Nuclear metrology

Nuclear data

Ensuring reliable and robust radiation measurements

The decay properties of radionuclides, such as half-lives, gamma emission probabilities and particle emission probabilities, are needed for instrument calibration. This is key for environmental monitoring, patient dosimetry, decay-heat calculations for the nuclear industry and shielding calculations. NPL is contributing to international efforts to evaluate decay data.

The decay properties of radionuclides have been measured extensively, largely in order to study the fundamental physics of nuclear structure. With a few exceptions, where the data are poorly known and further experimental work is needed, much of the effort is now focused on establishing a coherent dataset that is accepted internationally. The experimental studies are of varying quality. Information on the calculation of uncertainties is often limited and there is little information on the experimental methods used. Evaluation is the process of pulling data together from the published measurements while taking into account knowledge of the physical processes to determine recommended values with uncertainties for the key parameters.

High quality nuclear data are crucial in the design of Generation IV reactors. Our facilities are used to measure neutron-induced fission cross sections, as part of the work to reduce uncertainties in nuclear data related to fast reactors. The neutron fluences delivered during these experiments are known to be high precision, so the reaction cross sections are measured absolutely. This is advantageous as most measurements are made relative to other cross sections which introduces higher uncertainties.

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