Large Q-values Research Articles

Novel evidence for the σ-bond linear-chain molecular structure in 14C * *Supported by the National Key research and development Program of China (2018YFA0404403), the National Natural Science Foundation of China (11875074, 11875073, 12027809, 11635015, 11961141003) and the Continuous Basic Scientific Research Project (WDJC-2019-13)

A multi-nucleon transfer and cluster decay experiment, Li( B, C + Be) , is conducted at an incident beam energy of 55 MeV. This reaction channel has a significantly large Q-value, which favors populating the high lying resonant states in C. The decay paths, from these resonances to various states of the final nucleus Be, can be selected, owing to the experimentally achieved optimal resolution of the Q-value spectrum. A number of resonant states are reconstructed from the forward emitting Be + fragments, and their major molecular structures can be detected according to the selective decay paths and relative decay widths. A state at 22.4(2) MeV validates the previously measured and theoretically predicted band head of the positive-parity -bond linear-chain molecular band. Two additional resonances at 22.9(2) and 24.2(2) MeV are identified and consistent with the predicted and members of the same molecular band, thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes. A few high energy resonances, which also indicate the presence of the -bond molecular structure, are observed; however, further studies are still required to clarify their ascription in band systematics.

Bosonic and magnonic magnon dispersions

The analytical crossover events in the magnon dispersion relations are discussed. As the available experimental data show, only a few types of magnon dispersion relations are observed for all spin- and lattice-structures. When the magnon spectrum exhibits a finite energy gap at q = 0 the dispersion consists of two q-sections with different functions of wave vector. Such analytical changes indicate that two mechanisms dominate the dispersion relation alternately. For magnon energies of larger than the gap, the dispersion exhibits over a finite q-range a single qx power function of wave vector. Within the experimental error limits, the exponent x is a rational number and is independent of the spin structure, i.e. universal, but depends on whether the spin quantum number is integer or half-integer. As we now know, this is the typical indication that the qx function is determined by the bosons of the continuous magnetic medium. The qx function holds up to the crossover to a sine-function of wave vector for antiferromagnets but to a sine-function squared for ferromagnets. One therefore has to distinguish between the bosonic part of the magnon dispersion relation, at small q-values, and the magnonic part at large q-values. As is well known, sine functions of wave vector are the dispersion of the linear spin chain. Since the linear spin chain is not ordered at any finite temperature it follows that the observed magnons are not indicative of a long-range magnetic order. From the fact that no principal change of the magnon dispersions occurs upon crossing the magnetic ordering temperature it follows that the exchange interactions are not involved directly in the magnetic ordering process. The long-range ordered system is the boson field. At the critical temperature, the boson field orders. Ordering of the boson field is associated with the formation of domains and with the emergence of a magnon gap. In the ordered state, propagation of the bosons is restricted to the few different domain axes. The dimensionality of the ordered boson field can be recognized from the number of the in-equivalent domain orientations. For all lattice structures the boson field within each magnetic domain is perfectly one-dimensional, and aligns all spins parallel. This is the origin of the linear chain dispersion. The mass-less bosons are, however, not visible for neutrons. If the magnon-boson interaction is strong, the q-range of the sine functions is small. It then proves necessary to add a phenomenological phase shift in the argument of the sine function. As a consequence, magnon dispersions cannot be understood considering exchange interactions alone.

Intrinsic dissipation mechanisms in metallic glass resonators.

Micro- and nanoresonators have important applications including sensing, navigation, and biochemical detection. Their performance is quantified using the quality factor Q, which gives the ratio of the energy stored to the energy dissipated per cycle. Metallic glasses are a promising material class for micro- and nanoscale resonators since they are amorphous and can be fabricated precisely into complex shapes on these length scales. To understand the intrinsic dissipation mechanisms that ultimately limit large Q-values in metallic glasses, we perform molecular dynamics simulations to model metallic glass resonators subjected to bending vibrations at low temperatures. We calculate the power spectrum of the kinetic energy, redistribution of energy from the fundamental mode of vibration, and Q vs the kinetic energy per atom K of the excitation. In the harmonic and anharmonic response regimes where there are no atomic rearrangements, we find that Q → ∞ over the time periods we consider (since we do not consider coupling to the environment). We identify a characteristic Kr above which atomic rearrangements occur, and there is significant energy leakage from the fundamental mode to higher frequencies, causing finite Q. Thus, Kr is a critical parameter determining resonator performance. We show that Kr decreases as a power-law, Kr ∼ N-k, with increasing system size N, where k ≈ 1.3. We estimate the critical strain ⟨γr⟩∼ 10-8 for micrometer-sized resonators below which atomic rearrangements do not occur in the millikelvin temperature range, and thus, large Q-values can be obtained when they are operated below γr. We also find that Kr for amorphous resonators is comparable to that for resonators with crystalline order.

A Three-Dimensional Finite Element Analysis Model for SH-SAW Torque Sensors.

In this paper, a three-dimensional finite element analysis (3D-FEA) model for shear horizontal surface acoustic wave (SH-SAW) torque sensors is presented. Torque sensors play a significant role in various fields to ensure a reliable torque transmission in drivelines. Featuring the advantages of high propagation velocity, large Q-value, and good power capacity, SH-SAW-based torque sensors are promising but very few studies have been carried out. In order to develop a successful sensor, understanding the characteristics of SH-SAWs produced on piezoelectric substrates and torque sensing modes is indispensable. Therefore, in this study, we first investigated the effect on the generation of waves when different Y-cut quartz substrates are engaged. Thereafter, analyses and comparisons regarding the effect on the polarized displacement, wave guidance, and wave mode were conducted for different configurations of wave-guide layer thickness to wavelength ratios (hlayer/λ) and materials. The results showed that Y-cut quartz at an angle close to 36° with a gold (Au) layer varying from hAu/λ = 0.02 to 0.03 thickness could be the most effective configuration for the excitation of SH-SAWs, compared to other combinations using platinum (Pt), titanium (Ti), and silicon dioxide (SiO2). Finally, based on the FEA SH-SAW torque sensor model configured with a Y + 36° quartz substrate and 0.025 λ-thick gold layer, the relationship between the applied torque and sensed voltage was examined, which shows a perfect linearity demonstrating the performance of the sensors.

Incorporating Realized Quarticity into a Realized Stochastic Volatility Model

This study proposes an extension of the realized stochastic volatility model by incorporating realized quarticity RQ into the volatility process. We employ an efficient Riemann Manifold Hamiltonian Monte Carlo method in a Markov Chain Monte Carlo algorithm to estimate parameters that could not be sampled directly. We investigate the empirical performance of the proposed model using data for six equity indices and 24 individual stocks listed on the Tokyo Stock Exchange. Parameter estimates and two Bayesian model selection criteria reveal evidence supporting RQ-based models that are driven by the maximum value of RQ data. That model consistently outperforms benchmark realized stochastic volatility models in capturing spikes in volatility caused by large RQ values. Including such stylised facts as the asymmetric effect of returns-volatility and heavy tailed returns, our results reveal that the proposed models exhibit a weaker correlation between stock returns and volatility and heavier tails in equity returns.

Hybrid nanodiamond and titanium dioxide nanobeam cavity design

Titanium dioxide is an emerging optical material, with a relatively high refractive index (n ∼ 2), which allows for high confinement of the electromagnetic field. Extensive research has been conducted on the negatively charged nitrogen vacancy centre in diamond due to its robust electronic and optical properties. In particular, its stable room-temperature photoluminescence properties have been considered for quantum optical applications. Nanobeam cavities are a geometry that offer exceptionally large-Q values given their minimal footprint, a must for high density and compact optical architecture. This paper presents an ultrahigh-Q nanobeam cavity within titanium dioxide in a low-refractive index environment operating at the negatively charged nitrogen vacancy centre of diamond. This research opens the possibility of hybrid optical devices utilising titanium dioxide and diamond.

Cluster decay of the high-lying excited states in 14C**Supported by the 973 Program of China (2013 CB834402) and National Natural Science Foundation of China (11275011, 11535004)

A cluster-transfer experiment of 9Be(9Be,14C → α+10Be)α at an incident energy of 45 MeV was carried out in order to investigate the molecular structure in high-lying resonant states in 14C. This reaction is of extremely large Q-value, making it an excellent case to select the reaction mechanism and the final states in outgoing nuclei. The high-lying resonances in 14C are reconstructed for three sets of well discriminated final states in 10Be. The results confirm the previous decay measurements with clearly improved decay-channel selections and also show a new state at 23.5(1) MeV. The resonant states at 22.4(3) and 24.0(3) MeV decay primarily into the typical molecular states at about 6 MeV in 10Be, indicating a well developed cluster structure in these high-lying states in 14C. Further measurements of more states of this kind are suggested.

Scintillating bolometers for the LUCIFER project

Neutrinoless double beta decay (0vββ) is one of the most sensitive probes for physics beyond the Standard Model, providing unique information on the nature and masses of neutrinos. In order to explore the so-called inverted neutrino mass hierarchy region a further improvement on the upcoming 0vββ experiment is needed. In this respect, scintillating bolometers are the suitable technology for achieving such goal: they ensure excellent energy resolution and highly efficient particle discrimination. The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of 0vββ of 82Se. The matrix which embeds the source is an array of Zn 82Se crystals, where enriched 82Se is used as decay isotope. Taking advantage of the large Q-value (2997 keV) and of the particle discrimination, the expected background rate in the region of interest is as low as 10-3 c/keV/kg/y. The foreseen sensitivity after 2 years of live time will be 1.8×1025 years. We will report on the potential of such technology and on the present status of the project.

Current status and perspectives of the LUCIFER experiment

The quest for Neutrinoless Double Beta Decay (0νDBD) represents one of the most promising ways to investigate the neutrino mass nature, Dirac or Majorana. A convincing detection claim demands for detectors with excellent energy resolution and almost zero background in the energy region of interest. These features can be obtained with the approach of the LUCIFER project, funded by an European grant, which is based on the double readout of the heat and scintillation light produced by ZnSe scintillating bolometers. The resulting identification and rejection of the α interactions, as well as the large Q-value of the emitter, will guarantee a background lower than 10−3 counts/keV/kg/y in the energy region of the 0νDBD of 82Se, an order of magnitude lower with respect to the present generation experiments. Despite the small mass of ∼17 kg, LUCIFER will reach a 90% CL sensitivity of 0.6×1026 y on the half-life of the decay.We describe the current status of the project, including results of the recent R&D activity.

THE SINS/zC-SINF SURVEY OFz∼ 2 GALAXY KINEMATICS: EVIDENCE FOR GRAVITATIONAL QUENCHING

As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive the radial distributions of H-alpha surface brightness, stellar mass surface density, and dynamical mass at ~2 kpc resolution in 19 z~2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. From these data we infer the radial distribution of the Toomre Q-parameter for these main-sequence star forming galaxies (SFGs), covering almost two decades of stellar mass (10^9.6 to 10^11.5 solar masses). In more than half of our SFGs, the H-alpha distributions cannot be fit by a centrally peaked distribution, such as an exponential, but are better described by a ring, or the combination of a ring and an exponential. At the same time the kinematic data indicate the presence of a mass distribution more centrally concentrated than a single exponential distribution for 5 of the 19 galaxies. The resulting Q-distributions are centrally peaked for all, and significantly exceed unity there for three quarters of the SFGs. The occurrence of H-alpha rings and of large nuclear Q-values is strongly correlated, and is more common for the more massive SFGs. While our sample is small and there remain substantial uncertainties and caveats, our observations are consistent with a scenario in which cloud fragmentation and global star formation are secularly suppressed in gas rich high-z disks from the inside out, as the central stellar mass density of the disks grows.

High-lying excited states in Gamow Teller strength and their roles in neutrino reactions

The Gamow Teller (GT) transition strengths deduced from charge exchange reactions (CEXRs) are very helpful for understanding the nuclear reaction induced by neutrinos, in particular, by the solar neutrino. For further study of supernovae (SNe) neutrinos in the cosmos, one needs to study high-lying GT states around a few tens of MeV region as well as other multipole transitions because of the high energy tail in the neutrino spectra emitted from the neutrino sphere. In this report, we address the importance of the high-lying GT excited states, whose data now become available from various CEXR experiments. For example, GT(± strengths up to 70MeV are successfully extracted by 90Zr(n, p) and 90Zr(p, n) reactions. Our discussions are extended to investigate roles of the high-lying states beyond a few low-lying states known in the old experiment on the reaction induced by SNe neutrinos particularly on 40Ar target. The nucleus was originally exploited to identify the solar neutrino emitted from 8B produced in the pp-chains on the Sun, and now lots of applications for more energetic neutrino detection are under progress. The expected large difference between the cross-sections of \( \nu_{e}^{}\) and \( \bar{{\nu}}_{e}^{}\) reactions on 40Ar , whose differences were anticipated because of the large Q-value in the \( \bar{{\nu}}_{e}^{}\) reaction, is significantly diminished compared to previous results. Our calculations are carried out by the Quasi-particle Random Phase Approximation (QRPA), which takes the neutron-proton pairing into account to the standard proton-neutron QRPA (pnQRPA) where only proton-proton and neutron-neutron pairing correlations are considered.

Recycling and Transport of Neutrals

Removal of helium, the ash from the D-T-fusion reaction, from a burning plasma flame, is one of the critical issues for future thermonuclear burning plasma. Even in plasmas driven by additional heating to large Q-values this is a severe problem. Recombination of fuel and ash ions at plasma exposed surfaces, re-emission as neutral particles and subsequent pumping (“recycling”) provides, at least in principle, the mechanism to flush the plasma from its ash. However, plasma surface interaction has to be limited in order to protect vessel components from excessive thermal load, often a conflicting requirement.

CLUSTERS IN THE BETA-DECAY OF LIGHT EXOTIC NUCLEI

The β-decay is a useful tool to study the peculiar features present in light exotic nuclei, such as halos and cluster structures. The large Q-values and low breakup thresholds in the daughter nuclei allow channels with feeding to continuum states and delayed emission of nucleons and light ions. We report experimental results obtained using a technique where the radioactive nuclei are implanted in a finely segmented detector, and the decay channels are identified through the correlation between the implanted nuclei and subsequent decays. Decays involving cluster and halo states in 12 C , 6 He , 11 Li and 11 Be were measured.

Reactions onAr40involving solar neutrinos and neutrinos from core-collapsing supernovae

We calculated neutrino reactions on {sup 40}Ar for detecting core-collapsing supernovae (SNe) neutrinos. The nucleus was originally exploited to identify the solar neutrino emitted from {sup 8}B produced in pp chains on the Sun. With the higher energy neutrinos emitted from the core-collapsing SNe, contributions from higher multipole transitions, as well as from the Gamow-Teller and Fermi transitions, are shown to be important ingredients for understanding reactions induced by the SN neutrino. Moreover, higher excited states beyond a few states known in experiment diminish significantly the expected large difference between the cross sections of {nu}{sub e} and {nu}-bar{sub e} reactions on {sup 40}Ar, which difference is anticipated because of the large Qvalue in the {nu}-bar{sub e} reaction. The reduction is shown to lead to a difference between them of only a factor of 2.

Recycling and Transport of Neutrals

Removal of helium, the ash from the D-T-fusion reaction, from a burning plasma flame, is one of the critical issues for future thermonuclear burning plasma. Even in plasmas driven by additional heating to large Q-values this is a severe problem. Recombination of fuel and ash ions at plasma exposed surfaces, re-emission as neutral particles and subsequent pumping (“recycling”) provides, at least in principle, the mechanism to flush the plasma from its ash. However, plasma surface interaction has to be limited in order to protect vessel components from excessive thermal load, often a conflicting requirement.

Synthesis of superheavy nuclei with 238U target

The production of superheavy nuclei with Z = 108−116 via hot fusion reactions of the neutron-rich projectiles with 238U target is systematically studied. The results show that the production cross sections of superheavy nuclei do not decrease monotonously as the atomic number Z increasing. The cross sections of the superheavy nuclei at Z = 112 and 115 are enhanced as compared with the whole Z-trend in synthesis of the superheavy nuclei, which clearly illustrates that the reactions with large negative Q-value and shell correction are more favorable to synthesize superheavy nuclei.

Structure and Rheology of Cationic Molecular Hydrogels of Quinuclidine Grafted Bile Salts. Influence of the Ionic Strength and Counter-Ion type

Quinuclidine grafted cationic bile salts are forming salted hydrogels. An extensive investigation of the effect of the electrolyte and counterions on the gelation has been envisaged. The special interest of the quinuclidine grafted bile salt is due to its broader experimental range of gelation to study the effect of electrolyte. Rheological features of the hydrogels are typical of enthalpic networks exhibiting a scaling law of the elastic shear modulus with the concentration (scaling exponent 2.2) modeling cellular solids in which the bending modulus is the dominant parameter. The addition of monovalent salt (NaCl) favors the formation of gels in a first range (0.00117 g cm(-3) (0.02 M) < T(NaCl) < 0.04675 g cm(-3) (0.8 M)). At larger salt concentrations, the gels become more heterogeneous with nodal zones in the micron scale. Small-angle neutron scattering experiments have been used to characterize the rigid fibers (<R> approximately 68 A) and the nodal zones. Stress sweep and creep-recovery measurements are used to relate the lack of linear viscoelastic domain to a mechanism of disentanglement of the fibers from their associations into fagots. The electrostatic interactions can be screened by addition of salt to induce a progressive evolution toward flocculation. SEM, UV absorbance, and SAXS study of the Bragg peak at large Q-values complete the investigation.

Recycling and Transport of Neutrals

Removal of helium, the ash from the D-T-fusion reaction, from a burning plasma flame, is one of the critical issues for future thermonuclear burning plasma. Even in plasmas driven by additional heating to large Q-values this is a severe problem. Recombination of fuel and ash ions at plasma exposed surfaces, re-emission as neutral particles and subsequent pumping (“recycling”) provides, at least in principle, the mechanism to flush the plasma from its ash. However, plasma surface interaction has to be limited in order to protect vessel components from excessive thermal load, often a conflicting requirement.

Sub-barrier fusion ofCa40+Zr94: Interplay of phonon and transfer couplings

A precise fusion excitation function has been measured for 40 Ca+ 94 Zr at near- and sub-barrier energies, and the fusion barrier distribution has been extracted. Comparing with the existing data for 40,48 Ca+ 90,96 Zr shows that couplings to inelastic excitations determine the fusion cross sections and the shape of the barrier distributions near the barrier. At lower energies, the two systems possessing neutron-transfer channels with large positive Q-values ( 40 Ca+ 94,96 Zr) have remarkably similar cross sections, and both show a large enhancement with respect to the other systems and to coupled-channels calculations including up to three quadrupole and octupole phonons in the Zr targets.

Optimal reactions for the synthesis of superheavy nucleus 270Hs

The superheavy nucleus 270Hs is expected to be a “double-magic” deformed nucleus. We have calculated its cross sections of evaporation residue for the reactions 248Cm(26Mg,4n)270Hs, 244Pu(30Si,4n)270Hs, 238U(36S,4n)270Hs and 226Ra(48Ca,4n)270Hs using a two-parameter Smoluchowski equation. It is found from our results that 226Ra(48Ca,4n)270Hs and 238U(36S,4n)270Hs are two optimal reactions for the synthesis of the superheavy nucleus 270Hs due to their large negative Q-values.