🔬 Determination of the activity (Bq) of gamma-ray emitting radionuclides in solid, liquid and gaseous test samples by high-resolution gamma-ray spectrometry — energy and detection efficiency calibration, net full-energy peak area by summation or fitting, dead-time correction, characteristic limits according to ISO 11929; energy range 5–3000 keV; in accreditation scopes caesium-137 (and caesium-134) in food, feed and water, PN-EN ISO 20042

Physicochemistry PN-EN ISO 20042

Overview

WHAT THE STANDARD COVERS. The scope on the PKN catalogue card of PN-EN ISO 20042:2022-01 (English version) begins (our translation): “This document describes methods for determining in test samples the activity in becquerels (Bq) of gamma-ray emitting radionuclides by gamma-ray spectrometry. Measurements are made in a test laboratory after appropriate sample preparation. Test samples can be solid, liquid or gaseous”; the card then lists the applications and reservations of Clause 1 of the standard (content consistent with the description below). We read the text of the standard in two iTeh samples: ISO 20042:2019 (French version) — from the contents through the foreword, introduction and Clauses 1–4 up to and including 5.2 (summation method); SIST EN ISO 20042:2021 (text of EN ISO 20042:2021) — title pages, European foreword and endorsement notice. Outside the samples remain 5.3 (fitting method), Clauses 6 (validation of measurements in seven steps), 7 (nuclear decay data, decay chains), 8 (energy and efficiency calibration, reference sources), 9 (containers), 10 (sampling, preparation, filling the container, recording and analysing the spectrum, background corrections), 11 (calculation of activity and characteristic limits), 12 (test report) and Annexes A–F (quality assurance, corrections to the analysis process, uncertainty, detector types, example calculation for caesium-137 in an aqueous sample, example simulation of corrections).

ACCORDING TO THE TEXT OF ISO 20042:2019 (introduction, Clauses 1–4, 5.1–5.2). The standard was prepared by ISO/TC 85 “Nuclear energy, nuclear technologies and radiological protection”, subcommittee SC 2 “Radiological protection”; CEN approved EN ISO 20042:2021 on 25 July 2021 without modification (taken over by CEN/TC 430). Introduction: the standard is used in a quality management system according to ISO/IEC 17025; it is the basis for the measurement tasks with gamma-ray spectrometry described in ISO 18589-3, ISO 18589-7, ISO 10703, ISO 13164-2 and ISO 13165-3 and belongs to a set of generic standards on measurement of radioactivity (e.g. ISO 19361); among anthropogenic radionuclides it mentions gamma emitters in waste, effluents, the environment, food and feed after authorised releases, fallout from nuclear explosions and the accidents at Chernobyl and Fukushima. Scope (1): activity in Bq in solid, liquid and gaseous test samples, measured in the laboratory after preparation; applications — routine surveillance of nuclear installations and of sites with elevated natural radioactivity, changes in environmental radioactivity, accident situations, waste from decommissioning of nuclear facilities, contamination of soil, food, water, groundwater, sea water and sewage sludge, estimation of intake by the body. It is assumed that the user knows the composition of the sample or site, and that the sample is homogenised and representative; some types of samples are prepared according to specific standards; the standard gives generic advice on choice of equipment, detectors, commissioning and validation, quality control and maintenance, but does not cover electrical tests of the detector and electronics; software is to be written and checked according to relevant standards (e.g. ISO/IEC/IEEE 12207); the principles also apply to in situ measurements, but detailed requirements for them are in ISO 18589-7. Energy: from 5 keV to 3000 keV, although most measurements lie between 40 keV and 2000 keV; activities from levels below 1 Bq in environmental samples to accident levels and high-level waste. Normative references (2) include standards for sampling oilseeds, milk, water, soil (ISO 18400 series) and cereals, ISO 10703, ISO 11929 (characteristic limits), ISO 18589-2 and -7, GUM and ISO/IEC 17025. Definitions (3): among others background continuum, dead time (real time minus live time), decision threshold and detection limit (according to ISO 11929), detection efficiency (probability that a photon of a given energy is recorded in the full-energy peak), full width at half maximum (FWHM, in keV), net peak area, peak-to-Compton ratio (for 60Co at 1332.5 keV against the mean of the range 1040–1096 keV), reference source (of known activity, traceable to national or international primary standards), true coincidence summing (simultaneous detection of at least two gamma rays from the cascade of one nucleus). Principle (5.1): usually high-resolution gamma-ray spectrometry, with identification and quantification by software; low-resolution detectors (e.g. sodium iodide, other scintillators — ISO 19581) are useful for rapid screening of food at a nuclear incident, but for complex mixtures, such as environmental samples, high resolution is essential; in a semiconductor detector the charge collected in the electric field is converted into a pulse whose height is proportional to the energy; the spectrum from the multichannel analyser has peaks of roughly Gaussian shape on a background continuum; the net peak area is proportional to the number of photons of a given energy during the counting time (after dead-time correction) and is determined by summation or fitting. Summation method (5.2): the sum of counts in the region of interest minus the background calculated assuming a linear continuum under the peak from the counts in the end channels, uncertainty assuming a Poisson distribution in each channel; the region of interest must be chosen carefully, especially when the peak lies near a discontinuity in the spectrum, next to another peak or on a high continuum; peak position — as a mean weighted by net counts.

STATUS (card as of 03.10.2026). The card of PN-EN ISO 20042:2022-01 (English version, published 19-01-2022, 66 pages, price group V) has no “Withdrawn” header: Machinery and Engineering Sector, KT 246 Radiological Protection, ICS 13.280, “Introduces: EN ISO 20042:2021 [IDT], ISO 20042:2019 [IDT]”; the card has no “Replaces” field. There is no Polish language version in the PKN search engine (term “PN-EN ISO 20042”, 03.10.2026). In the iTeh catalogue (read on 03.10.2026) ISO 20042:2019 has the status “Published” and stage 90.93 “International Standard confirmed” (completed 29.08.2026).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read on 03.10.2026). The number 20042 appears in 7 records at 5 laboratories: AB 377, AB 435, AB 519, AB 537, AB 585. In the current PCA documents (read on 03.10.2026, issues from 26.11.2025 to 07.08.2026) the number appears in 6 items of the same 5 laboratories (AB 519 — 2, the others 1 each). Notation everywhere “PN-EN ISO 20042:2022-01”. The “Laboratories” tab (“PN-EN ISO 20042”) shows the same 5 laboratories — checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). All items are “activity concentration of the radionuclide 137Cs”, gamma-ray spectrometry method. Food, agricultural products and feed: AB 377 — (0.5–10000) Bq/kg and Bq/l; AB 435 — 0.5 Bq/kg to 10000 Bq/kg (and Bq/l); AB 537 — food, (0.5–5000) Bq/kg or Bq/l; AB 585 — feed and food, (0.20–4806.01) Bq/kg, and in the same item also caesium-134 — (0.20–406.3) Bq/kg; AB 519 — milk, meat, poultry, eggs, fish, vegetables, fruit, mushrooms, cereals and raw feed, (0.1–1500) Bq/dm3 and Bq/kg. Water: AB 519 — water, surface water and drinking water, (0.1–1500) Bq/dm3, with PN-EN ISO 10703:2021-12; AB 377 and AB 435 measure caesium-137 in water according to PN-EN ISO 10703 alone, and in food and feed — according to this standard. Upper limits to hundredths (4806.01 and 406.3 Bq/kg at AB 585) are the notation of the PCA document, not of the standard. No item is suspended.

WHERE A SEEMINGLY CORRECT RESULT IS EASY. With the sample: the standard assumes that the sample is homogenised and representative and that the user knows its composition (1) — a result from a heterogeneous sample is calculated correctly but does not refer to the material tested; some matrices must be prepared according to specific standards. With the detector: a low-resolution detector is suitable for screening food at an incident, but not for complex mixtures of radionuclides (5.1) — unresolved peaks give a sum instead of the result for one radionuclide. With the peak area: the summation method assumes a linear continuum under the peak (5.2) — with a peak next to another peak, at a discontinuity in the spectrum or on a high background, a badly chosen region of interest shifts the result without any message from the software. With time: the peak area refers to the live time, not the real time — the difference is the dead time (3.5, 3.12). With calibration: the detection efficiency depends on the type and geometry of the detector and the sample (5.1), so a calibration made in a different geometry or density from the sample does not fit it; true coincidence summing (3.24) concerns radionuclides emitting cascades of gamma rays, and the corrections for it are described in Annex F, which we have not read.

WHAT WE DO NOT GIVE. We have not read 5.3, Clauses 6–12 or the annexes, so we do not give the validation steps, the recommended nuclear data (e.g. energies and emission probabilities of caesium-137 and caesium-134), the method of efficiency calibration, types of containers, preparation of food samples (drying, ashing, grinding), formulas for activity, the decision threshold and detection limit or the calculation example of Annex E. Nor do we give maximum permitted levels of contamination of food and feed — we have not read the texts of the regulations for this entry.

Method principle

The sample after preparation (e.g. homogenisation, drying or ashing) is placed in a container of known geometry at the detector, most often a high-resolution semiconductor; the charge produced by a gamma ray is converted into a pulse proportional to the energy, and a multichannel analyser records the spectrum. Each radionuclide gives full-energy peaks at known energies; the net peak area (after subtracting the background continuum, by summation or fitting, after dead-time correction) is divided by the detection efficiency from the calibration, the emission probability, the counting time and the mass or volume of the sample, with decay correction, giving the activity in Bq/kg or Bq/l with uncertainty and characteristic limits according to ISO 11929.

Applications

• Soil, food, drinking water, groundwater, sea water, sewage sludge — surveillance of radioactive contamination (1)
• Routine surveillance of nuclear installations, changes in environmental radioactivity, accident situations, waste from decommissioning of nuclear facilities (1)
• Gamma emitters in the range 5–3000 keV, usually 40–2000 keV; from levels below 1 Bq to high-level waste (1)
• Food, agricultural products, feed and water — activity concentration of caesium-137 (at one laboratory also caesium-134) in the accreditation scopes of 5 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 20042:2022-01

Title (PL)

Pomiary promieniotwórczości — Radionuklidy emitujące promieniowanie gamma — Ogólna metoda badania z zastosowaniem spektrometrii promieniowania gamma

Title (EN)

Measurement of radioactivity — Gamma-ray emitting radionuclides — Generic test method using gamma-ray spectrometry

Step-by-step procedure

1. Sampling and sample preparation

   Sampling according to the standards for the matrix (milk, cereals, water, soil); homogenisation and preparation — for some matrices according to specific standards. PN-EN ISO 20042:2022-01 current (PKN card as of 03.10.2026).

2. Calibration

   Energy and detection efficiency calibration with reference sources or numerical methods, in a geometry corresponding to the sample; we do not give the details (Clause 8).

3. Spectrum measurement

   Sample in the container at the detector; recording the spectrum with live and real time; background measurement.

4. Spectrum analysis

   Identification of full-energy peaks; net area by summation (linear continuum, careful choice of region) or fitting.

5. Result

   Activity in Bq/kg or Bq/l with decay and dead-time correction, with uncertainty and decision threshold and detection limit according to ISO 11929.

Required equipment and apparatus

Health and safety (OHS)

• Reference sources are radioactive — the radiation protection regulations applying to the laboratory are followed
• Samples from accident situations and waste may have high activity (1) — handling according to exposure assessment
• Semiconductor detectors operate at high voltage (5.1); electrical tests of the detector and electronics are outside the standard

Frequently asked questions