Electron-photon Coincidence Technique Research Articles

The Mobile Analyzer of Radioactive Gases OuTflows (MARGOT): A promising environmental xenon radionuclides detection system

An ultra-compact and unshielded spectrometer for analysis of atmospheric xenon radionuclides has been developed: the MARGOT system. This system works at ambient temperature and high pressure, and has a 54.3 cm3 inner active volume. Atmospheric xenon radionuclide activities are determined with the electron-photon coincidence technique using both NaI(Tl) detectors and large pixellized Si-PIN detectors. The MARGOT system integrates an enhanced version of the PIPSBox™, Geant4 simulation and first calibration results are discussed.

Electronic excitation of P-state of cadmium and zinc atoms

SynopsisThe electron-photon coincidence technique in coherence analysis version was used to study the electron impact excitation of first excited 1P1 states of cadmium and zinc atoms. The experimental results of the Stokes and Electron Impact Coherence Parameters (EICPs) for various collision energies are compared and presented alongside CCC and RDWA theoretical predictions.

Electron impact excitation of 41P1 zinc state for 40 eV incidence energy

SynopsisCoherence analysis version of the electron-photon coincidence technique was used to study the electron impact excitation of 41P1 state of zinc atoms. The first experimental results of the Stokes and Electron Impact Coherence Parameters (EICPs) for 40 eV collision energy are presented.

Experimental investigation of electron impact excitation of zinc atoms to the 41P1 state

Polarization analysis version of the electron-photon coincidence technique was applied to completely determine quantum state of zinc atoms excited to the 41P1 state by electron impact. We report first experimental values of Stokes parameters and Electron Impact Coherence Parameters (EICPs) for incident electron energy 80 eV.

Coincidence measurements of electron impact excitation of the 41P1 state of Zn

Electron-photon coincidence technique has been used to obtain Stokes and Electron Impact Coherence Parameters (EICPs) for excitation of 41P1 state of zinc atoms. We present an extended set of data for incident electron energy of 100 eV and electron scattering angles from 5° to 40°.

Coincidence measurements of electron-impact coherence parameters fore-Hescattering in the full range of scattering angles

Electron impact coherence parameters for inelastic $e\text{-He}$ scattering have been measured for the excitation to the $2\text{ }{^{1}\text{P}}_{1}$ state at collision energy of 100 eV. The experiment was conducted using angular correlation electron-photon coincidence technique with a magnetic angle changer allowing measurements in full range of scattering angles. The results are compared with other experimental data and theoretical predictions available for this collisional system.

Magnetic angle changer—a new device allowing extension of electron–photon coincidence measurements to arbitrarily large electron scattering angles

The electron–photon coincidence technique has been used as the most sensitive tool for investigating inelastic collisions of atoms with electrons and heavy particles and led to new insights into collision dynamics theory. However, for purely geometrical reasons, due to finite sizes of the electron energy analysers and electron beam sources, the measurements have not been carried out for the largest scattering angles. We present a novel system for electron–photon coincidence experiments on electron inelastic scattering with the magnetic angle changer allowing determination of excitation parameters at arbitrarily large scattering angles. As shown by experimental tests, our device can be successfully used in the electron–photon coincidence experiment and it has unprecedented efficacy—deflection angle up to 60° for 100 eV electrons, without a ferromagnetic core.

Coincidence study of excitation of cadmium atoms by electron impact

We present experimental values of the electron impact coherence parameters (EICP) and reduced Stokes parameters for excitation of 51P1 state of cadmium atoms. The results have been obtained using electron–photon coincidence technique for incident electron energies 80 eV and 60 eV and electron scattering angles in the range of 5° to 50°. We also present an additional set of data for electron energy 100 eV and scattering angle 50° which complements our previous results. All the experimental values are compared with theoretical relativistic distorted-wave approximation (RDWA) calculations. The first Born approximation (FBA) predictions of the alignment angle are also presented. The theoretical results are in good qualitative agreement with the experimental data.

Orientation propensities in spin-resolved electron-impact excitation ofmercury

The atomic orientation J⊥+generated by polarized-electron impact excitation of Hg (6s2)1S0 →(6s6p)3P1 is studied using the electron–photon coincidence technique. J⊥+ shows asignificant dependence on the spin projection of the incident electrons. Experimentalresults are compared with theoretical predictions employing a semi-relativistic five-stateR-matrix(close-coupling) description and the relativistic distorted-wave approximation.The experimental data show, in qualitative agreement with the calculations, thatthe well established orientation propensity rules for light atoms are apparentlyviolated if the electron spin is initially down with respect to the scattering plane.The applicability of the propensity rules to electron-impact excitation of heavyatoms is analysed. The observed apparent violation is attributed to a quantummechanical interference caused by ‘intermediate coupling’ within the excited state.A re-evaluation of the data supports the validity of the orientation propensityrules.

Electron–photon polarization correlation study of the 51P1 state of Cd atomsexcited by electron impact

Experimental values of the electron impact coherence parameters for excitation ofthe 51P1 state of cadmium atoms are reported along with relativisticdistorted-wave approximation calculations. The electron–photon coincidencetechnique has been used in measurements for incident electron energy 100 eV andat scattering angles 10°, 15°, 20°, 30° and 40°. Theoretical results are in goodqualitative agreement with experimental data.

Electron-photon coincidence study of the collisional excitation of the Ca state

Experimental values of the electron-impact coherence parameters (EICP) are reported for electron-impact excitation of the state of Ca. The results have been obtained using electron-photon coincidence techniques for incident electron energies of 45 and 60 eV and scattering angles of and . EICP values determined at 45 eV are compared with similar data obtained by other groups with coincidence and optical pumping methods. Our data do not show a disagreement with the theoretical calculations based on a relativistic distorted-wave approximation (RDWA) that was reported for earlier experimental coincidence results.

Review of advances in describing the 31D-state excitation of helium

Recent advances in describing the electron impact excitation of the 31D state of helium are reported for an incident energy of 40 eV and scattering angles from 10° to 40°. Measurements of the Stokes parameters have been made using the polarized photon–photon and electron–photon coincidence techniques. The partial cross section σm for the magnetic sublevels in the collision frame indicate that the m = 0 excitation is favoured. For the above scattering kinematics the data are in agreement with convergent close coupling calculations. The deduced scattering amplitudes, in the natural frame, show that the m = 2 excitation becomes dominant at the larger angles. Progress is reported on the complete determination of the scattering amplitudes and their relative phases using the triple-coincident detection of the scattered electron with the two sequential cascading photons.

Electron impact excitation of the 1(1)S-->3(1)P transition in helium.

In the first direct application of the electron-photon coincidence technique for differential cross-section measurements, experimentally determined ratios of the differential cross sections for the electron impact excitation of the $1^{1}S\ensuremath{\rightarrow}2^{1}P$ to the $1^{1}S\ensuremath{\rightarrow}3^{1}P$ transitions are presented at 30 and 40 eV incident electron energies. Differential cross sections for the $1^{1}S\ensuremath{\rightarrow}3^{1}P$ transitions are derived by normalizing these ratios to available experimental differential cross sections for the $1^{1}S\ensuremath{\rightarrow}2^{1}P$ transition.

Electron impact coherence and polarization parameters for the excitation of the 51P state in strontium

The electron impact excitation of the 51P state in strontium has been studied by the electron-photon coincidence technique. The Stokes parameters P1, P2, and P3, of the decay transition 51P1-51S0 at lambda =460.7 nm have been measured for an incident electron energy of 45 eV. The measurements extend over the electron scattering angles 30 degrees to 113 degrees . The polarization correlation data have been analysed to yield the electron impact coherence parameters (EICP) for the excitation of the Sr(51P) state. The results of the total polarization vector provide evidence of the coherent nature of the 51S0-51P1-51S0 excitation/de-excitation process in this relatively heavy He-like atom. The measurements provide a sensitive test for the theoretical models which involve the influence of strong electron correlation effects. Substantial agreement is found between these first measurements and the two calculations which have just become available.

Application of stepwise electron and laser excitation techniques to electron-photon correlation studies: II. Experiment

For pt.I see ibid., vol.23, no.19, p.3373-92 (1990). A stepwise excitation electron-photon correlation experiment is presented in which a combination of electron-photon coincidence and laser excitation techniques is used. Atomic collision parameters were measured for the electron impact excitation of the Hg 61P0-61P. (185 nm) transition at 16 eV incident electron energy and for electron scattering angles in the range 5'-30'.

Electron detachment and excitation processes in F--He,Ne collisions: electron and optical emissions from excited F- and F states

The relative importance of electron detachment and excitation processes in 0.5-15 keV F--He,Ne collisions has been studied by electron and optical spectrometry. The dominant excitation process populates the F (1D)nl states. For both collision systems, the population of doubly excited F- states is rather weak. By means of an electron-photon coincidence technique, low-energy electrons recently reported to be emitted from doubly excited F- states have been shown to originate from the decay of the F-(1D)3s2 1D level to the F (3P)3p 2P and 2D states. The branching ratio for the depopulation of this F- level has been determined experimentally and compared with theoretical calculations.

Lifetimes of the 3 1,3P and 3 1,3D states of helium

Measurements have been made of the helium n = 3 singlet and triplet P and D state lifetimes using the electron photon coincidence technique. For each state visible n = 3 to n = 2 photons were detected in coincidence with the inelastically scattered electron. The 3 1P lifetime as a function of atomic beam density shows the influence of resonance radiation imprisonment as applicable to He(n 1P) coincidence studies. Self absorption of the emitted radiation from the other n = 3 levels due to increased source density has also been investigated.

Electron-photon coincidence studies in magnesium

Electron impact excitation of the 31P state in magnesium has been studied by electron-photon coincidence techniques. Two types of experiments have been performed. An extensive set of measurements have been undertaken in which the three components of the Stokes vector were measured at incident energies of 20 and 40 eV for electron scattering angles between 5 and 20'. These measurements not only provide data on the coherence of the excitation process but also they form a basis by which approximations in scattering theory can be tested. In addition, an angular correlation function has been measured at 40 eV and at a scattering angle of 7'. The scattering parameters derived from this measurement agree with those measured in the polarisation study. The scattering parameters derived from the present work are in very good agreement with the recent close-coupling calculation of Mitroy and McCarthy (1989).

Electron-polarised photon coincidence experiments on the 32P state in sodium

Components of the Stokes vector have been measured using an electron-photon coincidence technique for radiation emitted normal to the scattering plane in the electron excitation of the 32P state in sodium at several energies from 5.1 to 30 eV. The coherence of the excitation process is probed through the concept of the reduced polarisation. The data are compared with those derived from optical pumping experiments, which are the time-reversed equivalent of the present experiments. In general, very good agreement is found with the data from the two techniques. Scattering amplitudes derived from the components of the Stokes vector are compared with theoretical predictions. It is observed that there is only moderate agreement between theory and experiment.

Angular correlations in the electron-impact excitation of sodium.

An electron-photon coincidence technique has been used to measure an angular-correlation function for the excitation of the 3 $^{2}P$ state in sodium at an incident electron energy of 54.4 eV; the scattered electrons are detected at 5\ifmmode^\circ\else\textdegree\fi{}. It is shown that the depolarizing influence of the hyperfine structure in the excited state is such that the angular correlation is essentially isotropic. Thus severe limitations are imposed on the use of this technique for the study of scattering amplitudes in the electron-impact excitation of sodium atoms.