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Macroscopic description of the interaction between two complex nuclei

Description: Assuming that the particle number is large, and using the leptodermous idealization that the ratio of the surface thickness to the cube root of nuclear volume is very small, an attempt is made to give an account of the time evolution of the shape of a nuclear system. It is suggested that a one-body, dissipation dominated approach to nuclear dynamics should be a reasonable starting point. (SDF)
Date: September 1, 1975
Creator: Swiatecki, W.J.
Partner: UNT Libraries Government Documents Department

New <sup>88</sup>Sr(n,<font face="symbol">g</font>)Astrophysical Reaction Rate from Resonance Analysis of New High-Resolution Neutron Capture and Transmission Data

Description: Because of its small cross section, the <sup>88</sup>Sr(n,<font face="symbol">g</font>) reaction is an important bottleneck during <i>s</i>-process nucleosynthesis. Hence, an accurate determination of this rate is needed to better constrain the neutron exposure in <i>s</i>-process models and to more fully exploit the recently discovered isotopic anomalies in certain meteorites. We have completed the resonance analysis of our new and improved measurements of the neutron capture and total cross sections for <sup>88</sup>Sr made at the Oak Ridge Electron Linear Accelerator (ORELA). We describe our experimental procedures and resonance analysis, compare our results to previous data, and discuss their astrophysical impact.
Date: August 30, 1999
Creator: Koehler, P.E.
Partner: UNT Libraries Government Documents Department

Strangeness production in relativistic nuclear collisions

Description: A review of strange particle production in heavy ion collisions from AGS to SPS energies is presented. Implications of the newest developments in understanding the collision dynamics and the role of strange particle production in the search for a new phase of matter, in both experimental and theoretical sectors, are discussed.
Date: January 1, 1998
Creator: Odyniec, G.J.
Partner: UNT Libraries Government Documents Department

Multifragmentation at intermediate energy: Dynamics or statistics

Description: In this report the authors consider two contradictory claims that have been advanced recently: (1) the claim for a predominantly dynamical fragment production mechanism; and (2) the claim for a dominant statistical and thermal process. They present a new analysis in terms of Poissonian reducibility and thermal scaling, which addresses some of the criticisms of the binomial analysis.
Date: January 1, 1998
Creator: Beaulieu, L.; Phair, L.; Moretto, L.G. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department

Proposed solution to the {open_quotes}k{sub eff} of the world{close_quotes} problem

Description: In 1971 Whitesides posed a Monte Carlo (MC) problem which he called {open_quotes}computing the k{sub eff} of the world.{close_quotes} This problem is still troublesome today. The problem arose in MC studies of a 9 x 9 x 9 configuration of weakly coupled Pu spheres, initially identical, with the whole array surrounded by water. The MC eigenvalue for this array was .93. When the central sphere was replaced by another, just critical in isolation, the MC eigenvalue was still .93. Here we consider a model problem somewhat analogous to Whitesides`, and use it (1) to illustrate the difficulties in the simplest traditional MC approach, and (2) to explore an alternative approach.
Date: December 31, 1995
Creator: Gelbard, E.M. & Roussel, B.
Partner: UNT Libraries Government Documents Department

Nuclear structure and reactions with stored nuclei

Description: The use of ion-storage rings is discussed for studies of nuclear reactions and structure, with emphasis on energetic beams of short- lived, radioactive nuclei. Aspects of internal versus external luminosity are considered as well as other issues connected with the inverse kinematics of reactions induced by a circulating beam of complex nuclei. Some of the physics motivation that is driving studies with radioactive beams is described.
Date: December 31, 1996
Creator: Henning, W.
Partner: UNT Libraries Government Documents Department

The equivalent fundamental-mode source

Description: In 1960, Hansen analyzed the problem of assembling fissionable material in the presence of a weak neutron source. Using point kinetics, he defined the weak source condition and analyzed the consequences of delayed initiation during ramp reactivity additions. Although not clearly stated in Hansen`s work, the neutron source strength that appears in the weak source condition corresponds to the equivalent fundamental-mode source. In this work, we describe the concept of an equivalent fundamental-mode source and we derive a deterministic expression for a factor, g*, that converts any arbitrary source distribution to an equivalent fundamental-mode source. We also demonstrate a simplified method for calculating g* in subcritical systems. And finally, we present a new experimental method that can be employed to measure the equivalent fundamental-mode source strength in a multiplying assembly. We demonstrate the method on the zero-power, XIX-1 assembly at the Fast Critical Assembly (FCA) Facility, Japan Atomic Energy Research Institute (JAERI).
Date: February 1, 1997
Creator: Spriggs, G.D.; Busch, R.D.; Sakurai, Takeshi & Okajima, Shigeaki
Partner: UNT Libraries Government Documents Department

Prompt muon-induced fission: A probe for nuclear friction in large-amplitude collective motion

Description: Excited muonic atoms in the actinide region may induce prompt fission by inverse internal conversion, i.e. the excitation energy of the muonic atom is transferred to the nucleus. The authors solve the time dependent Dirac equation for the muonic spinor wave function in the Coulomb field of the fissioning nucleus on a 3-dimensional lattice and demonstrate that the muon attachment probability to the light fission fragment is a measure of the nuclear energy dissipation between the outer fission barrier and the scission point.
Date: January 1, 1998
Creator: Oberacker, V.E.; Umar, A.S.; Wells, J.C.; Strayer, M.R.; Maruhn, J.A. & Reinhard, P.G.
Partner: UNT Libraries Government Documents Department

Reducible emission probabilities and thermal scaling in multifragmentation

Description: Intermediate-mass-fragment multiplicity distributions for a variety of reactions at intermediate energies are shown to be binomial and thus reducible at all measured transverse energies. From these distributions a single binary event probability can be extracted that has a thermal dependence. A strong thermal signature is also found in the charge distributions. The {eta}-fold charge distributions are reducible to the {eta}-fold charge distributions through a simple scaling that is dictated by fold number and charge conservation.
Date: August 1, 1995
Creator: Moretto, L.G.; Phair, L. & Tso, K.
Partner: UNT Libraries Government Documents Department

Event generator overview

Description: Due to their ability to provide detailed and quantitative predictions, the event generators have become an important part of studying relativistic heavy ion physics and of designing future experiments. In this talk, the author will briefly summarize recent progress in developing event generators for the relativistic heavy ion collisions.
Date: December 1, 1997
Creator: Pang, Y.
Partner: UNT Libraries Government Documents Department

Vector meson production and nuclear effects in FNAL E866

Description: Fermilab E866/NUSEA is a fixed-target experiment which has made a number of measurements of the production of vector mesons by 800 GeV protons. The nuclear dependence results include measurements for J/{psi}, {psi}{prime} and {phi} production over very broad ranges in {chi}{sub F} and p{sub T}, and the J/{psi} decay angular distribution at very large {chi}{sub F}. Preliminary results from measurements on Be, Fe and W targets are presented and discussed in the context of nuclear effects such as energy loss and multiple scattering of the partons, absorption of the produced c{bar c} pairs, and shadowing. Production mechanisms involving color-singlet or color-octet states for the c{bar c} pair which eventually forms a J/{psi} or {psi}{prime}, have implications on the strength of absorption in the nucleus and on the angular distribution of the decay muons. Their preliminary results on the angular distributions versus {chi}{sub F} and p{sub T} indicate some transverse polarization of the J/{psi} as predicted by models of production through the color octet state. The measurements of dimuons in the 1 to 3 GeV region explore the nuclear dependence of the {phi} meson and also the composition of the continuum between the {phi} and the J/{psi}. These studies of vector meson production and it`s nuclear dependence are critical in furthering the understanding of these processes towards future measurements at RHIC and new results from NA50 at CERN, where J/{psi} suppression is predicted to be an important signature of the creation of quark-gluon plasma in heavy-ion collisions.
Date: December 31, 1998
Creator: Leitch, M.J. & Collaboration, E866 /NUSEA
Partner: UNT Libraries Government Documents Department

Point kinetics modeling

Description: A normalized form of the point kinetics equations, a prompt jump approximation, and the Nordheim-Fuchs model are used to model nuclear systems. Reactivity feedback mechanisms considered include volumetric expansion, thermal neutron temperature effect, Doppler effect and void formation. A sample problem of an excursion occurring in a plutonium solution accidentally formed in a glovebox is presented.
Date: December 31, 1996
Creator: Kimpland, R.H.
Partner: UNT Libraries Government Documents Department

Antiproton catalyzed fusion

Description: Because of the potential application to power production, it is important to investigate a wide range of possible means to achieve nuclear fusion, even those that may appear initially to be infeasible. In antiproton catalyzed fusion, the negative antiproton shields the repulsion between the positively charged nuclei of hydrogen isotopes, thus allowing a much higher level of penetration through the repulsive Coulomb barrier, and thereby greatly enhancing the fusion cross section. Because of their more compact wave function, the more massive antiprotons offer considerably more shielding than do negative muons. The effects of the shielding on fusion cross sections are most predominate, at low energies. If the antiproton could exist in the ground state with a nucleus for a sufficient time without annihilating, the fusion cross sections are so enhanced that at room temperature energies, values up to about 1,000 barns (that for d+t) would be possible. Unfortunately, the cross section for antiproton annihilation with the incoming nucleus is even higher. A model that provides an upper bound for the fusion to annihilation cross section for all relevant energies indicates that each antiproton will catalyze no more than about one fusion. Because the energy required to make one antiproton greatly exceeds the fusion energy that is released, this level of catalysis is far from adequate for power production.
Date: May 15, 1995
Creator: Morgan, D.L. Jr.; Perkins, L.J. & Haney, S.W.
Partner: UNT Libraries Government Documents Department

Neutral pion production in nucleus-nucleus collisions at 158 and 200 GeV/nucleon

Description: Two years ago, at the 12th Winter Workshop on Nuclear Dynamics held here in Snowbird, the authors presented WA80 limits on direct photon production in 200-GeV {sup 32}S + Au collisions. It was found that the results were consistent (within 1{sigma}) with the absence of an excess of photons over those that can be accounted for by the two-photon decay branches of {pi}{sup 0} and {eta} mesons and by the small photon contributions from other radiative decays. They are in the process of finalizing the direct-photon production results from collisions of lead nuclei at 158 GeV/nucleon. The author briefly discusses the status of the analysis and gives some preliminary results at the end of this talk. However, most of this presentation is concerned with a very different aspect of the photon measurements: distributions of neutral pions. In contrast to direct photons which probe initial collision conditions, hadrons, such as neutral pions, interact strongly and decouple late in the reaction evolution and, thus, provide information concerning the system at freeze out. Transverse momentum spectra at low and intermediate p{sub T} relate to thermodynamic and hydrodynamic descriptions of the hot, dense systems. In addition, the high-p{sub T} region reflects the hard-scattering regime and may help one understand initial-state particle production by forming a bridge to proton-proton and proton-nucleus results. It follows that it is essential that the {pi}{sup 0} measurements cover a large p{sub T} range.
Date: February 1, 1998
Creator: Plasil, F.; Collaboration, WA80 & Collaboration, WA98
Partner: UNT Libraries Government Documents Department

Parameter-Free Calculation of the Solar Proton Fusion Rate in Effective Field Theory

Description: Spurred by the recent complete determination of the weak currents in two-nucleon systems up to O(Q{sup 3}) in heavy-baryon chiral perturbation theory, we carry out a parameter-free calculation of the solar proton fusion rate in an effective field theory that combines the merits of the standard nuclear physics method and systematic chiral expansion. Using the tritium {beta}-decay rate as an input to fix the only unknown parameter in the effective Lagrangian, we can evaluate with drastically improved precision the ratio of the two-body contribution to the well established one-body contribution; the ratio is determined to be (0.9 {+-} 0.1)%. This result is essentially independent of the cutoff parameter for a wide range of its variation (500 MeV {le} {Lambda} {+-} 800 MeV), a feature that substantiates the consistency of the calculation.
Date: June 1, 2001
Creator: Park, T.-S.; Marcucci, L.E.; Schiavilla, R.; Viviani, M.; Kievsky, A.; Rosati, S. et al.
Partner: UNT Libraries Government Documents Department

Verification and validation of fast systems with ENDF/B data.

Description: An extensive and systematic verification, validation and data testing effort using diverse Monte Carlo and deterministic methods with ENDF/B data (Versions V.2 and VI.5) is in progress. Methods verification is obtained by comparing independent methods, including continuous-energy Monte Carlo methods using the VIM and MCNP codes and 1D and 2D transport calculations using multigroup cross section sets generated with the ETOE-II/MC-2 system combined with the TWODANT code. Each of these code systems relies on independently processed data libraries. Inter-comparison of these results is used for verification. Further verification is achieved by comparing and plotting the point-wise cross section libraries of VIM and MCNP. Where possible, benchmark models are taken from both the ICSBEP Handbook and the CSEWG Benchmark Specifications. Inter-comparison of these results quantifies the generally small differences between these references. Calculations are repeated with both ENDF/B-V.2 and ENDF/B-VI.5 data. Inter-comparison of these results quantifies their data dependence. Analyses of criticality and reaction rate ratios are used for the validation and data testing. Calculated neutron balances and neutron energy spectra are also obtained and analyzed to explain the observed differences.
Date: August 22, 2001
Creator: Stenberg, C. G. & McKnight, R. D.
Partner: UNT Libraries Government Documents Department