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The purpose of this research is to design and optimize the performance of a unique, inexpensive 6Li neutron-capture pulse-mode ion chamber (LiPMIC) for neutron detection that overcomes the fill-gas contamination stemming from outgas of detector components. This research also provides a demonstration of performance of LiPMICs. Simulations performed with GARFIELD, a drift-chamber simulation package for ion transport in an electrostatic field, have shown that argon-methane mixtures of fill-gas allow maintenance of electron drift velocity through a surprisingly wide range of fill-gas content. During the design stage of LiPMIC development, the thicknesses of lithium metallization layer, the neutron energy conversion site of the detector, and the thickness of neutron moderator, the high-density polyethylene body, are optimized through analytical and MCNPX calculations. Also, a methodology of obtaining the suitable combination of electric field strength, electron drift velocity, and fill-gas mixtures has been tested and simulated using argon-methane gas mixtures. The LiPMIC is shown to have comparable efficiency to 3He proportional counters at a fraction of cost. Six-month long baseline measurements of overall detector performance shows there is a 3% reduction in total counts for 252Cf sources, which provides a good indicator for the longevity of the detector.

No description available.

<p> The relative cumulative yields of krypton and xenon isotopes from the thermal neutron fission of 237Np and Np238 and from the fast neutron fission of Np237 have been measured by means of a mass spectrometer. These are the first fission yield results for 238Np, and the first for 237Np at thermal neutron energies. The results are compared with those from other fissioning nuclides.</p> <p> Independent yields of the shielded nuclides 80Br, 82Br, 128I, and 130I from the thermal neutron fission of 235U, 233U, 239Pu, and 238Np have been determined by mass spectrometric analyses of the krypton and xenon β-decay products. The results are discussed in terms of conventional charge distribution theories, and also in terms of neutron emission effects.</p> / Thesis / Doctor of Philosophy (PhD)

The ranges and stragglings of fission fragments from the thermal neutron fission of U-235 have been measured. Particular attention was given to the preparation of very thin uranium sources, the design of a well collimated recoil system and the preparation of the fragment catcher. The ranges and range distributions in aluminum of fission products of mass numbers 95, 140, 141 and 147 have been obtained. The range values obtained agree with previous determinations within the experimental error. The refined techniques developed in this work have enabled differential range distributions to be obtained which are more precise than any previous determinations. / Thesis / Master of Science (MSc)

Isotopic abundances of the elements barium, cerium, neodymium, samarium and europium formed in the thermal neutron fission of have been studied with a mass spectrometer. Suitable analyses of very young and old fission products have made possible the normaliza­tion of the isotopic abundances of each of these elements through iso­baric nuclides. In this manner the relative cumulative fission yield of every fission chain from mass 137 to 154 has been obtained. These yields, together with previously reported relative yields of masses 131 to 137 when normalized to total 100%, give the absolute cumulative yield of all the significant heavy fragment chains. The origin of the fine structure found in this mass yield distribution is discussed. It has been found that all fine structure can be explained in terms of a smooth primary mass-yield curve and a simple neutron distribution both of which are compared with experimental data from other laboratories. / Thesis / Doctor of Philosophy (PhD)

<p> Thermal neutron capture studies have been made of the odd-odd nuclei, 20F, 24Na, 28Al, 32P, 36Cl and 40K. The gamma ray spectra have been studied using a Ge(Li) pair spectrometer and revised decay schemes are presented for these nuclei. The Q-values and gamma ray multiplicities have been obtained for the reactions studied. The average partial widths for primary Ml and El transitions have been calculated for the six nuclei and compared with the theoretical estimates. The features of the capture gamma ray spectra are discussed and it is observed that for the six nuclei studied, the total intensity in the spectrum above the energy of 0.3 times the Q-value is nearly the same (~1.4 photons/capture).</p> / Thesis / Doctor of Philosophy (PhD)

<p> An attempt was made to measure the yields of the stable cadmium isotopes produced in the thermal-neutron fission of 233U and 235U using a solid-source mass spectrometer. The results for 235U fission indicate that there is structure in the mass-yield curve for the region studied which takes the form of a depression around masses 112-114. The origin of this structure is discussed in terms of the various mechanisms which have been proposed to explain the nature of the mass distribution in the symmetric region.</p> <p> The 233U study was unsuccessful because of the experimental difficulties encountered, primarily the interference from terrestrial cadmium and the low recovery of the fission products. </p> / Thesis / Master of Science (MSc)

<p> Fine structure in thermal neutron (n, α) reactions has been studied for 149Sm, 147Sm, and 143Nd by means of an instrument called an electrostatic particle guide. This device, which was designed to eliminate the problems of background and low energy tailing in (n,α) spectroscopy, is described in detail. Alpha decay has been observed from thermal neutron capture states to levels in the daughter nucleus to greater than 2 MeV excitation. Cross sections and alpha energies are presented for each transition and as well, the alpha decay schemes for 146Nd, 144Nd, 140Ce. Experimental reduced widths have been calculated and are discussed in terms of Mang's theory of alpha decay. Evidence is presented for the (n, γα) process in the 143Nd (n,α) 140Ce reaction. </p> / Thesis / Doctor of Philosophy (PhD)

This thesis deals with the description of $\gamma-$ray deexcitation of neutron resonances produced in thermal neutron capture below neutron separation energy. A subject of this thesis is obtaining information on absolute value of \textit{photon strength function} (PSF) achieved from primary transitions in thermal neutron capture. The aim is to map and bring new information on absolute value of photon strength function (PSF) in $^{156}$Gd and $^{158}$Gd. The method which was used in this thesis can lead to refusion of several models of PSF a level density. Powered by TCPDF (www.tcpdf.org)