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At least 163 records · Page 9

Relativistic distorted-wave collision strengths and oscillator strengths for the 185Δn=0 transitions with n=2 in the 67 C-like ions with 26≤Z≤92

Relativistic distorted-wave collision strengths have been calculated for the 185 Δn=0 transitions with n=2 in the 67 C-like ions with nuclear charge number Z in the range 26≤Z≤92. The calculations were made for the six final, or scattered, electron energies E{sup ′}=0.03,0.08,0.20,0.42,0.80, and 1.40, where E{sup ′} is in units of Z{sub eff}{sup 2} Ry with Z{sub eff}=Z−4.17. In addition, electric dipole oscillator strengths are provided. In the present collision-strength calculations, an improved “top-up” method, which employs relativistic plane waves, was used to obtain the high partial-wave contribution for each transition, in contrast to the partial-relativistic Coulomb–Bethe approximation used in previous work by Zhang and Sampson [H.L. Zhang, D.H. Sampson, At. Data Nucl. Data Tables 63 (1996) 275]. In that earlier work, collision strengths were also provided for the same 185 Δn=0 transitions in C-like ions, but for the more limited list of 46 ions with Z in the range 9≤Z≤54. The collision strengths covered in the present work, particularly those for optically allowed transitions, should be more accurate than the corresponding data given by Zhang and Sampson [H.L. Zhang, D.H. Sampson, At. Data Nucl. Data Tables 63 (1996) 275] and are presented here to replace those earlier results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

{sup 11}B and Constraints on Neutrino Oscillations and Spectra from Neutrino Nucleosynthesis

We study the sensitivity to variations in the triple-alpha and {sup 12}C({alpha},{gamma}){sup 16}O reaction rates, of the yield of the neutrino-process isotopes {sup 7}Li, {sup 11}B, {sup 19}F, {sup 138}La, and {sup 180}Ta in core-collapse supernovae. Compared to solar abundances, less than 15% of {sup 7}Li, about 25%-80% of {sup 19}F, and about half of {sup 138}La is produced in these stars. Over a range of {+-}2{sigma} for each helium-burning rate, {sup 11}B is overproduced and the yield varies by an amount larger than the variation caused by the effects of neutrino oscillations. The total {sup 11}B yield, however, may eventually provide constraints on supernova neutrino spectra.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Nonlinear Longitudinal Space Charge Oscillations in Relativistic Electron Beams

In this Letter we study the evolution of an initial periodic modulation in the temporal profile of a relativistic electron beam under the effect of longitudinal space-charge forces. Linear theory predicts a periodic exchange of the modulation between the density and the energy profiles at the beam plasma frequency. For large enough initial modulations, wave breaking occurs after 1/2 period of plasma oscillation leading to the formation of short current spikes. We confirm this effect by direct measurements on a ps-modulated electron beam from an rf photoinjector. These results are useful for the generation of intense electron pulse trains for advanced accelerator applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Measuring the Hubble constant and spatial curvature from supernova apparent magnitude, baryon acoustic oscillation, and Hubble parameter data

Cosmic microwave background (CMB) anisotropy (spatial inhomogeneity) data provide the tightest constraints on the Hubble constant, matter density, spatial curvature, and dark energy dynamics. Other data, sensitive to the evolution of only the spatially homogeneous part of the cosmological model, such as Type Ia supernova apparent magnitude, baryon acoustic oscillation distance, and Hubble parameter measurements, can be used in conjunction with the CMB data to more tightly constrain parameters. Recent joint analyses of CMB and such non-CMB data indicate that slightly closed spatial hypersurfaces are favored in nonflat untilted inflation models and that dark energy dynamics cannot be ruled out, and favor a smaller Hubble constant. Here, we show that the constraints that follow from these non-CMB data alone are consistent with those that follow from the CMB data alone and so also consistent with, but weaker than, those that follow from the joint analyses of the CMB and non-CMB data.

79 ASTRONOMY AND ASTROPHYSICS↗

High intensity neutrino oscillation facilities in Europe

The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fréjus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of μ + and μ – beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular 6 He and 18 Ne, also stored in a ring. The far detector is also the MEMPHYS detector in the Fréjus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. Furthermore, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.

43 PARTICLE ACCELERATORS↗

Novel Cascaded Ring Oscillator Vernier based TDC Architecture with a Feedthrough Reference Oscillator

Time to digital converters (TDCs) are widely used in particle physics and medical imaging to determine the relative arrival time of photons and other particles. Vernier TDCs are one of the most attractive options due to their power consumption efficiency and their small footprint. We present our newly patented innovative architecture of cascaded-stage Vernier TDCs comprised of a feedthrough reference oscillator. This architecture lead to successive Vernier measurements that result in a lower number of cycles for the same dynamic range to resolution ratio (DRRR), leading to reduced conversion time and lower jitter. To validate this architecture, a test chip was designed in 0.18~μm TSMC technology, integrating four types of cascaded Vernier TDCs with an increasing number of stages. The performance of the chip was assessed using a modular test platform specifically designed for TDCs. For comparison purposes, all TDCs were tested with a LSB of 50~ps and a dynamic range of 20~ns. The experimental results demonstrate the highest gain in performance between 1 stage Vernier and 2 stage Vernier TDCs with the precision improved from 36~ps~rms to 21~ps~rms, the maximum number of turns from 110 to 25 counts and the dead time, from 266.4~ns to 76.5~ns, on average. Adding Vernier stages is only relevant for a higher DRRR. Therefore, the 3-stage and 4-stage Vernier TDCs also show performance gains, but improvements are limited.

Scarpellini, Robin↗

Oscillations in an isothermal atmosphere - The solar five-minute oscillations.

The motions generated in an atmosphere by pressure fluctuations at its base have been investigated. Particular attention was given to the problem of whether there is a divergence in the velocity amplitude at any particular frequency. Two of the current interpretations of observed oscillations of the solar atmosphere, for which the expected motion in the atmosphere is very similar, are discussed.

Worrall, G.↗