A normal mixture of the stable neon isotopes, Ne²⁰ 90.51%, Ne²¹ 0.28%, Ne²² 9.21%, has been bombarded with 2.68 Mev. neutrons from the reaction H²(dn)He³ . A gridded ion chamber, with 1 litre sensitive volume, filled with neon to 6¼ atmospheres pressure, was used to detect disintegrations. Pulses from the ion chamber were amplified, arid recorded on an 18-channel kicksorter. The ground-state transition of Ne²⁰(nα)O¹⁷ was observed, with 1% counting statistics. The Q,-value was measured as -0.77±0.08 Mev., in fair agreement with previously reported results. Careful search failed to reveal any evidence of excited states in O¹⁷. A level at 0.87 Mev. is known, and one at 1.6 Mev. is suspected, but calculation of barrier penetrability for alpha particles corresponding to these levels indicates that they are not likely to be observed at the neutron energy used. A second reaction, with disintegration energy corresponding to a Q-value of +0.48±0.10 Mev. was also observed. It was not clear whether this reaction was N¹⁴(np)C¹⁴ or Ne²¹(nα)O¹⁸. This point is to be clarified by further investigation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In order to use inelastic neutron scattering to isomeric levels as a tool in evaluating nuclear strength functions, we derive the appropriate evaporation formulae; both with and without corrections for the statistical fluctuations of the compound nucleus reduced partial widths. The isomeric activity induced by inelastic neutron scattering is calculated for: In¹¹⁵, Rh¹º³, Y⁸⁹ and Nb⁹³; and is used to illustrate the effect of the fluctuation corrections and the level spin and parity assignments, on the calculated cross sections. Comparison with experimental data is used to infer probable assignments of level spins and parities for In¹¹⁵ and Rh¹º³. We also show that for any nucleus lying near an even or odd partial wave strength function resonance, the inelastic neutron scattering cross section to isomeric levels will be directly proportional to l ≥ 2 strength functions. In the examples cited above, it is the d-wave strength function; and the isomeric cross section shows the corresponding dependence on the optical model potential, being directly proportional to the strength of the imaginary part and insensitive to the real part of the potential. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The U.B.C. Hanson-McKibben type Long Counter has been modified to permit insertion of a larger diameter BF₃ proportional counter. An investigation was made to determine the effects of the modification on the neutron detection characteristics of the counter. 2.60 MeV and 3.09 MeV neutrons were obtained from the reaction D(d,n)³ He and 4.5 MeV neutrons from a standard²⁴¹AmBe source. The efficiency of the Long Counter was determined in terms of counting rate per unit neutron flux occurring at the effective centre of the counter. The count rate used was that due to the ¹ºB(n,α)⁷Li pulses from the BF₃ counter located in the centre of the Long Counter. The effective centre was defined as that point inside the counter such that the counting rate varied as the inverse square of the distance of the source from the effective centre. The following table lists the neutron energy, efficiency and distance from the front reference face of the Long Counter to the effective centre. [ Formulas omitted ] The efficiency for 4.5 MeV neutrons was found to have increased by at least an order of magnitude from that of the original Long Counter. However, the dependence of the efficiency on energy has been increased, varying by 50% over the range of energies measured. The shielding on the sides of the Long Counter was found to reduce the intrinsic efficiency for neutrons incident from the side to 0.4 of that for neutrons incident on the front face. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An Optical Model study has "been made for the elastic scattering of 4.2 MeV. neutrons from three heavy nuclei, Lead, Bismuth and Uranium. The Optical Model used included a real, imaginary, and spin-orbit potential well. Its parameters were determined from a least square fitting to the experimental scattering data available in the literature for angles from 15 to 180 degrees. The model is then used to estimate the nuclear scattering to be expected at small scattering angles. It is shown that Schwinger scattering and incident neutron polarization significantly alter the shape of the elastic cross section at angles less than 10 degrees. At 5 degrees this change is about 3%. Additional effects due to Electric Polarizability scattering are shown to be very small and not sufficient for a determination of the polarizability of the neutron from the elastic scattering data at this energy. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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by Hong Kuen Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1976. / Includes bibliographical references (leaves 112-121).

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