ISO/ASTM 51650:2013

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

• 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.

• 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.

• 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.

• 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.