Overview
ISO/ASTM 51401:2013 defines practice for the preparation, testing and use of the acidic aqueous silver dichromate dosimetry system to measure absorbed dose to water when exposed to ionizing radiation. The standard covers the dosimeter (solution in sealed glass ampoules), required analytical instrumentation, and spectrophotometric analysis procedures. The dichromate system is classified as a type I dosimeter, and may be used as either a reference standard or a routine dosimetry system. It applies specifically to gamma radiation, X‑radiation/bremsstrahlung, and high‑energy electrons.
Key Topics
- System components: acidic aqueous silver/dichromate solution contained in sealed glass ampoules and a calibrated spectrophotometer for absorbance measurement.
- Spectrophotometric analysis: procedures to determine dose via absorbance change after irradiation. Calibration and instrument performance checks are required.
- Performance influences: temperature during irradiation, radiation type/energy, dose rate and chemical impurities can affect response.
- Temperature sensitivity: the dosimeter response shows a measurable temperature dependence (notably between typical operating ranges). The standard requires irradiation temperatures above 0°C and recommends keeping temperatures below ~80°C; documented coefficients are provided for the usable range and should be applied as correction factors.
- Contamination control: the dosimetric solution is sensitive to trace organic impurities. Use analytical‑grade reagents and high‑purity water (double‑distilled or equivalent with low TOC). Avoid reactive plastics and ensure cleaned, compatible glassware.
- Calibration & traceability: calibration of the dosimetry system and traceability to recognized laboratories (for example, ISO/IEC 17025 accredited labs) is emphasized. Documentation, calibration records and uncertainty estimation are required.
Applications
- Reference and routine absorbed‑dose measurements in radiation processing and irradiation facilities.
- Dose verification for gamma sterilization, X‑ray/bremsstrahlung processing and high‑energy electron beam applications.
- Use in audits, process validation, batch release and intercomparisons where spectrophotometric chemical dosimetry is appropriate.
Practical recommendations include: prepare solutions using analytical reagents and certified high‑purity water, fill and seal glass ampoules under controlled conditions, pre‑irradiate bulk solution where advised to reduce impurity effects, perform spectrophotometer performance checks, and apply temperature and radiation‑type corrections during dose calculation.
Related Standards
- ISO/ASTM Practice 52628 - Dosimetry in radiation processing (companion document)
- ISO 51261 - Calibration of routine dosimetry systems
- ISO/ASTM 51707 / JCGM 100 (GUM) - Uncertainty estimation guidance
- ISO/IEC 17025 - Competence of testing and calibration laboratories
- ASTM Guide 52701 - Performance characterization of dosimeters
This standard is intended to be read in conjunction with ISO/ASTM Practice 52628 and other referenced guides to ensure compliant and reliable dichromate dosimetry practice.