Norman E. Holden

Spontaneous fission half-lives for ground-state nuclide (Technical report)

Measurements of the spontaneous fission half-lives of nuclides of elements Z = 82 through 109 have been compiled (cutoff date of April 1998) and evaluated. Recommended values are tabulated along with total half-lives.

Total half-lives for selected nuclides

Measurements of the half-lives of 3 H, 10 Be, 14 C, 26 Al, 40 K, 39 Ar, 53 Mn, 87 Rb, 92 Nb, 129 I, 138 La, 147 Sm, 176 Lu, 174 Hf, 180 Ta, 187 Re, 186 Os, 190 Pt, 204 Pb, 210 Pb, 210 Po, 222 Rn, 224 Th, 226 Ra, 227 Ac, 228 Ra, 228 Th, 230 Th, 232 Th, 231 Pa have been compiled and evaluated. The effect of the 14 C half-life value on carbon dating ages is discussed as well as the stability of 204 Pb

Atomic weights of the elements 2013 (IUPAC Technical Report)

Abstract The biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of 19 elements. The standard atomic weights of four elements have been revised based on recent determinations of isotopic abundances in natural terrestrial materials: cadmium to 112.414(4) from 112.411(8), molybdenum to 95.95(1) from 95.96(2), selenium to 78.971(8) from 78.96(3), and thorium to 232.0377(4) from 232.038 06(2). The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) also revised the standard atomic weights of fifteen elements based on the 2012 Atomic Mass Evaluation: aluminium (aluminum) to 26.981 5385(7) from 26.981 5386(8), arsenic to 74.921 595(6) from 74.921 60(2), beryllium to 9.012 1831(5) from 9.012 182(3), caesium (cesium) to 132.905 451 96(6) from 132.905 4519(2), cobalt to 58.933 194(4) from 58.933 195(5), fluorine to 18.998 403 163(6) from 18.998 4032(5), gold to 196.966 569(5) from 196.966 569(4), holmium to 164.930 33(2) from 164.930 32(2), manganese to 54.938 044(3) from 54.938 045(5), niobium to 92.906 37(2) from 92.906 38(2), phosphorus to 30.973 761 998(5) from 30.973 762(2), praseodymium to 140.907 66(2) from 140.907 65(2), scandium to 44.955 908(5) from 44.955 912(6), thulium to 168.934 22(2) from 168.934 21(2), and yttrium to 88.905 84(2) from 88.905 85(2). The Commission also recommends the standard value for the natural terrestrial uranium isotope ratio, N(238U)/N(235U)=137.8(1).

Temperature Dependence of the Westcott g-factor for Neutron Reactions in Activation Analysis

The Westcott g-factors, which allow the user to determine reaction rates for nuclear reactions taking place at various temperatures, have been calculated using data from the Evaluated Neutron Nuclear Data Library, ENDF/B-VI. Nuclides chosen have g-factors which are significantly different from unity and result in different reaction rates compared to nuclides whose neutron capture cross section varies as the reciprocal of the neutron velocity. Values are presented as a function of temperature up to 673.16 K (400 °C).

Spontaneous fission half-lives for ground state nuclides

Measurements of the spontaneous fission half-lives of nuclides of elements Z = 90 to 107 have been compiled and evaluated. Recommended values are presented. 126 refs., 96 tabs.

Prompt neutron emission multiplicity distribution and average values (Nubar) at 2200 m/s for the fissile nuclides

The prompt neutron emission multiplicity distribution P/sub v/ and its average value (i.e., nubar) have been determined at the standard neutron energy of 0.0253 eV for the neutron-induced fission of the four fissile nuclides /sup 233,235/U and /sup 239,241/Pu. Revised values of have been obtained by reevaluating experiments measured at 2200 m/s relative to the from the spontaneous fission of /sup 252/Cf. These revised values of have been used to renormalize the measured P/sub v/ values. The revised values of are all --0.25 to 0.5% smaller than the corresponding values of ENDF/B-V.

IUPAC-IUGS common definition and convention on the use of the year as a derived unit of time (IUPAC Recommendations 2011)* , **

The units of time (both absolute time and duration) most practical to use when dealing with very long times, for example, in nuclear chemistry and earth and planetary sciences, are multiples of the year, or annus (a). Its proposed definition in terms of the SI base unit for time, the second (s), for the epoch 2000.0 is 1 a = 3.1556925445 × 107 s. Adoption of this definition, and abandonment of the use of distinct units for time differences, will bring the earth and planetary sciences into compliance with quantity calculus for SI and non-SI units of time.

Prompt neutron multiplicities for the transplutonium nuclides

The direct determination of the average prompt neutron emission values is reviewed, and a method of comparing different sites of neutron emission multiplicity distribution values is described. Measured and recommended values are tabulated for these nuclides: /sup 241/Am, /sup 242/Am, /sup 242/Cm, /sup 243/Cm, /sup 244/Cm, /sup 246/Cm, /sup 247/Cm, /sup 248/Cm, /sup 250/Cm, /sup 245/Cm, /sup 249/Bk, /sup 246/Cf, /sup 249/Cf, /sup 250/Cf, /sup 252/Cf, /sup 254/Cf, /sup 251/Cf, /sup 253/Es, /sup 254/Es, /sup 244/Fm, /sup 246/Fm, /sup 255/Fm, /sup 252/No, /sup 254/Fm, /sup 256/Fm, /sup 257/Fm. 59 refs., 24 tabs. (LEW)

Mean fission neutron spectrum energies for 252Cf and fissile nuclides 233U, 235U, 239Pu and 241Pu

Abstract The spectra of prompt fission neutrons are of interest for the study of the neutron emission mechanism as well as for their relevance to the practical problems of nuclear reactors. The mean neutron energy of the fission spectrum directly impact the interpretation of experiments on the average number of prompt neutrons released in a fission. In order to make efficiency corrections in the measurements of the nubar ratio of the fissile nuclides to 252Cf, the mean energy of each fission spectrum has been evaluated for these nuclides. There were not enough data available for the fissile nuclides to treat the problem of the dependence of the average energy of the fission spectrum on the incident neutron energy. In the case of 235U, the mean energy is larger than earlier measurements indicated because the neglect of the effects of multiple scattering lowered the mean energy results for those earlier experiments.

Review of footnotes and annotations to the 1949–2013 tables of standard atomic weights and tables of isotopic compositions of the elements (IUPAC Technical Report)

Abstract The Commission on Isotopic Abundances and Atomic Weights uses annotations given in footnotes that are an integral part of the Tables of Standard Atomic Weights to alert users to the possibilities of quite extraordinary occurrences, as well as sources with abnormal atomic-weight values outside an otherwise acceptable range. The basic need for footnotes to the Standard Atomic Weights Table and equivalent annotations to the Table of Isotopic Compositions of the Elements arises from the necessity to provide users with information that is relevant to one or more elements, but that cannot be provided using numerical data in columns. Any desire to increase additional information conveyed by annotations to these Tables is tempered by the need to preserve a compact format and a style that can alert users, who would not be inclined to consult either the last full element-by-element review or the full text of a current Standard Atomic Weights of the Elements report. Since 1989, the footnotes of the Tables of Standard Atomic Weights and the annotations in column 5 of the Table of Isotopic Compositions of the Elements have been harmonized by use of three lowercase footnotes, “g”, “m”, and “r”, that signify geologically exceptionally specimens (“g”), modified isotopic compositions in material subjected to undisclosed or inadvertent isotopic fractionation (“m”), and the range in isotopic composition of normal terrestrial material prevents more precise atomic-weight value being given (“r”). As some elements are assigned intervals for their standard atomic-weight values (applies to 12 elements since 2009), footnotes “g” and “r” are no longer needed for these elements.