SENSOR CALIBRATION | RADIATION MONITORING
However, since each standard only offers information at a limited number of energies, multiple sources may be required to establish calibration across the wider energy range encountered during routine measurements. Mixed radionuclide solutions take a different approach
by combining several radionuclides within a single source. By delivering a practical means of establishing calibration across various gamma-ray energies, mixed radionuclide solutions allow multiple calibration reference points to be measured from a single reading. This gives sufficient coverage across a wide energy range while reducing the number of necessary individual standards.
Tailored emission peaks Carefully formulated mixtures of radionuclides can provide emission lines spanning much of the energy range typically encountered during routine measurements. By selecting radionuclides with suitable characteristics and activity levels, the resulting spectrum contains multiple peaks that can be used to assess detector performance and establish calibration curves. An important consideration is the relative intensity of these peaks. Mixed radionuclide solutions are typically prepared so that individual emission lines produce peaks of comparable intensity at a defined reference date. This helps to create spectra that are easier to interpret and enables more effective calibration across the full energy range of interest, as shown in Figure 1 (below right). For laboratories carrying out regular measurements, this approach offers both practical and technical advantages. Rather than relying on a series of individual standards, users can assess detector performance using one carefully prepared source. This can make calibration activities more efficient while helping to maintain consistency between measurements and over time. By providing multiple reference points across a broad energy range within a single standard, mixed radionuclide solutions deliver a practical and reproducible means of calibrating gamma spectrometry. The usefulness of a mixed radionuclide solution depends on the confidence users can place in its assigned activity values. This is why traceability is such an important part of the production process. Traceability links measurements back to recognised
standards through a documented chain of comparisons. For users, this means calibration activities can be connected to nationally recognised measurement capabilities, again helping to ensure consistency between laboratories and over time. Combined with robust quality processes, traceable
mixed radionuclide solutions provide a reliable basis for calibration and trust in the measurements that follow. For organisations operating in regulated sectors, traceability is also a frequent compliance and accreditation requirement. Demonstrating that measurements are connected to recognised standards helps to assure regulators, customers and other stakeholders that results are reliable and defensible.
Critical measurement applications The value of mixed radionuclide solutions extends beyond the calibration process itself. They help laboratories to establish and maintain reliable gamma spectrometry performance for a wide range of activities
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where accurate radioactivity measurements are essential. From monitoring the environment and characterising radioactive waste to research and analytical services, these solutions provide the traceable measurement foundation needed for informed decision making. One example of this practice in action is in
environmental monitoring programmes that depend on highly sensitive instruments that can detect low levels of radioactivity in both marine and terrestrial ecosystems. These measurements help to identify potential hazards and form the backbone of regulatory reporting, giving teams the reassurance that environmental controls are functioning as intended. Gamma spectrometry plays an important role in this work because it allows laboratories to identify and quantify specific radionuclides within complex environmental samples. However, achieving reliable results at low activity levels requires careful calibration and ongoing verification of instrument performance. Mixed radionuclide solutions support these activities by supplying traceable reference materials that laboratories can use to maintain confidence in their measurements. This helps to ensure that results remain accurate and comparable over time, allowing organisations to make informed decisions based on reliable data.
Passive gamma spectrum of natural UO 2 and low enriched (LEU) UO 2, with focus on the 30keV-500keV and 500keV-2000 keV. Asterisks indicate energies from 235 U and its daughters while the remainder of the peaks indicate energies from 238 U and its daughters. Source: Mona Tohamy et al, Egyptian Atomic Energy Authority
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