Radioactivity Data

Induced radioactivity in materials is important in a number of areas of nuclear technology, including fission-reactor afterheat (heat removal, meltdown accidents), fission-reactor operations (parasitic absorption, decay contributions to heat production), fusion-reactor waste discharge isotopics (waste disposal), accelerator operations (personnel exposure, air activation, requirements for remote handling, discharge isotopics of waste materials), and the production of medical isotopes. Radioactivity calculations require four components:
  • A library of activation cross sections,
  • A library of fission product yields,
  • A library of decay properties (half lives, energies, spectra), and
  • An inventory calculation code.
Our Group is active in all four areas. The work is focused around the development and use of our radioactivity code, CINDER.

Activation Cross Sections

Developing libraries of activation cross sections for use in radioactivity calculations is very difficult because of the wide range of nuclides involved in the different applications of interest. Fission reactor calculations require good capture cross sections for about 200 important fission-product nuclides, and they need capture, fission, and higher reactions for a large number of actinide isotopes. These values have been commonly available for some time, but newer applications proposed for high-current accelerators (such as tritium production, waste transmutation, or even energy production) will require even more cross sections. Basically, all reaction channels are needed, for all targets with significant lifetimes, for energies up to perhaps 150 MeV, for both neutrons and protons! These requirements total up to perhaps 10 or 20 thousand important reactions, and many of them have never been measured.

Our approach to this problem has three components: (1) gather all the best current evaluations for activation cross sections, (2) test against experimental data when available, (3) make incremental improvements to evaluations that disagree with experiment using nuclear model codes, and (4) do global calculations for unmeasured reactions using modern nuclear model codes.

Some of the fruits of component 1 are available on this web site. The main libraries for ENDF/B-VII, JENDL-4, and JEFF-3.0 contain some of the activation cross sections of interest. However, many of the evaluation communities have also provided separate libraries of activation cross sections, and some of them are available through our nuclear data viewer; currently, the ADL-3T library of 20,000 activation cross sections from Russia and the EAF-2010 library from Europe with 66,000 reactions.

Fission Product Yields

When a nucleus fissions, the two fission fragments are not normally equal in size. And every fission can result in slightly different products. The result is a distribution of possible fission fragments known as a fission-product yield distribution, which has two peaks. These distributions are very important for the operation of fission power reactors; they affect parasitic absorption, on-power decay heat, decay heat after shutdown or emergency scram, and delayed neutrons (which are important factors for reactor kinetics and control). Because of their importance for both operations and safety, fission-product yield distributions have been studied extensively and made available in computer files for reactor calculations. In the US, the standard set of data is part of ENDF/B-VII. Much of this work was done in our Group, and the defining publication is available on line in our publications area under the title "Fission Product Yields." For the convenience of the reader, we provide additional links here to the paper T. R. England and B. F. Rider, "Evaluation and Compilation of Fission Product Yields," Los Alamos National Laboratory report LA-UR-94-3106 (Oct. 1994). Because this paper contains about 80,000 lines of text, we break into parts for this web site. The General Discussion and Bibliography is given as a Postscript file (1.75 MB). A PDF version is also available. The recommended yields, original data, and reference sources are presented in a series of appendices in the form of ordinary computer text files:
  • Appendix A (3.24 MB): U-235F, U-235HE, U-238F, U-238HE, Pu-239T,Pu-239F, Pu-241T, U-233T, and Th-232F.
  • Appendix B (1.49 MB): U-233F, U-233HE, U-236F, Pu-239H, Pu-240F, Pu-241F, Th-232H, Np-237F, and Csf-252S.
  • Appendix C (1.35 MB): U-234F, U-237F, Pu-240H, U-234HE, U-236HE, Pu-238F, Am-241F, Am-243F, Np-238F, Cm-244F.
  • Appendix D (1.18 MB): Th-227T, Th-229T, Pa-231F, Am-241T, Am-241H, Am-242MT, Cm-245T, Cf-249T, Cf-251T, Es-254T.
  • Appendix E (1.06 MB): Cf-250S, Cm-244S, Cm-248S, Es-253S, Fm-254S, Fm-255T, Fm-256S, Np-237H, U-232T, U-238S.
  • Appendix F (0.93 MB): Cm-243T, Cm-246S, Cm-243F, Cm-244F, Cm-246F, Cm-248F, Pu-242H, Np-237T, Pu-240T, and Pu-242T.
In these yield-set names, S stands for spontaneous fission, T for thermal energies, F for fission spectrum energies, and H or HE for high energy (14 MeV). For more information on the yield sets, see the yld.txt file.

Decay Data

The lifetimes and modes of decay of radioactive nuclei have been studied intensively over the history of nuclear physics. The literature for this active field is summarized in a bibliography called "Nuclear Science References" (NSR) available at the National Nuclear Data Center (NNDC). These data are gathered together and evaluated by the members of the US Nuclear Data Network (USNDN). The evaluations make an attempt to come up with a consistent set of "best" data for each nuclide. The result is the Evaluated Nuclear Structure Data File, ENSDF, which is maintained at the NNDC. Printed information that has resulted from this evaluation project is also available in the Table of Isotopes books, which have recently been upgraded and published by John Wiley & Sons.

However, this work has a definite physics outlook. The people most closely involved in it are most interested in things like spin assignments to levels, the effect of deformation on the level structure, and so on. For use in application calculations, different representations of the data are more convenient, and such a format is part of the Evaluated Nuclear Data File (ENDF). The decay-data sublibrary of ENDF/B-VII.1 contains sections that describe the decay modes, mode lifetimes, decay energies, and spectra of decay products (neutrons, alphas, beta-plus, beta-minus, gamma rays, and x rays). Because each section must be complete in order to be of use for application calculations, they have sometimes been extended past the experimental limits using model calculations. The final results are available from the NNDC.

For the convenience of users around the world, we provide a simpler interface to the recent ENDF/B-VII.1 decay data. This link provides you with a list of all the nearly 4000 nuclides available. Clicking on one of the nuclides will bring up an HTML page with an interpreted version of the ENDF file. It is not necessary to know how to read the format to understand this listing. Just look for interesting parameters like "half life," "Egamma," or "spin & parity."

Inventory Codes

Once the basic data as described above are available, you can proceed to calculate the inventories of radionuclides as a function of time for a system exposed to a flux of radiation (neutrons or protons, usually). This calculation requires you to solve a set of coupled differential equations stating the balance between producing (by a reaction, or as a fission product) and destroying (by a reaction, or by decay) each possible nuclide.

Our code for computing nuclide inventories is called CINDER. It was originally written by Tal England for fission-reactor problems, and it went through a number of versions, culminating in ?? which is reported in ??. The classical CINDER code worked by dividing the process up into a set of "chains." This has the effect of reducing the size of the coupled system that has to be solved, thus giving more precise control over calculational errors. The final nuclide inventories were determined by summing up the contributions from the different chains. These chains were always chosen by hand to work well for fission reactor problems. More recently, CINDER has been extended to work for more general fusion and accelerator problems by importing libraries from the REAC code (reference) and teaching the code how to determine its chains automatically. This is necessary, because so many more reaction paths are available at higher energies, and many more nuclides are involved. The set of chains found for a given run depends on the conditions for that run.

We are working on this section....

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12 March 1997 (updated May 2012)