ISO 19361:2025 PDF

Overview

ISO 19361:2025 - Measurement of radioactivity: Determination of beta emitters activities by liquid scintillation counting - is a generic international standard that defines the test method using liquid scintillation counting (LSC) to quantify activity concentration of beta-emitting radionuclides. It covers the preparation of scintillation sources (mixing test sample with a scintillation cocktail), the measurement procedure and the expression of results for liquid and solid samples (including particles, filters and planchets). The standard applies to activity concentrations from about 1 Bq·L−1 to 1×10^6 Bq·L−1 and addresses instrumentation, calibration, quench correction and uncertainty evaluation.

Key technical topics and requirements

• Scope and applicability: Liquid samples (aqueous or organic) and solid samples converted to LSC-compatible sources; specific pre‑treatments (e.g., distillation for 3H or benzene synthesis for 14C) are outside the scope and covered by dedicated methods.
• Sample preparation: Preparation of scintillation sources by mixing test portion with scintillation cocktail; for solids, ensure the activity of prepared source is compatible with the counter.
• Interference control: Identification and, where necessary, chemical separation or extraction to isolate the radionuclide of interest when other alpha, beta or gamma emitters are present.
• Counting and calibration:
  • Determination of background and counting efficiency
  • Quench correction and use of quench agents or correction curves
  • Measurement conditions, control and calibration of the liquid scintillation counter
• Performance metrics and results:
  • Calculation of activity concentration, decision threshold, detection limit, and coverage intervals
  • Guidance on measurement range linked to sample portion, cocktail composition and counting assembly
• Reagents, equipment and quality control: Specifications for blank materials, calibration source solutions, scintillation cocktails, counting vials and instrument calibration procedures.
• Informative annexes: Internal standard method, TDCR (triple-to-double coincidence ratio) LSC, and Cerenkov counting options.

Practical applications and users

ISO 19361:2025 is intended for laboratories and organizations performing radionuclide monitoring and compliance testing, including:

• Environmental monitoring and water quality labs (drinking water, effluents)
• Nuclear facility monitoring and decommissioning teams
• Regulatory and public-health laboratories
• Research and radiochemistry laboratories using LSC for beta emitter analysis
• Accredited testing labs seeking reproducible, internationally comparable results

Practical benefits include standardized workflows for LSC measurements, improved comparability of activity concentrations, reliable detection limits for low-level beta monitoring, and guidance for handling interfering radionuclides.

Related standards and context

• Aligned with ISO/TC 85 (Nuclear technologies) and developed in collaboration with CEN/TC 430.
• Complements specific LSC methods for radionuclide‑specific sample pretreatment (e.g., 3H, 14C) and benefits from principles in the ISO 11929 series for expressing measurement results, detection limits and uncertainty.