Answer to Question #847 Submitted to "Ask the Experts"

1. What are the main features of radiometric film dosimetry (RFD)?
2. What are its advantages over TLD?
3. Is this technology the same as that offered by Luxel OSL dosimetry?
4. Are the RFD badges reusable in the same sense as TLD badges?
5. Is RFD able to measure all types of radiation using one holer?

Radiochromic film uses radiochemical processes to impart a change in the optical absorbance of the film for specific wavelengths of light. As the name implies, the dosimeters consist of thin plastic films impregnated with radiation-sensitive chemicals or radiochromic dyes. The technology is predominantly used to measure the very high doses associated with industrial irradiators and accelerators. It is not sufficiently sensitive or robust for routine personal monitoring for health protection. The films require special packaging to avoid errors associated with exposure to light and humidity. The radiochemical processes are also influenced by temperature. Radiochromic films offer excellent spacial resolution of dose variations and the films have been used to measure the isodose lines from ⁹⁰Sr opthalmic irradiation sources. The optical absorbance of the films can be evaluated multiple times and the films can be stored for some time, although not like photographic film. The films can only be used once, whereas your LiF TLD can be annealed and reused many times. In addition, the response of the films varies from lot to lot so calibration dosimeters must be matched to the same lot. Radiochromic film dosimetry is much different from Luxel OSL dosimetry.

OSL is more analogous to TLD than radiochromic films. OSL differs from TLD in that trapped charges are released to combine with luminescence centers using optical energy rather than thermal energy. The optical energy required to generate luminescence is very low and only a small fraction of the trapped charge is released. Therefore, an irradiated OSL dosimeter can be repeatedly stimulated to provide multiple dose evaluations for improved precision or confirmation of an earlier analysis. OSL dosimeters can be reused if enough optical energy is supplied to release all of the trapped charge. By eliminating the high temperatures associated with TLD, OSL materials such as the aluminum oxide powder used in the Luxel dosimeter can be coated onto thin, clear plastic films. OSL is not a radiochemical process.

Craig Yoder, PhD, CHP