Rates For Capture Research Articles

Measurement of the40Ca(3He,t)40Screaction

Levels in ${}^{40}\mathrm{Sc}$ below 2.5 MeV excitation energy have been populated in a high-resolution study of the ${}^{40}\mathrm{Ca}{(}^{3}\mathrm{He}{,t)}^{40}\mathrm{Sc}$ reaction. Three new states have been observed at energies ${E}_{x}=1703,$ 1871, and 1925 keV. Correspondence of the observed ${}^{40}\mathrm{Sc}$ levels with known $T=1$ states in ${}^{40}\mathrm{K}$ and ${}^{40}\mathrm{Ca}$ are based on predictions provided by the isobaric multiplet mass equation. Our results confirm recently estimated stellar reaction rates for proton capture on ${}^{39}\mathrm{Ca}.$

Charge transfer as responsible for H +2 dissociation on aluminum surfaces

The neutralization rates for resonant capture into the b 3 Σ + u state and Auger capture into the X 1 Σ + g are calculated for H + 2 ions impinging on an aluminum surface. The neutralization of the ion into the b state leaves the molecule in an excited dissociating state, whereas neutralization into the X state leaves the molecule in its stable ground state. In the present work we compare the resonant/Auger population ratio with experimental estimates based on the dissociation of H 2 molecules during H + 2 and H 2 collisions on surfaces.

A k.p model for carrier capture by a quantum well

A k.p model for electron and hole capture by a quantum well has been applied to the calculation of the rates for capture via phonon and alloy scattering by a 30 AA In0.7Ga0.3As-InGaAs quantum well, a system which is suitable for lasers operating at a wavelength of 1.55 mu m. The standard approach to carrier capture by a quantum well, namely the application of Fermi's Golden Rule, has been adapted in order to derive the dimensionless local capture efficiency per unit incident particle current density. This has the advantage that the capture data can be more readily incorporated into many-particle transport simulations of quantum well lasers. Structure is observed in the capture efficiency as a function of the energy and in-plane wavevector of the incident carrier. This is partly attributed to instances where incident electrons or holes in barrier states undergo strong transmission into the well region, but mixing between the quantum well subbands is also important through the effect upon both the density of final states and the scattering matrix elements for capture transitions.

A k.p model for hole capture into a quantum well

A k.p model for hole capture into a quantum well has been applied to the calculation of the rates for capture via phonon and alloy scattering into a 30Å In 0.7Ga 0.3As-InGaAsP quantum well, a system which is suitable for lasers operating at 1.55 μm. The well has three subbands, derived from the HH1, LH1 and HH2 zone centre states. Capture of holes into the HH2 subband is predicted to be dominated by polar optical phonon emission, whereas scattering into the other two bands proceeds mainly by non-polar optical phonon emission or alloy scattering. There is structure in the capture rate plotted as a function of the energy and in-plane wavevector of the incident hole, which is attributed to instances where incident holes in barrier states undergo strong transmission into the well region. Mixing between the quantum well subbands is important through the effect upon the density of final states in capture transitions, but is less significant with respect to its effect on the scattering matrix elements.

Nuclear transition rates in micro-catalyzed p-d fusion.

Nuclear transition rates in \ensuremath{\mu}-catalyzed p-d fusion have been calculated using numerically converged $^{3}\mathrm{He}$ bound-state and p-d scattering wave functions for the first time. The transition rates for M1 radiative capture in both quartet and doublet initial states have been computed using a model of meson-exchange currents which reproduces the thermal n-d capture cross section, and are in excellent agreement with experiment. The muon internal-conversion rate is in very good agreement with a recent reanalysis of old bubble-chamber measurements. Furthermore, our nonvanishing quartet capture rate resolves the anomaly in the Wolfenstein-Gerstein effect.

Total radiative capture rates for three- and four-nucleon pionic atoms.

A corrected closure approximation is used to calculate the reduced rates for radiative capture of negative pions from 1s and 2p orbitals in /sup 3/H, /sup 3/He, and /sup 4/He. For /sup 3/He and /sup 4/He the calculated rates are in good agreement with experimental data. In the case of /sup 3/H, the calculated value for 1s capture is combined with the measured radiative capture branching ratio to obtain a value of GAMMA/sub tot//sup 1//sup s/ = 2.2 +- 0.4 eV for the total width of the 1s level in the /sup 3/H pionic atom. This value when compared to the measured total width of the 1s level in pionic /sup 3/He implies a small but definite contribution of singlet spin nucleon pairs to absorption of s-wave pions.

Transesophageal Atrial Pacing Using a Pill Electrode for the Termination of Atrial Flutter

To determine the efficacy of transesophageal rapid atrial pacing with a "pill-electrode" for the termination of atrial flutter, we studied 14 consecutive unselected patients presenting with atrial flutter of various etiologies. The bipolar pill-electrode (interelectrode distance 13 mm) was introduced orally without sedation. Of 14 pacing attempts, atrial capture was obtained in 13 (93 percent), and sustained alteration in rhythm (atrial fibrillation, sinus rhythm or type 2 flutter) in 12 (86 percent). Normal sinus rhythm occurred in six (43 percent), in all of whom it was preceded by transient atrial fibrillation. There was no difference in baseline flutter rates, pacing rates for atrial capture, or duration of flutter between patients reverting to sinus rhythm and those remaining in flutter or converting to atrial fibrillation. Pacing was well tolerated in all but one subject. Thus, esophageal pacing with the pill-electrode was simple to perform, well-tolerated and highly successful for atrial capture in patients with atrial flutter. Although it had a lower success rate than DC cardioversion in producing sinus rhythm, the simplicity of application makes it a useful initial alternative, particularly in patients in whom cardioversion may be hazardous.

Inclusive radiative pion and muon capture in N = Z nuclei

Sum rule techniques are used to predict average excitation energy and total capture rates for inclusive radiative pion and muon capture in N = Z nuclei. The processes under consideration are shown to exhibit different excitation features because of the strong dependence on the orbit of the captured particle. Results are given for 16O and 40Ca. A semi-quantitative agreement with experimental data is found, amenable to the approximations in the treatment of nuclear dynamics.

Coincidence Observations of Strong Correlations between Bound- and Continuum-State Electron Capture by Fast, Highly Ionized Ions in Gases

Comparative rates for simultaneous capture of zero, one, two, and three electrons into bound states measured in coincidence with an electron capture to continuum states, have been determined for 7-9-a.u. velocity ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions in Ar. Estimates based on the high correlations observed lead to the conclusion that traditionally measured cross sections for single and multiple bound-state capture have often been inappropriately compared with pure bound-state capture theories, tacitly ignoring an important unseen channel.

Radiative Pion Capture from the1sLevel inLi6

Partial rates for radiative capture from the $1s$ atomic level in $^{6}\mathrm{Li}$ to the lowest two $^{6}\mathrm{He}$ states have been determined by measuring, with the necessary energy resolution, x rays and high-energy photons in coincidence. A comparison of our results and other related experimental results with different theoretical approaches shows that phenomenological wave functions consistently describe photopion processes as well as electromagnetic and weak transitions between low-lying $^{6}\mathrm{Li}$ and $^{6}\mathrm{He}$ states.

Muon capture in deuterium with realistic potentials

Abstract The transition rates for muon capture in deuterium are calculated using the Reid soft-core deuteron, and 1 S 0 and 3 P J (J = 0, 1, 2) neutron-neutron wave functions. The validity of the closure approximation and of the Omnes-Muskhelishvili method is studied. The off-shell effects admissible in a class of phase-shift-equivalent potentials by present experimental data are evaluated.

Muon-Capture Rates in Deuterium and the Weak Form Factors in the Timelike Region

The rates for muon capture in deuterium from the doublet and quartet states are calculated by the use of the elementary-particle treatment. The matrix elements of the vector and axial-vector currents are each constructed in terms of two independent form factors. The form factors describing the matrix element of the vector current are obtainesd in the spacelike region from electrodisintegration and photodisintegnation data by the use of the conserved- vector-current hypothesis. The form factors describing the matrix element of the axial-vector current are obtained in the spacelike region by the use of the hypothesis, of partial conversation of axial-vector current and arguments based on the impulse approximation. The capture rates are found to be sensitive to the behavior of the form factors near q/sup 2/ = m/sub mu //sup 2/. The capture rates from the doublet and quartet states are fou nd t, be GAMMA /sub d/ = 374 plus or minus 18 sec/sup -1/ and GAMMA /sub q/ = 6.07 plus or minus 0.04 sec/ sup muons plus :q1; muons minus :q1; gev range 10-100; It is shown that 25.6% of the contribution to GAMMA /sub d/ comes from the timelike region and that an analytic continuation of themore » dipole fit for the form factors to the timelike region from the spacelike region is consistent with experimental data. (auth)« less

The capture of muons by complex nuclei

A comparison is made of different theoretical approaches for calculating the total rates for capture of muons by complex nuclei. The merits of the closure approximation and shell model calculations are discussed. The application of the closure approximation to a statistical model of the nucleus is worked out in some detail. A tentative explanation of the experimental data in terms of a universal Fermi interaction is given.