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Studies of nuclear reaction at very low energies

Description: The deuteron radiative capture reactions on {sup 2}H, {sup 6}Li and {sup 10}B have been measured between center of mass energies of 20 and 140 keV. Of note is the observation that the gamma ray-to-charged particle branching ratio for the DD reaction appears independent of energy down to a center of mass energy of 20 keV, consistent with some and contrary to other theoretical models. We have investigated the ratio of the reactions D(d,p)T and D(d,n){sup 3}He down to c.m. energies of 3 keV and the ratio of the reactions 6Li(d,p){sup 7}Li and {sup 6}LI(d,{alpha}){sup 4}He down to a c.m. energy of 19 keV. The DD reaction ratio is independent of energy while the (d,p) branch of the D-{sup 6}Li evinces a significant enhancement at the lowest measured energies. We have continued our investigation of charged particle production from deuterium-metal systems at a modest level of activity. Noteworthy in this investigation is the observation of 3 MeV protons from deuteron beam loaded Ti and LiD targets subjected to extreme thermal disequilibria. Significant facility improvements were realized during the most recent contract period. Specifically the downstream magnetic analysis system proposed to eliminate beam induced contaminants has been installed and thoroughly tested. This improvement should allow the D(a,{gamma}){sup 6}Li reaction to be measured in the coming contract period. A scattering chamber required for the measurement of the {sup 7}Li({sup 3}He,p){sup 9}Be reaction has been designed, fabricated and installed on the accelerator. A CAMAC based charged particle identification system has been assembled also for use in our proposed measurement of the {sup 7}Li({sup 3}He, p){sup 9}Be.
Date: January 15, 1992
Creator: Cecil, F.E.
Partner: UNT Libraries Government Documents Department

Fusion cross sections from Los Alamos R-matrix analyses

Description: We have been using R-matrix theory many years at Los Alamos to describe reactions in light systems, especially those containing fusion reactions. The theory is ideally suited for describing the resonances that are usually seen in light-element reactions, and at the same time it builds in the correct energy dependence of the transition matrix elements at low energies by making explicit use of the solutions for the external parts of the interaction. Thus, the method gives reliable extrapolations to low energies for both neutron- and charged-particle-induced reactions. We will present here the results of analysis that have been done, or are in progress, for reactions in the four- and five-nucleon systems, containing the fusion reactions of major interest: T(d,n){sup 4}He, {sup 3}He,D(d, p)T, and D(d,n){sup 3}He. These analyses contain all possible types of data that have been measured for the two-body reactions of these systems, a method that we have found crucial for determining their true resonant structures, and for ensuring reliable R-matrix interpolations and extrapolations of even the cross-section data. Integrated cross sections will be presented in the form of astrophysical S-functions, as functions of center-of-mass energy, in order that their low energy behavior might be better displayed. In addition to the R-matrix results, we will also show earlier cross-section parametrizations by Duane and Peres that still are used widely within the function reactor community. Some severe shortcomings of these earlier data sets are revealed by comparison with modern measurements and with the R-matrix calculations. More details about these comparisons and useful representations of the R-matrix cross sections and their associated reactivities (<{sigma}v>) recommended for use in fusion reactor design are given in a paper by Bosch and Hale has been submitted for publication.
Date: January 1, 1991
Creator: Hale, G.M.
Partner: UNT Libraries Government Documents Department

High field optical-pumping spin-exchange polarized deuterium source

Description: Recent progress in the performance of laser-driven source of polarized deuterium is described. Optical pumping of potassium atoms followed by spin exchange scattering with deuterium atoms in a high magnetic field and RF transitions in a medium field was found to produce an intense, highly spin-polarized beam of deuterium atoms. In particular, the atomic polarization of deuterium was determined to be 73{plus minus}3% at an intensity of 2.1 {times} 10{sup 17} Atomsis. The RF transition efficiency was measured and found to be 92{plus minus}5%.
Date: January 1, 1991
Creator: Zghiche, A.; Coulter, K.P.; Holt, R.J.; Kinney, E.R.; Kowalczyk, R.S.; Potterveld, D.H. et al.
Partner: UNT Libraries Government Documents Department

Effects of. Delta. -isobar degrees of freedom on the reactions sup 3 He(n,. gamma. ) sup 4 He and sup 3 He(p,e sup +. nu. sub e ) sup 4 He at low-energy

Description: The cross sections of the radiative {sup 3}He(n,{gamma}){sup 4}He and weak {sup 3}He(p,e{sup +}{nu}{sub e}){sup 4}He capture reactions at thermal neutron and keV proton energies have been calculated with the Variational Monte Carlo method. The ground state and low-energy continuum wave functions have been determined variationally from a realistic Hamiltonian, and include both nucleon and {Delta}-isobar degrees of freedom. The electroweak transition operator contains one- and two-body components in the N + {Delta} Hilbert space.
Date: January 1, 1991
Creator: Schiavilla, R.
Partner: UNT Libraries Government Documents Department

A fresh look at (e,e prime ) scattering from light nuclei: A GFMC approach

Description: Green's function Monte Carlo methods are used to calculate, in light nuclei, the Euclidean proton response, defined as the Laplace transform of the longitudinal response function measured in inclusive electron scattering. The calculations are based on a realistic Hamiltonian containing two- and three-nucleon interactions. Final-state-interaction effects are exactly included in this approach. The calculated Euclidean proton response functions for the {sup 4}He nucleus are found to be in excellent agreement with those obtained from an analysis of the Bates and Saclay longitudinal data.
Date: January 1, 1992
Creator: Schiavilla, R. (INFN sezione di Lecce, Lecce, Italy Argonne National Lab., IL (United States))
Partner: UNT Libraries Government Documents Department

Electromagnetic interactions with nucleons and nuclei

Description: Our primary research effort continues to be at the LEGS project at Brookhaven National Laboratory. The LEGS facility has made a transition in the last year from a combination of experiment and facility construction to full time experimental work. The first experiment, photodisintegration of the deuteron with polarized {gamma} rays, is completed and partially published. A second experiment, {sup 3}He({gamma},NN), has also been completed and analysis has begun. We except to begin two more experiments in the next year. Other research efforts are primarily related to CEBAF and this work is growing, since major CEBAF experimental equipment is now being constructed. We are heavily involved in the CLAS collaboration in Hall B which will build the CEBAF Large Acceptance Spectrometer. Our contributions to the CEBAF experimental program and equipment construction are described. The {sup 3}He({gamma}, NN) experiment at LEGS was the second use, in a new format, of the University of Virginia Nucleon Detector System. It is now a fully developed system. We also describe a new area of instrument development, applications of waveshifting optical fibers to novel position sensitive detectors for neutral particles.
Date: October 30, 1991
Creator: Thornton, S.T. & Sealock, R.M.
Partner: UNT Libraries Government Documents Department

Narrow structure in. Lambda. d scattering near the. Sigma. threshold ( sub. Sigma. sup 3 He states)

Description: A separable-potential, Faddeev-type calculation of {Lambda}-deuteron scattering near the threshold for {Sigma} production is shown to produce structure (a resonance peak) in the cross section which lies below the {Sigma} threshold for two different YN ({Lambda}N-{Sigma}N coupled-channel) potential models. In one case the {Sigma}NN eigenvalue corresponds to a pole which lies below threshold (bound) and in the second case the poles lies above the threshold.
Date: January 1, 1991
Creator: Gibson, B.F. (Los Alamos National Lab., NM (United States)) & Afnan, I.R. (Flinders Univ. of South Australia, Bedford Park (Australia). School of Physical Sciences)
Partner: UNT Libraries Government Documents Department

Wave function calculations in finite nuclei

Description: One of the central problems in nuclear physics is the description of nuclei as systems of nucleons interacting via realistic potentials. There are two main aspects of this problem: (1) specification of the Hamiltonian, and (2) calculation of the ground (or excited) states of nuclei with the given interaction. Realistic interactions must contain both two- and three-nucleon potentials and these potentials have a complicated non-central operator structure consisting, for example, of spin, isospin and tensor dependencies. This structure results in formidable many-body problems in the computation of the ground states of nuclei. At Argonne and Urbana, the authors have been following a program of developing realistic NN and NNN interactions and the methods necessary to compute nuclear properties from variational wave functions suitable for these interactions. The wave functions are used to compute energies, density distributions, charge form factors, structure functions, momentum distributions, etc. Most recently they have set up a collaboration with S. Boffi and M. Raduci (University of Pavia) to compute (e,e[prime]p) reactions.
Date: January 1, 1993
Creator: Pieper, S.C.
Partner: UNT Libraries Government Documents Department

The weak decay of helium hypernuclei

Description: A [Lambda] hyperon replaces a neutron in a nucleus to form a hypernucleus via the [sup A]X(K[sup [minus]], [pi][sup [minus]]) [sub [Lambda]][sup A]X reaction at 750 MeV/c (Brookhaven Experiment 788). The free [Lambda] decay rates [Gamma]([Lambda] [yields] p[pi][sup [minus]]) and [Gamma]([Lambda] [yields] n[pi][sup 0]) are diminished due to Pauli blocking; but a non-mesonic decay mode, nucleon stimulated decay N[Lambda] [yields] Nn, is present and is detected via the energetic decay nucleon(s) ([approx] 400MeV/c). Measurements of the various hypernuclear decay rates [Gamma]([Lambda] [yields] p[pi][sup [minus]]), [Gamma]([Lambda] [yields] n[pi][sup 0]) and [Gamma]([Lambda]n [yields] nn) provides insight into the strong modification of the weak interaction such as the baryon-baryon [Delta]I =[1/2] rule. The hypernuclear state is isolated by momentum analysis of (K[sup [minus]], [pi][sup [minus]]) target reaction. Out-of-beam large volume scintillation detectors and tracking chambers axe used to make particle identification of the hypernuclear decay products by time-of-flight, dE/dx, and range. The kinetic energy of the decay neutrons are measured by time of flight using the large volume 100 element neutron detector system. The hypernuclear lifetime is directly measured using precision scintillator counters and tracking chambers. Measurements of the various decay rates as well as the total lifetime are discussed for [sub [Lambda]][sup 4]He.
Date: August 1, 1992
Creator: Athanas, M.J.
Partner: UNT Libraries Government Documents Department

Hypernuclear physics with a neutral meson spectrometer

Description: The (K[sup [minus]], [pi][degrees]) reaction, which complements the (K[sup [minus]], [pi] [sup [minus]]) and the ([pi][sup +], K[sup +]) reactions, offers another means to study hypernuclear physics. The physics motivation for measuring the (K[sup [minus]], [pi][degrees]) reaction is discussed. The feasibility for detecting [pi][degrees] using the LAMPF Neutral Meson Spectrometer is studied with Monte-Carlo simulations. We conclude that the (K[sup [minus]], [pi][degrees]) reaction can be well measured at existing kaon beam lines.
Date: January 1, 1993
Creator: Peng, J.C.
Partner: UNT Libraries Government Documents Department

Polarization experiments with hadronic and electromagnetic probes. [2. 1 and 4. 4 GeV]

Description: The following research activities were carried out during the past year Calibration of focal plane polarimeter POMME up to 2.4 GeV at Saturne National Laboratory (LNS) in Saclay. Measurement of tensor analyzing power T[sub 20] and polarization transfer [kappa][sub 0] at Saturne up to 2.1 GeV in elastic backward dp scattering [rvec d]p [yields] [rvec p]d. Measurement of tensor analyzing power T[sub 20] at synchrophasotron in Dubha up to 4.4 Gev in elastic backward dp scattering [rvec d]p [yields] pd. Resubmission of conditionally Approved G[sub EP] proposal 89-14 at CEBAF. Start construction of focal plane polarimeter (FPP) for CEBAF hall A hadron spectrometer. The planned work for the next year includes: Construction of FPP for CEBAF hall A hadron spectrometer; measurement of polarization transfer [kappa][sub 0] and tensor analyzing power T[sub 20] in elastic backward dp scattering at Saturne; measurements of tensor analyzing power in [sup 1]H([sup 6]Li,d)X, [sup 1]H([sup 6]Li,[alpha])X, [sup 1]H([sup 6]Li,t)X and [sup 1]H([sup 6]Li,[sup 3]He)X reactions at Saturne; and study of polarization transfer in [sup 2]H([rvec e],e[prime][rvec p])n reaction at Bates.
Date: March 30, 1993
Creator: Punjabi, V.
Partner: UNT Libraries Government Documents Department

Nuclear interactions in high energy heavy ions and applications in astrophysics. [Dept. of Physics and Astronomy, Louisiana State Univ. , Baton Rouge]

Description: The overall objective is to study the mechanisms and the energy dependence of heavy ion fragmentation by studying the reactions of heavy ion projectiles (e.g. [sup 4]He, [sup 16]O, [sup 20]Ne, [sup 28]Si, [sup 56]Fe) in a variety of targets (H, He, C, Si, Cu, Pb) and at a number of beam energies exceeding 0.1 GeV/nucleon. The results have application to questions in high-energy nuclear astrophysics. Most of the discussion is on low-energy [sup 16]O,[sup 28]Si data analysis. The description includes analysis procedures and techniques, detector calibrations, data selections and normalizations. Cross section results for the analysis are also presented. 83 figs., 6 tabs., 73 refs.
Date: January 11, 1993
Creator: Wefel, J.P. & Guzik, T.G.
Partner: UNT Libraries Government Documents Department