Standard Practice for Dosimetry in an X-Ray (Bremsstrahlung) Facility for Radiation Processing at Energies between 50 keV and 7.5 MeV

Importancia y uso:

4.1 A variety of products and materials are irradiated with X-radiation to modify their characteristics and improve the economic value or to reduce their microbial population for health-related purposes. Dosimetry requirements might vary depending on the type and end use of the product. Some examples of irradiation applications where dosimetry may be used are:

4.1.1 Sterilization of health care products;

4.1.2 Treatment of food for the purpose of parasite and pathogen control, insect disinfestation, and shelf life extension;

4.1.3 Disinfection of consumer products;

4.1.4 Cross-linking or degradation of polymers and elastomers;

4.1.5 Curing composite material;

4.1.6 Polymerization of monomers and oligomer and grafting of monomers onto polymers;

4.1.7 Enhancement of color in gemstones and other materials;

4.1.8 Modification of characteristics of semiconductor devices; and

4.1.9 Research on materials effects of irradiation.

Note 3: Dosimetry with measurement traceability and with known measurement uncertainty is required for regulated irradiation processes, such as the sterilization of health care products and treatment of food. Dosimetry may be less important for other industrial processes, such as polymer modification, which can be evaluated by changes in the physical properties of the irradiated materials. Nevertheless, routine dosimetry may be used to monitor the reproducibility of the radiation process.

4.2 Radiation processing specifications usually include a pair of absorbed-dose limits: a minimum value to ensure the intended beneficial effect and a maximum value that the product can tolerate while still meeting its functional or regulatory specifications. For a given application, one or both of these values may be prescribed by process specifications or regulations. Knowledge of the dose distribution within irradiated material is essential to help meet these requirements. Dosimetry is essential to the radiation process since it is used to determine both of these limits and to confirm that the product is routinely irradiated within these limits.

4.3 Several critical parameters must be controlled to obtain reproducible dose distributions in the process load. The absorbed-dose distribution within the product depends on the overall product dimensions and mass and irradiation geometry. The processing rate and dose distribution depend on the X-ray intensity, photon energy spectrum, and spatial distribution of the radiation field and conveyor speed.

4.4 Before an irradiator can be used, it must be qualified (IQ, OQ) to determine its effectiveness in reproducibly delivering known, controllable absorbed doses. This involves testing the process equipment, calibrating the equipment and dosimetry system, and characterizing the magnitude, distribution and reproducibility of the absorbed dose delivered by the irradiator for a range of product densities.

4.5 To ensure consistent dose delivery in a qualified irradiation process, routine process control requires procedures for routine product dosimetry and for product handling before and after the treatment, consistent product loading configuration, control and monitoring of critical process parameters, and documentation of the required activities and functions.

Subcomité:

E61.03

Volúmen:

12.02

Número ICS:

17.240 (Radiation measurements)

Palabras clave:

absorbed dose; bremsstrahlung; dose distribution; dose mapping; dosimeter; dosimetry; electron accelerator; electron beam; ionizing radiation; irradiator characterization; photon; radiation; radiation dosimetry; radiation processing; X-radiation; X-ray; X-ray processing; X-ray target; X-ray utilization;