- SI Unit for absorbed dose is the gray (Gy)
- 1 Gy = 1 Joule per kilogram
- Absorbed dose received by a material depends on the composition of the material. Therefore dose is typically expressed in a standard material as ‘dose to water’.
Radiation processing is a term describing a vast number of industrial applications where ionizing radiation from gamma, electron beam, or X-ray sources is used to achieve a desirable effect in a product. A good example is the medical device manufacturing industry, in which radiation is used to sterilize medical devices. A large variety of industries use radiation processing for such activities as microbial reduction, polymer modification, curing of inks and coatings, phytosanitization and many others. #test
Dosimetry is used for process validation as well as quality control and quality assurance of the ongoing process.
The measurement of radiation dose is an essential tool for determining, validating and maintaining the radiation process outputs. Along with other controls, dosimetry helps assure that medical devices are sterile, that food is safe for consumers, and manufactured products meet quality expectations.
Doses delivered to products in industrial processes vary widely depending on the application and range from 10 Gy to 800 kGy (kilogray) or more. In some processes it can be very difficult to measure the dose due to practical reasons.
There is not a single measurement system with a capability spanning the radiation processing range or that is practical for use in every application. Different systems are used for different dose ranges, and dosimetry system selection is dependent upon the specific factors and requirements of each process and application.
A dosimeter is a device that, when irradiated, exhibits a quantifiable change in some property of the device that can be related to absorbed dose in a given material using appropriate analytical instrumentation and techniques. (ASTM E170)
Dose is measured using a dosimetry system. A dosimetry system consists of dosimeters, measurement instruments and their associated reference standards, and procedures for the system’s use. A dosimetry system takes the name of the dosimeter used in the system and the proper function of the entire system is integral to the dose measurement.
There are two classes of dosimetry systems that are of interest to industry.
(References: ASTM E-2628 Sections 6.3.1 and 6.3.2 and ICRU 80 Section 5)
The response of a dosimeter is the change in the signal or indication of the dosimeter, as measured by the dosimetry system. Often the normalized signal (signal change per unit mass or unit thickness) is used as the response.
1 to 120 kGy (Films)
|10 Gy to 120 kGy (Pellets)||X|
1.5 to -15 kGy (Graphite)
|3.0 to 40 kGy (Polystyrene)||X|
10 to 300 kGy
5.0 to 50 kGy (Harwell Red)
|1.0 to 15 kGy (Harwell Amber)|
|1.0 to 150 kGy (RadixW)|
1.0 to– 150 kGy (GEX B3)
|1.0 to 150 kGy (B3)||X|
|1.0 to 80 kGy (FWT-60)||X|
|10 to 4000 Gy (GAF HD-810)||X|
Dosimetry batch calibration is the process where the response of a dosimetry system is characterized through comparison with a traceable reference (standard). The calibration method for the dosimetry system is designed to ensure the integrity of the measurements made with the user’s dosimetry system. Dosimetry Systems must be calibrated for each batch of dosimeters. In addition, a separate calibration is required for each measurement instrument.
All dosimetry systems must be calibrated traceable to a national or international standard. Dosimeter manufacturers may provide response functions on their websites or in product literature, but these are for general information only. Therefore, the end-user must calibrate the measurement system as a whole (the dosimetry system) and ensure that the calibration is suitable for the conditions of use.
Routine dosimetry systems should be calibrated in accordance with the requirements of ISO/ASTM 51261. Reference dosimetry systems should be calibrated in a manner to meet the requirements of ISO 17025.