Overview
ISO/ASTM 51650:2013 is a practice for using a cellulose triacetate (CTA) dosimetry system to measure absorbed dose in materials irradiated by photons or electrons, reported in terms of absorbed dose to water. The CTA system is classified as a routine dosimetry system and the CTA dosimeter is a type II dosimeter due to the complex influence quantities that affect its response. This standard is intended to be read in conjunction with ASTM E2628 and is part of a suite of standards for dosimetry in radiation processing.
Key measured ranges and addressed conditions in the standard include:
- Absorbed dose range: 10 kGy to 300 kGy
- Absorbed-dose rate range: 3 Gy/s to 4310 Gy/s
- Photon energy range: 0.1 to 50 MeV
- Electron energy range: 0.2 to 50 MeV
The standard emphasizes traceable calibration, measurement uncertainty, and documentation to support routine, compliant dosimetry practice.
Key Topics
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Dosimetry system components: CTA film, calibrated spectrophotometer (or equivalent) for optical absorbance measurement, and supporting calibration and documentation. CTA film is commonly supplied as an 8 mm wide strip on spools for high-resolution dose mapping.
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Influence quantities: Pre-irradiation and post-irradiation conditions (temperature, relative humidity, time since manufacture, exposure to UV/light), absorbed-dose rate, dose fractionation, and irradiation temperature. The practice requires these effects be characterized for a given system and process.
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Calibration and reference systems: Routine systems must be calibrated against an appropriate reference standard dosimetry system. Calibration procedures, measurement management, and documentation requirements are covered to ensure traceability and reproducibility.
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Measurement and analysis: CTA response is expressed as specific net absorbance (change in absorbance divided by optical pathlength). The analysis wavelength affects sensitivity and stability; manufacturers’ recommended wavelengths and spectrophotometer performance should be used.
Applications
The standard supports practical uses where routine, reliable dose measurements are required, for example:
- Radiation processing quality control and process monitoring
- Sterilization verification of healthcare products
- Polymer modification and materials processing that require absorbed-dose mapping
- High-resolution dose mapping using CTA strips to produce one-, two- or three-dimensional dose distributions
Practical benefits include improved process control, repeatable dose mapping, and a pathway to compliance with ASTM E2628 when using CTA systems.
Related Standards
- ASTM E2628 - Practice for Dosimetry in Radiation Processing (to be read in conjunction)
- ISO/ASTM 51261 - Calibration of routine dosimetry systems for radiation processing
- ISO/ASTM 51707 - Guide for estimating uncertainties in dosimetry for radiation processing
- ICRU and JCGM guidance referenced within the practice for quantities, units and uncertainty evaluation
Note: Users should follow manufacturer guidance for dosimeter conditioning, recommended analysis wavelengths, and storage/packaging practices. The standard also includes annex tables listing CTA properties and known suppliers of dosimeters and reading equipment to assist implementation.