Supplement to Lecture 1: Nuclear Data Compilation and Evaluation

As an addendum to our brief overview of basic nuclear concepts (Lec 1) we call attention to an im portant as pect of the study of nuclear phenom e na that does not get much e m phasis in the class room , or at exam inations. This is the topic of how inform ation on nuclear data is gathered, an alyzed, and m a de a v ailable to users on a world-wide basis. Data co m p ilation and evaluation are co ntinuously on-going activities in the developm ent and applications of nuclear science and engineering. Their im portance can never be overestim ated in view o f the critical need for accurate cross sections and other data in a nuclear calculati on of any practical consequence. It is not

surprising that an entire indus try has evolved on nuclear da ta technology which continues to play a vital role in the m a intainence and im provem e nt of a huge existing database which is also expanding. It is beyond the scope of this class to go into any kind of detail on nuclear data beyond a general understanding of what types of data are available.

We confine our discussion to tw o sources of nuc lear d a ta, th e Chart of N u clides and the Table of Isotopes. The f o rm er used to be f a m iliar and commonly availab l e to students and faculty as a fold-out insert in a nuclear physics te xt, or as a w a ll chart. The latter contains m u ch more vol um inous data, the seventh (and the last) edition of which has grown by 1978 into a large volum e too cu mbersom e to be carried around. For the purposes of this class the relevant inf o rm ati on can be obtained from an on-line versions of the Chart of Nuclides, a convenient sour ce being the Table of Nuclides that is m a intained by the Korean Atom ic Energy Research Institute (KAERI) – http://atom.k aeri.re. k r/ . T h is Table provides the basic data on nuclides – mass, half life, decay schem e s and cross sections. For speci al data not available in the Table of Nuclides, th e studen t m a y wish to co nsult th e Ta ble of Isotop es which is adm ittedly a less than convenient reference source.

In addition, there are m a ny sources of cr oss section data that have com p iled and evaluated. Com p ilation and evaluation of nucle ar data are carried out at m a ny national laboratories and research centers all o v er the world. In the U.S. the focal point of this activity has been the National Neutron Cross Section Center at the Brookhaven National Laboratory. Going back about 20 to 30 years, perhaps the m o st significant contribution of this Center was a library of evaluated nuclear data, known as the Evaluated Nuclear

Data File ( ENDF ), which was developed for the stor age and retrieval of nuclear data needed for neutronic and photonic calculations. At one tim e there were two libraries. ENDF/A was a collectio n of us eful evaluated data sets. ENDF/B contain e d the reference data sets recomm ended by the Cross Secti on Evaluation W o r k ing Group. At any given tim e there was only evaluated data set for a particular m a terial. Most users were concerned only with the B version.

Evaluation of nuclear data m eans the assi gnm ent of the m o st credib le value after consideration of all the pertinent inform ation. The evaluation was supported by docum entation giving a description of how the value was determ ined and an estim a te of its uncertainty. As of 1975 the inform ation c ontained in EN DF consisted of: Resonance param e ters, cross section tables, angular distributions, energy distributions, double differential data in angle and energy, s cattering law data, and fission param e ters.

For a brief look at the contents of E NDF/B library, we note that ENDF/B-II contained 3 basic types of data stored on 13 m a gnetic tapes.

1. Scattering law data f o r 12 m oder a tor m a terials. For example, S (  ,  ) for a series of tem p eratures, 10 tem p eratures between 296 o K and 2000 o K in the case of graphite.

2. Neutron cross sections for 78 fissile, fertile, structural, and other m a terials, each being an elem ent or an isotope -- total and any si gnificant partial cro ss sections, reactions producing o u tgoing neu t rons, angular and ener gy distribution s , radioactiv e decay chain data, fission product yield,  ( E ) .

3. Photon interaction cross s ections for 87 elem ents from Z = 1 to 94 -- photon cross sections, angular and energy dist ributions of secondary photons.

Over the years a num ber of active compilation groups have issued library files: KEDAK fro m Karlsruhe, Germ a ny, JAERI (Japan), UKNDL fro m E ngland, a nd various libraries f r om U.S. nationa l labo r a tor i es such as Oak Ridge, Los Alamos, and Lawrence Liverm ore.