Safeguarding public and animal health
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Emitters
Alpha emitters
Alpha particles are a highly ionising form of nuclear radiation, which have low penetration characteristics. They consist of two protons and two neutrons, bound together and are indistinguishable from a helium nucleus. Alpha particles are usually only emitted during the decay of nuclei that have an atomic mass greater than 209 e.g. 239Pu. Some alpha emitters are found in everyday items such as 241Am used in smoke detectors. A wide range of alpha emitting radionuclides can be determined in food samples at low-levels including 210Po, 234 / 235 / 238U, 230 / 232Th, 238 / 239 / 240Pu, 226Ra. The radionuclide of interest is separated by radiochemical techniques including ion-exchange chromatography and subsequently detected by silicon-based alpha spectrometry detectors.
Beta emitters
Beta particles are electrons or positrons emitted from decaying nuclei. They are more penetrating than alpha particles as they have a smaller mass. The range of energies generally encountered range from about 18keV for 3H to 1.70MeV for 32P. A wide range of beta emitting radionuclides can be determined in food samples at low-levels, including 3H, 14C, 32P, 35S, 90Sr, 99Tc, 137Cs, 210Pb, 241Pu, using radiochemical separation and a range of detection techniques including gas-flow proportional counting and liquid scintillation counting. An in-house developed oxidiser is used for the determination of 14C and 3H simultaneously. Organic molecules in food samples are oxidised and trapped separately as 14CO2 and 3H2O, and the beta emissions are subsequently detected using low-background liquid scintillation counting.
Gamma emitters
Gamma radiation (also called gamma photons) are a form of electromagnetic radiation formed as a consequence of nuclear decay. Often they occur as a consequence of alpha or beta decay of an atomic nucleus. The determination of a broad range of gamma emitting radionuclides is carried out using non-destructive gamma spectrometry. The Unit is equipped with a range of germanium-based high resolution gamma spectrometers, many with automatic sample changers for efficient throughput of samples, 24 hours a day. Detectors are calibrated for energy and efficiency, and a typical calibration spectrum is shown.