Atomic Mass Difference Research Articles

Direct Measurement of the Mass Difference of (163)Ho and (163)Dy Solves the Q-Value Puzzle for the Neutrino Mass Determination.

The atomic mass difference of (163)Ho and (163)Dy has been directly measured with the Penning-trap mass spectrometer SHIPTRAP applying the novel phase-imaging ion-cyclotron-resonance technique. Our measurement has solved the long-standing problem of large discrepancies in the Q value of the electron capture in (163)Ho determined by different techniques. Our measured mass difference shifts the current Q value of 2555(16) eV evaluated in the Atomic Mass Evaluation 2012 [G. Audi et al., Chin. Phys. C 36, 1157 (2012)] by more than 7σ to 2833(30(stat))(15(sys)) eV/c(2). With the new mass difference it will be possible, e.g., to reach in the first phase of the ECHo experiment a statistical sensitivity to the neutrino mass below 10 eV, which will reduce its present upper limit by more than an order of magnitude.

First-principles calculations of the lattice instability and the symmetry-lowering modulation of PtSi

We have investigated the vibrational properties of orthorhombic PtSi by performing first-principles calculations. The calculated phonon band structure shows unstable phonon modes around the Γ-point. The ionic displacement vectors associated with the unstable Γ-point phonon mode suggest a structural modulation to a lower-symmetry phase, which was confirmed by comparing the theoretical equations of states of the modulated (P212121) and the unmodulated (Pnma) PtSi. The symmetry-reduced modulated orthorhombic PtSi shows a phonon band gap. We attribute the origin of the phonon band gap to the separation of the low-frequency Pt phonon modes and the high-frequency Si phonon modes due to the large atomic mass difference between Pt and Si.

Direct determination of the atomic mass difference ofRe187andOs187for neutrino physics and cosmochronology

For the first time a direct determination of the atomic mass difference of $^{187}\mathrm{Re}$ and $^{187}\mathrm{Os}$ has been performed with the Penning-trap mass spectrometer SHIPTRAP applying the novel phase-imaging ion-cyclotron-resonance technique. The obtained value of $2492({30}_{\mathrm{stat}})({15}_{\mathrm{sys}})$ eV is in excellent agreement with the $Q$ values determined indirectly with microcalorimetry and thus resolves a long-standing discrepancy with older proportional counter measurements. This is essential for the determination of the neutrino mass from the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{187}\mathrm{Re}$ as planned in future microcalorimetric measurements. In addition, an accurate mass difference of $^{187}\mathrm{Re}$ and $^{187}\mathrm{Os}$ is also important for the assessment of $^{187}\mathrm{Re}$ for cosmochronology.

Interplay of force constants in the lattice dynamics of disordered alloys: Anab initiostudy

A reliable prediction of interatomic force constants in disordered alloys is an outstanding problem. This is due to the need for a proper treatment of multisite (atleast pair) correlation within a random environment. The situation becomes even more challenging for systems with large difference in atomic size and mass. We propose a systematic density functional theory (DFT) based study to predict the ab-initio force constants in random alloys. The method is based on a marriage between special quasirandom structures (SQS) and the augmented space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc. bcc TaW and fcc NiPt alloys are considered as the two distinct test cases. Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than those in pure Ta (W), which, in turn, yields stiffer (softer) force constants for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be softer compared to Ni-Ni, due to a large bond distance of the former. Our calculated force constants, phonon spectra and DOS are compared with experiments and other theoretical results, wherever available. Correct trend of present results for the two alloys pave a path for further future studies in more complex alloy systems.

Effect of Silicide/Silicon Hetero-Junction Structure on Thermal Conductivity and Seebeck Coefficient

We fabricated a thermoelectric device with a silicide/silicon laminated hetero-structure by using RF sputtering and rapid thermal annealing. The device was observed to have Ohmic characteristics by I-V measurement. The temperature differences and Seebeck coefficients of the proposed silicide/silicon laminated and bulk structure were measured. The laminated thermoelectric device shows suppression of heat flow from the hot to cold side. This is supported by the theory that the atomic mass difference between silicide and silicon creates a scattering center for phonons. The major impact of our work is that phonon transmission is suppressed at the interface between silicide and silicon without degrading electrical conductivity. The estimated thermal conductivity of the 3-layer laminated device is 126.2 +/- 3.7 W/m. K. Thus, by using the 3-layer laminated structure, thermal conductivity is reduced by around 16% compared to bulk silicon. However, the Seebeck coefficient of the thermoelectric device is degraded compared to that of bulk silicon. It is understood that electrical conductivity is improved by using silicide as a scattering center.

Penning-trap mass spectrometry for neutrino physics

Penning-trap mass spectrometry (PT-MS) has proved itself a useful tool for exploring neutrino properties. PT-MS can contribute with direct high-precision measurements of atomic mass differences to the determination of the neutrino mass, to revealing the Majorana or Dirac nature of the neutrino, to neutrino oscillometry, and to the search for the existence of keV-sterile neutrinos. The scope of this review is a brief presentation of the major achievements and the future of PT-MS in the field of neutrino physics.

Search for resonant enhancement of neutrinoless double-electron capture by high-precision Penning-trap mass spectrometry

The search for neutrinoless double-electron capture can be a good alternative to the neutrinoless double-beta-decay experiments in shedding light on such aspects of neutrino physics as the neutrino type, non-conservation of the total lepton charge and magnitude of the effective Majorana neutrino mass. The probability of neutrinoless double-electron capture can be resonantly enhanced by some orders of magnitude. Although the phenomenon of the resonant enhancement was predicted some decades ago, the search for resonantly enhanced neutrinoless double-electron-capture transitions was hampered by a lack of precise experimental values of the atomic mass differences of the transition initial and final states. Only recent progress in high-precision Penning-trap mass spectrometry has finally provided suitable means for a determination of atomic masses with a sufficient precision and thus given rise to the experimental campaign for a search for resonantly enhanced transitions. In this article, after an introduction to the theory of neutrinoless double-electron capture and the Penning-trap technique, a review is given on the results of systematic very precise direct Penning-trap measurements of the atomic mass differences of the nuclides which can undergo double-electron capture. The mass differences of 14 nuclear pairs have already been determined with a typical uncertainty of tens to a few hundreds of eV. Partial or even full resonant enhancement of the neutrinoless double-electron-capture probability has been discovered for 152Gd and 156Dy. In 156Dy a multiple resonance phenomenon has been revealed. For some transitions the half-lives have been estimated (152Gd, 164Er, 180W, 156Dy).

Improved Thermoelectric Performance in Cu-Based Ternary Chalcogenides Using S for Se Substitution

Cu-based ternary chalcogenide semiconductors are a promising class of p-type thermoelectric materials. Here we show that S for Se substitution is a promising route for improving the thermoelectric performance of these compounds, in particular for Cu3SbSe4 and Cu2SnSe3. Phonon scattering due to the combined effects of the atomic mass and size difference between S and Se produces a significant reduction in lattice thermal conductivity over a wide temperature range, and limits the phonon mean free path to its minimum possible value at high temperature. The small electronegativity difference between S and Se is ideal for conserving carrier mobility, as demonstrated by the reasonably large hole mobility in the disordered Cu3Sb(Se1−x S x )4 compounds. These effects along with the low-cost, environmentally benign nature of S, make S for Se substitution a simple yet effective method of improving the thermoelectric performance of Cu-based ternary selenides.

Plasma-dust structures in He-Ar DC glow discharge

The gas mixture discharge has a number of features which can appear in experiments with dusty plasma. For example, in the case of a significant difference in atomic masses of ions and atoms, strong anisotropy of the distribution function over ion velocities takes place, which in turn can cause a significant change in properties of dust structures. In this work, experiments on the study of the dust structures in the gas discharge of a mixture of light and heavy gases, i.e., helium and argon, are analyzed. The results of numerical simulation of ion and electron drift in the mixture of these gases and dust particle charging processes are presented.

Double-beta decay Q values of 116Cd and 130Te

The Q values of the 116Cd and 130Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between 116Cd and 116Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for 130Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01±0.32 keV (Scielzo et al., 2009) [1], but differs from the Florida State University trap value of 2527.518±0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in 116Cd and 130Te. Hence, our Q values were used to compute accurate phase-space integrals for these double-beta decay nuclei. In addition, experimental two-neutrino double-beta decay nuclear matrix elements were determined and compared with the theoretical values. The neutrinoless double-beta decay half-lives for these nuclei were estimated using our precise phase-space integrals and considering the range of the best available matrix elements values.

Kendrick-Analogous Network Visualisation of Ion Cyclotron Resonance Fourier Transform Mass Spectra: Improved Options for the Assignment of Elemental Compositions and the Classification of Organic Molecular Complexity

Here, we propose a novel computational and visual approach for the analysis of high field Fourier transform ion cyclotron resonance mass spectra (FTICR/MS) based on successive and multiple atomic and Kendrick analogous mass difference analyses. Compositional networks based on elemental compositions and functional networks based on selected functional groups equivalents enable improved assignment options of elemental composition and classification of organic complexity with tunable validation windows. The approach is demonstrated through the analysis of a 12T FTICR mass spectrum of an intricate water soluble extract of a secondary organic aerosol with a previously established abundance in CHNOS molecules.

Lattice thermal conductivity of the Cu3SbSe4-Cu3SbS4 solid solution

The compositional dependence of the crystal structure and lattice thermal conductivity in the Cu3SbSe4-Cu3SbS4 system has been studied. The lattice parameters of the Cu3SbSe4-xSx compounds decrease linearly with x, and the tetragonal structure (space group 14−2m no. 121) of the end compounds is maintained at all compositions. The lattice thermal conductivity is much lower than that predicted by a simple rule of mixtures, which is typical for a solid solution. The Debye model produces a very reasonable fit to the experimental lattice thermal conductivity data when phonon scattering due to atomic mass and size differences between Se and S is taken into account. Compounds in this series are likely to improve upon the thermoelectric performance of Cu3SbSe4, which has shown ZT = 0.72 when optimized.

Preparation and Thermal Conductivity of Y<sub>2</sub>Ce<sub>2</sub>O<sub>7</sub> Ceramic Material

Y2Ce2O7 ceramic material was prepared by solid reaction at 1600°C for 10h. The phase composition, microstructure and thermal conductivity of this material were investigated. XRD results reveals that single phase Y2Ce2O7 with fluorite structure was synthesized. Microstructure of Y2Ce2O7 was dense and no other unreacted oxides or interphase existed in the interfaces between grains. Because of phonon scattering by oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivty of Y2Ce2O7 is lower than that of 8YSZ, which implies that this ceramic can be used as novel candidate materials for thermal barrier coatings in the future.

Preparation and Thermal Conductivity of Dy2Ce2O7 Ceramic Material

Dy2Ce2O7 ceramic material was prepared by solid reaction method at 1600 °C for 10 h. The phase composition, microstructure, and thermal conductivity of this material were investigated. XRD results reveal that single-phase Dy2Ce2O7 with fluorite structure was synthesized successfully. Microstructure of Dy2Ce2O7 was dense and no other unreacted oxides or interphase existed in the interfaces between grains. Because of phonon scattering by oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivity of Dy2Ce2O7 is lower than that of 8YSZ, which implies that this ceramic can be used as novel candidate materials for thermal barrier coatings in the future.

Preparation and thermal conductivities of Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 ceramics for thermal barrier coatings

Two kinds of rare earth cerium oxides Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 were prepared by solid state reaction method at 1600 °C for 10 h. The phase compositions, microstructures, and their thermal conductivities of these materials were investigated. XRD results revealed that single phase Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 with fluorite structure were synthesized. Results of SEM and EDS showed that the microstructures of these materials were dense and no other phases existed among grains. Because of phonon scattering resulted by the oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivities of Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 are lower than that of 8YSZ at 800 °C, and thermal conductivity of (Gd 0.9Ca 0.1) 2Ce 2O 6.9 is lower than that of Gd 2Ce 2O 7. These results imply the Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 can be used as novel candidate materials for thermal barrier coatings in the future.

QValue ofIn115→Sn115(3/2+): The Lowest Known EnergyβDecay

Using precision, cryogenic, Penning-trap mass spectrometry we have measured the atomic mass difference M[;{115}In]-M[;{115}Sn] to be 497.489(10) keV/c;{2}. Combined with the energy of the 3/2;{+} first excited state of ;{115}Sn [J. Blachot, Nuclear Data Sheets 104, 967 (2005)10.1016/j.nds.2005.03.003], the Q value of the ;{115}In(9/2;{+}) --> ;{115}Sn(3/2;{+}) beta decay is determined to be 155(24) eV. This confirms the inference of Cattadori [Nucl. Phys. A 748, 333 (2005)10.1016/j.nuclphysa.2004.10.025] that this small branching-ratio beta decay has the lowest-known Q value. We also report improved values of the individual atomic masses: M[;{115}In] = 114.903 878 774(16) u and M[;{115}Sn] = 114.903 344 697(17) u.

AccurateQValue for theSn112Double-βDecay and its Implication for the Search of the Neutrino Mass

The Q value of the ;{112}Sn double-beta decay was determined by using a Penning trap mass spectrometer. The new atomic-mass difference between ;{112}Sn and ;{112}Cd of 1919.82(16) keV is 25 times more precise than the previous value of 1919(4) keV. This result removes the possibility of enhanced resonance capture of the neutrinoless double-EC decay to the excited 0;{+} state at 1871.00(19) keV in ;{112}Cd.

Thermoelectric Properties of Directionally Solidified Half-Heusler (M 0.5 a ,M 0.5 b )NiSn (Ma, Mb = Hf, Zr, Ti) Alloys

To evaluate the effect of the substitution of the M-site atoms Ti, Zr, and Hf on thermoelectric properties, nearly single-phase (M0.5a,M0.5b)NiSn alloys (Ma, Mb = Hf, Zr, Ti) were fabricated by directional solidification. The lattice thermal conductivity can be most effectively reduced in the (Ti0.5,Hf0.5)NiSn alloy, probably due to the solid-solution effect, since the difference in atomic size and atomic mass are maximized between Ti and Hf. Moreover, we have found the phase separation between Ti-rich and Ti-poor half-Heusler phases in (Ti0.5,Hf0.5)NiSn and (Ti0.5,Zr0.5)NiSn alloys through observation of microstructure, chemical concentration measurement, and x-ray diffractometry.

Atomic dynamics in liquid KxSb1−x alloys

The atomic dynamics of liquid KxSb1−x alloys are studied using cold neutron inelastic scattering. Dynamical properties extracted from the experimental spectra, like the dispersions obtained from the maxima of the longitudinal current correlation function, Jl(Q,ω), and the vibrational spectra, show a strong dependence on concentration. With increasing content of Sb, higher frequency modes are observed in the vibrational spectrum. For the Sb-rich compositions the dispersion is split into two branches. This indicates the de-coupling of the dynamics of the two components, due to the difference in atomic mass, already around the position of the principal peak of the static structure factor, S(Q). The observations are consistent with results from earlier experiments on similar systems and from ab initio molecular dynamics simulations.

Beta decay of 115In to the first excited level of 115Sn: Potential outcome for neutrino mass

Recent observation of beta decay of 115-In to the first excited level of 115-Sn with an extremely low Q_beta value (Q_beta ~ 1 keV) could be used to set a limit on neutrino mass. To give restriction potentially competitive with those extracted from experiments with 3-H (~2 eV) and 187-Re (~15 eV), atomic mass difference between 115-In and 115-Sn and energy of the first 115-Sn level should be remeasured with higher accuracy (possibly of the order of ~1 eV).