Novel proton detectors, ultra-cold neutron decay and electron backscatter.

摘要

The recent development of a solid deuterium super-thermal source of Ultra-Cold Neutrons (UCNs) offers orders of magnitude improvement in the density of UCNs available for high-precision studies of neutron decay. Previously impractical measurements are now statistically feasible. High-precision studies measure the CKM matrix element V_ud and look for new physics by testing the conserved vector current hypothesis, limiting the existence of right-handed and second-class currents, probing for signatures of supersymmetry and testing time reversal invariance in neutron decay.; To facilitate these experiments, we invented a 1000Å thick foil (∼10μg/cm2), which spans at least 5cm x 5cm, is extremely strong, and converts 30keV protons into an average of 10 low-energy (∼1eV) electrons. Within this thesis we describe the manufacture and test of prototype detectors, including the construction of a 50keV mini-proton accelerator. We designed three angular correlation measurements, which could utilize the proton detectors, and analyzed the limiting systematic errors of these experiments. Calculations indicate that proton detection would aid a planned 0.1% measurement of the electron-neutron angular correlation, A, by eliminating the neutron polarization systematic error. The neutrino-neutron spin angular correlation, B, could be measured to a systematics limited precision of 0.1%, a factor of four improvement over present limits. It may be possible to measure the electron-neutrino angular correlation, a, to a precision of 0.1%, a factor of 50 improvement. A cell-type apparatus, in which the proton detectors also define the UCN storage volume, could measure the time reversal violating electron neutrino neutron spin angular correlation, D, at the level of the final state effect (∼2 x 10 −5), a factor of 50 improvement over the current limit, and a factor of 5 improvement over planned measurements with cold neutrons.; In addition, we have performed original measurements of the properties of electron backscatter from beryllium, silicon and plastic scintillator and compared this data to a comprehensive analysis of published backscatter literature and three commonly used Monte Carlo electron transport codes. Our measurements confirm the validity of the Monte Carlo program PENELOPE to the 10% level in beryllium and silicon and to the 30% level in plastic scintillator at electron energies below 120keV.