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

The excitation function for the reaction ⁵⁶F(p,y)⁵⁷Co has been measured from 1200 - 3000 KeV proton energy using enriched ⁵⁶Fe targets. Gamma-ray spectra were measured using Ge(Li) and NaI(T£) detectors. The resonance strength, 10^, has been determined for the studied resonances. Gamma-ray angular distributions were measured using NaI(T£) detectors. In the energy region between 1240 and 1272 KeV, the gamma-ray angular distributions were measured using the Ge(Li) detector. Gamma-ray angular distributions have been measured for resonances corresponding to excitation energies in ⁵⁷Co of 7253, 7267, 7272, 7598, 7622, 7641, 7647, 7925, 8192 and 8450 KeV. The-branching ratios, spins and parities of the resonance levels as well as some of the low-lying states in ⁵⁷Co have been established. The reaction Q-value derived from these measurements is Q = 6027 ± 3 KeV. From the gamma-ray spectra and angular distributions which have been studied the levels at 7253, 7267 and 7272 KeV excitation in ⁵⁷Co are identified as the split analogue of the T = 5/2 corresponding to the first bound state in the parent nucleus ⁵⁷Fe at 14 KeV. The group of levels at 7622, 7641 and 7647 KeV excitation in ⁵⁷Co are believed to form the split analogue of the 367 KeV bound state in 57Fe. The level at 8450 KeV excitation is tentatively identified as the isobaric analogue state of T = 5/2 corresponding to the 1196 KeV bound state in ⁵⁷Fe. The absence of the isobaric analogue resonance corresponding to the ground state in ⁵⁷Fe is discussed as a result of the present study. A coulomb displacement energy for ⁵⁷Co - ⁵⁷Fe of 8876 ± 6 KeV is deduced from these measurements. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Employing the semiclassical form of the density operator theory of dynamic processes, the transient nuclear spin behavior is analyzed for a range of motional parameters of significance for biological interpretations of nuclear magnetic relaxation data. Only relaxation which results solely from the reorientational modulation of the various spin couplings is considered. The bath correlation functions which enter into the theory are assumed to be completely characterized by two unique motional constants (a dynamic symmetric top approximation). The effects of slow, anisotropic modulation of spin-spin and spin-molecule interactions on T₁, T₂, T₁ ratios, T₂ ratios, and Overhauser enhancements are discussed. It is rationalized that in general, any parameter dependent upon the spectral density at zero frequency is independent of the magnitude of the asymmetry in the motion. Likewise, parameters independent of the near-zero frequency spectral component often are sensitive solely to the magnitude of the motional asymmetry. These considerations are extended to multispin systems and spin systems where nuclear magnetic relaxation proceeds by competing interactions characterized by nonvanishing interference or cross-correlation functions. In general, one cannot define unambigiously a unique T₁ or T₂ in such a case as the predicted decay is multi-(non)exponential. The spin behavior in such a situation is thoroughly analyzed and many intriguing predictions are presented. It is seen that the failure of a white spectral density approximation or a single exponential decay of the molecular correlation function often leads to predictions of extreme nonexponentiality of the magnetization decay. While the results of these calculations are of general interest, they are especially pertinent for those concerned with biological applications of NMR. Finally, the initial concepts are extended to a discussion of the potentially powerful Perturbed Angular Correlation experiment where it is shown that the coincidence counting rate will in general be influenced by anisotropic modulation of the quadrupolar perturbation. It is emphasized that a conventional interpretation of relaxation data is impregnated with hidden, "extreme-narrowed", reasoning. Extensive figures are provided which not only facilitate experimental application of the calculations, but also provide striking evidence for the caution which must be exercised in any biodynamical interpretation of nuclear spin relaxation. / Science, Faculty of / Chemistry, Department of / Graduate

The antiferromagnetic and spin-flop phases of MnCl‧4H₂O have been investigated by observing the nuclear orxentatxon of ⁵⁴Mn in that material. The sublattice magnetizations in the absence of an external field were found to lie in a direction between the a and c crystal axes at an angle of 11.5° ± 3.5° to the c axis. The field dependence of the spin configuration in the spin-flop state indicates that second order anisotropy is significant in this system. The molecular fields were determined by combining the results of this work with other measurements of the-critical fields (Rives and Benedict, 1975). The results are: the exchange field is 11.05 ± 0.21 KOe; the biaxial single ion anisotropy fields are 0.75 ± 0.22 KOe and 2.35 ± 0.23 KOe along the a* and b axes respectively; the second order anisotropy field is 1.45 ± 0.19 KOe and the anisotropic exchange field is 0.1 ± 0.3 KOe. The spin-flop transition region was found to be adequately described by a 'domain' structure in which regions of antiferromagnetic phase and regions of spin-flop phase co-exist in the crystal. Measurements were made of the temperature dependence of the spin-flop transition field and, contrary to the extrapolated results of Rives and Benedict (1975) , the spin-flop field was found to decrease with decreasing temperature from 0.3K to 0.15K. If there is a minimum in the transition field it must occur at lower temperatures. The cooling of the MnCl‧4H₂O crystal which was held in contact with a copper heat sink by Apiezon N grease was fitted to the relation Q = kA (T₁ⁿ-T₂ⁿ) where T₁ and T₂ are the temperatures of the crystal and copper heat sink respectively, and A is the contact area. For n = 4 the value obtained for the constant k is (8.2 ± 1.9) x 10³ ergK⁻⁴ sec⁻¹ cm⁻². Nuclear orientation experiments were also performed on the systems ¹⁰³Ru-Fe and ⁵⁹Fe-Fe. The gamma-ray anisotropies for these systems (at temperatures of 10 and 15 mK, respectively) were very small; however, it was possible to determine limits for the magnitudes of the nuclear magnetic moments of the active nuclei. The ¹⁰³Ru moment was found to be greater than 0.15uN and the ⁵⁹Fe moment was found to be less than 0.9uN. J.E. Rives and V. Benedict, Phys. Rev. B12, 1908 (1975). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The (π, πn) reaction is studied theoretically, the specific case examined being 0¹⁶(π⁺, π⁺p)N¹⁵. Calculations of the differential cross sections for 1P ½ and 1P 3/2 protons are made at various incident pion energies. The remaining kinematic variables are specified by a geometry which emphasizes the behavior of the two-body pion nucleon interaction. The aim is to examine the influence of the nucleus on the two-body interaction. In particular, the influences of Pauli exclusion of the nucleon, the off-shell effect, and the effective polarization of the nucleon are examined. The computation is performed using the factorized distorted wave impulse approximation. By evaluating the distorted wave matrix element in coordinate space the localization of the knock-out reaction in the nucleus is determined. The Pauli exclusion of the nucleon is found to have the largest influence on the differential cross section at incident pion energies of 116 MeV. At higher energies the knock-out reaction occurs at the extreme edge of the nucleus and the effect of Pauli exclusion is minimal. At lower energies, the two-body interaction itself is less sensitive to Pauli exclusion. Off-shell effects were found to be very small. The polarization of the proton was found to have a large influence on the cross sections. Furthermore, it is noted that comparing the cross sections for 1P ½ and 1P3/2 protons will indicate the effective polarization of the proton in the nucleus. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The E2 cross section for the ¹²C(p,Ύ₀)¹³N reaction has been measured from 10 MeV to 17 MeV in the laboratory system by bombarding an enriched carbon-12 target with beams of polarized protons. A 10 in. φ x 10 in, Nal(Tl) detector with a plastic anti-coincidence shield was used to detect the gamma rays. The total E2 capture cross sections were of the order of 0.2 ybarns and no resonance effects were observed. The amount of the E2 energy-weighted sum rule depleted in this energy range is (10.3 ± 4.0)%. Calculations based on a direct semi-direct capture model provide a good description of the experimental results by including only direct E2 capture and direct plus collective E1 capture. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Foi desenvolvido, implementado e testado um formalismo que permite descrever propriedades nucleares em regimes de deformação fora do equilíbrio, utilizando o método Macroscópico-Microscópico em associação com o Método Semimicroscópico Combinado. Esse formalismo foi utilizado para a interpretação e elucidação de alguns problemas abertos como as estruturas na seção de choque de fotofissão do 237.ANTPOT Np, distribuições angulares de fotofissão do 239.ANTPOT. Pu, e a concentração de transições M1 no 237.ANTPOT Np e 239.ANTPOT. Pu em baixas energias. Também, foram interpretadas informações experimentais referentes aos estados isoméricos do 237.ANTPOT Pu e 239.ANTPOT. Pu. Com relação ao potencial preditivo do formalismo, foram identificados os possíveis candidatos (spin e paridade) a estados isoméricos no 241.ANTPOT Np, bem como foi calculada também pela primeira vez a distribuição de momentos de nêutrons para o 239.ANTPOT Np fora da deformação de equilíbrio. / It was developed, implemented and tested a formalism suitable to the description of nuclear properties at non equilibrium deformations regime, by using the Macroscopic-Microscopic method in association with the Combined Semimicroscopic Method. This formalism was used for the interpretation and elucidation of some open problems, as the structures in the 237Np photofission cross section, photofission angular distributions of 239Pu, and the concentrations of low-energy Ml transitions in 237Np and 239Pu. Also, experimental information on 237Pu and 239Pu isomeric states was interpreted. Concerning the prediction potentialities of the formalism, were identified possible candidates (spin and parity) for the 241Pu isomeric states, as well as the 239Pu neutron momentum distributions, at non equilibrium deformation, was also calculated for the first time.

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.