National Physical Laboratory

Nuclear Decay Data

The decay properties of radionuclides (for example, half lives, gamma emission probabilities and particle emission probabilities) are needed for instrument calibration for environmental monitoring, for patient dosimetry, for decay-heat calculations for the nuclear industry and for shielding calculations (amongst many applications). NPL is contributing to international efforts to evaluate decay data.

The decay properties of radionuclides have been measured extensively over the last 50 years, 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 data set 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.

In order to gain international acceptance, a multinational team, including staff from Laboratoire National Henri Becquerel (LNHB, France), Khlopin Radium Institute (Russia), Argonne National Laboratory (US), China Institute of Atomic Energy, IFIN (Romania) and NPL is working on detailed evaluations of decay data using an agreed common methodology. These data are published periodically as BIPM Monographie 5 and also on the LNHB website.

A plot of the half-life evaluation data for Cs-137
A plot of the half-life evaluation data for Cs-137


NPL has recently provided evaluations of 228Ac, 231Pa, 232Th and 232U as part of an IAEA Coordinated Research Project 'Updated Decay Data Library for Actinides'. This work continues under the Acoustics and Ionising Radiation NMO-funded programme. NPL also maintains an enquiry service for nuclear data.

Download Nuclear Decay Data flyer Adobe Acrobat PDF file

Last Updated: 28 Mar 2012
Created: 14 Jun 2007

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