Martyn Hussey

Low energy (e, 2e) differential cross-section measurements on the 1πg and 4σg molecular orbitals of CO2

Ionization differential cross sections are presented for low energy electron scattering from the 1πg and 4σg orbitals of the tri-atomic molecule CO2, at incident electron energies ranging from 10 eV to 80 eV above the ionization threshold. The (e, 2e) experiments were conducted in a coplanar symmetric geometry, the outgoing electrons sharing the excess energy from the interaction equally. The results are compared to experiments previously conducted in the same geometry and over the same energy range from the 1πu and 3σg orbitals of N2. An unusual feature has been discovered ionizing from the 1πg orbital at a scattered and ejected electron energy of 10 eV, where a second forward scattering peak is found at low angles.

Coplanar symmetric and asymmetric electron impact ionization studies from the 1b1 state of H2O at low to intermediate impact energies

(e, 2e) ionization differential cross sections are presented for incident electron energies ranging from 15 eV to 95 eV above the ionization threshold of the 1b1 molecular state of H2O. Experimental results and theoretical analysis were derived for three energies in a coplanar symmetric geometry, and for three energies in an asymmetric geometry. The experimental data show a wide variation in the cross section over this range of energies, whereas the theoretical analysis carried out using a sophisticated molecular DWBA model, which includes the final state post collision interaction (PCI), shows best agreement at lower energies. The experimental techniques used to collect the data are described here as well as an improved theoretical approach using elastic scattering cross sections to evaluate the accuracy of the distorted waves utilized in the calculation of the ionization cross sections.

(e, 2e) ionization measurements from the 3σg and 2σu* states of N2—comparison between experiment and theoretical predictions of the effects of exchange, polarization and interference

Gao et al (2005 Phys. Rev. A 72 032721) have predicted a Youngs type interference effect in the fully differential cross sections for ionization of the 3σg state of N2 for highly asymmetric collisions with one electron detector fixed at very small scattering angles (1° or 10°). The purpose of this work was to look for this interference effect at a larger scattering angle. (e, 2e) ionization measurements have been conducted from the 3σg and 2σu* states of N2 in a coplanar asymmetric geometry, where one electron emerges in the forward direction and the correlated electron is measured as a function of scattering angle. Both final-state electrons have an energy of 30 eV, and the forward scattering angle was θa = 22° relative to the incident beam direction. The theoretical prediction is that there should be a strong interference peak near 180°. The measurements were carried out from the 3σg state over a range of scattering angles from θb ~ 10° to θb ~ 170° using a magnetic angle changing spectrometer. The present experimental results for 3σg find a normal binary peak plus another peak at back angles in the vicinity of 180°. Consequently, this work supports the possibility of a strong Youngs type interference effect for small fixed scattering angles.

Low energy (e, 2e) differential cross-section measurements on the 3σg and 1πu molecular orbitals of N2

Experimental results are reported for the (e, 2e) differential ionization cross-section from the 3σg and 1πu valence molecular orbitals of molecular nitrogen N2 at incident electron energies between 25.6 and 76.7 eV. The measurements have been conducted in a coplanar symmetric geometry in an energy regime where ionization is sensitive to contributions from shape resonances and autoionizing doubly excited states. The results suggest that these additional channels may contribute to the measured cross-section. The measurements also display trends qualitatively similar to previous results at higher incident electron energies using the same geometry.

Low energy (e,2e) differential cross-section measurements on the 3sg and 1pu molecular orbitals of N2.

Experimental results are reported for the (e, 2e) differential ionization cross-section from the 3σg and 1πu valence molecular orbitals of molecular nitrogen N2 at incident electron energies between 25.6 and 76.7 eV. The measurements have been conducted in a coplanar symmetric geometry in an energy regime where ionization is sensitive to contributions from shape resonances and autoionizing doubly excited states. The results suggest that these additional channels may contribute to the measured cross-section. The measurements also display trends qualitatively similar to previous results at higher incident electron energies using the same geometry.

Super-elastic electron scattering from the laser-excited 41P1 state of calcium at low incident energy

Atomic collision parameters have been measured for electron impact excitation of calcium using the superelastic scattering method, at incident electron energies equivalent to ~10 eV and ~12 eV. The parameters Plin, L⊥ and γ were derived for the 41P1 state, and the related Stokes parameters determined. The results are compared to previously published calculations from four different theories: a relativistic distorted wave calculation, an R-matrix calculation, an R-matrix theory using B-splines and a convergent close coupling theory.

Design and characterization of an atomic beam source with narrow angular divergence for alkali-earth targets

A new atomic beam source for use in laser-based experiments is described and characterized. The physically collimated source which has been tested using calcium, produces an atomic beam with low angular divergence and narrow transverse Doppler profile, as measured using fluorescence techniques with a near resonant laser beam. The low angular divergence of the source is essential for new experiments which study super-elastic scattering of electrons from laser prepared targets within a magnetic field, since the atomic beam must pass through a narrow gap between the coil windings. The beam density for calcium is calculated to be 2.8 × 109 atoms cm−3 when the source is operated at a temperature of 1090 K. This is sufficient to produce good electron energy loss and super-elastic scattering signals, while ensuring negligible radiation trapping within the atomic beam.

Hyperspectral selection based algorithm for plant classification

The popularity of using hyperspectral imaging systems in studying and monitoring plant properties and conditions has increased lately. This increase has been driven by both financial and environmental advantages of such systems. Using a nondestructive hyperspectral imaging system improves the breeding process, increases profit, and reduces the usage of herbicide, thus reducing side effects to plants and environment. This paper is concerned with the use of hyperspectral image analysis for differentiating different plant species as well as their conditions. The main contribution of the work lies in the use of feature selection for choosing relevant, discriminant spectral information as the input to the classifier (e.g. SVM), as compared to the use of empirical spectral indices. Two independent hyperspectral datasets, captured by different instrumentations, were used in evaluation. Experimental results show significant improvements in classification accuracy with several feature selection algorithms compared to with the spectral vegetation and disease indices. The study shows that systematically selection of wavelength features can shed light on attributes that differentiate plants and their conditions.

Super-elastic electron scattering from calcium over all angles

Experimental results are reported for the Atomic Collision Parameters of calcium over all scattering angles as derived from super-elastic scattering experiments performed using a new Magnetic Angle Changing (MAC) spectrometer. Results at 55eV incident energy are compared to theoretical calculations, and new data at 65eV are reported here for the first time.

Super-elastic scattering from calcium over the complete angular range using a magnetic angle changing device

Until recently it has not been possible to determine differential cross sections for excitation of atoms by electron impact over the complete scattering geometry, due to the physical constraints of the apparatus. The invention in Manchester of the Magnetic Angle Changing (MAC) device which steers electrons to and from the interaction region has now changed this. By utilising super-elastic electron scattering from laser excited atoms within a MAC device, the differential cross sections for electron impact excitation of calcium atoms to the 41P1 state have now been determined from near 0° to beyond 180°. The methods used in these experiments are discussed, and results are presented for the Natural frame parameter L⊥ at energies of 45eV and 55eV. The results are compared to recent calculations using a distorted wave Born approximation.