19 Search Results

In this paper we review the physics opportunities at linear $e^+e^-$ colliders with a special focus on high centre-of-mass energies and beam polarisation, take a fresh look at the various accelerator technologies available or under development and, for the first time, discuss how a facility first equipped with a technology mature today could be upgraded with technologies of tomorrow to reach much higher energies and/or luminosities. In addition, we will discuss detectors and alternative collider modes, as well as opportunities for beyond-collider experiments and R&D facilities as part of a linear collider facility (LCF). The material of this paper willmore » support all plans for $e^+e^-$ linear colliders and additional opportunities they offer, independently of technology choice or proposed site, as well as R&D for advanced accelerator technologies. This joint perspective on the physics goals, early technologies and upgrade strategies has been developed by the LCVision team based on an initial discussion at LCWS2024 in Tokyo and a follow-up at the LCVision Community Event at CERN in January 2025. It heavily builds on decades of achievements of the global linear collider community, in particular in the context of CLIC and ILC.« less

Alloy developers worldwide have struggled to create creep-resistant alumina-forming, iron-based austenitic stainless steels for use as high-temperature structural alloys, but with limited success in balancing alloy cost, oxidation, and creep resistance. Here, this article describes the research and development of a novel cast alumina-forming austenitic stainless steel. This work won the prestigious Engineering Materials Achievement Award presented at IMAT 2023 in Detroit.

Alumina-forming austenitic (AFA) alloys are relatively inexpensive high performance materials which combine the creep resistance of low-cost austenitic alloys and the oxidation resistance of expensive alumina forming alloys. However, a fundamental understanding of the role of key alloying elements such as Ni, Cr, Al, Nb, Ti, V, B and C in the experimentally observed oxidation behavior of these alloys is still lacking. The present work is a first in a series of studies aiming to quantitatively describe the role of Ni in promoting or disrupting protective Al₂O₃ scale formation on AFA alloys. Here, ternary Fe-Al-xNi model alloys with three differentmore » Ni contents were isothermally exposed in an atmosphere with a low partial pressure of oxygen between 800–1000 °C for 24 h to evaluate the role of Ni in the observed internal oxidation behavior. Increasing Ni contents had no impact on the internal oxidation behavior of the alloys. The experimental and theoretical analyses in the present work suggested a negligible effect of the internal oxide precipitates on the inward diffusion of oxygen, typically expected in these systems, while simultaneously highlighting the barriers in the development of reliable models for computation-assisted design of these alloys.« less

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide–bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite,more » and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu’s parent body formed ~2 million years after the beginning of Solar System formation.« less

Background: Superdeformed (SD) bands are suggested by theory around ${}_{40}\mathrm{Ca}$ and in lighter alpha-conjugate nuclei such as ${}_{24}\mathrm{Mg}$, ${}_{28}\mathrm{Si}$, and ${}_{32}\mathrm{S}$. Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in ${}_{40}\mathrm{Ca}$ and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. Additionally, the key evidence ofmore » superdeformation would be the observation of transitions with high $B$( $E2)$ transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in ${}_{28}\mathrm{Si}$ through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in ${}_{28}\mathrm{Si}$ were populated in the ${}_{28}\mathrm{Si}(\alpha ,{\alpha }^{\text{'}})$ reaction using a 130-MeV ${}_4\mathrm{He}$ beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of $9.1^{°}$ to favor the population of states with $J\approx 4$. Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large ${\mathrm{LaBr}}_3$ detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in ${}_{28}\mathrm{Si}$ in the vicinity of 10 MeV. However, while the candidate $4^{+}$ SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate $2^{+}$ SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of $B\left(E2\right)<43$ W.u. could be established. This contradicts AMD predictions of $\approx 200$ W.u. for such a transition. Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in ${}_{28}\mathrm{Si}$ represents an SD band, which demonstrates the potential of the methodology devised here.« less

²⁴Mg is a strongly deformed nucleus in the ground state. Deformation effects can be observed in the structure of the isoscalar giant monopole and quadrupole resonances. ²⁴Mg is also a nucleus that is well known to present different types of cluster-oscillation modes. Both giant resonances and cluster states are strongly populated by isoscalar transitions. To extract the E0, E1, and E2 transition strengths via ⁶Li scattering. The ⁶Li probe is a powerful tool for investigating the isoscalar nuclear response with a very favorable ratio of resonance-to-continuum background. Double-differential cross sections of ⁶Li inelastic scattering, at the beam energy of 100more » MeV/u, were measured in the excitation-energy range 10 – 40 MeV and scattering angles 0 - 3°. A multipole-decomposition analysis was performed for extracting the isoscalar E0 , E1, and E2 strength distributions. Results: The extracted multipole strengths were compared with predictions from consistent quasiparticle random phase approximation calculations. The theoretical predictions are in fair agreement with the experimental data. The E0 strength was also compared with results from antisymmetrized molecular dynamics calculations found in the literature. A few peaks in the experimental data might be associated with clustering in ²⁴Mg. Ground-state deformation effects were observed in the isoscalar giant monopole resonance (ISGMR) and isoscalar giant quadrupole resonance (ISGQR) distributions. The ISGMR strength is split in two peaks around 19 and 28 MeV. The ISGQR exhibits a pronounced peak at 20 MeV with a broadening at the low-energy region, similar to predictions from microscopic calculations. Signatures of excitation of cluster states were observed in the E0 response. Further studies including particle-decay measurements will be required to confirm the nature of the observed peaks.« less

The low-lying dipole strength in the ^90,94Zr nuclei was investigated via (ρ,ρ'γ) at 80 MeV and (α, α', γ) at 130 MeV. The experiments, made at RCNP, used the magnetic spectrometer Grand Raiden for the scattered particles and the array CAGRA with HPGe detectors for the γ-decay. For ⁹⁴Zr these are the first data for both reactions and for ⁹⁰Zr these are the first data with (ρ,ρ'γ) and the first ones at high resolution for (α, α', γ). The comparison of the present results for the two nuclei with existing (γ, γ') data shows that both nuclear probes produce anmore » excitation pattern different than that of the electromagnetic probes. DWBA calculations were made using form factors deduced from transition densities, based on RPA calculations, characterized by a strong neutron component at the nuclear surface. A combined analysis of the two reactions was performed for the first time to investigate the isoscalar character of the 1^- states in ^90,94Zr. The (ρ,ρ'γ) cross section was calculated using values for the isoscalar electric dipole energy-weighted sum rule (E1 ISEWSR) obtained from the (α, α', γ) data. The isoscalar strength for ⁹⁰Zr was found to exhaust 20 ± 2.5% of the EWSR in the energy range up to 12 MeV. In case of ⁹⁴Zr, a strength of 9 ± 1.1% of the EWSR was found in the range up to 8.5 MeV. Although an overall general description was obtained in the studied energy intervals, not all proton cross sections were well reproduced using the isoscalar strength from (α, α', γ). This might suggest mixing of isoscalar and isovector components and that this mixing and the degree of collectivity are not the same for all the 1^- states below the particle binding energy.« less

Inelastic ${}_6\mathrm{Li}$ scattering at 100 MeV/u on ${}_{12}\mathrm{C}$ and ${}_{93}\mathrm{Nb}$ has been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^{°}<{\theta }_{\text{lab.}}<2^{°}$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}_6{}^{more »}\mathrm{Li}$ scattering allowed for precise determination of the $E0$ strengths in ${}_{12}\mathrm{C}$ and ${}_{93}\mathrm{Nb}$. Additionally, it was found that the monopole strength in ${}_{12}\mathrm{C}$ exhausts $52\pm 3^{\text{(stat.)}}\pm 8^{\text{(sys.)}}\%$ of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $\alpha$-scattering experiments. The monopole strength in ${}_{93}\mathrm{Nb}$ exhausts $92\pm 4^{\text{(stat.)}}\pm {10}^{\text{(sys.)}}\%$ of the EWSR, and it is consistent with measurements of nuclei with mass number of $A\approx 90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.« less