When testing the sediments, the type and energy of radiation, along with the composition of the sample being measured effects how easy it is to measure the amount of radioactivity.
Generally, a radioactive atom emits either an alpha or beta particle. This is usually accompanied by a gamma-ray.
Due to this fact, the most common means of measuring radiation is to use a technique called gamma ray spectroscopy. This allows you to detect the majority of alpha, beta and gamma emitting radionuclides, identify the radionuclides present and measure the amount radioactivity.
As some radionuclides only emit alpha or beta particles, with no gamma-ray, there are some cases where additional testing may be needed, however this is usually not required.
In the case of the sampling of the sediments at Hinkley Point C, the testing and sampling plan was developed independently by CEFAS (an executive agency of the UK Government), which carries out work to the highest international standards.
The analysis techniques include the use of high resolution gamma-ray spectroscopy, allowing the identification of a wide range of alpha, beta and gamma emitting radionuclides, and thorough assessment of any radioactivity in the sediment.
Additional reassurance monitoring is to be undertaken as part of the 2020 sampling campaign to determine the presence of pure alpha emitting radionuclides. This will reaffirm the suitability of high resolution gamma-ray spectroscopy providing a thorough assessment of any radioactivity in the sediment.