Instrumentation, and Control. DOE Fundamentals Handbook, Volume 2 of 2. June 1992.

Nuclear and Reactor Physics:

J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.

See above:

Radiation Dosimeter