Policies

POLICIES General Plan Nuclear Data, Section B, presents the experimental results on radioactivity, nuclear moments, and nuclear reactions which give information about nuclear energy levels. The results for all nuclei of one mass number (or A-number) are grouped together into an " A - c h a i n . " In each i s s u e of about 100 pages, subscribers to Section B will receive an up-to-date revision of some five to ten A-chains, depending on their complexity. One i s s u e a year will be devoted to Recent References, covering all A-chains and bringing the subscriber up-to-date with references to (and a key-word description of) articles published since the last issue of Recent References. The material for an A-chain consists of three parts: the level schemes, compiler's analysis sheets, and the data sheets. From the collected data listed on the.data sheets, the compilers construct the level scheme which, in their view, gives the most consistent and plausible interpretation of the experimental determinations. In c a s e s where choices are possible, various " C o m m e n t s " on the " C o m p i l e r s ' Analysis S h e e t s " indicate which data were selected in the preparation of the drawing. If the scheme presented is based chiefly on the work of one or two experimental papers, this fact is noted. Often the comments also contain discussions of discrepancies in the data, calculations of quantities of interest such as rotational-model parameters, and observations on regional trends. In addition to the comments, the " C o m p i l e r s ' Analys i s S h e e t s " contain the reasons for all the spinparity assignments given on the level scheme. Study has shown that the data sheets offer subscribers a compaction factor of about 50, the level schemes one of about 500; that is, a data sheet summarizes the material appearing in about 50 pages of journal literature while a level scheme presents the e s s e n c e of about 500 pages. The material for each A-chain is assembled in the following order:

Lions such as B I - I - 1 , B1-1-2, which indicate Volume B1, i s s u e No. 1, pages 1 a~nd 2, respectively. It is suggested that this page number be used when referring to data quoted on this page. In addition, the data sheets for a nucleus will be numbered in the upper outside corner of the page; for example, la2Ta-1, tS2Ta-2, etc.

Types of Data Included on the Data Sheets In general, each data sheet contains all or part of the results for a single nucleus. At present, the types of data distinguished and the order in which they are presented are as follows: Ground s t a t e Best values of J , / t , Q, l), natural abundance, and thermal neutron absorption cross s e c tion. See Auxiliary Compilations below. Ground-state decay Data on half-lives, energies and intensities of c~'s, /g's, y ' s , coincidences, angular correlations, etc. Metastable s t a t e Data on J , / ~ Q, f~ (Half-life data may be included under this heading if no other decay data exists.) Metastable-state decay Same as ground-state decay Reaction data Data on resonances, capture y ' s , Coulomb excitation, other reactions, Q's Mass-spectrometer data References to mass-doublet measurements

Types of Information Given on Drawings The drawings present the energy level diagram for the entire A-chain showing the levels and the known transitions between them. The following information is given:

Title P a g e giving the compiler, nuclei discussed, and literature cut-off date Drawings (Level Schemes) Compilers' Analysis Sheets Data Sheets References for all A-chains are combined and placed at the back of the issue. The sheets of each i s s u e will be numbered consecutively at the bottom of the page by designa-

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Nuclear level properties Energy Half-life Spin and parity In deformed region the Nilsson model quantum numbers Letter code indicating which nuclear reac, tions are known to excite the level Transition properties ct-, /]-, y-energies and intensities Multipolarities of y-rays Log It's of t - t r a n s i t i o n s

POLICIES Mass differences Total 13-disintegration energies and neutron and proton separation energies

pared with input data of the Mainz-Amsterdam group and the reasons for any differences ascertained, if desired. A section on Adjusted Mass Differences at the back of every issue, therefore, presents the input data used for regional mass adjustments as well as adjusted outputs.

Uncertainties (Errors) and Averages Experimental uncertainties in the last figure, as reported by authors, are shown in italics after numbers in upright type. For example, 0.297 25 is used to express 0.297 + 0.025. From time to time both weighted and unweighted averages are presented. With weighted averages the uncertainty given is the larger of the internal and external errors:

Auxiliary Compilations Although in general the Data Sheets list all for a particc a s e s where other specialare:

relevant experimental measurements ular nuclear property, there are five adopted values are taken from some ized compilation. T h e s e five c a s e s

1. Nuclear spins and moments. Rounded-off values are quoted from Nuclear Moments, compiled by G. H. Fuller and W. V. Cohen. (65FuCo)

e - 2 (internal) = ~. e l - 2 !

ei-2(E i_~)2 e 2 (external) = i

2. Relative isotopic abundances. Adopted values are taken from Relative Isotopic Abundances compiled by G. H. Fuller. (59Full)

(n -- 1) Z e i - 2 i

Here e i is the uncertainty in the value of El, is the weighted average, and n the number of measurements. With unweighted averages the uncertainty given is just

3. Thermal neutron absorption cross sections. Values presented are those recommended by Sigma Center, Brookhaven National Laboratory. (65Sigm)

e 2 = .~ (E i - E)2/n(n - 1) . l

4. Neutron resonance parameters. Values presented are those recommended by Sigma Center, Brookhaven National Laboratory.

Mass Differences In order to obtain adopted values of mass differences the experimental values listed in Adjusted Mass Differences have been used a s input data in a computer program for a least-squares mass adjustment. This program, which was developed by Mr. Wemer Thiele of the Max-Planck Instirut fiir Chemic at Mainz, was very kindly put at the disposal of the Nuclear Data Group by Professor J. H. E. Mattauch of the Max-Planck Institut f/Jr Chemic and Professor A. H. Wapstra of the Instituut voor Kemphysisch Onderzoek, who have collaborated on the production of lists of leastsquares-adjusted mass values for the entire periodic table. 1 The gift of the program enables the Nuclear Data Group to make adjustments in limited mass regions in the intervals between the publication of complete lists by the Mainz-Amsterdam group. Since the values found in the limited-region mass adjustments will differ slightly from those of the big list, it seemed important to s e t forth very clearly the input data so that these may be corn-

5. Mass-spectrometer data. All experimental data are listed in a section on Adjusted Mass Differences (65Mass) preceding references in every issue. See paragraph on Mass Differences above.

Level-Scheme Self-Consistency Although the level schemes presented are those believed by the compilers to be the best possible at the moment, they are not always selfconsistent. Adopted values of energies and intensifies based on weighted averages of experimental data may not always lead to perfect energy and intensity balances. However, it has always seemed better to exhibit the i n c o n s i s t e n c i e s , whether large or small, than to force the data into a consistent looking pattern which may cover up some real difficulties. T h e s e inconsistencies, the most glaring of which are mentioned in the comments, should point the way to fruitful new experiments.

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