A new upper limit on the electron anti-neutrino rest-mass

The β-spectrum of 3H has been measured near the end-point using a Langmuir-Blodgett film of tritiated cadmium palmitate as the source. An upper limit of 35 eV at 95% C.L. has been obtained on the mass of the electron anti-neutrino. This thesis describes the preparatory developments of the Oxford neutrino mass experiment and the final measurement of the electron anti-neutrino mass. To measure the β-spectrum we used a cylindrical mirror analyser (CMA) which has an optical response of ∼ 27 eV FWHM, primarily determined by the exit slit width. The luminosity of the instrument is ∼ 1x10-2 cm2. The electrons were pre-accelerated and analysed at a fixed energy of 22.6 keV and to obtain the β-spectrum near the end-point, the source voltage was varied from -5 KV to -3.5 KV. The electrons were detected by a liquid nitrogen cooled Si(Li) detector with a resolution of ∼ 2 keV. Our background, primarily due to cosmic rays and natural radioactivity, was ∼ 8 cts hr-1 which was the same as the tritium source rate 60 eV below the end-point. The optical response was determined by Monte Carlo calculations and was checked by use of a thin band source of 169Yb at several positions in the source focal plane. Further measurements on the instrument were carried out by an electron gun which included checks on the grid wires. A tritium run was performed which lasted for ∼ 27 days. The total number of counts in the last 100 eV below the end-point is 690 cts and using the valine molecular final states spectrum, the best fit value for mv2 is -698±734 eV2. The value for the end-point E0 is 18573±10 eV which is in agreement with recent determinations. (author)