2010 Review of Neutron and Non-Neutron Nuclear Data

: The results of a review and evaluation of neutron and non-neutron nuclear data published in the scientific literature over the past three years are presented. The status of new chemical elements is examined. Ten elements have had their atomic weight and uncertainty replaced by interval values of upper and lower bounds. Data on revised values for the isotopic composition of the elements are reviewed and new recommended values are presented for germanium. Radioactive half-lives are reviewed and latest values presented which include measurements on nuclides of interest and very long-lived nuclides such as double beta decay, double electron capture, long-lived alpha decay and long-lived beta decay. The latest information and the status on the evaluation of atomic masses are discussed. Data from new measurements on the very heavy elements (trans-meitnerium elements) are discussed and tabulated. Data on various recent neutron cross-section and resonance integral measurements are also discussed and the latest measurements are tabulated in both cases. The JENDL-4.0 and ENDF/B-VII.1 nuclear data libraries are discussed. A new initiative on the existence and importance of isotopes is presented.


Introduction
The published scientific literature is scanned and periodically reviewed for both neutron and non-neutron nuclear data.The data collected from this literature search are evaluated and the resulting recommendations are published in the Handbook of Chemistry and Physics [1,2].In this paper, the results of the most recent review of the nuclear data that had been published in the scientific literature during the period from about 2007 through the end of 2010 are presented.The nuclear data on the one hundred eighteen chemical elements with over thirty-two hundred nuclides (3255) and the hundreds of meta-stable states (680) with half-lives that are greater than one microsecond (10 -6 second) have been reviewed.Significant data in a number of topic areas are discussed and presented.

Periodic Table of the Chemical Elements
There have been recent measurements reported in the literature on the data for the very heaviest elements.Included among these recent measurements, the new chemical element of atomic (proton) number 117 has been reported to be synthesized.
The history of the process of discovery and the naming of chemical elements has been discussed previously [3].The joint committee formed by IUPAC (the International Union of Pure and Applied Chemistry) and IUPAP (the International Union of Pure and Applied Physics) has the responsibility to review the claims of discovery of a new element and to investigate whether or not there has been a verification of each discovery.The claim of discovery of the element with atomic (proton) number Z = 112 has been approved and the element, called copernicium with the chemical symbol Cn, has been added to the Periodic Table [4].Data on the elements with Z = 113, 114, 115, 116, 117 and 118 are presently undergoing review by the joint committee.A decision on some additional elements may be made sometime later this year.If a decision is made, new names and chemical symbols will be available in the near future.
Ten chemical elements have stable isotopic ratios that vary in nature to such an extent that their atomic weight values calculated from these isotopic ratios now exceed the uncertainty in the best measurement of their standard atomic weight.To distinguish these elements, their atomic weight value with its uncertainty is now being expressed as an upper and lower bound, called the interval to emphasize that atomic weight values are not constants of nature as had been assumed during the previous two centuries.The ten elements whose atomic weight values vary in nature are hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium [5].These ten elements that are assigned an interval are shown in Table 1.

Isotopic Composition of the Elements
Changes in the isotopic composition of the elements could impact the evaluation of the response from neutron activation detectors used in reactor dosimetry.An irradiated detector usually has a normal composition of naturally occurring stable isotopes of an element.The measured reaction rate will depend on the natural abundance of the stable isotope undergoing the reaction in the foil.
New measurements of isotopic ratios performed on chemical elements often result in improved values of the isotopic abundances.These new values of the isotopic abundance are recommended for use both in determining the atomic weight values of the elements from their isotopic masses and for use in fitting measured values of the neutron crosssections of the isotopes of an element with the measured value of the cross-section for the natural element.
The element germanium is the only element whose measured isotopic composition has been revised, as reported by the Sub-committee on Isotopic Abundances Measurements (SIAM) to the Commission on Isotopic Abundance and Atomic Weights (CIAAW) [6,7].The change in the composition is shown in Table 2.The issue of the neutron cross section values will be discussed later in this paper.

Tables of Atomic Masses
The last published version of the Atomic Mass Evaluation appeared in print during 2003.There are now plans to publish a new atomic mass evaluation at the end of 2012 or during the early part of 2013.In the interim before the next published evaluation, given the fact that the previous evaluations are more than 7 years old, the Atomic Mass Center has decided to release a series of tables and figures containing the present status of the work on updating these mass files.These files should be considered as "not published" but they may be quoted as a private communication from Georges Audi and Wang Meng (April 2011).Although the final published version of the atomic mass table in 2013 may differ in some cases, this interim version will significantly improve on the presently available data, which was last evaluated during 2003.

Radioactive Decay Constants
The radioactive half-life of a nuclide (the reciprocal of the radioactive decay constant) is of interest to reactor dosimetry because the half-life of the product nucleus in a nuclear reaction has a direct impact on the determination of the reaction rates.
There have been a number of new measurements of the radioactive half-lives in the past few years, including many values for the recently discovered nuclides (more than 160 new nuclides have been found), many of which are near the extreme limits of the proton and neutron drip lines.There are a number of radioactive nuclides of uranium, plutonium and others, whose half-life value may be of interest in the area of reactor dosimetry.The latest measured half-life values and uncertainties of these radio-nuclides have been listed in Table 3.
A few years ago, half-lives and decay modes of long-lived nuclides were presented [8].A latest revision [1] of these data is presented in Table 4.Only double beta decay (ββ) modes that involve the emission of two neutrinos are listed in the table, since (ββ) decay modes without the emission of neutrinos (0ν) have never been detected.Their lower limits are one or more orders of magnitude larger than (2ν ββ) decay modes.Only nuclides whose data have changed since the last report are listed in the table.

Data on the Very Heavy Chemical Elements
For very heavy elements (the trans-meitnerium elements, Z>109), there are other modes of decay (determining factors in nuclide stability), such as, spontaneous fission (sf) decay and cluster decay.Spontaneous fission decay is radioactive decay in which the nucleus breaks up into two approximately equal reaction products, both of which have very heavy masses (some fifteen to forty times larger than the alpha particle).Cluster decay is radioactive decay in which the emitted particle has a much smaller mass than that of a fission product but it is still a larger mass than the alpha particle (some three to eight times larger).For very heavy chemical elements, a path to the super-heavy elements is being explored.In the process of this investigation, new nuclides and elements are being discovered.The present list [1] of the highest Z elements (Z>109) and their nuclides is shown in Table 5.
Note that in both Tables 4 and 5, the uncertainty is not shown in the Tables.The unlisted uncertainty is considered to be 5 or less in the last digit quoted, unless the value is preceded by an approximate sign (~), in which case the uncertainty is considered to be greater than 6 and in fact it could be a two digit uncertainty, e.g., 34 ±10 would be listed as ~34.

Neutron Cross Sections
The fourth version of the Japanese Evaluated Nuclear Data Library, JENDL-4.0, has recently been released and information published with an emphasis on raising the reliability of fission product data and minor actinoid data [9].New evaluations were performed for thirty fission product nuclides that were not contained in the previous library, JENDL-3.3, which had been released in 2002 and co-variances were estimated for the actinoids.80 thermal neutron capture and fission cross sections were determined for the actinoids.New data on fission energy release for 31 nuclides was provided for energy deposition calculations.There are 215 fission product nuclides in JENDL-4.0, while there are data for a total of 406 nuclides in the JENDL-4.0 library.The number of co-variance files in the library is about 23%.
ENDF/B-VII.0 was released in 2006.ENDF/B-VII.1 is planned to be released in December 2011 [10].Some of the highlights of the new release are the following.There are improvements to the structural materials.The JENDL-4.0 co-variances were adopted for the minor actinides.Improvements to fission, capture and (n, 2n) cross sections were made from critical assembly reaction rate data.There are new evaluations for 4 He, 6 Li, 9 Be, 16 O and 23 Na.There is a new evaluation including co-variances for 241 Am.There are new evaluations in the fast neutron energy region with co-variances for 46 Ti, 47 Ti, 48 Ti, 49 Ti, 50 Ti, 51 V, 180 W, 182 W, 183 W, 184 W and 186 W.There are new evaluations in the fast neutron energy region for 78 Kr, 123 Xe, 124 Xe, 180 Ta, 181 Ta, 185 Re, 187 Re, 237 U, 239 U, 238 Pu and 240 Pu.The number of co-variance files in the library has improved from about 4% in ENDF/B-VII.0 to about 30% in ENDF/B-VII.1.Some deficiencies have been eliminated and errors fixed.There are 418 materials in the new release, with 168 new or revised materials and 62 totally or partially new materials.
There have been many new neutron cross-section and resonance integral measurements in the last few years across the periodic table of elements, since a previous report [8].I have separated the list of the measured values into measurements of reported thermal cross sections only, resonance integral values only and finally reports on both thermal cross sections and resonance integrals in the same measurement as given in the Tables 6, 7 and 8, respectively.Note that these values of cross sections and resonance integrals are expressed in units of barns, where 1 barn = 10 -28 m 2 .In some cases, the symbol, mb, is used which refers to the unit milli-barns or 10 -31 m 2 .The barn is a non-SI unit that is allowed by the SI [11].The symbol (m + g) for the isotope 209 Bi in refers to the total thermal neutron capture cross section to the meta-stable state, m, and to the ground state, g, combined.For the various Tables, the cross section, σ, usually refers to the thermal neutron capture cross section.In a few cases, the symbol, σ f , is used and refers to the thermal neutron fission cross section.The symbol I f refers to the neutron fission resonance integral, rather than the implied neutron capture resonance integral in a few cases in Table 7.

New Initiative on Isotopes
The need for a change in the recommended atomic weight values and uncertainties to an upper and lower bound, an atomic weight interval, was caused by the natural variation in the ratio of the stable isotopes for some elements.To understand this change requires that the audience be aware of the existence of both stable and radioactive isotopes in all of the chemical elements.An effort has been started in the past few years to introduce material about isotopes and their importance in everyday life to both students and teachers and the scientific and general public.Some of the examples that were provided about the various isotopes include measurement of the stable carbon isotope ratio to detect the difference between natural and synthetic testosterone that is used in the sports doping field and the use of the radioactive isotope 241 Am that is used for smoke detectors.Other examples were provided on the use of radioactive isotopes in the field of medical diagnosis and treatment.As the public becomes more aware of the existence and use of stable and radioactive isotopes, it is hoped that there will be less fear about radioactivity in the future among the general public.

Conclusions
It can be concluded from this brief survey of nuclear data in the above discussions that both neutron and non-neutron nuclear data are very robust fields.There has been more than a 5% increase in the number of known nuclides in the past few years.New

Table 1 .
Value and Uncertainty of Atomic Weights of the Elements Revised to Atomic

Table 2 .
Changes in the Isotopic Composition of Germanium

Table 3 .
Latest Measured Half-life Values of Some Radioactive Nuclides of Interest

Table 4 .
Radioactive Half Lives and Decay Modes of Long-Lived (Quasi-Stable) Nuclides

Table 5 .
Nuclear Data of the Very Heavy Chemical Elements

Table 6 Table 6 .
Latest Measured Values of Thermal Neutron Cross Sections

Table 7 .
Latest Measured Values of Resonance Integrals