Decay-data requirements for decay-heat calculations are parametrically limited to half-lives (through the decay constants, Лі (t>/2 = ln2/A,)) and the mean alpha, beta and gamma energy releases per disintegration of the nuclides (Ea, Ep and Er) . Ideally, the mean energies are systematically determined from the discrete alpha, beta and gamma transitions and other relevant emissions, which extends the decay-data needs dramatically.

(a) The mean alpha energy is the mean energy of all heavy particles (alpha particles, recoil nuclei, protons, neutrons, and spontaneous fission fragments):

all a all recoil all protons all neutrons fission frag

Ea = X Ea"Pa, + X ERjPRj + X Epk Ppk + X Enl Pnl + X EFm Pf

i j k l m

where Ea,, Erj, Epk, Eni and EFm are the mean alpha, recoil nucleus, proton, neutron and fission fragment energies of the ith, jth, kth, lth and mth component of each type respectively, and Pa, PR, Pft, Рщ and PF^ are the corresponding

absolute emission probabilities per disintegration.

(b) The mean beta energy is the mean energy of all electron emissions:

all в all в+ all Auger all conversion

E в= X EP РвГ + X ‘Ев+ Pfi+ + X EAkPAk + X Ece. pce,

i j k l

where Eв — , Eв+ , EAk, and Ecel are the mean negatron, positron, Auger electron and conversion-electron energies of the ith, jth, kth and lth transition of each type respectively, and P, P„+ , PA and Pce are the corresponding

Pi вj k l

absolute emission probabilities per disintegration.

(c) The mean gamma energy includes all the electromagnetic radiation such as gamma rays, x-rays, annihilation radiation and bremsstrahlung:

where E7i and Ex, are the mean gamma and x-ray energies of the ith and jth transition of each type respectively, and PY and PX are the corresponding
emission probabilities per disintegration; E pt is the mean internal bremsstrahlung energy of the 1th beta transition with absolute emission probability, and P^+ is the absolute emission probability of positron

transition k.

Data files containing these nuclear parameters have been assembled over many years to assist analysts and spectroscopists to identify and quantify radionuclides. As the emissions from nuclides have been characterised in greater detail and their decay — scheme data defined with increased confidence, extended libraries of nuclear data have been compiled in agreed formats for use by the nuclear industry. These libraries are also used in decay-heat calculations, and are updated at regular intervals through either international consensus, or more localised efforts based on specific national needs.

The contents of a decay-data library need to be complete and consistent in order to model decay heat with confidence. The normal procedure would be to evaluate and prepare individual files of decay data that have been internally tested for consistency between the various decay-scheme parameters (i. e., a, P and у transitions), and to validate the complete library against benchmark experiments.

Evaluated decay-data libraries are used for many different purposes, as well as decay-heat calculations. Files of discrete decay data can aid in the measurement and quantification of the radionuclidic composition of a sample, and provide spectroscopists with the necessary high-quality standards data for detector efficiency calibration. Ideally, a comprehensive set of such data files should encompass all of the important fission products, actinides and their decay-chain nuclides, and provide the user with the necessary half-lives, mean energies and isomeric branching ratios to carry out decay-heat calculations with confidence. Unfortunately, this requirement cannot be realised because of the difficulty of measuring comprehensively the discrete data for the many short-lived fission products, along with the added complications that occur when studying some of the more complex decay schemes (pandemonium (Hardy et al, 1977)).