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Interactions of 100 MeV/nucleon /sup 40/Ar with uranium

Description: Fragments produced in the interactions of 100 MeV/nucleon /sup 40/Ar projectiles with a uranium target were measured at energies from 10 to 130 MeV/nucleon at angles from 10 to 170/sup 0/. Nuclei with charge 5 less than or equal to Z less than or equal to 10 were observed. The data can roughly be divided into two groups, corresponding to central and pripheral collisions. The central collision data can be fit with a thermal model that uses two recoiling sources. The source velocities are consistent with predictions of the fireball and target explosion models, but the source temperatures inferred from the data are higher than one would expect on the basis of energy and momentum conservation. These results are similar to those obtained in previous studies at beam energies of 400 and 500 MeV/nucleon. The data also follow the pattern of a universal curve of invariant cross section vs momentum. The projectile fragmentation data are also fit by two thermal sources. There are indications that the observed temperatures are higher than one would expect on the basis of other projectile fragmentation studies. The projectile fragmentation data are studied in terms of a simple friction model. Order-of-magnitude estimates show that the data may be consistent with the model, but further development, calculation, and experimentation are necessary to check the validity of the model at this beam energy. A preliminary investigation is made of the possibility that the projectile may pick up one or more target nucleons before it fragments. This process leads to widening of the distributions at large momentum transfers. Much of the spectrum can be described by falling exponentials in energy in the emitting frames. It is concluded that the observed spectrum is due to nonthermal sources as the temperatures derived from the slopes of the exponentials are greater ...
Date: December 1, 1979
Creator: Frankel, K.A.
Partner: UNT Libraries Government Documents Department

Neutron cross sections for fusion. [Review]

Description: First generation fusion reactors will most likely be based on the /sup 3/H(d,n)/sup 4/He reaction, which produces 14-MeV neutrons. In these reactors, both the number of neutrons and the average neutron energy will be significantly higher than for fission reactors of the same power. Accurate neutron cross section data are therefore of great importance. They are needed in present conceptual designs to calculate neutron transport, energy deposition, nuclear transmutation including tritium breeding and activation, and radiation damage. They are also needed for the interpretation of radiation damage experiments, some of which use neutrons up to 40 MeV. In addition, certain diagnostic measurements of plasma experiments require nuclear cross sections. The quality of currently available data for these applications will be reviewed and current experimental programs will be outlined. The utility of nuclear models to provide these data also will be discussed. 65 references.
Date: October 1, 1979
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

Calculation of spin cutoff parameters using moment techniques

Description: Spectral distribution methods are often applied to the calculation of nuclear level densities. If their distribution in spin is required in addition to the total number of levels at each energy, the spin-cutoff parameter and its energy dependence must be known. Recent calculations of the spin-cutoff parameters have shown qualitative agreement with data. Reasons for the remaining discrepancies are discussed, and proecdures for improving agreement between theory and experiment are suggested. 8 figures.
Date: September 1, 1979
Creator: Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Limits of thermodynamic models for nuclear level densities. [Review]

Description: The current status of thermodynamic models as applied to nuclear level densities is reviewed. Considerable refinement has taken place during the last fifteen years, with the result that some of the undesirable assumptions originally required by the model are no longer necessary. Some problems remain, however, particularly in calculating level densities for deformed nuclei. Furthermore, some related parameters, such as the positive-parity negative-parity ratio for levels and the spin cutoff parameter are more sensitive to the presence of two-body interactions than the total level density. Improvement in characterization of nuclear level densities will require use of techniques which can incorporate the effects of two-body interactions in the level density calculation. 25 references.
Date: September 1, 1979
Creator: Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Representative-vector method for calculating operator-moments

Description: The utility of operator-moments or traces in the various applications of spectral-distribution theory is well documented. To take full advantage of the powerful entree that spectral distribution theory offers in nuclear physics, it may be generally necessary to have many moments beyond th first two hamiltonian moments <H> and <H/sup 2/>. In order to calculate, for one example, level densities reliably in the excitation-energy regions of physical interest, it may be necessary to have the moments <J/sub z//sup 2/H/sup n/> and of course <H/sup n/> with n ranging as high as 8 or so. The subject of this paper is a new method for obtaining these higher moments which is based on the use of random multiparticle vectors, called random representative vectors (RRV), in conjunction with an appropriate shell-model space and hamiltonian. With this method it is possible to calculate average properties of very large spaces with well-defined symmetries by averaging the results over a relatively few RRV. The demonstration of the statistical formulas of the RRV method is given in the next section. In the following section numerical results are given for the test case of 5 nucleons in the single-particle orbits 1d/sub 5/2/, 2s/sub 1/2/; and 1d/sub 3/2/ (A = 21), as well as some results for 12 nucleons in the same orbits plus the 1f/sub 7/2/ orbit (A = 28). With the representative-vector method one can evaluate average moments of any operator O that commutes with H so long as the application of O to the RRV does not produce a new vector which exceeds the memory capacity of the computer. 3 figures, 5 tables. (RWR)
Date: September 1, 1979
Creator: Bloom, S.D. & Hausman, R.F. Jr.
Partner: UNT Libraries Government Documents Department

Decay of deformed and superdeformed nuclei formed in heavy ion reactions

Description: The importance of considering the deformation of nuclei at high angular momenta in computing transmission coefficients for their decay is examined. Deformations based on the rotating liquid drop model were used to generate transmission coefficients versus compound nucleus angular momentum. The results were then used in a Hauser-Feshbach code that included fission competition to assess the ultimate importance of deformation-modified transmission coefficients. It was found that for a broad range of prolate nuclei (superdeformed) the course of deexcitation predicted changes totally from predominant fission to predominant ..cap alpha.. decay due to a new mechanism called ..cap alpha.. decay amplification. The phase space relationships responsible for this new mechanism are presented. It is shown that this predicted new decay mode of superdeformed nuclei is consistent with a large body of existing experimental results, although more explicit experiments must be completed to confirm the new mechanism. 23 figures, 4 tables.
Date: August 1, 1979
Creator: Blann, M. & Komoto, T.T.
Partner: UNT Libraries Government Documents Department

Nuclear structure of tellurium 133 via beta decay and shell model calculations in the doubly magic tin 132 region. [J,. pi. , transition probabilities, neutron and proton separation, g factors]

Description: An experimental investigation of the level structure of /sup 133/Te was performed by spectroscopy of gamma-rays following the beta-decay of 2.7 min /sup 133/Sb. Multiscaled gamma-ray singles spectra and 2.5 x 10/sup 7/ gamma-gamma coincidence events were used in the assignment of 105 of the approximately 400 observed gamma-rays to /sup 133/Sb decay and in the construction of the /sup 133/Te level scheme with 29 excited levels. One hundred twenty-two gamma-rays were identified as originating in the decay of other isotopes of Sb or their daughter products. The remaining gamma-rays were associated with the decay of impurity atoms or have as yet not been identified. A new computer program based on the Lanczos tridiagonalization algorithm using an uncoupled m-scheme basis and vector manipulations was written. It was used to calculate energy levels, parities, spins, model wavefunctions, neutron and proton separation energies, and some electromagnetic transition probabilities for the following nuclei in the /sup 132/Sn region: /sup 128/Sn, /sup 129/Sn, /sup 130/Sn, /sup 131/Sn, /sup 130/Sb, /sup 131/Sb, /sup 132/Sb, /sup 133/Sb, /sup 132/Te, /sup 133/Te, /sup 134/Te, /sup 134/I, /sup 135/I, /sup 135/Xe, and /sup 136/Xe. The results are compared with experiment and the agreement is generally good. For non-magic nuclei: the lg/sub 7/2/, 2d/sub 5/2/, 2d/sub 3/2/, 1h/sub 11/2/, and 3s/sub 1/2/ orbitals are available to valence protons and the 2d/sub 5/2/, 2d/sub 3/2/, 1h/sub 11/2/, and 3s/sub 1/2/ orbitals are available to valence neutron holes. The present CDC7600 computer code can accommodate 59 single particle states and vectors comprised of 30,000 Slater determinants. The effective interaction used was that of Petrovich, McManus, and Madsen, a modification of the Kallio-Kolltveit realistic force. Single particle energies, effective charges and effective g-factors were determined from experimental data for nuclei in the /sup 132/Sn region. 116 references.
Date: August 1, 1979
Creator: Lane, S.M.
Partner: UNT Libraries Government Documents Department

Comparison of fragmentation calculations within microscopic and macroscopic frameworks

Description: The calculation of the isotopic production cross sections from high-energy heavy-ion reactions has proceeded along two divergent paths. From the regime of relativistic heavy-ion reactions comes the abrasion--ablation model, which is dependent on the quick nature of these collisions and the separation of the reactant nuclei into participants and spectators. From the intermediate energy regime comes the intranuclear cascade model, where the reaction is treated as a sum of nucleon--nucleon scattering events inside a nuclear potential well. Both frameworks are able to treat projectile as well as target fragmentation. In this report the results of both model calculations are compared with recent experimental data for the fragmenta--ion of 213-MeV/A /sup 40/Ar projectiles by /sup 12/C nuclei and for the fragmentation of /sup 209/Bi target nuclei by a 400-MeV/A /sup 20/Ne beam. These comparisons show the importance of the statistical decay process in determining the distribution of final products as well as the deficiencies of the two models. 3 figures.
Date: July 1, 1979
Creator: Morrissey, D.J.
Partner: UNT Libraries Government Documents Department

In search of high density collective phenomena in nuclear collision. [0. 2 to 2. 0 GeV/nucleon]

Description: The progress made toward uncovering signatures of collective phenomena is reviewed. Elements of the basic reaction mechanism leading to a complex background are first discussed. Possible hints of collective phenomena in proton and pion single and double inclusive spectra as well as ..pi../sup -/ multiplicity data are then described. 6 figures, 2 tables.
Date: June 1, 1979
Creator: Gyulassy, M.
Partner: UNT Libraries Government Documents Department

Angular momentum and the collective modes excited in deep-inelastic processes and in fission. [288 MeV]

Description: The angular momentum effects in deep inelastic processes and fission were studied in the limit of statistical equilibrium. The model consists of two touching liquid drop spheres. Angular momentum fractionation was found to occur along the mass asymmetry coordinate. Thermal excitation of fragment spin is predicted to occur in the degrees of freedom which can bear angular momentum, like wriggling, tilting, bending, and twisting. 17 references.
Date: May 1, 1979
Creator: Moretto, L.G.
Partner: UNT Libraries Government Documents Department

Collective properties of odd-mass Sb, I, Cs, and La nuclei. [Bands, quasi-proton states, unexpected properties]

Description: The collective properties for the Z approximately greater than 50 transition region were studied via heavy-ion induced ..gamma..-ray experiments using /sup 6/ /sup 7/Li, /sup 10/B, /sup 12/ /sup 13/C, /sup 14/N, and /sup 16/O beams. The high-spin systematics for odd-mass /sup 113 -125/Sb (Z = 51), /sup 115 -127/I (Z = 53), /sup 119 -133/Cs (Z = 55), and /sup 125 -127/La (Z = 57) nuclei were obtained. Two collective features were observed, the first being systematic ..delta..J = 1 bands built on low-lying 1g/sub 9/2/ proton-hole states, and the second systematic ..delta..J = 2 bands built on 2d/sub 5/2/, 1g/sub 7/2/, and 1h/sub 11/2/ quasi-proton states. Unexpected properties were observed. 27 references.
Date: May 1, 1979
Creator: Fossan, D.B.
Partner: UNT Libraries Government Documents Department

Perspective on relativistic nuclear collisions

Description: The importance of experiments detecting more than one particle is pointed out. The production of nuclei far from stability in peripheral collisions and the expectations for the explosive disassembly of dense nuclear matter (nuclear fireball) and some evidence for it are related. Pion interferometry concerns the measurement of correlations in the momentum and energy of two identical pions; the subject is discussed in relation to incoherent production, coherent production, partially coherent production, final-state interactions, impact parameter average, and outlook. Much of the paper deals with an assessment of the possibility of determining the form of the hadronic spectrum in the high-mass region through nuclear collisions at ultrarelativistic energies. The subject is developed under the following topics: perspective, the initial fireball, isoergic equilibrium expansion of the fireball, quasi-dynamical expansion, quark matter, and the mass degree of freedom. The quasi-dynamical model obtained indicates that certain parameters, such as the ..pi../N and K/N ratios at high kinetic energy, will survive the collision; therefore, a determination of the asymptotic form of the hadron spectrum probably can be made by studying nuclear collisions at very high energies (10 GeV/nucleon in the center of mass). 16 figures. (RWR)
Date: May 1, 1979
Creator: Glendenning, N.K.
Partner: UNT Libraries Government Documents Department

Quantized gauge invariant periodic TDHF solutions

Description: The time-dependent Hartree-Fock method (TDHF) is used to study steady state large-amplitude collective motions, such as vibration and rotation. The central aspect explored is the periodicity. By a close analogy with the exact Schroedinger eigenstates, a subset of periodic TDHF solutions, the gauge invariant periodic solutions are considered. The TDHF supports a continuous family of periodic solutions, but only a discrete subset of these is gauge invariant. Also it is proven that these discrete gauge invariant periodic solutions obey the Bohr--Summerfeld quantization rule. The energy spectrum of the gauge invariant periodic solutions is compared with the exact eigenenergies in one specific example. The study implies that the gauge invariant periodic TDHF solutions are a very promising approximate description of the exact Schroedinger eigenstates. 10 references. (JFP)
Date: April 1, 1979
Creator: Kan, K. K.; Griffin, J. J.; Lichtner, P. C. & Dworzecka, M.
Partner: UNT Libraries Government Documents Department

Status of ENDF/B-V neutron emission spectra induced by 14-MeV neutrons. [Partial and total spectra, cross sections, graphs]

Description: ENDF/B-V neutron emission spectra induced by 14.6 MeV incident neutrons are graphically compared with experimental data. The elements selected for the comparisons include Na, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Ni, Cu, Nb, W, and Pb. Partial as well as total spectra from the ENDF/B-V evaluations are shown in each graph, while experimental data were available only for the total. Energy distribution laws utilized for the reaction types in each element are explained. Agreement between evaluated and experimental data is discussed, and recommendations for improvements are made. In general, evaluations which utilized advanced nuclear model codes, including precompound effects, agree well with measured spectra.
Date: April 1, 1979
Creator: Hetrick, D. M.; Larson, D. C. & Fu, C. Y.
Partner: UNT Libraries Government Documents Department

Multipion production in nuclear collisions

Description: Two aspects of multipion production in nuclear collisions are discussed: the negative pion multiplicity distribution and the ..pi../sup -/..pi../sup -/ correlation function. The emphasis is on how these observables could be used to search for signals of collective phenomena in nuclear collisions. 2 figures.
Date: March 1, 1979
Creator: Gyulassy, M.
Partner: UNT Libraries Government Documents Department

Nuclear structure from continuum. gamma. -rays

Description: The properties of states of spins of 20 to 60 are considered using the liquid-drop model and some shell effects. The angular momenta at which the fission barrier becomes zero or 8 MeV as a function of mass number, moments of inertia and rotational energies and the various gamma spectra for some specific nuclei are plotted. 15 references. (JFP)
Date: March 1, 1979
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department

Role of deep inelastic processes in nuclear physics: experimental and theoretical aspects of deep inelastic reactions. [Mass asymmetry, diffusion, charge and angular distributions, energy and momentum transfer]

Description: The collective modes excited in deep-inelastic reactions and their natural hierarchy provided by their characteristic relaxation times is described. The relaxation of the mass asymmetry mode is discussed in terms of a diffusion process. Charge distributions and angular distributions as a function of Z calculated with this model are in good agreement with experimental data. This diffusion model also treats the transfer of energy and angular momentum in terms of particle transfer, and is successfully compared with experimental ..gamma..-ray multiplicities as a function of both Q-value and mass asymmetry. The angular momentum transfer is again considered in connection with the sequential fission of heavy, deep-inelastic fragments and the excitation of collective modes in the exit channel is considered. The role of the giant E1 mode in the equilibration of the neutron-to-proton ratio is discussed. 39 references.
Date: March 1, 1979
Creator: Moretto, L.G.
Partner: UNT Libraries Government Documents Department

Analysis of neutron yield produced by high energy proton. [400 and 660 MeV]

Description: Vasil'kov et al.'s experiments for neutron yield and neutron capture distribution produced by 400 and 660 MeV protons were analyzed by using ENDF/B-IV data and the BNL codes NMTC and TWOTRAN. The calculated total neutron radiative capture by /sup 238/U is 77 and 60% of the measured values for protons of 660 and 400 MeV, respectively. The calculated distribution has the higher peak in the central part of the target system, and steeper gradient both in the r and z directions, compared to experimental. The leakage rate of neutrons from the target assembly is calculated as more than 20%, which is much higher than the 10% estimated from the experiment. The total neutron captures determined using ENDF/B-IV are 3.8 and 3.0% higher than those determined using ENDF/B-III for protons of 660 and 400 MeV, respectively. 12 references.
Date: January 1, 1979
Creator: Takahashi, H. & Nakanara, Y.
Partner: UNT Libraries Government Documents Department

Application of catastrophe theory to nuclear structure

Description: Three two-parameter models, one describing an A-body system (the atomic nucleus) and two describing many-body systems (the van der Waals gas and the ferroelectric (perovskite) system) are compared within the framework of catastrophe theory. It is shown that each has a critical point (second-order phase transition) when the two counteracting forces controlling it are in balance; further, each undergoes a first-order phase transition when one of the forces vanishes (the deforming force for the nucleus, the attractive force for the van der Waals gas, and the dielectric constant for the perovskite). Finally, when both parameters are kept constant, a kind of phase transition may occur at a critical angular momentum, critical pressure, and critical electric field. 3 figures, 1 table.
Date: January 1, 1979
Creator: Scharff-Goldhaber, G. & Dresden, M.
Partner: UNT Libraries Government Documents Department

Application of nuclear models. [1 to 40 MeV, review]

Description: The development of extensive experimental nuclear data base over the past three decades has been accompanied by parallel advancement of nuclear theory and models used to describe and interpret the measurements. This theoretical capability is important because of many nuclear data requirements that are still difficult, impractical, or even impossible to meet with present experimental techniques. Examples of such data needs are neutron cross sections for unstable fission products, which are required for neutron absorption corrections in reactor calculations; cross sections for transactinide nuclei that control production of long-lived nuclear wastes; and the extensive dosimetry, activation, and neutronic data requirements to 40 MeV that must accompany development of the Fusion Materials Irradation Test (FMIT) facility. In recent years systematic improvements have been made in the nuclear models and codes used in data evaluation and, most importantly, in the methods used to derive physically based parameters for model calculations. The newly issued ENDF/B-V evaluated data library relies in many cases on nuclear reaction theory based on compound-nucleus Hauser-Feshbach, preequilibrium and direct reaction mechanisms as well as spherical and deformed optical-model theories. The development and applications of nuclear models for data evaluation are discussed with emphasis on the 1 to 40 MeV neutron energy range.
Date: January 1, 1979
Creator: Young, P.G.; Arthur, E.D. & Madland, D.G.
Partner: UNT Libraries Government Documents Department

Calculated particle production spectra and multiplicities from nucleon-fissile element collisions at medium energies

Description: A fission channel was added to the intranuclear-cascade-evaporation model of nuclear reactions so that this model could be used to obtain the differential particle production data that are needed to study the transport of medium-energy nucleons and pions through matter. The earlier work of Hahn and Bertini on the incorporation of fission-evaporation competition into the intranuclear-cascade-evaporation model was retained, and the statistical model of fission was utilized to predict particle production from the fission process. Approximate empirically derived kinetic energies and deformation energies are used in the statistical model. The calculated residual nuclei distributions are in reasonable agreement with experimental data, but the neutron multiplicities at the higher incident nucleon energies greater than or equal to 500 MeV are sensitive to the level density parameter used. 4 figures.
Date: January 1, 1979
Creator: Alsmiller, F.S.; Alsmiller, R.G. Jr.; Gabriel, T.A.; Lillie, R.A. & Barish, J.
Partner: UNT Libraries Government Documents Department

Calculation of neutron cross sections for tungsten isotopes. [Pre-equilibrium statistical model, 1 to 20 MeV preliminary calculations]

Description: Neutron-induced cross sections on tungsten isotopes were calculated in the energy range between 1 and 20 MeV using preequilibrium-statistical model techniques. The success of these calculations, which form part of an effort to improve the evaluated neutron and gamma-ray production cross sections for tungsten appearing in ENDF/B, depends strongly on the determination of consistent input parameter sets applicable over the entire range of interest. For example, neutron optical model parameters were derived through a simultaneous analysis of total cross sections, resonance data, and angular distributions. These parameters, when used in multistep Hauser-Feshbach calculations, produce good agreement with varied experimental data such as neutron inelastic scattering excitation functions and (n, 2n) cross sections. Likewise, gamma-ray strength functions were determined through fits to neutron capture data that produce calculated results that compare well to measured gamma-ray production cross sections. A description of the techniques used in such parameter determinations as well as comparison of calculated results to experimental data will be presented.
Date: January 1, 1979
Creator: Arthur, E.D. & Philis, C.A.
Partner: UNT Libraries Government Documents Department

Calculation of prompt fission neutron spectra. [0. 53 MeV]

Description: A new calculation of the prompt fission neutron spectrum N(E) is presented as a function of both the fissioning nucleus and its excitation energy. The calculation, based upon standard nuclear-evaporation theory, accounts for the physical effects of the distribution of fission-fragment residual nuclear temperature and the energy dependence of the cross section for the inverse process of compound-nucleus formation. With the use of a residual nuclear temperature distribution based upon the Fermi-gas model, calculations were performed for two different assumptions concerning the cross section for compound-nucleus formation. Use of a constant cross section leads to a closed expression for the neutron energy spectrum, while use of an energy-dependent cross section, calculated with the optical model, yields a numerical integration. Results obtained for the two assumptions agree well with experimental data, although there is a preference for the energy-dependent cross section calculation. 7 figures.
Date: January 1, 1979
Creator: Madland, D.G. & Nix, J.R.
Partner: UNT Libraries Government Documents Department