No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

A vacuum phototriodes (VPT) are the photodetectors used in the endcaps of the Electromagnetic Calorimeter of the Compact Muon Solenoid experiment at the Large Hadron Collider at CERN. Software, interfacing with the commercial program “SIMION 3D” was written to allow the simulation of the temporal response of the VPT. Applying Ramo’s Theorem enabled the time development of the VPT signal to be calculated. In order to validate the simulations, experiments were performed using a 60 ps laser pulses (λ = 435 nm) incident on a number of VPT samples. The simulation reproduced the basic features of the operation of the VPT such as gain vs. voltage, and gain vs. magnetic field strength. The simulation also confirmed the need for a fine mesh anode to achieve a useful gain when operating at high magnetic fields. The experimental work represents the first measurements of the time response of a VPT when excited with a very fast light pulse. Both the simulated and experimental response from the VPT were observed to be fast (few ns) and quite complex. Discrepancies between the simulated and experimental signals were partially explained by a SPICE model which includes the VPT interelectrode capacitances and lead inductances. We conclude that the VPT are fast photodetectors with an intrinsic response time of order 1ns for this geometry. The VPT high-voltage filter cards, which operate at 1 kV and in an intense radiation environment, are critical components. A number of commercial off-the-shelf high voltage resistors and capacitors were evaluated at gamma doses up to 345 kGy. No significant change in value or leakage current was observed. As a result of these studies we were able to demonstrate that these inexpensive components were suitable for use in the 3100 filter cards subsequently installed in the CMS apparatus.

The fission yields of ten nuclides ((^84)3r, (^91)Sr, (^93)Y, (^99)Eo. (^105)Ru, (^112)Pd, (^113)Ag, (^129)Sb, (^132)Te and (^143)Ce) from the fission of (^231)Pa by 14 Mev neutrons have been determined relative to the fission yield of (^97)Zr. The protactinium (as oxide) in thin uniform adherent layers (about 1 mg. cm(^-2) lightly covered with gold (about 0.5 mg. cm(^-2) was supported an circular discs of platinum foil (2 cm. diameter). Recoiling fission products were collected in thin catcher foils of various substances (aluminium, polystyrene or copper) the choice depending on the elements to be recovered. Preliminary experiments using target discs prepared in a similar way from uranium-238 (oxide) showed that good agreement is obtained between relative yields measured by this method and by irradiation of bulk samples of uranium. The relative yields from (^231)Pa have been corrected to total chain yields by application of the equal charge displacement hypothesis and converted to absolute yields by imposing the condition that the sum of the yields of all the fission products must be 200%. The value of ū was, taken to be 4.25; this was found to give a good fit of reflected points on the mass yield curve. Mien chain yields are plotted against mass number a mass-yield curve is obtained showing three maxima at mass numbers 93, 114 and 135. The yields at the maxima are 6.80%, 2.48% and 6.80% and the peak widths at half height are 14, 17.5 and 14 mass units.

The Faddeev equations for three particles are given a basis of representation according to the group Su(3). The usefulness of this representation is investigated by application to neutron-deuteron scattering.

A presentation of the formation and properties of the positronium atom are given in the early part of the thesis from a more or less historical viewpoint. This is followed by the major part of the thesis dealing with the scattering of orthopositronium by helium atoms in two approximations. The first is the static approximation including exchange and the elastic scattering cross sections and the corresponding phase shifts are calculated. The second calculation allows for the long range van der Waal's forces acting between the neutral atoms. The evaluation of the long range potential in the adiabatic approximation using a Rayleigh-Ritz method is presented and the elastic cross sections and phase shifts are re-computed with the potential included in the analysis. Little difference is found in the values from the two approximations - except at very low energies. A survey is presented of the quenching phenomena exhibited by positronium in gases and the quenching of orthopositronium in helium is studied in detail. Measurements of the quenching rate of orthopositronium in helium determine the parameter Ƶeff the effective number of electrons per atom in a singlet state relative to the positron. This number may be calculated from the wave function for the orthopositronium-helium atom system. Since we have computed this wave-function in two approximations for the scattering problem we have utilised the results to calculate Ƶeff. At thermal energies we find Ƶeff = 0.037 and Ƶeff = 0.048 in the static exchange case and long range polarisation case respectively. These results are considerably smaller than the most recent, measured values of Ƶeff ~ 0.1-0.25, and the possible reasons for the discrepancy are discussed. The presence of a resonance in positron-atom scattering can be viewed as the attachment of a positron to the atom or as the binding of a positronium atom to the positive ion. The process is likely to be important in various scattering problems and the simplest case, that of positron attachment to a hydrogen atom, is considered here. The method used is that of the projection operator in conjunction with a Rayleigh-Ritz variational technique. The evidence for a positron-hydrogen atom bound state is presented as a result of the calculation and comparison made with the results of other workers.