Through the technique of adiabatic demagnetization of paramagnetic salts substances may be cooled to temperatures of the order of 0.1° K and 0.01° K. At these low temperatures the hyperfine structure interaction can produce an appreciable degree of nuclear orientation. The orientation of an assembly of radioactive nuclei may be detected by measuring the anisotropy in the emission of gamma radiation. By this method we have investigated nuclear orientation in paramagnetic, antiferromagnetic and ferromagnetic substances. We have studied the nuclear orientation of Pr¹⁴² and Yb¹⁷⁵ introduced as impurities in paramagnetic single crystals of cerium magnesium nitrate. The anisotropy of the 1.57 Mev. γ-ray of Pr¹⁴² was measured as a function of temperature in the range of 0.003° K to 1.0° K both in zero external magnetic field and in a field of 320 gauss parallel to the trigonal crystal axis. Values for the magnetic moment of Pr¹⁴² were assigned from our results for two assumed decay schemes, these are 0.11 nuclear magnetons for the spin assignments 2→[formula omitted] and 0.15 nuclear magnetons for the spin assignments [formula omitted]. Similar experiments were carried out on Yb¹⁷⁵. Measurements were made in a variety of external magnetic fields up to 700 gauss, and at temperatures as low as 0.003⁰K. No anisotropy was observed for the 396 kev γ-ray, nor for the 282 kev γ-ray. The most likely explanation for this result is that the lifetime of the γ - emitting state is about 10⁻¹⁰ seconds. This conclusion has since received independent confirmation. We have established that nuclear orientation can be produced in antiferromagnetic single crystals. We have explored some of the possibilities and features of nuclear orientation in this class of substances by investigating salts of manganese and cobalt with transition temperatures differing by an order of magnitude. Single crystals of these antiferromagnetic salts were cooled in thermal contact with potassium chrome alum and the anisotropy of the gamma radiation emitted by Co⁶⁰ and Mn⁵⁴ introduced in the lattice was observed. These measurements show that the hyperfine structure splittings in the antiferromagnetic state are comparable to those found in the paramagnetic state and give indications that nuclear spin relaxation times may be of the order of minutes and hours in antiferromagnetic materials at temperatures below 1°K. We have attempted to detect nuclear orientation arising from a possible hyperfine structure interaction at the anion in antiferromagnetic MnBr₂4 H₂O and MnCl₂4 H₂O. To detect the nuclear orientation we observed the anisotropy of the gamma radiation emitted by Br⁸² introduced into MnBr₂4 H₂O and I¹⁸¹ in both McCl₂4 H₂O and MnBr₂4 H₂O. This attempt yielded negative results. The anisotropy of the gamma radiation of Co⁶⁰ in a ferromagnetic single crystal of cobalt metal was measured before and after heat treatment of the crystal. The results before heat treatment show a significant discrepancy with the data reported by other workers and differ from those found for the heat treated crystal. A qualitative explanation of these results in terms of crystalline stacking faults in cobalt metal is presented. Work was initiated on nuclear orientation in binary ferromagnetic alloys. The nuclear orientation may arise from the hyperfine structure interactions which may exist in one or both components of a ferromagnetic binary alloy. The inter-metallic compound chosen for special study was MnBi. Although only preliminary and inconclusive results on the orientation of Mn⁵⁴ nuclei in this substance were obtained the technique adopted is briefly described. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The differential cross section for the capture of tritium by alpha particles to form Li⁷ has been measured using a tritium-zirconium target and 1.64 mev. alpha particles. The differential cross section for the gamma-ray transition to the ground state of Li⁷ was found to be 2.54± .46 x 10¯³¹ cm.² per steradian at 90° to the incident alpha beam direction. At the same energy, the ratio of the differential cross section at 90° for transitions to the first excited state to that for transitions to the ground state of Li⁷ was found to be approximately 0.40. The T(α,ɣ )Li⁷ 90° differential cross section has been measured relative to the differential cross section at 1.64 mev. using alpha particles of energies 0.515, 0.72, 0.98, 1.23, and 1.94 mev. From the smooth change of the reaction cross section with energy it can be concluded that the reaction proceeds by direct radiative capture. At all energies, the ratio of the differential cross section at 90° for transitions to the first excited state to that for transition to the ground state was approximately 0.4. Preliminary angular distribution measurements at 0° and at 90° to the incident alpha beam direction indicate that the angular distribution is not isotropic. The ratio of the yield at 0° to the yield at 90° was found to be 1.40 ± 0.37 at an alpha particle energy of 1.64 mev. Differential cross section measurements for direct radiative capture of protons by 0¹⁶ have been made relative to the cross section at 800 kev., using a solid tungsten-dioxide target and protons of energies 0.618, 09823, 1.13, 1.536, and 2.04 mev. Absolute 90° differential cross section values were based on the measurement of the 90° differential cross section for transitions to the first excited state in F¹⁷ at 800 kev. of 10.4 ± 1.3 x 10¯³² cm.² per steradian made by Robertson. The differential cross section for the gamma ray transitions to the first excited state of F¹⁷, at 90° to the incident proton beam direction, was found to vary smoothly from 0.41 x 10¯³¹ cm.² per steradian at 0.618 mev. to 11.9 x 10¯³¹ cm.² per steradian at 2.04 mev. At all energies the ratio of the differential cross section at 90° for transitions to the ground state to that for transitions to the first excited state was approximately 0.20. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Measurements of the angular distributions of the gamma-rays from the reaction N¹⁵ (p,αɤ)C¹² indicate that the 4.43 Mev excited state of C¹² has spin 2 and even (+) parity and that the 12.51 Mev and 12.95 Mev levels of O¹⁶ have spin 2 and odd (-) parity. The level in O¹⁶ at 13.24 Mev was not determined uniquely since the theoretical distributions for assignments 3- and 4+ differ only by small amounts. The angular distribution of the ground-state alpha-particles from the reaction N¹⁵(pα) C¹²has been studied for proton energies from 500 kev to 975 kev. The most striking feature of the angular distribution patterns is the strong forward-backward asymmetry which indicates interference between levels of the compound nucleus of opposite parity. The distributions can be explained most simply by assuming two levels in O¹⁶; one at 12.43 Mev excitation with spin O and even parity; the other at 13.09 Mev excitation with spin 1 and odd parity. The strong interference term can also be explained by assuming that there exist broad unresolved O+ and 2+ energy levels in this region, as suggested by recent work on the elastic scattering of alpha-particles by C¹². A fast neutron spectrometer, using the time-of-flight method, which may also be used to study reactions involving the simultaneous emission of neutrons and gamma-rays, is described. One stilbene scintillation counter is placed close to the source, the other a suitable distance away. The two counters are connected to a new type of coincidence time-sorter which converts delay-time between associated events into a pulse-amplitude distribution which may be analysed by a "kicksorter," enabling the whole range of delay times or energies to be displayed and recorded at one time. The delay time may result from the neutron flight-time following scattering in the first counter or from the time-of-flight of a neutron from the target when a coincident gamma-ray has been detected in the first counter. Typical results are presented for the reactions D(dn)He³ and Be⁹(dn i )B¹⁰. The reaction Li¹⁶ (dn ɤ)Be¹⁷ has been studied with the new type of neutron spectrometer. This spectrometer has made possible the- study of the angular correlations between the monoenergetic neutron group to the 0.43 Mev state of Be⁷ and the gamma-rays which follow neutron emission. The results of these angular correlations indicate that the first excited state of Be⁷ has spin ½ and odd parity in agreement with values found for the mirror nucleus Li⁷. The excitation function for the neutron group to the first excited state of Be⁷ has also been studied for deuteron-bombarding energies from 300 kev to 1500 kev and was found to be very similar in shape to that found by other workers for the total neutron yield from the reaction Li⁶+ d. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The pure quadrupole resonance frequencies due to B¹¹ nuclei at two different sites (denoted by E and F) in a single crystal of kernite (Na₂B₄O₇.4H₂O) have been determined both by observing the B¹¹ lines in zero external magnetic field, and also by investigating their Zeeman splitting in magnetic fields up to 30 gauss. The values obtained are 1281.1 ± 2 Kc/sec and 1287.0 ± 1 Kc/sec for the E and F sites respectively. These frequencies agree within experimental error with values predicted on the basis of studies in a high magnetic field. The agreement for the F site is much better than for the E site. Some other interaction, such as asymmetric nuclear shielding, may account for the discrepancy. Resonances also have been obtained in zero field with a polycrystalline sample. Indications of B¹⁰ resonances were observed at the frequencies expected assuming Dehmelt's value for the ratio of the quadrupole coupling constants for B¹¹ and B¹⁰. A Na²³ resonance line was observed at 1560 ± 1 Kc/sec in agreement with Proctor's result for this line. The other Na²³ resonance expected from high field work has not been observed to date. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The general case of the dependence on crystal orientation of the frequency splitting of the nuclear magnetic resonance absorption line in a single crystal sample into 21 components due to the coupling between the nuclear electric quadrupole moment and the electric field gradient in the crystal at the site of the nuclei in question is examined both theoretically and experimentally. The theoretical part of this thesis consists of a detailed exposition of the first order perturbation theory applicable to crystals with axially symmetric fields which was outlined in condensed form by Prof. R. V. Pound, and of the extension of this first order theory to non-axially symmetric cases suggested by Prof. G. M. Volkoff. The experimental part of this thesis consists of the description of an exploratory experiment proposed by the author, and performed by him, with some assistance from Mr. H. E. Petch, for the purpose of obtaining a preliminary check on the theory, and of demonstrating the feasibility of a later more carefully performed experiment. Such an experiment with an improved crystal mount has since then been performed by Mr. Petch. A single crystal of spodumene was used, and the angular dependence of the frequency splitting for Li⁷was measured as the crystal was rotated about the C-axis of its monoclinic structure. The apparatus used was an oscillating detector type of nuclear magnetic resonance spectrometer previously designed and built by Dr. T. L. Collins. The axis of rotation of the crystal was kept perpendicular to the uniform magnetic field of the spectrometer. The direction of the b-axis of the crystal inferred from this rotation was found to coincide within experimental error with, its orientation as obtained later by standard optical methods. An experiment was designed to indicate the relative magnitudes of the spin-lattice relaxation by magnetic dipole and electric quadrupole coupling is proposed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Let J’, J, J" represent the total angular momenta of the initial, intermediate, and final states of a nucleus respectively and J₁, J₂ the total angular momenta of the first and second emitted particles. Then, in terms of this notation, the following results can be found in this thesis. α – γ and γ – γ correlation functions have been calculated explicitly in terms of cos²θ for those transition schemes satisfying the following conditions: (i) J' = J +J₁, J = J" + J₂ for arbitrary J₁, J₂ = 1, 2. (ii) J' = J - J₁, J = J" - J₂ for arbitrary J₁, J₂ = 1, 2. (iii) J' = J₁ - J, J = J" +J₂ for arbitrary J₁, J₂ = 1, 2. (iv) J' = J - J₁, J = J₂ - J" for J₁ = 1, 2, arbitrary J₂. These are called the "special transitions" in the text. α – mixed γ correlation functions have been tabulated explicitly in terms of cos²θ for an α particle with total angular momentum 1 or 2 and a photon corresponding to a mixture of electric quadrupole and magnetic dipole radiation. For an α particle with total angular momentum 3 the α –mixed γ correlation functions can be obtained from a table which lists the sums of products of angular momentum coefficients appearing in these correlation functions. These correlation functions are too clumsy to be expressed explicitly In terms of cos²θ in general, however they can be fairly easily evaluated once numerical values of the angular momenta of the nuclear states are prescribed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The gamma-rays and the conversion electrons emitted following the beta decay of ¹⁶⁰Tb--> ¹⁶⁰Dy have been studied using Ge(Li) and Si(Li) detectors. The measured energies and intensities of these transitions, together with the results of gamma-gamma coincidence measurements, have allowed us to construct the decay scheme of ¹⁶⁰Dy. Four new transitions , namely 97.7, 111.8, 148.5 and 320.5 kev, are placed in the decay scheme on the basis of energy fit and coincidence results. The angular momentum and the parity of the excited states of this nucleus have been deduced as confirmations of previous assignments. The energies and the electromagnetic properties of these states are compared to the predictions of the theory of a rigid asymmetric rotor. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis reports the HAPPEX measurement of the parity-violating asymmetry for longitudinally polarized electrons elastically scattered from protons in a liquid hydrogen target. The measurement was carried out in Hall A at Thomas Jefferson National Accelerator Facility using a beam energy E = 3 GeV and scattering angle ⟨&thetas;lab⟩ = 6°. The asymmetry is sensitive to the weak neutral form factors from which we extract the strange quark electric and magnetic form factors ([special characters omitted] and [special characters omitted]) of the proton. The measurement was conducted during two data-taking periods in 2004 and 2005. This thesis describes the methods for controlling the helicity-correlated beam asymmetries and the analysis of the raw asymmetry. The parity-violating asymmetry has been measured to be APV = -1.14 ± 0.24 (stat) ± 0.06 (syst) ppm at ⟨Q 2⟩ = 0.099 GeV2 (2004), and APV = -1.58 ± 0.12 (stat) ± 0.04 (syst) ppm at ⟨Q 2⟩ = 0.109 GeV2 (2005). The strange quark form factors extracted from the asymmetry are [special characters omitted] + 0.080[special characters omitted] = 0.030 ± 0.025 (stat) ± 0.006 (syst) ± 0.012 (FF) (2004) and [special characters omitted] + 0.088[special characters omitted] = 0.007 ± 0.011 (stat) ± 0.004 (syst) ± 0.005 (FF) (2005). These results place the most precise constraints on the strange quark form factors and indicate little strange dynamics in the proton.

The technique of Virtual Compton Scattering (VCS) has become a valuable tool in the study of nucleon structure. In this thesis we describe the use of VCS to measure generalized Polarizabilities (GPs) of the proton. The GPs are fundamental properties of the proton and their precise measurement will set limits on models of nucleon structure. The VCS experiment was performed at the MIT-Bates Linear Accelerator Center at fixed virtual photon three-momentum of qi = 240 MeV/c and virtual photon polarization ϵ = 0.9, corresponding to a four-momentum transfer squared of Q 2 ∼ 0.06 GeV2/c2. At this low momentum transfer the measured coincident cross sections are proportional to response functions PLL-PTT/ϵ and PLT. The response functions are linear combinations of the GPs.

Polarized nuclear Compton scattering on a proton target provides a test of low energy QCD. The beam-target asymmetries of a circularly polarized Bremsstrahlung photon beam on a transversely polarized butanol target (Σ2 x) and on a longitudinally polarized butanol target (Σ 2z), and the beam asymmetry of a linearly polarized Bremsstrahlung beam on an unpolarized hydrogen target (Σ 3) are sensitive to the proton spin polarizabilities, third order terms in the energy expansion of the Compton scattering amplitude. This experiment consisted of the Σ2x measurement, both just below and above two-pion threshold.