Stark broadened He I 3965 (4P-2S) has been studied experimentally using a plasma jet as a source. Integrated intensity profiles were obtained by scanning the cylindrically symmetric plasma across its width and using a spectrometer and optical multichannel analyser coupled to a magnetic tape drive system to record the profiles. The resulting data was converted to spectral line shapes as a function of plasma radius through the use of an Abel unfolding procedure carried out by a computer program. The radial dependence of the plasma temperature and density was determined and then used to match experimentally determined profiles with theoretical profiles which take the two forbidden components of the Stark broadened levels into account. Comparison of the experimental and theoretical profiles yielded good agreement. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An absolute calibration of the analysing powers of hydrogen and helium-4 has been performed at 24° and 15° lab, respectively, for protons between 200 and 520 MeV with a typical uncertainty of ±2%. In a double scattering experiment, the TRIUMF polarized proton beam was scattered, first at 15° on a liquid helium target, then a second time at 24° on a polyethylene target. The method combines the advantages of the very high analysing power of helium and the small difference in incident energies on both scatters. The analysing power of helium-4 was measured to be 0.964 ± .012, 0.792 ± .011 and 0.476 ± .018 at energies of 222, 325 and 518 MeV, respectively. The analysing power of hydrogen was found to be 0.294 ± 0.003, 0.354 ± 0.005 and 0.412 ± 0.013 at proton energies of 205, 308 and 499 MeV, respectively. This represents a great improvement over previous p-p data which was not known to better than ±6%, and so will permit a more accurate determination of nucleon-nucleon phase shifts. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis looks at a Schroedinger equation and the Born approximation.

It is well known that most liquids exhibit a tensile strength which is much smaller in magnitude than the tensile strength predicted by homogeneous nucleation theory. This lack of agreement is usually attributed to the difficulty of preparing liquid samples free from foreign gases which act as heterogeneous nucleation sites. Liquid helium occupies a unique place among liquids for tensile strength measurements because all foreign gases are frozen out at liquid helium temperatures. Furthermore, superfluid 4He should fill all crevices on solid surfaces, eliminating the chance of heterogeneous nucleation on helium vapor pockets. Despite the quantum mechanical nature of liquid helium, Becker-Doring theory of nucleation of the vapor phase from the liquid phase should be valid down to 0.3 K in 4 He, yet previous results have been in stark disagreement with the theory. In this study, a piezoelectric transducer in the form of a hemispherical shell was used to focus high-intensity ultrasound into a small volume of 4He . The transducer was gated at its resonant frequency of 566 kHz with gate widths of less than 1 msec in order to minimize the effects of transducer heating and acoustic streaming. The onset of nucleation was detected from the absorption of acoustic energy and the scattering of laser light from microscopic bubbles. A new theory for the diffraction of light from the focal zone of a spherical converging sound wave was developed to confirm calculations of the acoustic pressure amplitude at the focus of the piezoelectric transducer, calculations which were based on the acoustic power radiated into the liquid and the nonlinear absorption of sound. The experimental results were in agreement with homogeneous nucleation theory for a nucleation rate of approximately 1015 critical size bubbles/sec-cm3. This is only the third liquid for which the theoretical tensile strength has been reached and it confirms homogeneous nucleation theory over a range three times greater than any other experiment. A noticeable decrease in the magnitude of the tensile strength was noted at temperatures near the lambda transition and a hypothesis that bubbles are being nucleated heterogeneously quantized vortices is presented.

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