What Does a Dosimeter Measure?

Radiation dosimetry is the calculation of the dose absorbed into tissue that results from exposure to ionizing radiation. This dose is indicated in units of gray (Gy) for mass and the equivalent dose is indicated in units of sieverts (Sv) for biological tissue, where 1 Gy or 1 Sv equals 1 joule per kilogram. A radiation dosimeter is a device that measures the dose absorption of external ionizing radiation and is used by the person being monitored when using it as a personal dosimeter. It is a record of the radiation dose received. Modern electronic personal dosimeters can provide a continuous reading of the cumulative dose and the current dose rate, and can warn the user with an audible alarm when a specified dose rate or cumulative dose is exceeded.

Other dosimeters, such as thermoluminescent or film types, require post-use processing to reveal the cumulative dose received and cannot give a current dose indication while in use. Scientists measure radiation in different ways. Sometimes they measure the dose a person receives from a radioactive source, and sometimes they measure the amount of radioactivity in water, soil, or air. These steps are taken to determine if safety measures are needed. There are different but interrelated units for measuring radioactivity and estimating health effects. Radioactivity is a measure of the ionizing radiation released by a radioactive material.

Different types of ionizing radiation have the potential to damage human tissue. The radioactivity of a material is measured in becquerelos (Bq, international unit) and curios (Ci, U. S.). Because a Curie is a large unit, radioactivity results are usually shown in picocurios (PCi).

A picocurie is one billionth of a curie. The absorbed dose describes the amount of energy deposited per unit mass on an object or person. Units for absorbed dose are gray (Gy, international unit) and rad (rad, U. A milligray (mGy) is 0.001 gray. The effective dose takes the absorbed dose and adjusts it according to the type of radiation and the relative sensitivity of the organs. The result is an indicator of potential long-term health effects (i.e., it is used to establish regulatory limits that protect against long-term health effects of a population).

It also allows experts to compare the anticipated health effects of different exposure situations. The units for the effective dose are sievert (Sv, international unit) and rem (rem, U. One millisievert (mSv) is 0.001 sieverts. A radiation dosimeter is a device that measures exposure to ionizing radiation. Dosimeters usually record a dose, the absorbed radiation energy measured in gray (Gy), or the equivalent dose measured in sieverts (Sv).

A personal dosimeter is a dosimeter that the monitored person wears on the surface of the body and records the radiation dose received. Dosimeters are generally used outside clothing, around the chest or torso to represent the “whole body” dose. The electronic personal dosimeter, the most commonly used type, is an electronic device that has a number of sophisticated functions, such as continuous monitoring, which allows alarm warnings at preset levels and live reading of the accumulated dose. An electronic personal dosimeter is a modern dosimeter that can provide a continuous reading of the cumulative dose and the current dose rate and warn the person using it when a specified dose rate or cumulative dose is exceeded. Such devices are known as legal dosimeters if they have been approved for use in personnel dose recording for regulatory purposes. Radiographers, nuclear power plant workers, doctors using radiation therapy, hazardous materials workers, and others in situations involving the handling of radionuclides must often use dosimeters in order to record occupational exposure. A thermoluminescent dosimeter (TLD) is a passive radiation dosimeter that measures exposure to ionizing radiation by measuring the intensity of visible light emitted by a sensitive crystal in the detector when heated. Alternative high-k gate dielectric radiation dosimeters, such as hafnium dioxide and aluminum oxides, are also proposed as radiation dosimeters.

The personal ionizing radiation dosimeter is of fundamental importance in disciplines such as radiation dosimetry and radiation health physics and is primarily used to estimate the radiation dose deposited on a person wearing it. In radiation therapy dosimetry, MOSFET dosimeters often replace TLD dosimeters because they offer an immediate reading. Prior to use by the user, a dosimeter is charged to a high voltage, causing it to deflect due to electrostatic repulsion. A thermoluminescent dosimeter measures exposure to ionizing radiation by measuring the intensity of light emitted by a crystal doped with Dy or B in the detector when heated. Manufacturing processes that treat products with ionizing radiation, such as food irradiation, use dosimeters to calibrate doses deposited on matter being irradiated. Additional dosimeters can be used to assess doses in extremities or in radiation fields that vary greatly depending on orientation towards source.