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Extension of the T /sub z/ = -3/2 series of beta-delayed proton precursors in the fp shell. [excitation energy, transition rates, log FT values, B strength, J,. pi. ]

Description: Beta-delayed proton studies of the T /sub z/ = -3/2, A = 4n+1 series were undertaken to obtain high resolution low background spectra of /sup 29/S and to extend the series into the fp shell with the observation of /sup 53/Ni, /sup 57/Zn, and /sup 61/Ge. Development of a pulsed-beam system in which large detection geometries were obtained was crucial in characterizing the latter nuclei due to low production cross sections (50 to 90 nb) for the /sup 40/Ca(heavy ion, 3n) reactions. Spectroscopic studies of the beta-delayed proton decay of /sup 29/S have yielded branching ratios and log ft values for 21 proton unbound levels in /sup 29/P. Comparisons of excitation energies of these levels and ..beta..-decay transition rates feeding them are made to recent shell model predictions. Indications of possible isospin mixing with the lowest T = 3/2 state in /sup 29/P or the presence of a collective Gamow-Teller transition as predicted by the gross theory of ..beta..-decay are indicated by enhanced transition rates to T = 1/2 states located within 300 keV of the isobaric analog state. Comparing the ft values for ..beta../sup +/-decay of /sup 29/S to the mirror ..beta../sup -/-decay of /sup 29/Al resulted in (ft)/sup +//(ft)/sup -/ = 1.04+-0.07, indicating good mirror symmetry. Exploiting the unique signature of delayed proton emission, the decays of several nuclei in the unknown neutron-deficient region of the fp shell were characterized.The following precursors and delayed proton groups were observed. /sup 53/Ni - Ep(c.m.) = 1.94+-.05 MeV, T1/2 = 45+-15 ms; /sup 57/Zn - Ep(c.m.) = 1.95+-.05, 2.58+-.05, and 4.65+-.05 MeV, T1/2 = 40+-10 ms; /sup 61/Ge - Ep(c.m.) = 3.15+-.07 MeV, T1/2 = 40+-15 ms. All of these proton groups (except the 2.58 MeV group of /sup 57/Zn) are attributed to the decay of the lowest T = 3/2 ...
Date: December 1, 1978
Creator: Vieira, D.J.
Partner: UNT Libraries Government Documents Department

Large fragment production calculations in relativistic heavy-ion reactions. [Abrasion-ablation model, cross sections, fireball and firestreak models]

Description: The abrasion-ablation model is briefly described and then used to calculate cross sections for production of large fragments resulting from target or projectile fragmentation in high-energy heavy-ion collisions. The number of nucleons removed from the colliding nuclei in the abrasion stage and the excitation energy of the remaining fragments (primary products) are calculated with the geometrical picture of two different models: the fireball and the firestreak models. The charge-to-mass dispersion of the primary products is calculated using either a model which assumes no correlations between proton and neutron positions inside the nucleus (hypergeometric distribution) or a model based upon the zero-point oscillations of the giant dipole resonance (NUC-GDR). Standard Weisskopf--Ewing statistical evaporation calculations are used to calculate final product distributions. Results of the pure abrasion-ablation model are compared with a variety of experimental data. The comparisons show the insufficiency of the extra-surface energy term used in the abrasion calculations. A frictional spectator interaction (FSI) is introduced which increases the average excitation energy of the primary products, and improves the results considerably in most cases. Agreements and discrepancies of the results calculated with the different theoretical assumptions and the experimental data are studied. Of particular relevance is the possibility of observing nuclear ground-state correlations.Results of the recently completed experiment of fragmentation of 213 Mev/A /sup 40/Ar projectiles are studied and shown not to be capable of answering that question unambiguously. But predictions for the upcoming /sup 48/Ca fragmentation experiment clearly show the possibility of observing correlation effects. 78 references.
Date: December 1, 1978
Creator: Seixas de Oliveira, L.F.
Partner: UNT Libraries Government Documents Department

Non-equilibrium statistical mechanical approach for describing heavy ion reactions

Description: With the availability of heavy-ion projectiles (A > 4) at low to intermediate energies (4 < E/A < 10), products showing various stages of relaxation for certain macroscopic variables (center-of-mass energy, orbital angular momentum, etc.) were produced in various reactions. The distributions for these macroscopic variables showed a correlation between the stage of relaxation reached and the net amount of mass transfer which had occurred in the reaction. There was also evidence that there was an asymmetry in the number of net transfers necessary for complete relaxation between stripping and pickup reactions. A model for describing the time-evolution of these reactions was formulated, the keystone of which is a master-equation approach for describing the time-dependence of the mass-asymmetry. This, coupled with deterministic equations of motion for the other macroscopic coordinates in the reaction lead to calculated distributions which provide an excellent qualitative description of these reactions, and, in some cases, quantitatively reproduce the experimental data quite well. 61 figures, 2 tables.
Date: November 1, 1978
Creator: Sventek, J.S.
Partner: UNT Libraries Government Documents Department

Differential production cross sections of multiply charged fragments in 800 MeV proton-induced spallation of carbon, aluminum, and nickel

Description: Differential production cross sections for multiply charged fragments from 800-MeV proton-induced spallation of /sup 12/C, /sup 27/Al, and natural Ni were measured at 30 and 90 degrees. The ion fragments were identified by use of time-of-flight, ..delta..E--E detector telescope capable of complete particle identification for energies as low as .25 MeV/nucleon. The very short ranges of the particles of interest required the construction of very thin detectors with minimal deadlayer material. The time-pick-off detectors and gas ionization chamber developed are unique, and represent the state-of-the-art in fast timing for time-of-flight measurements and in construction of thin detectors. The resolutions achieved allowed the cross sections of /sup 3/He, /sup 4/He, /sup 6/Li, /sup 7/Li, /sup 7/Be, /sup 9/Be, /sup 10/Be, /sup 10/B, /sup 11/B, /sup 11/C, /sup 12/C, and /sup 13/C to be determined, along with those of nitrogen and oxygen without isotope separation. The cross sections were found to have weak angular dependence. Consequently, pseudo cross sections were calculated from the 90/sup 0/ data by integrating the differential cross sections from 0 to 25 MeV for each product and multiplying by 4..pi... Pseudo theoretical cross sections were similarly calculated from theoretical differential cross sections. These differential cross sections were calculated by use of a Monte Carlo computer code which incorporated the cascade-evaporation model of high-energy nuclear reactions. Implications are drawn for modifications of the model. The results suggest reducing the transparency of the struck nucleus to pions produced in the cascade stage of the reaction model in order that a higher excitation energy be left for the evaporation stage. Also, there is some evidence that evaporations of nuclear aggregates more massive than /sup 4/He occur. Inclusion of such evaporations should improve the model. 82 figures, 1 table.
Date: September 1, 1978
Creator: Luckstead, S.C.
Partner: UNT Libraries Government Documents Department

Correlations and total muon capture rates. [Primakoff effect, isospin, shell model]

Description: The total muon capture rate for s-wave muons can be accounted for by the Primakoff expression which gives the dependence of this rate on the mass number A and the proton number Z of the absorbing nucleus. The expression is a simple three parameter phenomenological formulae which accurately describes these rates from light weight nuclei to heavy nuclei. These parameters relate to the isospin structure of the squared isovector operator which appears in a sum rule approach to such rates. A microscopic analysis of the parameters appearing in the capture rate expression is presented in the light of recent developments concerning photonuclear reactions. A shell model analysis is given and it is found that the predictions of the unperturbed shell model and also Hartree-Fock theory are in complete disagreement with the data. Considerable improvement is obtained when long range correlations are included in the ground state wave function of the absorbing nucleus. 21 references.
Date: August 1, 1978
Creator: Mekjian, A.
Partner: UNT Libraries Government Documents Department

Central collisions of relativistic nuclei. [Cross sections, partial data analysis, yield 250 MeV/nucleon to 2. 1 GeV/nucleon]

Description: New data for relativistic heavy ion collisions are presented for the emitted protons and pions, and for the average multiplicities and angular correlations of the charged particles. Comparisons with several different theoretical approaches are made including the nuclear firestreak model. It appears that there is a group of nucleons with randomized motion and high temperature. The stage is reached where one is beginning to look for effects due to the expansion of a compressed region. 16 references.
Date: July 1, 1978
Creator: Poskanzer, A.M.
Partner: UNT Libraries Government Documents Department

Equilibration in the reaction of 175 and 252 MeV /sup 20/Ne with /sup 197/Au. [Energy, element, and angular distributions]

Description: The highly inelastic nuclear reaction of /sup 197/Au with /sup 20/Ne at 175 and 252 MeV laboratory energies is studied. Energy-, elemental-, and angular- distributions for atomic numbers 5 to 30 (175 MeV) or 34 (252 MeV) are presented. The means and widths of the kinetic energy spectra for detected elements are compared with a theoretical calculation. The calculation postulates thermalization of the incident projectile kinetic energy, and includes one sha(e-vibrational degree of freedom and rigid rotation of the reaction complex. The effect of particle evaporation is considered. Good agreement of the expurimental mean energies with the theory is obtained. Poorer agreement of the kinetic energy widths with the theory may be due to a low-temperature quantal effect. The relative elemental yields are analyzed for their degree of equilibration, based on a model of diffusive nucleon exchange as described by the master equation. A similar degree of equilibration is observed for both reaction energies. The absolute elemental yields are reproduced qualitatively by employing an advanced diffusion code, coupled with calculation of the subsequent fission of heavy reaction products, including the compound nucleus. The angular distributions are analyzed with a simple model, to estimate the reaction lifetime of selected elements.
Date: June 1, 1978
Creator: Moulton, J.B.
Partner: UNT Libraries Government Documents Department

Pion-nucleus scattering in the isobar formalism. [isobar - hole model]

Description: Lectures on the isobar-hole model for pion reactions include the isobar as an explicit degree of freedom and the connection with a purely pion and nucleon system, the formalism and its relation to the pion optical potential, the extended schematic model for pion scattering, a simple spinless s-wave model, application to pion-oxygen 16 scattering and comparison with elastic scattering data. In this way the extent is shown to which microscopic treatment of the many-body dynamics explains the data and the extent to which additional physical input is required. Another test is the various inelastic processes. Inclusive reactions are briefly discussed. 37 references (JFP)
Date: June 1, 1978
Creator: Moniz, E J
Partner: UNT Libraries Government Documents Department

Three-body molecular description of /sup 9/Be. I. Born--Oppenheimer approximation. [Three-cluster model, Born-Oppenheimer method]

Description: A three-cluster model composed of two ..cap alpha..-particles and a neutron is used to describe the low-lying spectrum of /sup 9/Be. The resulting three-body problem is solved by the Born-Oppenheimer method for different two-body n-..cap alpha.. and ..cap alpha..-..cap alpha.. potentials. Molecular energy curves are obtained that explain the binding mechanisms leading to both the ground state and first excited state of /sup 9/Be. 27 references.
Date: June 1978
Creator: Fonseca, A. C.; Revai, J. & Matveenko, A.
Partner: UNT Libraries Government Documents Department

Heavy ion clusters in the TDHF approximation. [112 to 384 MeV, cross sections]

Description: The time-dependent Hartree-Fock method is used to produce time dependent graphical representations of the density contours of the binary cluster in the reactions /sup 14/N(112 MeV) + /sup 12/C, /sup 16/O(384 MeV) + /sup 16/O, and /sup 20/Ne(164 MeV) + /sup 58/Ni. Alpha clustering and multipole shape vibrations are seen. Predictions for d sigma/d..cap omega.., d sigma/dZ/sub f/, and d/sup 2/sigma(E/sub f/)d..cap omega..dE/sub f/vertical/sub z//sub f/ are obtained in the case of /sup 14/N + /sup 12/C and found to agree well with available experimental data. It is concluded that cluster dynamics play an essential role in heavy-ion reactions.
Date: May 24, 1978
Creator: Cusson, R.Y.; Gomez del Campo, J. & Meldner, H.W.
Partner: UNT Libraries Government Documents Department

Scattering of 0. 8 GeV protons from lead-208, carbon-12, and carbon-13. [Angular distributions, J,. pi. ]

Description: The first angular distributions for elastic scattering of 0.8 GeV protons from /sup 12/C, /sup 13/C, and /sup 208/Pb, obtained using the High Resolution Spectrometer (HRS) at the Clinton P. Anderson Meson Physics Facility (LAMPF) at the Los Alamos Scientific Laboratory, are presented. A brief description is given of an analysis of the elastic scattering data in terms of the Kerman-McManus-Thaler formalism with spin dependent nucleon-nucleon amplitudes. The data are shown to be sensitive to details of proton and neutron matter distributions. The proton distributions as determined by electromagnetic probes are used along with the available spin independent nucleon-nucleon scattering amplitudes. Preliminary analyzing power measurements are used to fix the spin-dependent amplitudes. The neutron distributions are adjusted to fit the data. Inelastic scattering of protons, exciting the first two states of /sup 208/Pb and many states in /sup 13/C and /sup 12/C, is analyzed in terms of the distorted wave Born approximation (DWBA). The model of coupling a /sup 1///sub 2//sup -/ neutron to the excited states of /sup 12/C is found to explain some of the /sup 13/C excited states. Using this model a new assignment of J/sup ..pi../ = /sup 7///sub 2//sup +/ has been made to the 11.9 MeV state of /sup 13/C. A coupled channels calculation using a 0/sup +/, 2/sup +/, 4/sup +/ rotational band is found to explain the 4/sup +/, 14.1-MeV state in /sup 12/C.
Date: May 1, 1978
Creator: Blanpied, G.S.
Partner: UNT Libraries Government Documents Department

Study of the role of complete fusion in the reaction of /sup 48/Ca and /sup 56/Fe with cerium and terbium. [Cross sections, yield curves, tables]

Description: /sup 48/Ca and /sup 56/Fe beams from the Super HILAC accelerator were used to irradiate thick metal foils of cerium and terbium. Product gamma ray activities were detected offline and individual products were identified by half-life, gamma ray energy and gamma ray abundances. The production cross sections were iteratively fit to charge and mass dispersions to allow correction for parent decay and calculation of mass yields. From the mass yield curves contributions from quasielastic transfer, deep inelastic transfer and complete fusion reaction mechanisms were interred. Complete fusion was made up on contributions from both evaporation residue and fusion-fission products for the /sup 48/Ca induced reactions. However, only fusion-fission products were detected in the /sup 56/Fe induced reactions. Critical angular momenta for fusion were found to be 82 +- 8 h for /sup 48/Ca + /sup 159/Tb and 34 +- 5 h for /sup 56/Fe + /sup 140/Ce, which can be compared with 53 +- 8 h for /sup 12/C + /sup 197/Au (Natowitz, 1970) and 86 +- 5 h for /sup 40/Ar + /sup 165/Ho (Hanappe, 1973). All of these reactions lead to essentially the same compound nucleus and seem to show the dramatic decline in complete fusion for heavy ions larger than /sup 40/Ar. The prediction of this decline was found to be beyond the model calculations of Bass and the critical distance approach of Glas and Mosel.
Date: May 1, 1978
Creator: Morrissey, D.J.
Partner: UNT Libraries Government Documents Department

Decay of mass-separated /sup 118/Ag to levels in /sup 118/Cd

Description: A study of the gamma-ray de-excitation following the beta decay of /sup 118/Ag using the TRISTAN on-line isotope separator is reported. Gamma-ray singles, gamma-gamma coincidence, and gamma-ray multiscale measurements were made using Ge(Li) detectors. A total of 52 gamma rays were observed in the decay of /sup 118/Ag. Thirty-eight of these were placed in a level scheme for /sup 118/Cd consisting of 20 excited states up to 3382 keV. Gamma-ray multiscale measurements indicated that /sup 118/Ag has an isomeric state at 128 keV with a half-life of 2.0 +- 0.2 seconds. The ground state half-life is 3.76 +- 0.15 seconds. The /sup 118/Ag decay scheme is compared with a previous decay study. The level scheme systematics are discussed and compared with recent collective model calculations.
Date: April 1, 1978
Creator: Margetan, D. R.
Partner: UNT Libraries Government Documents Department

Particle production in relativistic heavy ion collisions. [Multiple scattering theory, production cross sections, nuclear models]

Description: Within the framework of multiple scattering theory both the conventional limiting case of independent multiple collisions of nucleons and the multiple scattering of collective degrees of freedom are presented and contrasted. Dramatically different predictions may be obtained for particle production in relativistic nucleon-nucleus and nucleus-nucleus collisions. First is studied the pion multiplicity distributions to uncover evidence for a coherent-collective mechanism. Attention is then focused on potentially more conclusive tests--subthreshold (in the nucleon-nucleon kinematics) production of massive particles: anti p, K/sup -/, psi/J and W, as examples. Evidence for a collective mechanism is found by examining subthreshold anti p production data in particle-nucleus collisions and contrasting with results from the IMC model including realistic Fermi motion. As perhaps the leading candidate for a coherent-collective mechanism the coherent tube model is specifically adopted to explain these data since it has been successful in high energy particle-nucleus collisions.
Date: April 1, 1978
Creator: Vary, J.P.
Partner: UNT Libraries Government Documents Department

Realistic nuclear shell theory and the doubly-magic /sup 132/Sn region. [Hamiltonians, review]

Description: Realistic nuclear shell theory, the union of the nuclear shell model with realistic nucleon-nucleon potentials through Brueckner theory, is outlined. A brief historical review of some key developments from 1962 to 1977 is presented. This includes recent applications which indicate that careful calculation of realistic Hamiltonians through low orders will provide descriptions of nuclear behavior which achieve reasonable accord with experiment. Currently available theoretical Hamiltonians are described and results for nuclei from oxygen to lead are discussed. It is argued that experimental results in the /sup 132/Sn region would be especially valuable for testing the next generation of realistic nuclear shell theory Hamiltonians.
Date: March 1, 1978
Creator: Vary, J. P.
Partner: UNT Libraries Government Documents Department

Coupled channel alpha decay theory for even- and odd-mass light and heavy nuclei

Description: Four major approaches to the theoretical calculation of alpha decay widths were examined for light and heavy, even- and odd-mass nuclei. Application of the microscopic shell model rate theory as well as macroscopic models utilizing the coupled-channel formalism were studied. Use of the R-matrix and S-matrix theories have been applied in order to overcome problems involving dependency on the connection radius and nuclear potential parameters of the relative and absolute alpha decay widths. 105 references. (JFP)
Date: February 1, 1978
Creator: Rauscher, E.A.
Partner: UNT Libraries Government Documents Department

Nuclear data development and shield design for neutrons below 60 MeV

Description: A nuclear data library was created for medium-energy-neutron-transport calculations. The 60-group library includes P/sub 5/ cross sections in standard LASL format for H, B, C, N, O, Si, Fe, and W. The 60-group structure was chosen from a sensitivity analysis of a thick iron shield calculated with a 50-MeV deuteron-on-beryllium neutron source spectrum and a 121-group cross-section set. The library combines processed ENDF/B-IV cross-section data below 20 MeV and higher-energy cross-section parameters calculated with the intranuclear-cascade and evaporation model. A 6-group version of the library is used in the design of a shield-collimator unit for fast-neutron radiotherapy. While the shield is specific for the 50-MeV d/sup +/--Be neutron source presently used in cancer therapy at Texas A and M University, the cross sections and methods developed are applicable to the problems of medium-energy-neutron shielding in general. 28 figures, 21 tables, 132 references.
Date: February 1, 1978
Creator: Wilson, W.B.
Partner: UNT Libraries Government Documents Department

1/2/sup +/. -->. 1/2/sup -/ beta decay of /sup 19/Ne and the parity nonconserving NN force

Description: A branching ratio of (1.20 +- 0.20) x 10/sup -4/ is obtained for the ..beta../sup +/ decay of /sup 19/Ne to the 110 keV 1/2/sup -/ level of /sup 19/F. This transition (presumably dominated by the ..delta..J/sup ..pi../ = 0/sup -/ axial charge operator) provides a crucial test of wavefunctions used in interpreting the parity mixing of the ground and 110 keV levels of /sup 19/F. These wavefunctions, which yield a parity mixing larger than that observed experimentally, also predict too large a ..beta../sup +/ decay rate.
Date: January 1, 1978
Creator: Adelberger, E.G.; Hindi, M.M.; Hoyle, C.D.; Swanson, H.E. & Von Lintig, R.D.
Partner: UNT Libraries Government Documents Department

Collective motions and band structures in A = 60 to 80, even--even nuclei. [Review]

Description: Evidence for and the theoretical understanding of the richness of the collective band structures as illustrated by at least seven bands seen in levels of /sup 68/Ge, /sup 74/Se are reviewed. The experimental data on even-even nuclei in the A = 60 to 80 region have now revealed a wide variety of collective bands with different structures. The even parity yrast cascades alone are seen to involve multiple collective structures. In addition to the ground-state bands, strong evidence is presented for both neutron and proton rotation-aligned bands built on the same orbital, (g/sub 9///sub 2/)/sup 2/, in one nucleus. Several other nuclei also show the crossing of RAL bands around the 8/sup +/ level in this region. Evidence continues to be strong experimentally and supported theoretically that there is some type of shape transition and shape coexistence occurring now both in the Ge and Se isotopes around N = 40. Negative parity bands with odd and even spins with very collective nature are seen in several nuclei to high spin. These bands seem best understood in the RAL model. Very collective bands with ..delta..I = 1, extending from 2/sup +/ to 9/sup +/ are seen with no rotation-alignment. The purity of these bands and their persistence to such high spin establish them as an independent collective mode which is best described as a gamma-type vibration band in a deformed nucleus. In addition to all of the above bands, new bands are seen in /sup 76/Kr and /sup 74/Se. The nature of these bands is not presently known. 56 references. (JFP)
Date: January 1, 1978
Creator: Hamilton, J.H.; Robinson, R.L. & Ramayya, A.V.
Partner: UNT Libraries Government Documents Department

Comparison of alpha decay and alpha transfer reactions in the lead region. [R matrix theory, absolute alpha widths, cross sections, 93 MeV]

Description: Data were taken for five transitions in the lead region allowing a quantitative comparison with corresponding alpha-decay data via R-matrix theory using the same target + alpha nuclear potential. Good agreement between the absolute reduced widths determined from the two sets of data suggests that in transfer reactions, as in alpha decay, an alpha particle in its ground state is transferred in a one-step process. In a separate analysis, elastic and total reaction cross sections for the systems ..cap alpha.. + /sup 208/Pb, /sup 209/Bi were analyzed to obtain a limited set of potentials which, in turn, were used to calculate absolute alpha widths. Existing shell model calculations give ..gamma../sub ..cap alpha..//sup 2/ values three orders of magnitude smaller.
Date: January 1, 1978
Creator: DeVries, R.M.
Partner: UNT Libraries Government Documents Department

Excited levels in /sup 231/Th from neutron capture. gamma. -ray measurements

Description: The excited levels in /sup 231/Th were studied using thermal and resonance neutron capture in /sup 230/Th. These data were used to establish a level scheme up to 1.1 MeV including spin assignments. Most of the levels are interpreted in terms of the Nilsson model. One rotational band is identified as a ..beta.. vibrational state coupled to the (631 arrow down) state.
Date: January 1, 1978
Creator: White, D H; Barreau, G; Boerner, H G; Davidson, W F; Hoff, R W; Jeuch, P et al.
Partner: UNT Libraries Government Documents Department

Experimental tests of recent nuclear models with the (n,. gamma. ) reaction. [E2 branching ratios]

Description: The nonselectivity of the (n,..gamma..) reaction provides a powerful tool for the study of those nuclear models of broad applicability whose characteristic excitations span a wide range of degrees of freedom. Several recent examples of this are discussed with particular emphasis on the recent discovery of the 0(6) limit of the interacting boson model and of a new interpretation of the Pt--0s transition region which consequently emerges. Other topics considered include recent extensions of the Nilsson model to new regions of nucleus, excitation energy and complexity of states. 43 references.
Date: January 1, 1978
Creator: Casten, R.F.
Partner: UNT Libraries Government Documents Department

Fermion Hamiltonians with monopole and quadrupole pairing

Description: Shell model Hamiltonians which have a set of eigenstates made up of only monopole and quadrupole pairs are presented. These Hamiltonians have many other types of states as well. The subspace of states made up of monopole and quadrupole pairs have a one-to-one correspondence to states made up of monopole and quadrupole bosons. Some properties of these Hamiltonians are discussed. 6 references.
Date: January 1, 1978
Creator: Ginocchio, J.N.
Partner: UNT Libraries Government Documents Department