Overview
ISO/ASTM 51026:2015 - Practice for using the Fricke dosimetry system - specifies procedures for preparing, testing and using an acidic aqueous ferrous ammonium sulfate solution (the Fricke solution) to measure absorbed dose to water from ionizing radiation. The standard covers the dosimeter composition, spectrophotometric analysis, instrumentation, calibration, uncertainty estimation and documentation, and it permits use of the Fricke system as either a reference or routine dosimetry system.
Key topics and requirements
- Dosimetry scope and limits
- Absorbed dose range: 20–400 Gy
- Maximum absorbed-dose rate: ≤ 10 Gy·s⁻¹
- Radiation types: gamma (photon energy > 0.6 MeV), X‑radiation (bremsstrahlung from electrons ≥ 2 MeV), high-energy electrons (> 8 MeV)
- Dosimeters thermal range: typically 10–60 °C
- Chemical dosimeter and reagents
- Uses an air‑saturated ferrous ammonium sulfate solution in acidic aqueous medium
- Reagent and water purity are critical; recommend analytical-grade chemicals and ultra‑pure water (very low TOC)
- Common reagents named: ferrous ammonium sulfate, sulfuric acid, sodium chloride
- Apparatus and measurement
- Spectrophotometric analysis is required (high-precision UV‑Vis spectrophotometer, quartz cuvettes, 5–10 mm pathlength)
- Use sealed glass ampoules (or conditioned plastic containers) for irradiation; avoid metal contact
- Influence, interferences and corrections
- Response depends on irradiation and measurement temperature; corrections for temperature dependence of molar absorption and chemical yield are required
- Extremely sensitive to organic impurities, trace metal ions and UV exposure; thermal oxidation can cause background signal
- Quality, calibration and uncertainty
- Calibration and traceability to a national metrology institute or ISO/IEC 17025 accredited lab are recommended
- Standard defines minimum documentation, procedures for calibration, and guidance on estimating measurement uncertainty
Applications and users
- Radiation processing quality assurance and dose mapping (e.g., sterilization, material processing)
- Dosimetry and calibration laboratories (reference and routine dose measurements)
- Metrology institutes and labs seeking traceable absorbed-dose to water measurements
- Users needing an absolute chemical dosimetry method where spectrophotometric analysis is feasible
Related standards
- ISO/ASTM 52628 - Practice for dosimetry in radiation processing (complementary)
- ISO/ASTM 51261 - Calibration of routine dosimetry systems
- ISO/IEC 17025 - Laboratory accreditation and traceability
- ICRU reports and JCGM 100 (GUM) guidance on uncertainty
Keywords: ISO/ASTM 51026, Fricke dosimetry, absorbed dose to water, ferrous ammonium sulfate, spectrophotometric dosimetry, radiation processing dosimetry, reference dosimetry, measurement uncertainty.