Nick Jelley

Abstract:

There is an important and growing class of elementary particle detectors which are characterized by a large sensitive volume (thousands of tonnes), very low radioactive backgrounds, and rely on the emission of light for particle detection. Water Cherenkov detectors come into this category; they have a large mass of water as the sensitive medium. Particles are detected when they interact with the water and produce Cherenkov light, so detection efficiency relies on having a huge light sensitive area at the periphery of the detector. The most cost-effective way of achieving this is by placing light concentrators on large photomultiplier tubes (PMTs). This paper describes the work carried out on light concentrators for the PMTs in the Sudbury Neutrino Observatory, a 1000 tonne heavy water Cherenkov detector. We discuss the advantages of using light concentrators, summarize the optical theory of non-imaging light concentration, and describe in detail the development and manufacture of the concentrators themselves.

Abstract:

An exhaustive study has been made of the β spectrum of35S, recorded with a Si(Li) detector. The object was to identify the origin of a distortion in the35S β spectrum some 17 keV below the end point, reported over three years ago and interpreted then as evidence for a 17 keV neutrino. Measurements with different source-detector spacings and with varied collimation have shown that there is a long range curvature in the Kurie plot which is a sensitive function of configuration, but the principal origin of the distortion is energy loss in the35S sources. The35S sources, prepared by chemical adsorption of Ba35SO4 on a gold substrate, are clumped and locally thick. Electrons near the end point lose ∼0.3 keV in the source material and if this is taken into account the spectra are well fitted without any admixture of 17 keV neutrino. The source thickness has been investigated with a proton microprobe and determined from both source tilting and the yield of barium K X-rays; these studies are discussed in detail. The uncertainties in and justification for the form of the electron response function employed are also thoroughly discussed. If there is no systematic error common to the majority of 14 independent sets of35S data, the admixture of 17 keV neutrino is <10-3 (95% CL). A simple search for a kink at 150 keV in the combined data from all 14 runs yielded a limit of 1.8×10-3 (95% CL). The end point of the35S β spectrum is found to be 167.60±0.05 keV. © 1995 Springer-Verlag.

Abstract:

An exhaustive study has been made of the β spectrum of 35S, recorded with a Si(Li) detector. The object was to identify the origin of the significant distortion in the 35S β spectrum some 17 keV below the end point, reported three years ago and interpreted then as evidence for a 17 keV neutrino. A variety of different geometries were used and the collimation was also varied. Proton microprobe studies, yield of barium X-rays and source tilting have shown that the 35S sources, prepared by hemical adsorption of Ba35SO4, are clumped and locally thick, causing an energy loss ∼ 0.3 keV at 150 keV electron energy. The spectra are well fitted without any 17 keV neutrino admixture if this is taken into account: neglect of this additional energy loss mimics presence of a 17 keV neutrino and the mechanism giving rise to this mimicry is elucidated. The apparent evidence for a 17 keV neutrino in the 35S β spectrum arose primarily because the sources were assumed thin. Neglect of scattering effects and of a low energy pile-up correction also contributed to the misinterpretation. © 1994.

Abstract:

We report on two high statistics measurements of the beta spectrum of 35S. Particular emphasis is given to the sensitivity of results on details of the electron response function. In both measurements we find an 8 standard deviation from the single component neutrino spectrum 17 keV below the endpoint. The data are in strong support of earlier claims that the neutrino emitted in beta decay contains a 17 keV mass component with a mixing probability given by sin2θ=0.0084±0.0006±0.0005. © 1991.