Search results for "Cross Section"

Determination of the Bi209(n,γ)Bi210g cross section using the NICE detector

2021

The capture cross section of $^{209}\mathrm{Bi}(n,\ensuremath{\gamma})^{210g}\mathrm{Bi}$ was measured at different astrophysically relevant energies including thermal capture cross section (25 meV), resonance integral, and the Maxwellian averaged cross section at a thermal energy of $kT=30$ keV. The partial capture cross section $({\ensuremath{\sigma}}_{g})$ was determined using the activation technique and by measuring the $^{210}\mathrm{Po}$ activity. The newly developed and tested NICE detector setup was used to measure the $\ensuremath{\alpha}$ activity of the $^{210}\mathrm{Po}$. Using this setup the thermal and resonance integral cross sections were determined to be $16.2\phantom{\ru…

Electron energy distribution in the photodetachment ofH−by two radiation fields

1993

We report on the energy distribution of the electrons emitted in two-color photodetachment of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ in a highly nonlinear regime, and compare these results with the ones found by averaging the cross section obtained in the presence of a static field over the values taken by the low-frequency field in a cycle. Similarities and differences are discussed.

Comment on "Total Cross Section for Photon Absorption by Two Protons inHe3"

1995

Radiation tail and radiative corrections for elastic electron scattering

1975

Abstract A set of formulae, which is currently used to calculate radiative effects in electron scattering experiments, is discussed. Since these formulae contain approximations which fail to describe radiation losses properly a modified set is proposed. The radiation unfolding procedure of elastically scattered electrons is investigated in detail, account is taken of the different sets of formulae and of the finite energy resolution. The cross sections extracted from measured spectra depend on the formulae used in the unfolding procedure. For two measured Bi spectra they differ by up to 11%. With the modified set of formulae the unfolding procedure yields the same cross section as the appli…

Quasi-resonant energy transfer in collisions: Na2(A1? u + )+K(4S)

1994

Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na2(A) to potassium atoms as described by Na2(A1Σu+,v′J′)+K(4S)→Na2 (X1Σg+,v″J″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimerv′J′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm−1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm−1) …

Measurements of the antiproton-proton elastic cross section in the beam momentum range between 180 and 600 MeV/c

1991

The differential cross section for antiproton-proton elastic scattering has been measured for the beam momenta between 180 and 600 MeV/c. The real-to-imaginary ratio of the forward elastic scattering amplitude is derived from the Coulomb-nuclear interference. The ratio is found to be close to zero between 180 and 500 MeV/c with a minimum ofρ=−0.14 at 260 MeV/c. This result is contrary to model predictions. The phase shifts for thes-,p- andd-waves are extracted. The partial wave compositions of the elastic and inelastic cross sections have been determined. A large contribution of thep-wave is identified in the antiproton-proton interactions at small momenta.

Evidence of a Resonant Structure in the Cross Section between 4.05 and 4.60 GeV

2019

The cross section of the process e^{+}e^{-}→π^{+}D^{0}D^{*-} for center-of-mass energies from 4.05 to 4.60 GeV is measured precisely using data samples collected with the BESIII detector operating at the BEPCII storage ring. Two enhancements are clearly visible in the cross section around 4.23 and 4.40 GeV. Using several models to describe the dressed cross section yields stable parameters for the first enhancement, which has a mass of 4228.6±4.1±6.3  MeV/c^{2} and a width of 77.0±6.8±6.3  MeV, where the first uncertainties are statistical and the second ones are systematic. Our resonant mass is consistent with previous observations of the Y(4220) state and the theoretical prediction of a D…

Coherent photoproduction of η-mesons off 3He – search for η-mesic nuclei

2012

Coherent photoproduction of $\eta$-mesons off $^3$He, i.e. the reaction $\gamma ^3{He}\rightarrow \eta ^3{He}$, has been investigated in the near-threshold region. The experiment was performed at the Glasgow tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS detector. Angular distributions and the total cross section were measured using the $\eta\rightarrow \gamma\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay channels. The observed extremely sharp rise of the cross section at threshold and the behavior of the angular distributions are evidence for a strong $\eta {^3{He}}$ final state interaction, pointing to the existence of a resonant …

Colloidal crystal motion in electric fields

2003

Abstract We report on the short and long time flow behaviour of colloidal crystals subjected to a homogeneous electrical square wave a.c.-field in closed cells of rectangular cross section. Local velocities are determined from Laser Doppler velocimetry, sample structure and morphology were observed by time resolved polarisation microscopy. We observe a complex time dependence of the flow behaviour. After each field reversal we find a transition from an initial parabola-like flow to a final plug-like flow. On the time scale of minutes to hours channel narrowing occurs, i.e. flow initially restricted by the cell walls becomes restricted to the cell centre by wall based stationary crystals. Wi…

Frontiers of Heavy - Ion Physics and Superheavy Elements

2003

This contribution will focus on three topics of GSI nuclear structure research: super heavy elements, direct mass measurements in the storage ring, and the measurement of spallation cross section in reversed kinematics. The GSI project for an extended synchrotron facility will be outlined.