Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The efficiency of NaI(T1) scintillation counters for the detection of gamma rays is discussed and experimentally determined. Experimental efficiencies, based upon the number of counts above a bias equal to one-half the gamma ray energy and a solid angle defined to the crystal effective centre, for a three-inch-diameter by three-inch long (3 x 3) crystal are given for gamma ray energies of 0.51, 1.275 and 6.14 MeV. Gamma ray spectra at 1.275 and 6.14 MeV are extrapolated to zero energy in order to compare theoretical efficiencies, based upon the integrated primary absorption, with the experimental results. These results show that, with experience, one can expect accuracy to better than 5% at these energies. Tables are given of the theoretical efficiency for 3x3, 2¾ x 4½ and 5x4 crystals for several gamma ray energies and source-to-counter distances of from 0.1 cm to 1 m. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The cross sections for the 0¹⁶ (p,ɤ) F¹⁷ transitions to the ground d-state and to an excited s-state of F¹⁷ have been measured in this laboratory and elsewhere, at different energies in the range from about 100 kev to 2.5 Mev incident proton energy. In this thesis an attempt is made to calculate these cross sections at several energies in the above range on the hypothesis of direct proton capture. Similar calculations have been made at the California Institute of Technology but have not been published. The standard formula for the cross section for an electric dipole transition from an incident p state to a final d-or s-state has been used. The matrix element appearing in this formula was split up into an angular part which can be evaluated exactly, and a radial integral which has to be calculated approximately. In the case of transitions to the excited s-state numerical calculations using tabulated wave-functions were made at center of mass proton energies of 150, 378 and 940 kev. The cross section at 150 kev was also calculated by the saddle point method using WKB approximations to the wave-functions, but this method was found to break down at energies above 200 kev due to difficulties with the WKB functions. Reasonably good agreement between the two methods was obtained at 150 kev. For transitions to the ground d-state the numerical method could not be used since tabulations of the required d-state wave-function are unavailable. Calculations were made only by the saddle point method at center of mass proton energies of 150, 378 and 500 kev. This method can not be used above 500 kev. The calculated ratio of [formula omitted] ≈ 9 at energies of 150 and 378 kev, and the absolute values of the cross sections agree reasonably well with the experimentally observed values. Some discrepancies are noted between these calculations and those carried out at the California Institute of Technology which are very briefly referred to in a preprint of an experimental paper, but a detailed comparison was not possible, as the details of those calculations are unavailable. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two boron trifluoride proportional counters, one containing normal isotopic boron and the other boron enriched to 96% B¹⁰, have been irradiated with 4.87-Mev neutrons from the D +.D reaction. In addition to the reactions B¹⁰(n,α)Li⁷and B¹⁰(n,α)Li⁷* with Q-values of 2.79 Mev and 2.31 Mev respectively, two other reactions have been observed, (i) F¹⁹(n,α)N¹⁶and F¹⁹ (n, α)N¹⁶* with Q-values of -1.43±0.15 Mev and -1.77±0.15 Mev and (ii) either B¹⁰ (n,p)Be¹⁰ or B¹⁰ (n,t)Be⁸ with a Q-value of +0.35±0.20 Mev. Due to the presence of these two reactions, the analysis of complex fast neutron spectra by the use of such counters is not feasible. The Q-values for reaction (i) yield a value of the N¹⁶ mass of 16.01110±.00020 MU. Neutrons from a pulsed deuterium beam impinging on a tritium target were used to bombard a boron trifluoride proportional counter containing the normal ratio of B¹¹ to B¹⁰. The half-life of the activity and the energy of the particles emitted indicated that they were due to the immediate breakup of Be⁸ into two alphas after the 0.89 sec. beta decay of the Li⁸ formed by the B¹¹ (n,α)Li⁸ reaction. The process was found to have a cross section of the order of 10 millibarns for 14-Mev neutrons. The angular distribution of the non-resonant gamma radiation from the proton bombardment of C¹² has been measured and found to obey the relation:- I(ɵ)α0.02±.02 + sin²ɵ, for a proton energy of 1,580 kev. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Detailed calculations have been carried out which indicate that the small-angle scattering of fast neutrons by lead depends on the polarization, or spin orientation, of the neutrons. When the scattering of neutrons whose spin vectors point upward is observed in the horizontal plane, more neutrons should be found scattered to the right than to the left. For completely polarized 3.1 Mev neutrons, the theory predicts a maximum "right to left" intensity ratio of 14.5:1 at a scattering angle of 0.5°, the ratio decreasing to 1.6:1 at 5°, and approaching unity rapidly as the scattering angle increases. An attempt to detect this effect with neutrons from the reaction D(d,n)He³ failed because the degree of neutron collimation attainable, while satisfactory for most scattering experiments, was insufficient to permit investigation of neutron scattering at very small angles. A three crystal pair spectrometer has been used to investigate the complex gamma ray spectrum arising from bombardment of B¹⁰with deuterons of several energies between 0.8 and 2.2 Mev. Gamma rays of energy 4.46 ≠.04, 4.75 ≠ .03, 5.03 ≠ .09, 5.35 ≠ .05, 6.52 ≠ .05, 6.78 ≠ .07, 7.29 ≠ .04, 8.27 ≠ .09, and 8.87 ≠ .02 Mev have been assigned to transitions in B¹¹ and C¹¹, with excellent agreement in almost all cases with the energy level schemes proposed from other experiments. The excitation curves of three of the gamma rays have been found to rise smoothly between bombarding energies of 0.8 and 2.2 Mev, indicating that the reactions B¹⁰(d,p [symbol omitted])B¹¹l and B¹⁰(d, n [symbol omitted])C¹¹ are primarily of non-resonant character, at least in this energy region. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A technique is described for improving wood fibre web strength by copolymerization of a hydrocarbon drying oil (CTLA Polymer) within hand-sheets made from pure and admixed forms of high yield chemical (sulfite and sulfate) and groundwood fibres. Oil polymerization can be initiated successfully by prolonged thermal treatment at 145°C, as well as by the novel method of low dosage gamma-ray irradiation. The treatment strengthens inter-fibre bonding. Evidence for copolymerization was sought through assessment of tensile and related strength data on variously treated standard handsheets. Effectiveness of the polymerization on pulp types investigated as initiated by heat and low dosage irradiation is strongly related to surface colloidal and basic physical and mechanical properties of the fibres. Maximum strength parameters were obtained with oil saturated sulfite and groundwood handsheets following polymerization by thermal treatment. Copolymerization efficiency by irradiation, on the other hand, is estimated as 73% for sulfite, 65% for groundwood and 50% for kraft handsheets. Effectiveness of oil polymerization by irradiation was found to be proportional to dosages up to 10⁵rad. As anticipated, limit of strength improvement was not set entirely by intrinsic fibre strength, but was also influenced by surface colloidal properties of the fibres. Blends made from chemical-groundwood fibre mixtures behaved more or less proportional to individual pulp strengths and extent of blending. Copolymerized sulfite-groundwood blends at equal proportions approximated the tensile strength of similar kraft papers suggesting better economy with kraft fibres when papers of limited strength are produced. All other strength parameters (elastic modulus, tensile strain and tensile energy absorption) followed similar trends, or if different were of aid in explaining certain phenomena characteristic to treated fibre webs. The presence of graft copolymer could not be conclusively proven, since both the copolymer and oil homopolymer are insoluble in the usual organic solvents. A dual character of the oil polymer was demonstrated with glass filterpaper and highly purified commercial cellulose fibres. Effectiveness of oil polymerization in highly lignified mechanical pulps was greatly depressed by mild sodium chlorite treatment, although the strength and bonding capacity of such fibres increased considerably. This was taken as direct evidence for the possibility of a lignin-CTLA Polymer copolymer system. Site of chemical reaction has not been described, although means for assessment of such information are suggested. The study proves the usefulness of gamma irradiation as energy source for the copolyerization of drying oils in handsheets as replacement for the prolonged thermal treatment hitherto used by the hardboard industry. Added advantages of irradiation processed copolymerized papers are less discoloration, especially with high lignin content pulps, and lower elastic modulus, a factor clearly objectionable for some paper uses. / Forestry, Faculty of / Graduate

The first part of this thesis describes measurements made with medical radium sources to determine the ratio of the exposure in a large (essentially infinite) water "phantom" to the exposure at the same point in air, i.e., to determine the fractional transmission in an "infinite" water phantom. The fractional transmission was measured as a function of the distance between the radium sources and the measuring instrument. The radium used was sealed in platinum containers which absorbed the primary alpha and beta rays from the radium so that the exposures were due to gamma rays only. All measurements were made with small air-filled ionization chambers with plexiglass walls. Ionization currents were measured with these chambers in water and in air. The corrections which were required to determine the ratio of exposure in water to exposure in air from these measurements and the preliminary experiments necessary to determine the required corrections are described in the thesis. The fractional transmission through water is shown graphically as a function of the distance between source and point of measurement. Also, the relationship is described by an empirical equation. The curve drawn fits the experimental points obtained under a variety of conditions of measurement within the experimental error of 1/2 to 1%. The second part of the thesis describes measurements of ionization currents made with an experimental set-up in which the ionization chamber was at a fixed distance vertically below the radium and the whole assembly was moved relative to the surface of a water phantom. From measurements made with the radium above the surface, in the surface and below the surface of the water, it was possible (a) to obtain data which could be compared with the results of Part I and (b) to obtain correction factors which could be applied to the results of Part I to correct for reduced scatter when the radium was in the surface, rather than well immersed in water. The results of the present experiment are compared with those of previous workers. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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