101.
NASA thermionic-conversion program
- Morris, J. F.; Lundholm, J. G.
Current out-of-core emphases allow converter material and design freedoms previously prohibited by in-core nucleonic and geometric restrictions. As a result, potential improvements indicate possibilities for severalfold increases in efficiencies. The new TEC-ART program concentrated initially on low-work function collectors and interelectrode-loss reduction and revealed much in a short time. This new emission capability coupled with improved collectors that maintain performance with emitter-vapor deposit accumulations are requisites for efficient, enduring thermionic converters.
102.
Zero-G flight test of a gauging system. Volume 1: Summary
The capability of a nucleonic gauging system to gauge the content of a reduced-scale storable liquid tank in a zero-g environment as provided by a KC-135 Zero-G Aircraft was demonstrated. Although the propellant-ullage interface never achieved the stable, zero-g equilibrium configuration, the gauging system gauged liquid quantity over all tank loadings to a total system accuracy the order of two percent. It was also determined that the gauging system presented no undue safety hazard to operating personnel in either ground and/or flight testing.
103.
Nuclear Transport at Low Excitations
- Helmut Hofmann; Fedor A. Ivanyuk
Numerical computations of transport coefficients at low temperatures are presented for shapes typically encountered in nuclear fission. The influence of quantum effects of the nucleonic degrees of freedom is examined, with pair correlations included. Consequences for global collective motion are studied for the case of the decay rate. The range of temperatures is specified above which this motion may be described as a quantal diffusion process.
104.
Role of the Delta (1232) in DIS on polarized $^3$He and extraction of
the neutron spin structure function $g_{1}^{n}(x,Q^2)$
- Boros, C.; Guzey, V.; Strikman, M.; Thomas, A. W.
We consider the effect of the transitions $n \to \Delta^{0}$ and $p \to
\Delta^{+}$ in deep inelastic scattering on polarized $^3$He on the extraction
of the neutron spin structure function $g_{1}^{n}(x,Q^2)$. Making the natural
assumption that these transitions are the dominant non-nucleonic contributions
to the renormalization of the axial vector coupling constant in the A=3 system,
we find that the effect of $\Delta$ increases $g_{1}^{n}(x,Q^2)$ by $10 \div
40$% in the range $0.05 \le x \le 0.6$, where our considerations are applicable
and most of the data for $g_{1}^{n}(x,Q^2)$ exist.
105.
Sigma-term physics in the perturbative chiral quark model
- Lyubovitskij, V. E.; Gutsche, Th.; Faessler, Amand; Drukarev, E. G.
We apply the perturbative chiral quark model (PCQM) at one loop to analyse
meson-baryon sigma-terms. Analytic expressions for these quantities are
obtained in terms of fundamental parameters of low-energy pion-nucleon physics
(weak pion decay constant, axial nucleon coupling, strong pion-nucleon form
factor) and of only one model parameter (radius of the nucleonic three-quark
core). Our result for the piN sigma term of about 45 MeV is in good agreement
with the value deduced by Gasser, Leutwyler and Sainio using
dispersion-relation techniques and exploiting the chiral symmetry constraints.
106.
Effective Field Theory for Low-Energy Two-Nucleon Systems
- Park, Tae-Sun; Kubodera, Kuniharu; Min, Dong-Pil; Rho, Mannque
We illustrate how effective field theories work in nuclear physics by using
an effective Lagrangian in which all other degrees of freedom than the
nucleonic one have been integrated out to calculate the low-energy properties
of two-nucleon systems, viz, the deuteron properties, the np 1S0 scattering
amplitude and the M1 transition amplitude entering into the radiative np
capture process. Exploiting a finite cut-off regularization procedure, we find
all the two-nucleon low-energy properties to be accurately described with
little cut-off dependence, in consistency with the general philosophy of
effective field theories.
107.
Relativistic Effects in Electroweak Nuclear Responses
- Barbaro, Maria B.
The electroweak response functions for inclusive electron scattering are
calculated in the Relativistic Fermi Gas model, both in the quasi-elastic and
in the $\Delta$ peak regions. The impact of relativistic kinematics at high
momentum transfer is investigated through an expansion in the initial nucleonic
momentum, which is however exact in the four-momentum of the exchanged boson.
The same expansion is applied to the meson exchange currents in the
particle-hole sector: it is shown that the non-relativistic currents can be
corrected by simple kinematical factors to account for relativity. The
left-right asymmetry measured via polarized electron scattering is finally
evaluated in the quasi-elastic and $\Delta$ peaks.
108.
Liquid-Drop Model and Quantum Resistance Against Noncompact Nuclear
Geometries
- Toke, Jan; Schroeder, W. Udo
The importance of quantum effects for exotic nuclear shapes is demonstrated.
Based on the example of a sheet of nuclear matter of infinite lateral
dimensions but finite thickness, it is shown that the quantization of states in
momentum space, resulting from the confinement of the nucleonic motion in the
conjugate geometrical space, generates a strong resistance against such a
confinement and generates restoring forces driving the system towards compact
geometries. In the liquid-drop model, these quantum effects are implicitly
included in the surface energy term, via a choice of interaction parameters, an
approximation that has been found valid for compact shapes, but has not yet
been scrutinized for exotic...
109.
Deep inelastic scattering from A=3 nuclei and the neutron structure
function
- Afnan, I. R.; Bissey, F.; Gomez, J.; Katramatou, A. T.; Liuti, S.; Melnitchouk, W.; Petratos, G. G.; Thomas, A. W.
We present a comprehensive analysis of deep inelastic scattering from He-3
and H-3, focusing in particular on the extraction of the free neutron structure
function, F_2^n. Nuclear corrections are shown to cancel to within 1-2% for the
isospin-weighted ratio of He-3 to H-3 structure functions, which leads to more
than an order of magnitude improvement in the current uncertainty on the
neutron to proton ratio F_2^n/F_2^p at large x. Theoretical uncertainties
originating from the nuclear wave function, including possible non-nucleonic
components, are evaluated. Measurement of the He-3 and H-3 structure functions
will, in addition, determine the magnitude of the EMC effect in all A < 4
nuclei.
110.
Nucleon polarization in deuteron electrodisintegration
- Mosconi, B.; Pauschenwein, J.; Ricci, P.
Outgoing nucleon polarization in exclusive deuteron electrodisintegration is
studied at the quasi-elastic peak in the standard theory with emphasis on the
effect of nucleonic and pionic relativistic corrections. The cases of polarized
beam or/and polarized target are considered. Sizeable relativistic effects are
pointed out in several polarization components. The sensitivity of nucleon
polarization to the neutron charge form factor $G_E^n$ is discussed. In
particular, it is shown that the longitudinal component of neutron polarization
with vector polarized deuterons is as sensitive to $G_E^n$ as the sideways beam
polarization transfer.
111.
Pions in the nuclear medium and Drell-Yan scattering
- Dieperink, A. E. L.; Korpa, C. L.
We investigate the modification of the pion-cloud in the nuclear medium and
its effect on the nuclear Drell-Yan process. The pion's in-medium self-energy
is calculated in a self-consistent delta-hole model, with particle-hole
contribution also included. Both the imaginary and real part of the pion's and
delta's self-energy are taken into account and related through a dispersion
relation assuring causality. The resulting in-medium pion light-cone momentum
distribution shows only a slight enhancement compared to the one of the free
nucleon. As a consequence the ratio of the cross-section for Drell-Yan
scattering on nuclear matter and nucleonic target is close to unity in
agreement with experiment.
112.
Mesonic and Binding Contributions to the Nuclear Drell-Yan Process
- Marco, E.; Oset, E.
We have evaluated the Drell-Yan cross section in nuclei paying special
attention to the meson cloud contribution from pion and rho-meson, for which an
accurate calculation using the meson nuclear spectral functions is used.
Similarly, the nucleonic contribution is evaluated in terms of a relativistic
nucleon spectral function. Fair agreement with experiment is found for
different nuclei and the results show a sizeable contribution from the
renormalized meson cloud. In order to reproduce the experiment a novel element
is introduced, consisting of a gradual energy loss of the incoming proton in
its pass through the nucleus which produces a strong A dependence at x_1 large.
113.
Off-shell effects in the electromagnetic production of strangeness
- Mizutani, T.; Fayard, C.; Lamot, G. -H.; Saghai, B.
Previous approaches to the photo- and electro-production of strangeness off
the proton, based upon effective hadronic Lagrangians, are extended here to
incorporate the so called off-shell effects inherent to the fermions with spin
>= 3/2. A formalism for intermediate-state, spin 3/2, nucleonic and hyperonic
resonances is presented and applied to the processes $\gamma + p ---> K^{+} +
\Lambda$, for $E_{\gamma}^{lab}$ <= 2.5 GeV, $e + p ---> e' + K^+ + \Lambda$,
as well as the branching ratio for the crossed channel reaction $K^- + p --->
\gamma + \Lambda$, with stopped kaons. The sensitivity, from moderate to
significant, of various observables to such effects are discussed.
114.
Properties of \beta-stable neutron star matter with hyperons
- Vidaña, I.; Polls, A.; Ramos, A.; Elgaroey, Oe.; Engvik, L.; Hjorth-Jensen, M.
We present results from many-body calculations for \beta-stable neutron star
matter with nucleonic and hyperonic degrees of freedom, employing the most
recent parametrizations of the baryon-baryon interaction of the Nijmegen group.
It is found that the only strange baryons emerging in \beta-stable matter up to
total baryonic densities of 1.2 fm^{-3} are \Sigma^- and \Lambda. The
corresponding equations of state are thence used to compute properties of
neutron stars such as the masses, moments of inertia and radii. We also study
the possibility of forming a hyperon superfluid and discuss its implications
for neutron stars.
115.
Axial form factor of the nucleon in the perturbative chiral quark model
- Khosonthongkee, K.; Lyubovitskij, V. E.; Gutsche, Th.; Faessler, Amand; Pumsa-ard, K.; Cheedket, S.; Yan, Y.
We apply the perturbative chiral quark model (PCQM) at one loop to analyze
the axial form factor of the nucleon. This chiral quark model is based on an
effective Lagrangian, where baryons are described by relativistic valence
quarks and a perturbative cloud of Goldstone bosons as dictated by chiral
symmetry. We apply the formalism to obtain analytical expressions for the axial
form factor of the nucleon, which is given in terms of fundamental parameters
of low-energy pion-nucleon physics (weak pion decay constant, strong
pion-nucleon form factor) and of only one model parameter (radius of the
nucleonic three-quark core).
116.
Nuclear structure far from stability
- Vretenar, D.
Modern nuclear structure theory is rapidly evolving towards regions of exotic
short-lived nuclei far from stability, nuclear astrophysics applications, and
bridging the gap between low-energy QCD and the phenomenology of finite nuclei.
The principal objective is to build a consistent microscopic theoretical
framework that will provide a unified description of bulk properties, nuclear
excitations and reactions. Stringent constraints on the microscopic approach to
nuclear dynamics, effective nuclear interactions, and nuclear energy density
functionals, are obtained from studies of the structure and stability of exotic
nuclei with extreme isospin values, as well as extended asymmetric nucleonic
matter. Recent theoretical advances in the description of structure phenomena
in exotic nuclei far from...
117.
A new population of very high energy gamma-ray sources in the Milky Way
- Aharonian, F. A.
Very high energy gamma-rays probe the long-standing mystery of the origin of
cosmic rays. Produced in the interactions of accelerated particles in
astrophysical objects, they can be used to image cosmic particle accelerators.
A first sensitive survey of the inner part of the Milky Way with the High
Energy Stereoscopic System (H.E.S.S.) reveals a population of eight previously
unknown firmly detected sources of very high energy gamma-rays. At least two
have no known radio or X-ray counterpart and may be representative of a new
class of `dark' nucleonic cosmic ray sources.
118.
Momentum-space description of three-nucleon breakup reactions
including the Coulomb interaction
- Deltuva, A.; Fonseca, A. C.; Sauer, P. U.
The Coulomb interaction between the two protons is included in the
calculation of proton-deuteron breakup and of three-body electromagnetic
disintegration of ${}^3\mathrm{He}$. The hadron dynamics is based on the purely
nucleonic charge-dependent (CD) Bonn potential and its realistic extension CD
Bonn + $\Delta$ to a coupled-channel two-baryon potential, allowing for single
virtual $\Delta$-isobar excitation. Calculations are done using integral
equations in momentum space. The screening and renormalization approach is
employed for including the Coulomb interaction. Convergence of the procedure is
found at moderate screening radii. The reliability of the method is
demonstrated. The Coulomb effect on breakup observables is seen at all energies
in particular kinematic regimes.
119.
Spin physics with antiprotons
- Maggiora, M.; Collaboration, for the ASSIA
New possibilities arising from the availability at GSI of antiproton beams,
possibly polarised, are discussed. The investigation of the nucleon structure
can be boosted by accessing in Drell-Yan processes experimental asymmetries
related to cross-sections in which the parton distribution functions (PDF) only
appear, without any contribution from fragmentation functions; such processes
are not affected by the chiral suppression of the transversity function
$h_1(x)$. Spin asymmetries in hyperon production and Single Spin Asymmetries
are discussed as well, together with further items like electric and magnetic
nucleonic form factors and open charm production. Counting rates estimations
are provided for each physical case. The sketch of a possible experimental
apparatus is proposed.
120.
Azimuthal asymmetries in unpolarized Drell-Yan events on nuclear targets
- Bianconi, A.; Radici, M.
We show that for Drell-Yan events by unpolarized hadronic projectiles and
nuclear targets, azimuthal asymmetries can arise from the nuclear distortion of
the hadronic projectile wave function, typically a spin-orbit effect occurring
on the nuclear surface. The asymmetry depends on quantities that enter also the
spin asymmetry in the corresponding Drell-Yan event on polarized free nucleonic
targets. Hence, this study can be of help in exploring the spin structure of
the nucleon, in particular the transverse spin distribution of partons inside
the proton. All arguments can be extended also to antinucleon projectiles and,
consequently, apply to possible future measurements involving nuclear targets
at the foreseen HESR ring at GSI.
