Super-elastic scattering measurements were taken from calcium using the spectrometer described in this thesis. Calcium atoms were excited from the 41S0 ground state to the 41P1 excited state using a high resolution continuous wave laser set to a wavelength of 423 nm. A beam of electrons with a well defined energy was directed at the laser excited calcium atoms. The excited state was then described by a set of atomic collision parameters P_lin, gamma and L_perp, found from measuring scattered electrons as a function of scattering angle and energy. The scattering chamber was held at a pressure of 3x10^-7 mbar. A resistively heated oven operating at 800 degrees celsius produced a well collimated calcium atomic beam containing the calcium atoms. The electron gun generated a beam of electrons of well defined momentum, whose energy could be changed from ~5 eV to over 100 eV. At energies less than 20 eV the rate of super-elastic electrons was very low, and so modifications were made to the spectrometer to automate data collection for long operating times without the need for user intervention. A new digitally controlled DC voltage supply was constructed to deliver the correct potentials to the electron-optical elements in the spectrometer. An internal microcontroller enabled supply voltages to be programmed either using the front panel or via an attached computer for automatic optimisation of spectrometer voltages using a simplex algorithm. New data was collected for the collision parameters over the full accessible angular range from 25--140 degrees, at energies of 8, 10 and 65 eV. The data at 8 and 10 eV was taken so as to resolve differences between theoretical models at low energies. Comparisons were made with a relativistic distorted wave calculation, an R-matrix calculation, an R-matrix calculation using B-splines and a convergent close coupling theory. A 2 eV discrepancy was identified in the measured electron energy which was thought to be due to stray fields in the chamber. With this considered, convergent close coupling predictions were found to be in excellent agreement with the experimental data.
|Date of Award||31 Dec 2012|
- The University of Manchester
|Supervisor||Andrew Murray (Supervisor)|