Metrology G


amma spectrometry is one of the most widely used techniques for identifying and quantifying gamma-emitting radionuclides within a sample. This technique


is common in laboratories that are monitoring environmental radioactivity, characterising radioactive waste and conducting analytical research. However, the reliability of results depends heavily on the accuracy of the instrument, which in turn hinges on proper calibration. Equipment can change over time as detector characteristics can drift, electronics can age and environmental conditions can influence their performance. This effectively changes the baseline upon which all measurements are made, and makes calibration vital for accurate and reproducible results. Reliable calibration ensures that a detector’s response remains accurate over time, and it also provides the traceable link between measurement results and recognised standards, which is particularly important in regulated environments. Without calibration, data quality can deteriorate, making comparisons between instruments and laboratories difficult. Rather than relying on multiple individual standards for calibration, laboratories can use a single carefully formulated solution containing several radionuclides. This generates multiple calibration reference points from one measurement, allowing detector performance to be assessed throughout a broad gamma-ray energy range.


WHY MIXED RADIONUCLIDE SOLUTIONS OFFER A PRACTICAL ADVANTAGE Single radionuclide standards continue to play an important role in gamma spectrometry. They provide well-characterised reference points at specific gamma-ray energies and can be particularly useful when a laboratory is investigating a certain radionuclide or examining specific aspects of detector performance. The challenge is that each standard only provides information at a limited number of energies, and establishing calibration for the full energy range encountered during routine measurements often requires several separate sources. Mixed radionuclide solutions address this challenge by combining multiple radionuclides within a single source. Carefully selected radionuclides generate emission lines across a wide energy range, providing numerous calibration points from one spectrum. A typical mixed radionuclide solution can produce 14 emission lines between 60 keV and 1836 keV, allowing users to evaluate detector response over the wide energy range encountered during routine gamma spectrometry measurements. The relative intensity of these peaks is another important consideration. Mixed radionuclide solutions are typically prepared so that individual


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MAINTAINING ACCURACY OF GAMMA SPECTROMETRY MEASUREMENTS


By Steven Bell, senior scientist, The National Physical Laboratory (NPL)


emission lines produce peaks of comparable intensity at a defined reference date. This allows users to create spectra that are easier to interpret and enables more effective calibration across the full energy range of interest (Figure 1). This approach offers both practical and technical advantages for laboratories carrying out regular measurements as, instead of relying on a series of individual standards, they can assess detector performance using one carefully prepared source. In this way, mixed radionuclide solutions can make calibration activities more efficient, helping to maintain consistency between measurements and over time.


CRITICAL APPLICATIONS


Ensuring accurate results is particularly vital for applications such as environmental monitoring, nuclear decommissioning and waste management, and research.


Environmental monitoring


Environmental monitoring programmes depend on highly sensitive instruments capable of detecting low levels of radioactivity in marine and terrestrial ecosystems. These measurements may involve a wide range of sample types, including air, water, soil and other environmental materials, where trace radionuclide signals must be distinguished from background radiation. The resulting data helps to identify potential hazards, demonstrate compliance with environmental regulations and verify that nuclear activities do not pose a risk to public health. Gamma spectrometry plays an important role in this work because it allows laboratories to identify and quantify specific radionuclides within complex environmental samples. Achieving reliable results at low activity levels requires careful calibration and continuous


verification of instrument performance. Mixed radionuclide solutions provide traceable reference materials that help laboratories to maintain confidence in their measurements, ensuring results remain accurate, reproducible and comparable over time.


Nuclear decommissioning and waste management


The nuclear sector places particularly demanding requirements on measurement accuracy. Throughout the nuclear fuel cycle, radiation measurements are used to monitor isotopic composition, assess radiation levels and track fission products, enabling fuel quality control, safe handling and process control. Once fuel has been used, characterisation measurements help to determine remaining fissile material and radiological hazards, informing decisions on storage, reprocessing and disposal. During decommissioning and waste management activities, it is mandatory for organisations to accurately characterise materials to determine how they should be handled, stored or disposed of. Waste classification decisions are often based on measured activity levels, meaning that confidence in these results is essential for environmental protection, operational efficiency and cost control.


Gamma spectrometry is widely used in these applications because it provides a practical method for identifying and quantifying radionuclides present in waste streams and other materials. Effective calibration is therefore fundamental to ensuring that measurement data can be trusted when making classification decisions. Reliable calibration using mixed radionuclide solutions enables laboratories to accurately characterise waste and maintain


August 2026 Instrumentation Monthly


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