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Scaling of cross sections in ion-atom collisions

Description: Differential electron emission at 15{degrees} is investigated for 50-500 keV/amu hydrogen impacting on He and H targets. From hydrogen particles (H, H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +}) ratios of cross sections relative to proton impact data, it is shown how bound projectile electrons influence the differential electron emission and where different ionization mechanisms are important. It is demonstrated that the H{sub 2}{sup +} and H{sub 3}{sup +} molecular ions interact as though they are composed of independent nuclei with the appropriate number of bound electrons, the electronic structure of the components appearing to be unimportant.
Date: November 1, 1994
Creator: DuBois, R.D.
Partner: UNT Libraries Government Documents Department

A search for the {Delta}{sup {minus}} wave-function component in light nuclei

Description: We have studied the ({pi}{sup +}, {pi}{sup {+-}}p) reactions on {sup 3}He, {sup 4}He, {sup 6}Li, and {sup 7}Li at incident energy 500 MeV in quasi-free kinematics. A signature attributable to pre-existing {Delta} components of the ground state wave function is observed.
Date: October 1, 1996
Creator: Morris, C.L.; Zumbro, J.D. & Boudrie, R.L.
Partner: UNT Libraries Government Documents Department

Many-body currents and the strange-quark content of {sup 4}He

Description: Meson-exchange current (MEC) contributions to the parity-violating (PV) asymmetry for elastic scattering of polarized electrons from {sup 4}He are calculated over a range of momentum transfer using Monte Carlo methods and a variational {sup 4}He ground state wavefunction. The results indicate that MEC's generate a negligible contribution to the asymmetry at low-{vert_bar}{anti q}{vert_bar}, where a determination of the nucleon's mean square strangeness radius could be carried out at CEBAF. At larger values of momentum transfer--beyond the first diffraction minimum--two-body corrections from the {rho}-{pi} strangeness charge operator enter the asymmetry at a potentially observable level, even in the limit of vanishing strange-quark matrix elements of the nucleon. For purposes of constraining the nucleon's strangeness electric form factor, theoretical uncertainties associated with these MEC contributions do not appear to impose serious limitations.
Date: April 1, 1994
Creator: Musolf, M.J.; Schiavilla, R. & Donnelly, T.W.
Partner: UNT Libraries Government Documents Department

Measurements of scattering processes in negative ion - atom collisions. Technical progress report - year 1, April 1, 1995--March 31, 1996

Description: This Technical Progress Report describes the progress made on the research objectives during the past twelve months. The objective of this research project is to provide absolute cross section measurements of various scattering processes which occur in negative ion collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. These processes include: elastic scattering, single- and double-electron detachment, and target-inelastic processes of excitation and ionization. Total cross sections for single- and double-electron detachment were recently published in Physical Review A from this research project. The researchers were successful this past year in acquiring the first cross section measurements of target excitation for H{sup -} impact on helium target atoms.
Date: December 1, 1995
Creator: Kvale, T.J.
Partner: UNT Libraries Government Documents Department

Experiments on the nuclear interactions of pion and electrons. Final progress report

Description: The work in this report is grouped into four categories. (1) The experiments in pion nucleus physics were primarily studies of pion absorption and scattering in light nuclei, carried out at the Los Alamos Meson Physics Facility (LAMPF). (2) The experiments on fundamental particle properties were carried out at LAMPF and at the Paul Scherrer Institute (PSI) in Switzerland, the pion-beta decay experiment is still under construction and will begin taking data in 1999. (3) The experiments in electro-nuclear physics were performed at the Stanford Linear Electron Accelerator (SLAC), at the Saclay Laboratory in France, at the LEGS facility at the Brookhaven National Laboratory, and at the Continuous Electron Beam Accelerator Facility (CEBAF) at the Jefferson Laboratory. These experiments relate mainly to the question of the role of longitudinal and transverse strength for inelastic scattering from nuclei, measurements of fundamental nuclear properties with tagged polarized photons, and to the quark structure of the nucleon and its excited states. (4) Experiments on absorption of antiprotons in heavy nuclei, were carried out by K. Ziock primarily while on a sabbatical leave in Munich, Germany.
Date: May 1, 1998
Creator: Minehart, R. C.
Partner: UNT Libraries Government Documents Department

Electromagnetic interactions with nucleons and nuclei. Progress report, November 1990--October 1991

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

A program in medium-energy nuclear physics. Progress report, September 1, 1992--June 30, 1993

Description: This report reviews progress on our nuclear-physics program for the last ten months, and includes as well copies of our publications and other reports for that time period. The structure of this report follows that of our 1992 Progress Report: Sec. II outlines our research activities aimed at future experiments at CEBAF, NIKHEF, and Bates; Sec. III gives results of our recent research activities at NIKHEF, LAMPF, and elsewhere; Sec. IV provides an update of our laboratory activities at GWU, including those at our new Nuclear Detector Laboratory at our Virginia Campus; and Sec. V is a list of our publications, proposals, and other reports. Copies of those on medium-energy nuclear physics are reproduced in the Appendix. The highlight of the year has been the approval by the NIKHEF and CEBAF PACs of all three of the proposals we have submitted. These are ``Recoil Polarization of the Neutron in the Reactions {sup 3}He(e,e{prime}n) and {sup 4}He(e,e{prime}n),`` NIKHEF Proposal 93-09, ``Photoreactions on {sup 3}He,`` CEBAF Proposal 93-044, and ``Photoabsorption and Photofission of Nuclei,`` CEBAF Proposal 93-019. The NIKHEF experiment involves the use of the High-Acceptance Recoil Polarimeter for detection and measurement of the polarization of the emitted neutron. We, together with our colleagues at Grenoble, are responsible for the design and construction of the wire chambers for this device; we have largely completed the design phase this past year. The CEBAF experiments involve the use of the Hall-B Photon Tagger for production of the monochromatic photon beam. We are responsible for the 432-scintillator focal-plane detector array for this device; again, most of the design work and some prototype testing have been completed this past year. In addition, we have continued to make progress on data analysis and publication of results of previous measurements at Bates, LAMPF, and NIKHEF.
Date: August 1, 1993
Creator: Berman, B. L. & Dhuga, K. S.
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: August 1, 1992
Creator: Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Spin effects in two-photon pair production

Description: The two-photon mechanism for lepton pair production is investigated. It is found that for pairs produced in certain kinematical regions the process is dominated by magnetic, spin-flip currents. Anomalous e{sup +}e{sup {minus}} pairs observed in 17 Gev/c pion-proton collisions are found to be predominantly produced by this spin-flip mechanism. A comparison between {sup 4}He + {sup 4}He collisions and {sup 3}He + {sup 4}He collisions is proposed as an experimental way of distinguishing between the electric, non spin-flip mechanism and the magnetic, spin-flip mechanism. 16 refs.
Date: January 1, 1990
Creator: Albert, C.J.; Ernst, D.J. (Texas A and M Univ., College Station, TX (USA)); Bottcher, C. & Strayer, M.R. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department

Unified approach to pion absorption and double-charge-exchange reactions

Description: Pion absorption and DCX Reactions are studied by using a unified theory of NN and ..pi..d scattering. It is shown that the theory can describe simultaneously the (..pi../sup +/,pp), (..pi../sup -/,pn) and (..pi../sup -/,..pi../sup +/) reactions of /sup 3/He. The study of absorption on heavy nuclei indicates the importance of inelastic absorption processes. It is suggested that the DCX reaction on heavy nuclei also involves multi-step processes which cannot be solved within the conventional distorted-wave theory. 4 refs.
Date: January 1, 1985
Creator: Lee, T.S.H.
Partner: UNT Libraries Government Documents Department

Cold fusion, Alchemist's dream

Description: In this report the following topics relating to cold fusion are discussed: muon catalysed cold fusion; piezonuclear fusion; sundry explanations pertaining to cold fusion; cosmic ray muon catalysed cold fusion; vibrational mechanisms in excited states of D{sub 2} molecules; barrier penetration probabilities within the hydrogenated metal lattice/piezonuclear fusion; branching ratios of D{sub 2} fusion at low energies; fusion of deuterons into {sup 4}He; secondary D+T fusion within the hydrogenated metal lattice; {sup 3}He to {sup 4}He ratio within the metal lattice; shock induced fusion; and anomalously high isotopic ratios of {sup 3}He/{sup 4}He.
Date: September 1, 1989
Creator: Clayton, E.D.
Partner: UNT Libraries Government Documents Department

Elastic scattering of tritons by helium-4

Description: Angular distributions of the differential cross section and of the analyzing power have been measured for the /sup 4/He(t,t)/sup 4/He reaction at 19 energies from 6 to 17 MeV. The relative errors of the cross section and analyzing power range from 2.0 to 2.5% and 0.005 to 0.01, respectively, and the scale errors are 1% in each case. Complete data tables are presented, and the experimental procedure is described for the present measurements and for earlier cross-section measurements. Graphs of the data are presented, as well as the curves resulting from an energy-independent phase-shift analysis.
Date: November 1, 1980
Creator: Jarmie, N.; Correll, F.D.; Brown, R.E.; Hardekopf, R.A. & Ohlsen, G.G.
Partner: UNT Libraries Government Documents Department

Final state effects in inclusive quasielastic electron scattering from nuclei: Clues from quantum fluids

Description: The impulse approximation (IA) predicts that momentum distributions, n/sub k/, in many-body systems should be measurable by inclusive quasielastic scattering at high energy and momentum (w,Q) transfer. The observations that the cross section appears to satisfy ''Y-scaling'' (i.e., is a function not of both w and Q of a single variable, Y) is usually taken as a signature of the IA. In nuclear physics, inelastic electron scattering at GeV energies should reveal the high momentum components of the nuclear wave function. In quantum fluids, neutron scattering at hundreds of MeV energies should measure the Bose condensate in superfluid /sup 4/He and the Fermi surface discontinuity and depletion of the Fermi sea in /sup 3/He. In molecular and condensed matter systems, X-ray Compton scattering at keV energies reveals electronic n/sub k/. Such experiments test many-body wave functions calculated by methods such as Green Function and Path Integral Monte Carlo, and Fermi Hypernetted Chain. However, an outstanding issue has been the corrections to the IA due to the scattering of the recoiling particle from neighboring particles, which are termed ''final state effects'' (FSE). The FSE should be especially important in nuclei and quantum fluids where the potentials have steeply repulsive cores. While there have been a variety of theories proposed for FSE, until now none has been adequately tested by experiment. Recently, the ''hard core perturbation theory'' (HCPT) for FSE in quantum fluids by Silver has been successfully compared to new neutron scattering measurements on /sup 4/He by P. E. Sokol and colleagues. In this paper, we shall discuss the lessons of this success for the extraction of n/sub k/ in nuclei by inclusive ''quasielastic electron-nucleus scattering'' (QENS). 19 refs., 12 figs.
Date: January 1, 1988
Creator: Silver, R.N. & Clark, J.W.
Partner: UNT Libraries Government Documents Department

/sup 4/He(d pol,d)/sup 4/He scattering from 12 to 17 MeV. [Differential cross sections and vector and tensor analyzing powers, phase-shift analysis]

Description: Differential cross sections and vector and tensor analyzing powers were measured for vector d + /sup 4/He elastic scattering at deuteron lab energies of 12, 14, 15, and 17 MeV. The data were tabulated and compared with predictions from a recent phase-shift analysis, which did not include the present results in the fitting procedure. Significant discrepancies between the predictions and measurements occur, principally for the tensor analyzing powers at backward angles. It is concluded that the present data should be incorporated into the phase-shift analysis to obtain a more realistic solution. 3 figures, 5 tables.
Date: July 1, 1978
Creator: Brown, R.E.; Grueebler, W.; Hardekopf, R.A.; Correll, F.D.; Jarmie, N. & Ohlsen, G.G.
Partner: UNT Libraries Government Documents Department

Charged-particle elastic cross sections

Description: Modern treatments of energy loss in plasmas through elastic scattering of energetic ions require complete knowledge of charged-particle elastic cross sections. R-matrix theory provides an explicit separation of nuclear and Coulomb effects in these cross sections, and gives reasonable extrapolations to small angles and low energies, where data may be scarce. We outline the calculation of charged-particle elastic cross sections from R-matrix parameters, and given examples for d-T, d-..cap alpha.., and t-..cap alpha.. scattering, obtained from comprehensive analyses of reactions in the /sup 5/He, /sup 6/Li, and /sup 7/Li compound systems. Expansion coefficients for an exact polynomial representation for the difference of the scattering and Rutherford cross sections (sigma/sub NI/) are given for d-T scattering. Integral quantities involving sigma/sub NI/ calculated from the present cross sections disagree substantially in some cases near resonances with a recent Livermore evaluation.
Date: January 1, 1982
Creator: Hale, G.M.; Dodder, D.C. & DeVeaus, J.C.
Partner: UNT Libraries Government Documents Department

Multi-nucleon phenomena in pion-nucleus reactions

Description: At the peak of the delta resonance, the pion is the most strongly interacting particle we know. It follows that interactions between pions and nuclei at these energies all tend to involve multiple scattering to some degree. Multiple scattering includes different kinds of processes. In its simplest forms, it involves a sequence of interactions with single nucleons that take place as the pion bumbles its way through a nucleus. Much more interesting is the possibility that there are interactions that in some sense directly involve several nucleons at once. If there are such interactions, can we distinguish between them and the simpler, more prosaic forms of multiple scattering Experimental study of pion-nucleus reaction mechanisms has produced intriguing suggestions that truly multi-nucleon interactions do occur. They are the subject of this paper. To develop this subject I will focus on reactions that cannot happen at all without the essential participation of two or more nucleons.
Date: January 1, 1990
Creator: Gram, P.A.M.
Partner: UNT Libraries Government Documents Department

Effect of the resonant structure of {sup 4}He on some of its charge-conjugate reactions

Description: The scheme of a Coulomb-corrected, charge-independent R-matrix analysis of the four-body system will be described. The consequences of the isospin structure of some of the resulting resonances for the charge-conjugate (p + t and n + {sup 3}He) branches of the d + d reaction and of {gamma} + {sup 4}He capture will be discussed. It appears that the sorts of differences between the branches seen in recent measurements for the fusion and capture reactions can be accounted for by this essentially charge-independent description of data for the four-body system.
Date: May 1, 1994
Creator: Hale, G. M.
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: May 1, 1993
Creator: Peng, J. C.
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

Interaction of fast neutrons with /sup 4/He, /sup 3/He, and /sup 1/H: additional and improved data. [20 MeV, differential cross sections, angular distributions]

Description: An improvement of previous elastic scattering data of neutrons in the 20-MeV range was made possible by the improved knowledge of the detection efficiency of the neutron detector. Thus revised absolute differential cross-section data for /sup 3/He(n,n)/sup 3/He and /sup 4/He(n,n)/sup 4/He were obtained with smaller uncertainties. Cross sections of nonelastic n-He reactions were obtained from recent data of the reciprocal reactions by detailed balance calculations. In addition, incomplete angular distributions for the reaction /sup 1/H(n,n)/sup 1/H between 22.5 MeV and 28.5 MeV are presented.
Date: May 1, 1978
Creator: Drosg, M.
Partner: UNT Libraries Government Documents Department

Measurements of pion-helium total cross sections at energies from 51 to 105 MeV

Description: Measurements of ..pi../sup + -/-/sup 4/He total cross sections have been made at energies from 51 to 105 MeV using a superfluid /sup 4/He target at the Low Energy Pion channel of the LAMPF accelerator in Los Alamos. Pions were selected with either a DISC counter or a time-of-flight system. The scattered pions were detected by a series of circular plastic scintillation counters using standard transmission techniques. The resulting partial removal cross sections were extrapolated to zero solid angle after being corrected for Coulomb effects, pion decay, accidental counts, counter absorption and efficiencies, and statistical correlations. The resulting statistical errors were generally approximately 3-5 percent. The measured total cross sections were found to be in good statistical agreement with previous measurements and in poor agreement with the predictions of several optical potentials in current use. Through an optical theorem the imaginary part of the forward scattering amplitude was found. The total cross sections have been used with previously-measured angular distributions through a phenomenological model to obtain the real part of the forward scattering amplitude at four energies between 50 and 75 MeV. These results were found to be in good agreement with forward dispersion relation calculations.
Date: October 1, 1976
Creator: Johnson, K. F.
Partner: UNT Libraries Government Documents Department

Design and construction of a spectrometer facility and experiment for intermediate energy proton scattering on helium. [Wave functions, preliminary experimental techniques]

Description: The goal of the research was to investigate proton scattering on nuclei at intermediate energies and in particular to investigate proton scattering on helium. A theoretical investigation of the helium nucleus and the nature of the intermediate energy interaction, design and optimization of an energy-loss spectrometer facility for proton-nucleus scattering, and the unique superfluid helium target and experimental design are discussed.
Date: December 1, 1976
Creator: Rolfe, R. M.
Partner: UNT Libraries Government Documents Department

Inclusive quasielastic and deep inelastic electron scattering at high energies

Description: With high electron energies a kinematic regime can be reached where it will be possible to separate quasielastic and deep inelastic scattering. We present a short description of these processes which dominate the inclusive spectrum. Using the highest momentum transfer data available to guide our estimates, we give the kinematic requirements and the cross sections expected. These results indicate that inclusive scattering at high q has a yet unfilled potential. 18 refs., 13 figs.
Date: January 1, 1990
Creator: Day, D.B.
Partner: UNT Libraries Government Documents Department