Dosimeter

Ionising radiation damage to the human body is cumulative, and is related to the total dose received, for which the SI unit is the sievert.

Additional dosimeters can be worn to assess dose to extremities or in radiation fields that vary considerably depending on orientation of the body to the source.

Radiation creates defects (acts like electron-hole pairs) in oxide, which in turn affects the threshold voltage of the MOSFET.

Alternate high-k gate dielectrics like hafnium dioxide[2] and aluminum oxides are also proposed as a radiation dosimeters.

Unlike thermoluminescent crystals, which store absorbed radiation to measure accumulated doses over a period of time, scintillation materials release light immediately, and do not need to be heated.

These were once sold surplus and one format once used by submariners and nuclear workers resembled a dark green wristwatch containing the active components and a highly sensitive IR wire ended diode mounted to the doped LiF2 glass chip that when the assembly is precisely heated (hence thermoluminescent) emits the stored radiation as narrow band infrared light until it is depleted [4] The main advantage is that the chip records dosage passively until exposed to light or heat so even a used sample kept in darkness can provide valuable scientific data.

As the gas in the dosimeter chamber becomes ionized by radiation the charge leaks away, causing the fiber to straighten and thereby indicate the amount of dose received against a graduated scale, which is viewed by a small in-built microscope.

[citation needed] LED units usually have a button to turn the display on and off for longer battery life, and an infrared emitter for count verification and calibration.

The voltage is derived from a separate pinned or wire-ended module that often uses a unijunction transistor driving a small step-up coil and multiplier stage.

[citation needed] These have the disadvantage that the stored dose in becquerels or microsieverts is volatile and vanishes if the power supply is disconnected, though there can be a low-leakage capacitor to preserve the memory for short periods without a battery.

Recently-designed units log dose over time to non-volatile memory, such as a 24C256 chip so it may be read out via a serial port.

The dosimeter is calibrated in a known radiation field to ensure display of accurate operational quantities and allow a relationship to known health effect.