Atomic Mass Difference Research Articles

Intercalant-Driven Superconductivity inYbC6andCaC6

Recently discovered superconductivity in YbC6 and CaC6, at temperatures substantially higher than previously known for intercalated graphites, raises several new questions. (1) Is the mechanism considerably different from that of previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given the extreme similarity between YbC6 and CaC6, why are their critical temperatures so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC6 and CaC6, but not in alkaline-intercalated compounds, and explain the difference in T(c) by the "isotope effect" due to the difference in Yb and Ca atomic masses.

Determination of the energy of the 1.75 MeV resonancein the 13C(p,γ)14N reaction in terms of a one-voltstandard

The energy of the narrow resonance at 1.75 MeV in the 13C(p,γ)14N reaction has been measured to be1746.618(17) keV, using the Auckland heavy-ion source system (HISS). When this result is used to derive a value for the (13C + 1H - 14N) atomic mass difference, it validates HISS at the 18(24) parts per million (ppm) level.

Calculation of QED Effects in Hydrogen

Atomic mass differences are influenced by QED corrections, and a reliable understanding of these corrections is therefore of importance for the current and next generation of high-precision mass determinations based on Penning traps. We present a numerical evaluation of the self-energy correction, which is the dominant contribution to the Lamb shift, in the region of low nuclear charge. Our calculation is nonperturbative in the binding field and has a numerical uncertainty of 0.8 Hz in atomic hydrogen for the ground state and of 1.0 Hz for L-shell states (2S1/2, 2P1/2, and 2P3/2).

Dynamical structure analysis applied to Si and Ge

The phonon frequencies of Ge, when rescaled according to the difference in atomic masses and lattice parameters, practically coincide with the results of ab initio calculations for Si. Some difference is observed with respect to the observed frequencies of TA modes along [100] and, in particular, [110] in Si. The supplementary information obtained from the measured structure factors of the [110]Σ 3 modes in Si and Ge permits us to locate the most important part of the difference between the lattice dynamics of Si and Ge in a coupling term responsible for mixing the [110] TA1 and LO modes.

The Mainz neutrino mass experiment

The endpoint region of the β-spectrum of tritium was remeasured by an electrostatic spectrometer with magnetic guiding field. It enabled the search for a rest mass of the electron anti neutrino with improved precision. The result is m ν 2 = (−39 ± 34 stat ± 15 syst )( eV/ c 2) 2, from which an upper limit of m ν < 7.2 eV/ c 2 may be derived. The experiment yields the atomic mass difference m(T) - m( 3He) = (18591 ± 3)eV/c 2 .

Precise atomic mass differences in Pb and Tl and the decay energy for 205Pb

The Manitoba II high resolution mass spectrometer has been used to measure precise values for the spacings of four mass doublets in the mass spectra of Tl and Pb chlorides. Our new data are combined with other precise experimental data to derive an improved value for the 205Pb- 205Tl atomic mass difference, viz., 51.06±0.51 keV. This value agrees with most previous data, identifies one inconsistent datum and substantially improves the precision of this mass difference. This improvement in precision, in turn, reduces the uncertainty in one aspect of the derivation of the cross section for the neutrino capture reaction, v+ 205 Tl → 205 Pb+erme −. This reaction has been proposed as the possible basis for a favourable solar neutrino detector.

A new upper limit of the electron anti neutrino rest mass from tritium β-decay

A new upper limit of the electron anti neutrino rest mass has been deduced from the tritium β-decay spectrum. A source of molecular tritium has been investigated with a new solenoid retarding spectrometer. The results are m ν ϵ 2 = −38.8 ± 34.1 stat ± 15.1 syst(eV) 2/c 4 from which we conclude m ν ϵ ≤ 7.2 eV/c 2 with 95% c.l. Our β-endpoint corresponds to a 3H- 3He atomic mass difference of Δm( 3H- 3He) = 18590.8 ± 3 eV/c 2 (1σ) .

Energy available for the double beta decay of 82Se

A high resolution mass spectrometer has been used to determine the atomic mass difference 82Se 82Kr to be 3216.1 (16) μm or 2995.8 (15) keV.

A new upper limit of the electron antineutrino rest mass from tritium β-decay

A new upper limit of the electron antineutrino rest mass has been deduced from the tritium β-decay spectrum. A source of molecular tritium has been investigated with a new solenoid retarding spectrometer. The results are mv̄e2 = −39 ± 34stat ± 15syst(eV)2c4 from which we conclude mv̄e ≤ 7.2 eV with 95% c.l. Our β-endpoint corresponds to a 3H3He atomic mass difference of Δm(3H3He) = 18591 ± 3 eV/c2 (1σ).

Improved limit on the electron-antineutrino rest mass from tritium β-decay

The endpoint region of the β-spectrum of tritium was remeasured by an electrostatic spectrometer with magnetic guiding field. It enabled the search for a rest mass of the electron-antineutrino with improved precision. The result is m 2 v =−39±34 stat±15 syst(eV/ c 2) 2, from which an upper limit of m v <7.2 eV/ c 2 may be derived. The experiment yields the atomic mass difference m( T)−m( 3 He)=18 591±3 eV/c 2 .

Bremsstrahlung technique for measuring the end point of tritium beta decay.

Bremsstrahlung from tritium--rare-gas mixtures enclosed in low-permeability glass bulbs has been observed with a Si(Li) detector. The end point of the x-ray spectrum, 18 556(6) eV, implies a {sup 3}H-{sup 3}He atomic-mass difference of 18 595(6) eV.

Binding of hydrogen and helium in silicon, the mass difference between 3H and 3He, and the mass of nu e.

Precision measurements of the $^{3}$H${\mathrm{\ensuremath{-}}}^{3}$He atomic mass difference afford a means for assessing the reliability of measurements of the electron antineutrino mass from tritium \ensuremath{\beta} decay. We show that a long-standing discrepancy between measurements of the $^{3}$H${\mathrm{\ensuremath{-}}}^{3}$He mass difference obtained with tritium-implanted silicon detectors and those obtained by other techniques is due to neglect of chemical binding effects in the former experiments. The correction reconciles the silicon-detector results with modern determinations made by mass spectrometry and by \ensuremath{\beta} spectrometry. With this and other new data, a revised average value for the $^{3}$H${\mathrm{\ensuremath{-}}}^{3}$He mass difference of 18 591(2) eV is found. The scatter in the extant data suggests the presence of systematic errors in some of the modern measurements, and at present there seems to be no compelling basis for a model-independent lower limit on the mass of ${\ensuremath{\nu}}_{e}$. .AE

Energy of the 32-keV transition of 83Krm and the atomic mass difference between 3H and 3He.

The energy of a gamma transition in the decay of $^{83}\mathrm{Kr}^{\mathrm{m}}$ has been determined to be 32 147.3(16) eV in a comparison with transitions in $^{241}\mathrm{Am}$ decay. This value, substantially more precise than previous ones, leads to a corresponding improvement in precision in the atomic mass difference between $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$ as determined from an experiment on the beta decay of free molecular tritium. The mass difference, 18 589.0(26) eV, is in agreement with some independent determinations but disagrees with others, most notably with some recent ion-cyclotron-resonance data. The latter disagreement calls into question the 17-eV lower limit on the mass of the electron antineutrino claimed by Boris et al.

An electron-gamma coincidence system for the NPL beta-ray spectrometer

An electron-gamma coincidence system has been developed for the NPL double-focussing, iron-free beta-ray spectrometer. The beta-ray spectrum from the decay of 47Ca has been measured, and a value of (1991.2±1.8) keV obtained for the 47Ca − 47Sc atomic-mass difference.

Evaluation of the3H-3He atomic mass difference

All significant experimental results on the 3 H-3 He mass difference are reviewed. The weighted average of mass doublet measurements is 18596.7±3.6 eV, of tritium β measurements in magnetic spectrometers is 18610±7 eV and in implanted Si(Li) detectors is 18578±6 eV. The data within each group are consistent but there are discrepancies among the groups; possible explanations are proposed. Our best estimate for the 3 H-3 He atomic mass difference is 18599.4 ± 3.0 eV.

Atomic mass differences in gadolinium and terbium and the K-capture of 158Tb as an indicator of neutrino mass

A high-resolution mass spectrometer has been used to determine six precise atomic mass differences in gadolinium and terbium. These are combined with nuclear reaction and decay Q -values in a least-squares adjustment to give “best” values for the mass differences. The Q EC -value of 1220.64±0.83 keV for 158 Tb precludes K-capture to the 1187 keV state in 158 Gd.

Precise atomic mass differences amongst isotopes of Hg, Tl, Pb, and Bi (and a least-squares mass evaluation for 78 ≤ Z ≤ 84)

The 1.00-m radius, high resolution mass spectrometer at the University of Manitoba has been used to determine the spacings of a series of mass spectral doublets. These give improved values for the mass differences between the stable nuclides in Tl, Pb, and Bi and relate these values to previous atomic masses and mass differences for the isotopes of Hg. A least-squares adjustment has been performed on all available atomic mass data (including the mass spectroscopic results from this laboratory) for the region 78 ≤ Z ≤ 84.

End-point energy of 3H beta decay.

The extrapolated end-point of the tritium beta spectrum has been measured in a tritium-implanted Si(Li) detector for which the radiation damage has been kept small. The result is 18577\ifmmode\pm\else\textpm\fi{}7 eV. Adding the maximum recoil energy, the $^{3}\mathrm{\ensuremath{-}}^{3}$He atomic mass difference is taken to be 18580\ifmmode\pm\else\textpm\fi{}7 eV.

Beta - decay of 158Tb.

The ${\ensuremath{\beta}}^{\mathrm{\ensuremath{-}}}$ decay energy of $^{158}\mathrm{Tb}$ has been =929\ifmmode\pm\else\textpm\fi{}16 keV. The beta shape is treated within the modified ${B}_{\mathrm{ij}}$ approximation. has been combined with atomic mass differences known from mass spectroscopy to infer the electron capture decay energy of the nucleus $^{158}\mathrm{Tb}$, ${Q}_{\mathrm{EC}=1221\ifmmode\pm\else\textpm\fi{}17}$ keV. When additional information from similarly decaying rotational nuclei is used, the recent suggestion that $^{158}\mathrm{Tb}$ may allow one to measure effects of a finite neutrino mass seems improbable.

Precise atomic mass difference determinations between some stable isotopes of Ge, As and Se

The 1 m radius, high-resolution mass spectrometer at the University of Manitoba (“Manitoba II”) has been used to determine 11 atomic mass differences between some stable isotopes of Ge, As and Se. These values are of greater accuracy and precision than existing data. Their consistency has been checked by a major least-squares adjustment involving relevant data in the region. Results include improved S 2n values for several nuclides and the energies available for the ββ decays of 76Ge and 74Se, respectively.