The University of British Columbia Van De Graaff generator was used to study the resonant capture of α-particles by Li⁷ to form B¹¹ in the three excited states at 8.92 Mev, 9.19 Mev and 9.28 Mev. B¹¹, being in the middle of the p shell, has been rather extensively studied in the past decade with considerable disagreement between results obtained from the Li⁷ (α,γ) B¹¹ and B¹⁰ (d, p) B¹¹ reactions. With seven particles outside the closed shell theoretical calculations are difficult and the calculations of Kurath have been limited to the negative parity states only. The energies, intensities and angular distributions of the γ-rays which de-excite the three states of B¹¹ have been studied. It was found that the 9.28 and 9.19 Mev states cascade through the 6.76 Mev and 4.46 Mev states and negligibly, if at all, through the 6.8l Mev state. The γ-ray widths for many of the γ-ray transitions have been obtained and compared with the average radiative widths reported by Wilkinson. On the basis of the angular distribution results spins and parities have been assigned to some of the B¹¹ levels up to an excitation of 9.28 Mev. The results are in good agreement with recent work on the B¹⁰ (d, p) B¹¹ reaction. Tentative speculations concerning the nature of some of the transitions have been made, although no detailed comparison with theory seems possible at the moment. The assignments based upon the present work are [assignments omitted]. The assignment of 5/2⁻ to the 4.46 Mev state was well known previously. For the 8.92 Mev state the present work favours 5/2⁺ and in this is supported by recent results from the stripping reaction B¹⁰0 (d, p) B¹¹ which suggests positive parity for the level; however, the present results do not rule out the possibility of 5/2⁻ and formation of the state by d-wave α-particles. A three crystal pair spectrometer was used to determine accurately the energies of the γ-rays from Zn⁶⁵ and Na²². The energies of these γ-rays are above 1.022 Mev and since the accurately known rest mass of the pair electrons is subtracted from each incident photon by pair production, a measurement of the small remaining kinetic energy of the pair electrons with moderate accuracy gives the energy of the γ-rays with considerably greater percentage accuracy. The present results are, Zn⁶⁵ γ-ray Energy 1.1124 ± 0.0019 Mev Na²² γ-ray Energy 1.2736 ± 0.0018 Mev The pulse height spectrum and absolute efficiency of a ZnS-lucite fast neutron counter, consisting of a number of thin sheets of lucite coated with zinc sulphide and sandwiched together to form a rectangular block, was investigated using neutrons with energies from 280 Kev. to 16 Mev and γ-rays with energies of 1 Mev and 6 Mev. At a bias setting where the absolute neutron detection efficiency varied from 0.15% for 2 Mev neutrons to 0.3% for 4 Mev neutrons, the 6 Mev γ-ray sensitivity was less by a factor of 10⁹. Using this counter the yield and angular distribution of neutrons was measured from thick and thin heavy ice targets bombarded with protons below the D (p, n) 2p threshold. The yield and the angular distribution data fit very well with theoretical results calculated by Y.I. Ssu on the hypothesis that neutrons are produced by deuterons, scattered in the target by incident protons, which, then, collided with other target deuterons producing D (d, n)He³ neutrons. A semi-empirical method has been developed to calculate the γ-ray detection efficiency of NaI (TlI) crystals for γ-rays from 0.5 Mev to 12 Mev. The results were compared with the experimental efficiencies at .5 Mev, 1.25 Mev, 4 Mev, 6 Mev and 12 Mev, independently determined by absolute methods at .5 Mev, 1.25 Mev and 6 Mev and by relative comparison at 4 Mev and 12 Mev. The agreement is within 5% up to 6 Mev. The effects of scattered γ-rays by lead shielding was also investigated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Polyhedral boranes and carboranes have acquired their popularity for constructing meso and nano-size structures for an array of applications from pharmaceuticals to material science. These three-dimensional boranes range from 4 to 22 boron atom per molecules with delocalized bonding analogous to aromatic compounds. The unique vibrational spectroscopy of the BH function allows for possible application of these species to bioimaging. Silver nanoparticles functionalized with ortho-carboranes have been reported for bioimaging using Surface-enhanced Raman scattering (SERS). The silver nanoparticles were functionalized with antibodies specific to cancer cell receptors. Bonding thiol-substituted carboranes to these particles allowed for observation of enhanced Raman signals as the imaging mode. Here, attempts to synthesize second generation carborane molecules with additional Raman-active group such as nitrile were conducted. Hybrid diblock copolymers have the ability to self-assemble in different morphological patterns depending on the type and ratio of monomers and the compatibilities in various solvents. Linear hybrid diblock copolymers were synthesized by ring-opening metathesis polymerization (ROMP) reactions with norbornenyl-based decaborane and various amounts of norbornene and norbornenyl-ester derivative monomers. Their self-assembly behaviour in various solvents were characterized by NMR, TGA, DSC, and SEM. P(norbornene)60-b-p(norbornenyl-decaborane)40 polymers showed lamellar morphology patterns when slowly evaporated from chloroform. Based on results and the SEM images, a few of these diblock copolymers were used as ceramic precursors and pyrolyzed to elevated temperatures forming boron nitride and boron carbonitride nano-ordered ceramics

The effect of impurity concentration on the photoconductive spectrum of boron-doped silicon at helium temperatures was investigated. Photoconductivity was observed for excitations of the bound hole into the impurity excited states. The photoconductivity in this region depends strongly on impurity concentration and was interpreted as being conduction through excited state impurity bands. Two bands were observed to form, with excited states 3 and 4 in the boron spectrum forming one band and state 2 forming the other. A qualitative description of the mobility in the impurity bands was obtained using Baltensperger's theory and the additional assumption that the holes are scattered by "randomness" in the impurity array. Photoconductivity of holes in the valence band was also measured in order to obtain lifetimes and capture cross sections. Assuming the mobility in this region to be determined by neutral impurity scattering, the hole lifetime was estimated to be ~ 10⁻⁹ sec and the capture cross section of ionized boron ~ 3 x 10⁻¹⁰ cm². Assuming similar lifetimes for the holes in impurity bands, the peak mobility in band 3 and 4 was found to be ~ 150 cm² /volt-sec. The d.c. characteristics of the various samples, while at low temperature and exposed to room temperature radiation, were measured during the course of this investigation. All samples were observed to have a non-linear dependence between the current and applied field, terminated by a non-destructive low field breakdown. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In boron doped silicon, optical excitation of bound holes from the ground state to the various excited states of the neutral acceptor impurity leads to an absorption line spectrum. By applying an external strain, the degeneracies of the acceptor ground state and the four lowest "observable" excited states were determined and were found to only partially agree with theory (Schechter 1962). By applying a uniform electric field to compensated samples, the "Stark effect" for the acceptor states was observed. The Stark shift of the excited states is second order in the field as predicted by Kohn (1957) from symmetry considerations. The Stark broadening of the acceptor absorption lines was attributed to an unresolved partial removal of degeneracy of the excited states. The absorption line broadening mechanisms (phonon, dislocation, concentration, ionized impurity) were determined from new halfwidth measurements, which corrected an earlier study (Colbow 1963). The ionized impurity broadening is caused by the screened Coulomb "internal fields" of nearby ionized impurities which are present in uncompensated samples at temperatures greater than 50°K. A new theory of this broadening contribution (Cheng 1966) is in reasonable agreement with experiment; the earlier theory of the same effect (Colbow 1963) is shown to be inadequate. The effects of compensation on the boron absorption spectrum were measured and attributed to the unscreened Coulomb fields of ionized impurities present because of the compensation. The properties of a weak new absorption line which appeared in the compensated spectrum are described. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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