Dosimeter
Definition and meaning of Dosimeter in chemistry.
Dosimeter refers to a device or chemical system that measures the amount of ionizing radiation absorbed by a material, expressed as absorbed dose in gray (Gy) or rad. Chemical dosimeters rely on a radiation-induced reaction whose extent is proportional to the dose received.
In more detail
Chemical dosimeters exploit reactions with a well-characterized radiation chemical yield (G-value), so the amount of product formed can be converted into absorbed dose using known stoichiometry and molar absorptivity. The Fricke (ferrous sulfate) dosimeter is the classic example, valued for its reproducibility and use as a reference standard in radiation chemistry and radiotherapy calibration. Other dosimeter types, such as thermoluminescent dosimeters (TLDs) and film badges, use physical rather than chemical responses and are common for personal radiation monitoring.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Classic chemical dosimeter | Fricke dosimeter: Fe2+ → Fe3+ in 0.4 M H2SO4 |
| SI unit of absorbed dose | gray (Gy) = 1 J/kg |
| Fricke dosimeter G-value | ~15.5-15.6 Fe3+ ions per 100 eV absorbed |
In the Fricke dosimeter, an air-saturated solution of ferrous ammonium sulfate in 0.4 M sulfuric acid is exposed to gamma rays; the radiation oxidizes Fe2+ to Fe3+, and the Fe3+ concentration, measured spectrophotometrically at 304 nm, gives the absorbed dose directly.
Frequently asked questions
How does a dosimeter differ from a Geiger counter?
A Geiger counter reports real-time count rate or radiation intensity, whereas a dosimeter integrates exposure over time to give a cumulative absorbed dose.
Why is the Fricke dosimeter useful in chemistry?
Its oxidation of Fe2+ to Fe3+ has a precisely known, reproducible radiation chemical yield, making it a reliable chemical standard for calibrating absorbed dose from gamma or X-ray sources.