Nuclidic Masses Research Articles

The history of nuclidic masses and of their evaluation

This paper is centered on some historical aspects of nuclear masses, and their relations to major discoveries. Besides nuclear reactions and decays, the heart of mass measurements lies in mass spectrometry, the early history of which will be reviewed first. I shall then give a short history of the mass unit which has not always been defined as one twelfth of the carbon-12 mass. When combining inertial masses from mass spectrometry with energy differences obtained in reactions and decays, the conversion factor between the two is essential. The history of the evaluation of the nuclear masses (actually atomic masses) is only slightly younger than that of the mass measurements themselves. In their modern form, mass evaluations can be traced back to 1955. Prior to 1955, several tables were established, the oldest one in 1935.

Nuclear mass systematics using neural networks

New global statistical models of nuclidic (atomic) masses based on multilayered feedforward networks are developed. One goal of such studies is to determine how well the existing data, and only the data, determines the mapping from the proton and neutron numbers to the mass of the nuclear ground state. Another is to provide reliable predictive models that can be used to forecast mass values away from the valley of stability. Our study focuses mainly on the former goal and achieves substantial improvement over previous neural-network models of the mass table by using improved schemes for coding and training. The results suggest that with further development this approach may provide a valuable complement to conventional global models.

A retrospective reliability test for numeric data sets applied by example to atomic-mass values of some nuclides

Under favorable conditions, a retrospective test for reliability of published sets of physical property data becomes possible. The test and the necessary conditions for its use are discussed. The test is applied, by example, to well-documented, periodically republished nuclidic (atomic) masses of nine low atomic number nuclides. An index of reliability is suggested and evaluated for the example.

The atomic weight of europium

Absolute isotopic abundances of europium in 12 samples from various origins were determined by using thermal ionization mass spectrometry. For this purpose, synthetic mixtures of independently known isotopic compositions prepared from chemically pure and nearly isotopically pure separated europium isotopes served to calibrate the mass spectrometer. The resulting true 151Eu/ 153Eu ratio is 0.90673 ± 0.00235, which yields the mean isotopic abundances (47.554 ± 0.065) at.% 151Eu and (52.446 ± 0.065) at.% 153Eu at the 95% confidence limit. From these data and the relevant nuclidic masses the atomic weight of europium was calculated to be 151.9695 ± 0.0013.

THE ATOMIC WEIGHT OF ANTIMONY

With enriched antimony isotopes of 99.224 atom% ~(121)Sb and 99.528 atom% ~(123)Sb, two tracer solutions were prepared, whose antimony content was ascertained by the isotopic dilution analysis utilizing an accurately assayed laboratory standard. Mass spectrometric measurements were made on a Finnigan MAT- 261 instrument to find the ratio of masses 121 and 123. Five synthetic mixtures formed from the tracers served to determine the correction factor of mass discrimination. The isotopic abundances thus found for the anti- mony in the mineral stibnite together with the known nuclidic masses yield an accurate atomic weight of antimony as 121 .7575± 0 .0009.

Isotopic Abundances and Atomic Weights of the Elements

A large number of measurements describing the isotopic composition of the elements using a variety of analytical methods have been reported since the discovery of the first isotope in 1912. During the past several decades, however, mass spectrometric methods have been used, almost exclusively, to determine the isotopic composition, and thus the atomic weights, of the elements. This evaluated compilation reports the literature references for all complete mass spectrometric measurements published during the period 1920 through 1983. Also given are the isotopic compositions, the isotope ratios, the atomic weights calculated from the data, the appropriate nuclidic masses and an evaluation of the errors of the measurements. For each polynuclidic element, a best measurement has been selected.

Spectrometer for on-line analysis of radionuclides (Solar)

A mass spectrometer has been built for on-line analysis of fission product nuclides. The spectrometer ion source is located inside the thermal column of a TRIGA reactor and consists of a high-temperature oven containing fissile target material. Fission product nuclides born in the target are thermally ionized and accelerated out of the reactor through a 2.3 m long flight tube. Outside the reactor the ion beam is deflected 90° by an electrostatic mirror. Mass analysis of the ions takes place in a 30.5 cm radius, 60° deflection magnetic field. The system is intended initially to measure relative independent and cumulative yields of Rb, Cs, Br, and I isotopes with half-lives as short as 0.1 s. Other applications include nuclear spectroscopy, delayed-neutron emission measurements, and measurements of nuclidic masses and nuclear moments of the separated isotopes produced by the system.

A FORTRAN nuclidic-mass table with self-modification feature

A computer program is described which is a FORTRAN subroutine to provide nuclidic masses in amu for any Z and A by a table look-up method. A companion program modifies the internal tables of the subroutine when changes or additions to the known masses become available.

Potential Applications of the X-Ray/Density Method for the Comparison of Atomic-Weight Values

Without presenting experimental details, this report outlines and reappraises the principles involved in measurement of crystal lattice parameters and density for the determinations of atomic-weight values.Attention is drawn to the advantages to be derived from a comparison of densities and lattice spacings with those of a crystal of mononuclidic elements, rather than from absolute measurements of X-ray spacings and density.Errors arising from physical and chemical imperfections are discussed as are the general techniques of adequate precision for density and lattice spacings measurements.Recent literature data are used by way of illustration to derive the effective atomic weight of calcium appertaining to a group of calcite samples from that of a group of silicon crystals (not an optimum "standard"). The calcium value obtained is 40.0795 ± 0.0019 (probable error); it compares with IUPAC's adopted 40.08 and a "physical value" of 40.078 from nuclidic masses and isotopic abundance measurements. There are several elements for which the X-ray/density method is judged to be potentially the most promising for atomic weight re-determinations in the foreseeable future.

The absolute abundance of the lithium isotopes in natural sources

The absolute abundance of the lithium isotopes in natural sources from North America and Africa has been determined. The absolute 6Li/ 7Li ratio from thirteen spodumene samples was found to be 0.08182 ± 0.00033. This ratio for a batch of reagent Li 2CO 3 was found to be 0.d07926 and for Li 2NaPO 4 from Searle's Lake was found to be 0.07957. Considering the thirteen spodumene samples to represent the principal commercial sources of lithium, an atomic weight of 6.9403 ± 0.0005 is calculated for the element on the basis of these absolute abundances and values for the nuclidic masses.

Uniqueness of the Mass-surface Relative to Iron-56

IN practice, the mass of a neutral atom is expressed in terms of a particular nuclidic mass which is assumed to have an integral value and is termed the primary standard. With 12C as the primary standard (126M = 12u) nuclidic masses are found to be close to integral values and the difference between the measured mass (AZM) and the integral value Au is called the ‘mass excess’1. Alternatively, the mass of a nuclide (A, Z) relative to 12C could be expressed in the form: where Z(Δ)A12 is a small proper fraction (±) which will be referred to as the ‘mass fraction’. It should be noted that the ‘mass fraction’ is a dimensionless quantity whereas the ‘mass excess’ equals Z(Δ)A12 u.

New values for the physical constants

A new, consistent set of values for the physical constants has been recommended by the Committee on Fundamental Constants of the National Academy of Sciences—National Research Council. These values were presented to the Second International Conference on Nuclidic Masses held in Vienna, July 15–19, 1963. At the General Assembly meeting of the International Union of Pure and Applied Physics held in Warsaw, September 18–23, 1963, the following statement was adopted: “The Commission [on Nuclidic Masses and Related Atomic Constants] expects that these values will be widely used and will help to remove many of the confusions that have arisen from the use of differing sets of constants. In addition, it is expected that the appearance of this list will encourage further experimental work aimed at improving our knowledge of these values.”

Mass-spectroscopic atomic mass differences

New mass-spectroscopic data on atomic mass differences published since 1957 in the medium and heavy mass regions have been compiled and tabulated. Corresponding values in the new scale based on12C as the standard are also given. Unadjusted experimental values for nuclidic masses in the new scale have been listed. For a large number of stable nuclides in the region from strontium to antimony the newer values obtained from the data ofDemirkhanovet al. are more accurate than the corresponding values listed in the recent exhaustive mass table ofKoniget al. Attention is drawn to the advantages of the isotopic doublets over the published conventional mass doublets in the heavy mass region.

Image intensifier tubes and astronomy

This paper describes the second part of the least squares computation of nuclidic masses from all available data. A compilation of all measurements relevant to the mass range 70 < A < 200 is given.

763. New scale of nuclidic masses and atomic weights: E. Wichers, Nature, Lond., 194 (4829), 19 May 1962, 621–624.

763. New scale of nuclidic masses and atomic weights: E. Wichers, Nature, Lond., 194 (4829), 19 May 1962, 621–624.

Life indicating valves

This paper describes the procedure used in computing nuclidic masses for A ≧ 200 from tabulated experimental data, and gives a list of all reaction energies of some types of reactions calculated from the mass list.

New Scale of Nuclidic Masses and Atomic Weights

A discussion is presented of the situation which led to the existence of the chemicai scale (atomic weight of element O = l6) and the physical scale (atomic weight of principal O isotope = 16) and of the considerations that led to their replacement by a new scale. ln 1959, the lnternatlonal Commission of Atomlc Weights recommended the adoption of C12 as the reference species wlth assigned relative mass of 12, since this isotope was acceptable to both chemists and physicists. The lnternational Union of Pure and Applied Physlcs and the International Unlon of Pure and Applled Chemlstry adopted this recommended scale. A table of atomic weights developed from a complete review of experimental data on the basis of the new scale ls presented together wlth a separate table for radloactive elements. (D.L.C.)

New relative nuclidic masses

The present paper gives the experimental data and the procedures used to compute a number of relative nuclidic masses in addition to or in replacement of those given earlier 1), the masses themselves are given in the companion paper.

Adjustment of relative nuclidic masses (II) 70 < A < 200

This paper describes the second part of the least squares computation of nuclidic masses from all available data. A compilation of all measurements relevant to the mass range 70 < A < 200 is given.

Adjustment of relative nuclidic masses (III) [formula omitted

This paper describes the procedure used in computing nuclidic masses for A ≧ 200 from tabulated experimental data, and gives a list of all reaction energies of some types of reactions calculated from the mass list.