Apresentamos nesse trabalho as medidas de seção de choque absoluta de eletrodesintegração e da taxa de produção da fotodesintegração para a reação 232Th(e,n) 231Th. A análise dos resultados de eletrodesintegração foi realizada pelo método dos fótons com a finalidade de determinar as multipolaridades das transições nucleares envolvidas nessa reação. As medidas foram realizadas no Laboratório do Acelerador Linear do Instituto de Física da USP, tendo se estendido de 7,5 a 26 MeV no caso das medidas de eletrodesintegração e de 20 a 25 MeV no caso das de fotodesintegração. Essas medidas foram feitas para testar a compatibilidade de nossas medidas com as realizadas com o uso de fótons monocromáticos, utilizadas na análise dos resultados de eletrodesintegração. Mostramos que a eletrodesintegração por emissão de um nêutron no tório se processa exclusivamente através de transições de dipolo elétrico. Nossos dados excluem uma contribuição das transições de quadrupolo elétrico maior do que 0,7% da intensidade das transições de dipolo elétrico. A nossa sugestão sobre o decaimento da ressonância isoescalar de quadrupolo elétrico é que este deve se processar preferencialmente pelo canal de fissão, comportamento similar ao do 238U. / The results of the absolute electro disintegration cross section as well the photodisintegration yield of the reaction 232Th(e,n) 231Th, are reported. We used the virtual photon formalism in the analysis of the electro disintegration data in order to establish the multipolarities of the nuclear transitions involved in the reaction. The measurements have been performed using the electron beam of the Linear Accelerator of the IFUSP, ranging from 7,5 to 26 MeV for the electro disintegration and from 20 to 25 MeV for the photodisintegration data. The photodisintegration yield has been measured to check the agreement between our data and those obtained with monochromatic photons, which are used in the analysis of the electro disintegration data. We show that electro disintegration by one neutron emission in thorium can be explained by a E1 process. Our data set up an upper limit to the E2 contribution of 0,7% of the E1 strength. We suggest that the isoescalar giant electric quadrupole resonance (GQR) decays dominantly through the fission channel, as in the 238U case.

The states populated in the beta decay of As⁷⁶ and Ga⁷² were investigated by measuring the gamma-ray transitions in Se⁷⁶ and Ge⁷² using 25cc., 33cc. and 60cc. true-coaxial Gs(Li) detectors. A dual-parameter data collection system was constructed to study gamma-gamma coincidence. Options were provided to enable corrections of the undesired contributions from Compton background and chance coincidences. Its performance was shown to be very reliable and effective. Coincidence experiments were performed with the 25cc. and 33cc. Ge(Li) detectors using the conventional fast-slow system in the case of As⁷⁶ and the dual-parameter system was used in coincidence work on Ga⁷² employing the 33cc. and 60cc. detectors. The energies and intensities of measured gamma-rays were determined. The level schemes were constructed and the log ft and parity were deduced. The collective aspects of certain states were discussed and some comparisons with the pure vibrational and two other collective models were attempted.

We present a computer program tailored to the calculation of single particle inclusive reaction observables and two models for the incorporation of absorptive type corrections in the triple Regge region which do not require the inclusion of free parameters. We conclude that the first model we present is not sufficiently realistic and so requires the derivation of the second, more sophisticated model in the Regge-eikonal approximation. Both models were used to examine the observables for pseudo-scalar meson production via charge exchange.

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<p> Space radiation exposure to astronauts will need to be carefully monitored on future missions beyond low earth orbit. NASA has proposed an updated radiation risk framework that takes into account a significant amount of radiobiological and heavy ion track structure information. These models require active radiation detection systems to measure the energy and ion charge Z. </p><p> However, current radiation detection systems cannot meet these demands. The aim of this study was to investigate several topics that will help next generation detection systems meet the NASA objectives. Specifically, this work investigates the required spatial resolution to avoid coincident events in a detector, the effects of energy straggling and conversion of dose from silicon to water, and methods for ion identification (Z) using machine learning. </p><p> The main results of this dissertation are as follows: 1. Spatial resolution on the order of 0.1 cm is required for active space radiation detectors to have high confidence in identifying individual particles, i.e., to eliminate coincident events. 2. Energy resolution of a detector system will be limited by energy straggling effects and the conversion of dose in silicon to dose in biological tissue (water). 3. Machine learning methods show strong promise for identification of ion charge (Z) with simple detector designs.</p><p>

The first measurement of muon catalyzed dt fusion (dtμ→⁴He+n+μ⁻) in solid HD at ~ 3 K has been performed. The theory describing the formation of the [(dtμ)pee] muonic molecule from the resonant reaction tμ+HD → [(dtμ)pee], a key process in the dt fusion cycle, can now be tested against the experimental results. Using an experimental technique which employs solid layers of hydrogen isotopes, the energy of molecular formation is determined via time of flight, and dt fusion time spectra in solid HD have been measured. The theory describing the resonant formation of the dtμ muonic molecule is compared to the experimental results through Monte Carlo simulations. The energy dependent molecular formation rates calculated for HD at 3 K have been employed in the Monte Carlo with the resultant simulated fusion time spectra in fair agreement with the experimental results. / Graduate

The statefunctions of massless particles described by a tensor field are classified by expressing them in terms of the eigenstates of the operator of angular momentum. The general tensor statefunction can also be separated into functions of different parity. By identifying the graviton as a special case obtained by imposing certain auxiliary conditions, familiar from the classical theory of gravitation, one arrives at a multipole analysis of single graviton state-functions. Employing standard composition methods one can use these results to arrive at selection rules governing the decay of objects into two or more gravitons. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A theoretical study of the reaction D(pγ)He³ is made in an attempt to explain the experimental data for the reaction obtained by Fowler et al. (1949), Wilkinson (1952), Griffiths and Warren (1955) and Griffiths, Larson and Robertson (1961). The angular distribution of the emitted gamma radiation, measured with respect to the incident proton beam, is predominantly proportional to sin²θ. Measurements of the polarization of the radiation by Wilkinson (1952) indicate that the sin²θ component is electric dipole radiation. In addition there is a small, possibly isotropic, component. The proportion of the total yield coming from the smaller 'isotropic' component is 0.035 at a proton energy of 1 Mev, and this proportion increases with decreasing proton energy. The sin²θ component has been interpreted by Griffiths and Warren as coming from an electric dipole transition from an initial state of a P-wave proton (L = 1, L₂ =0) and ³S deuteron to the ²S ground state of He³. This interpretation is supported by the present calculations. They also suggest that the smaller 'isotropic* component could be either a magnetic dipole transition of S-wave protons to the ²S state of He³ or an electric dipole transition involving spin-orbit coupling. In this present work the cross-sections are examined for all possible channels which might conceivably contribute to the reaction. The channels considered are 1. electric dipole transitions for a. P-wave protons to the ²S state b. P-wave protons to the ⁴D state c. F-wave protons to the ⁴D state 2. electric quadrupole transitions for a. S-wave protons to the ⁴D state b. D-wave protons to the ²S state 3. the magnetic dipole transition for S-wave protons to the ²S state. Three-body wave functions are constructed, following Verde (1950) and Derrick and Blatt (1956), making use of the symmetry properties in spin space, isotypic spin space and in ordinary space. In addition to the states of total isotropic spin T = ½ considered by Derrick and Blatt the states of total isotopic spin T = 3/2 are included. The radiation matrix elements for the above channels are calculated and are expressed in terms of integrals over the three internal coordinates. These radial integrals are estimated by using very simple radial functions which are valid outside the range of the nuclear forces and which also disregard coulomb forces. The cross-sections depend on the unknown amplitudes and relative signs of the various possible symmetry states. Therefore the size, although not the angular dependance or the general energy dependance, of the cross-sections can be used only as an order-of-magnitude estimate. By comparison of the size, angular distribution and energy dependance of the calculated cross-sections with the experimental data it is shown conclusively that the sin²θ component of the radiation comes from the electric dipole transition of P-wave protons to the ²S state of He³. The smaller 'isotropic' component of the radiation comes from either (a) an electric dipole transition of P-wave protons to the ⁴D state, giving an angular distribution proportional to 1 – (1/7)cos²θ, or (b) a magnetic dipole transition of S-wave protons to the ²S state, giving an isotropic angular distribution. The observed energy dependence of the relative yield of the small component suggests the interpretation in terms of the magnetic dipole transition. The cross-sections of the other transitions examined are too small to explain the experimental results. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This work was undertaken to verify the results of Pennington and Petch. They studied the effect of quadrupole perturbation on the n. m .r. spectrum of B¹¹ in inderite and from these studies found the values of quadrupole coupling constants and asymmetry parameters of the crystalline electrostatic fields for different sites of B¹¹. This data has been used in the present work to predict the "pure" quadrupole resonance frequencies. The resonance frequency for the M site has been experimentally measured. The result is within 1% of the predicted value. The improvements made in the spectrometers are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate