Radioactive Substance Analysis: Testing Methods, Nuclides, Standards, and Applications

Radioactive substance analysis is the laboratory determination of radionuclide activity concentrations in food, water, soil, building materials, and consumer products using techniques such as gamma spectrometry, alpha spectrometry, and liquid scintillation counting. Accredited third-party laboratories perform these tests to verify compliance with national and international limits for artificial and naturally occurring radionuclides, supporting food safety, environmental monitoring, and import–export control. This article explains the analytical principles, sample types, target nuclides, standard methods, applications, and frequently asked questions related to radioactive substance analysis.

Technical Overview

Radioactive substance analysis refers to the qualitative and quantitative determination of radionuclides in samples of environmental, biological, or industrial origin. Radionuclides are unstable atomic nuclides that undergo spontaneous nuclear decay and emit ionizing radiation, primarily alpha particles, beta particles, gamma rays, and characteristic X-rays. The fundamental measurand in radiochemical analysis is activity, expressed in becquerels (Bq), where 1 Bq corresponds to one nuclear decay per second. Results are typically reported as activity concentration in Bq/kg for solids and Bq/L for liquids.

Radioactive contamination may originate from artificial sources, such as nuclear weapons testing, nuclear facility accidents, and medical or industrial sealed sources, or from naturally occurring radioactive materials (NORM), such as the uranium-238, thorium-232, and potassium-40 decay chains present in minerals, soils, and water. Analytical results are compared against regulatory limits—for example, the radionuclide limits in foods specified in GB 14882, the radionuclide limits for building materials in GB 6566, and the radioactivity indicators for drinking water in GB 5749—to assess whether a sample is suitable for consumption, use, or release into the environment.

Testing Samples

Food and Agricultural Products

Foods of both domestic and imported origin, including drinking water, dairy products, vegetables, grains, meat, seafood, tea, and wild mushrooms, are analyzed for artificial gamma emitters such as cesium-137 and strontium-90, particularly following nuclear incidents or as part of routine import surveillance at ports and borders.

Water Samples

Drinking water, surface water, groundwater, seawater, and industrial wastewater are screened for gross alpha and gross beta activity, followed by nuclide-specific confirmation where screening levels are exceeded.

Soil, Sediment, and Solid Waste

Environmental samples are tested to characterize contamination gradients, support site remediation, and verify waste classification for disposal or clearance in accordance with ISO 18589 series standards for the measurement of radioactivity in soil.

Building Materials

Cement, gypsum board, natural stone, ceramic tiles, sand, gravel, blast furnace slag, and fly ash are tested for natural radionuclides to calculate the internal exposure index and external exposure index defined in GB 6566.

Metals and Recycled Scrap

Scrap metal, steel, aluminum, and copper feedstock are screened for orphan sealed sources and contaminated material using radiation portal monitors, followed by laboratory confirmation.

Consumer Goods and Electronics

• Luminous products such as watches, instrument dials, and exit signs containing tritium (H-3) or promethium-147
• Smoke detectors containing americium-241
• Optical components containing thoriated glass and gas mantles containing thorium
• Fertilizers, phosphate minerals, zircon sands, and rare earth raw materials classified as NORM

Testing Items

Typical testing items cover screening measurements and nuclide-specific determinations:

• Gross alpha and gross beta activity (screening indicators for water and other matrices)
• Artificial gamma-emitting radionuclides: Cs-137, Cs-134, I-131, Co-60, Ag-110m, Ru-106, Ce-144, Ba-140/La-140
• Natural radionuclides: K-40, Ra-226, Ra-228, Th-232 series nuclides, U-238 series nuclides, Pb-210, Po-210
• Strontium-90 (pure beta emitter requiring radiochemical separation)
• Tritium (H-3) and carbon-14 (C-14) in water, organic materials, and luminous devices
• Uranium and thorium isotopic composition, plutonium isotopes (Pu-238, Pu-239/240), and americium-241
• Radon-222 concentration and radon exhalation rate for indoor air and building materials
• Derived indices such as the internal exposure index (IRa) and external exposure index (Iγ) per GB 6566

Testing Methods

Gamma spectrometry is the primary technique for gamma-emitting nuclides. High-purity germanium (HPGe) semiconductor detectors provide high energy resolution and low minimum detectable activity (MDA), typically 0.1–2 Bq/kg for common nuclides in food matrices, while sodium iodide NaI(Tl) scintillation detectors are used for rapid screening. Samples are sealed in Marinelli beakers or petri dishes, held for secular equilibrium where required, and counted for 3 to 72 hours depending on the required detection limit. Calibration is performed using certified reference materials, in accordance with methods such as GB/T 16145, ISO 18589-3, and ASTM D3648.

Gross alpha and gross beta activity are measured by gas proportional counting or liquid scintillation counting (LSC) after evaporation to a thin residue or direct mixing with scintillation cocktail, following ISO 9696 and ISO 9697 for water. Alpha spectrometry with passivated implanted planar silicon (PIPS) detectors is applied to alpha emitters such as Po-210, Ra-226, uranium and thorium isotopes, plutonium, and americium after radiochemical separation and source preparation by electrodeposition or spontaneous deposition. Liquid scintillation counting is the method of choice for tritium, carbon-14, and strontium-90, supported by IEC 61452 and related instrument standards for emission rate measurement.

Inductively coupled plasma mass spectrometry (ICP-MS) complements radiometric methods for long-lived nuclides such as U-238, Th-232, and plutonium at ultra-trace levels. Radon is measured with activated charcoal collectors, electret ion chambers, or continuous radon monitors according to the ISO 11665 series and GB/T 14582. All analytical work is performed under a quality management system accredited to ISO/IEC 17025, incorporating procedural blanks, matrix spikes, duplicate samples, background subtraction, and regular participation in interlaboratory proficiency testing.

Applications

• Food safety and import–export compliance: verification of Cs-134, Cs-137, I-131, and Sr-90 levels in foods against GB 14882 and destination-market requirements
• Drinking water quality: confirmation of gross alpha and gross beta compliance with GB 5749 and international guidelines
• Environmental and nuclear facility monitoring: routine surveillance around nuclear installations, site characterization, and emergency response after radiological incidents
• Building material conformity: calculation of IRa and Iγ indices per GB 6566 for cement, stone, tiles, and industrial by-products
• Metal recycling and smelting: screening of scrap to detect orphan sources and prevent furnace contamination
• NORM industry management: characterization of scales, sludge, and residues from phosphate, rare earth, zircon, and oil and gas operations
• Consumer product conformity: verification of tritium and beta-luminous devices, smoke detectors, and thoriated optical components
• Decommissioning and waste management: clearance measurement, waste classification, and free-release verification of materials and soils

FAQ

What detection limits can be achieved?

With HPGe gamma spectrometry and counting times of 24–72 hours, minimum detectable activities of approximately 0.1–2 Bq/kg are achievable for Cs-137, I-131, and Co-60 in food and environmental matrices. For water, gross alpha detection limits of 0.02–0.05 Bq/L and gross beta detection limits of 0.05–0.1 Bq/L are typical.

How much sample is required for testing?

Gamma spectrometry generally requires 1–3 kg of fresh food or 50–500 g of ashed material to fill a Marinelli beaker. Water analysis requires 1–10 L depending on the method, while alpha spectrometry and Sr-90 determination may require 5–50 g of ash with radiochemical processing.

How long does radioactive substance analysis take?

Counting alone ranges from 3 hours for screening to 72 hours for low-level environmental measurements. Including sample preparation such as drying, ashing, sealing, and equilibrium holding, the total turnaround time is typically 5–10 working days.

What is the difference between gross screening and nuclide-specific analysis?

Gross alpha and gross beta measurements provide a rapid, low-cost total activity screening. If screening results exceed regulatory reference levels, nuclide-specific analysis such as gamma spectrometry, alpha spectrometry, or ICP-MS is performed to identify and quantify individual radionuclides for accurate dose assessment and compliance decisions.

Which standards govern radioactive substance analysis?

Commonly applied standards and specifications include GB 14882 for radionuclide limits in foods, GB 6566 for building materials, GB 5749 and GB/T 5750.13 for drinking water, GB/T 16145 for gamma spectrometry, the ISO 18589 series for soil, ISO 9696/9697 for gross alpha and beta in water, the ISO 11665 series for radon, and ASTM methods for radioactivity measurement in water and other matrices.

Are the samples hazardous to laboratory personnel?

The activity concentrations encountered in food, water, consumer goods, and routine environmental samples are extremely low and do not pose an external exposure hazard to analysts. Testing is performed in accredited third-party laboratories using standard radiation protection practices, controlled areas for higher-activity reference sources, and appropriate containment during radiochemical separations.