Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAbsolute cross sections for photoionization of Xe$^{q+}$ ions (1 $le$ q $le$ 5) at the 3d ionization threshold
99
0
0.0
(
0
)
Authors
S. Schippers
Ask ChatGPT about the research
No Arabic abstract
The photon-ion merged-beams technique has been employed at the new Photon-Ion spectrometer at PETRA III (PIPE) for measuring multiple photoionization of Xe$^{q+}$ (q=1-5) ions. Total ionization cross sections have been obtained on an absolute scale for the dominant ionization reactions of the type h u + Xe$^{q+}$ $to$ Xe$^{r+}$ + (q-r) e$^-$ with product charge states q+2 $le$ r $le$ q+5. Prominent ionization features are observed in the photon-energy range 650-750 eV, which are associated with excitation or ionization of an inner-shell 3d electron. Single-configuration Dirac-Fock calculations agree quantitatively with the experimental cross sections for non-resonant photoabsorption, but fail to reproduce all details of the measured ionization resonance structures.
rate research
Read More
The exclusive electroproduction process $vec{e}p to e^prime n pi^+$ was measured in the range of the photon virtuality $Q^2 = 1.7 - 4.5 rm{GeV^2}$, and the invariant mass range for the $npi^+$ system of $W = 1.15 - 1.7 rm{GeV}$ using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive $pi^+$ production from protons with nearly full coverage in the azimuthal and polar angles of the $npi^+$ center-of-mass system. The $npi^+$ channel has particular sensitivity to the isospin 1/2 excited nucleon states, and together with the $ppi^0$ final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the $sigma_{LT}$ structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections.
We demonstrate rather interesting manifestations of co-existence of resonance features in characteristics of the photoionization of 3d-electrons in Xe@C60. It is shown that the reflection of photoelectrons produced by the 3d Xe photoionization affects greatly partial photoionization cross-sections of and levels and respective angular anisotropy parameters, both dipole and non-dipole adding to all of them additional maximums and minimums. The calculations are performed treating the 3/2 and 5/2 electrons as electrons of different kinds with their spins up and down. The effect of C60 shell is accounted for in the frame of the orange skin potential model.
The differential cross sections sigma_0=sigma_T+epsilon sigma_L, sigma_{LT}, and sigma_{TT} of pi^0 electroproduction from the proton were measured from threshold up to an additional center of mass energy of 40 MeV, at a value of the photon four-momentum transfer of Q^2= 0.05 GeV^2/c^2 and a center of mass angle of theta=90^circ. By an additional out-of-plane measurement with polarized electrons sigma_{LT} was determined. This showed for the first time the cusp effect above the pi^+ threshold in the imaginary part of the s-wave. The predictions of Heavy Baryon Chiral Perturbation Theory are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.
Absolute cross sections for electron-impact single ionisation (EISI) of multiply charged tungsten ions (W$^{q+}$) with charge states in the range $ 11 leq q leq 18$ in the electron-ion collision energy ranges from below the respective ionisation thresholds up to 1000~eV were measured employing the electron-ion crossed-beams method. In order to extend the results to higher energies, cross section calculations were performed using the subconfiguration-averaged distorted-wave (SCADW) method for electron-ion collision energies up to 150~keV. From the combined experimental and scaled theoretical cross sections rate coefficients were derived which are compared with the ones contained in the ADAS database and which are based on the configuration-averaged distorted wave (CADW) calculations of Loch et al. [Phys. Rev. A 72, 052716 (2005)]. Significant discrepancies were found at the temperatures where the ions investigated here are expected to form in collisionally ionised plasmas. These discrepancies are attributed to the limitations of the CADW approach and also the more detailed SCADW treatment which do not allow for a sufficiently accurate description of the EISI cross sections particularly at the ionisation thresholds.
The absolute electron capture cross sections for single and double charge exchanges between the highly charged ions O6+ and CO2, CH4, H2, N2, the dominant collision processes in the solar wind, have been measured in the energy from 7 keV*q (2.63 keV/u) to 52 keV*q (19.5 keV/u). These measurements were carried out in the new experimental instrument set up at Fudan University, and the error of cross sections for single and double charge exchanges at the 1{sigma} confidence level are about 11% and 16%, respectively. Limited agreement is achieved with single electron capture results calculated by the classical over-barrier model. These cross sections data are useful for simulation ion-neutral processes in astrophysical environments and to improve the present theoretical model of fundamental atomic processes.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
