4,189 research outputs found
Monte Carlo simulation of a collimation system for low-energy beamline of ELI-NP Gamma Beam System
ELI-nuclear physics (NP) Gamma Beam System (GBS) is an intense and monochromatic gamma beam source based on inverse Compton interaction, currently being built in Bucharest, Romania. The gamma beam produced, with energy ranging from 0.2 to 20 MeV, energy bandwidth 0.5% and flux of about , will be devoted to investigate a broad range of applications such as nuclear physics, astrophysics, material science and life sciences. The radiation produced by an inverse Compton interaction is not intrinsically monochromatic. In fact, the energy of the photons produced is related to the emission angle, therefore the energy bandwidth can be modified adjusting the collimation of the gamma beam. In order to define the optimal layout and evaluate the performance of a collimation system for the ELI-NP-GBS low-energy beamline (0.2-3.5 MeV), a detailed Monte Carlo simulation activity has been carried out. The simulation, using Geant4 and MCNPX codes, included the transport of the gamma beam from the interaction point to the experimental area passing through vacuum pipes, vacuum chambers, collimation system and relative shielding. The effectiveness of the collimation system, in obtaining the required energy distribution and avoiding the contamination due to secondary radiation production, was evaluated. Also, the background radiation generated by collimation and the shielding layout have been studied
Radicalism in Law and Criminology: A Retrospective View of Critical Legal Studies and Radical Criminology
Correctional Administrators Assess the Adequacy and Impact of Prison Legal Services Programs in the United States
Radicalism in Law and Criminology: A Retrospective View of Critical Legal Studies and Radical Criminology
Electromagnetic Form Factors of the Nucleon in a Relativistic Quark Pair Creation Model
We study the effects of the | qqq q\bar{q} > component of the hadronic wave
function on the description of the electromagnetic structure of the nucleon.
Starting with a qqq baryonic wave function which describes the baryonic and
mesonic low energy spectrum, the extra q\bar{q} pair is generated through a
relativistic version of the 3P_0 model. It is shown that this model leads to a
renormalization of the quark mass that allows one to construct a conserved
electromagnetic current. We conclude that these dynamical relativistic
corrections play an important role in reproducing the Q2 dependence of the
electromagnetic form factors at low Q^2.Comment: 15 pages, 3 figures. Minor change
Splitting of the pi - rho spectrum in a renormalized light-cone QCD-inspired model
We show that the splitting between the light pseudo-scalar and vector meson
states is due to the strong short-range attraction in the ^1S_0 sector which
makes the pion and the kaon light particles. We use a light-cone QCD-inspired
model of the mass squared operator with harmonic confinement and a Dirac-delta
interaction. We apply a renormalization method to define the model, in which
the pseudo-scalar ground state mass fixes the renormalized strength of the
Dirac-delta interaction.Comment: 9 pages, 2 figures, revtex, accepted by Phys. Rev. D; Corrected typo
A consistent explanation of the Roper phenomenology
We study the electromagnetic transitions of the Roper N(1440) resonance. Our
results, when combined with the previously obtained for the mass and the pionic
strong decay widths of the Roper, show that within a non-relativistic
constituent quark model scheme, a comprehensible understanding of the Roper
phenomenology can be achieved. They also seem to support the view of the Roper
as a radial excitation of the nucleon, though more experimental data are needed
to reach a definitive conclusion.Comment: 14 pages, 4 figures (7 postscript files). Some referencess adde
Space-like and time-like pion electromagnetic form factor and Fock state components within the Light-Front dynamics
The simultaneous investigation of the pion electromagnetic form factor in the
space- and time-like regions within a light-front model allows one to address
the issue of non-valence components of the pion and photon wave functions. Our
relativistic approach is based on a microscopic vector meson dominance (VMD)
model for the dressed vertex where a photon decays in a quark-antiquark pair,
and on a simple parametrization for the emission or absorption of a pion by a
quark. The results show an excellent agreement in the space like region up to
-10 , while in time-like region the model produces reasonable
results up to 10 .Comment: 74 pages, 11 figures, use revtex
Electromagnetic structure and weak decay of meson K in a light-front QCD-inspired
The kaon electromagnetic (e.m.) form factor is reviewed considering a
light-front constituent quark model. In this approach, it is discussed the
relevance of the quark-antiquark pair terms for the full covariance of the e.m.
current. It is also verified, by considering a QCD dynamical model, that a good
agreement with experimental data can be obtained for the kaon weak decay
constant once a probability of about 80% of the valence component is taken into
account.Comment: 4 pages and 1 figure eps. To appear Nucl. Phys. A (2007
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