Developing novel sample preparation procedures for end users in the nuclear sector
Accurate measurement of radionuclides is dependent on effective sample preparation, which often requires novel approaches to overcome challenges associated with the starting materials and possible external influences, or interferences. We have developed a range of effective and efficient procedures for many applications. This includes the use of lithium borate fusion for dissolution of matrices including titanium dioxide, concrete and graphite from a range of starting samples. This is important for the characterisation of decommissioning samples or reference materials.
A second common application is developing separation techniques that combine a high recovery of the radionuclide of interest, and complete removal of interferences. Applications include long-lived, high activity radionuclides that must be purified prior to standardisation by the Nuclear Medicine Group, and low-level environmental samples where radionuclides must be pre-concentrated prior to measurement. We work in collaboration with manufacturers of sample preparation and separation equipment and materials, and contribute towards characterisation and validation of new products. We also have expertise in the use of irradiation facilities for production of radionuclides, including the use of the neutron irradiation facility at NPL, followed by separation and standardisation.
Effective measurement is an additional part of the radiochemical procedure process. This includes measurement by atom counting using mass spectrometry, decay counting using alpha spectrometry, liquid scintillation counting and gamma spectrometry. We also use portable measurement techniques with a smaller laboratory footprint that have the potential to be deployed for remote off-site measurement.
Mass spectrometry for radionuclides
We use the latest plasma mass spectrometry to expand the number of radionuclides measurable by end users.
Inductively coupled plasma mass spectrometry (ICP-MS) has been increasingly used for measurement of long-lived radionuclides. The accurate measurement of radionuclides using this technique is hampered by multiple interferences, which must be separated prior to measurement. The latest generation tandem ICP-MS/MS instruments offer enhanced interference removal capability, using a combination of collision and reaction gases to remove interferences selectively and enable accurate measurement of the radionuclide of interest. This capability has expanded the number of radionuclides we can measure, whilst the measurement time of several minutes per sample means up to several hundred samples can be measured in a single day.
The key applications of ICP-MS for radionuclide measurement are:
- Decommissioning – ICP-MS offers a rapid and cost-effective alternative to decay counting techniques for some radionuclides that must be accurately characterised during clean-up of nuclear sites
- Long-lived radionuclides – these contribute significantly to the total waste inventory over long timescales, and measurement is important with regards to monitoring of storage and disposal facilities
- Nuclear forensics – ICP-MS enables measurement of isotopic ratios that can be used to determine the source of contamination, for example locating the origin of illegally acquired nuclear material
- Nuclear decay data – a number of half-life measurements for long-lived radionuclides suffer from high uncertainties or outdated measurements. This can be improved using a combination of ICP-MS and decay counting techniques