115 research outputs found
Thermal bremsstrahlung probing the thermodynamical state of multifragmenting systems
Inclusive and exclusive hard-photon (E 30 MeV) production in five
different heavy-ion reactions (Ar+Au, Ag, Ni,
C at 60{\it A} MeV and Xe+Sn at 50{\it A} MeV) has been
studied coupling the TAPS photon spectrometer with several charged-particle
multidetectors covering more than 80% of 4. The measured spectra, slope
parameters and source velocities as well as their target-dependence, confirm
the existence of thermal bremsstrahlung emission from secondary nucleon-nucleon
collisions that accounts for roughly 20% of the total hard-photon yield. The
thermal slopes are a direct measure of the temperature of the excited nuclear
systems produced during the reaction.Comment: 4 pages, 3 figures, Proceedings CRIS 2000, 3rd Catania Relativistic
Ion Studies, "Phase Transitions in Strong Interactions: Status and
Perspectives", Acicastello, Italy, May 22-26, 2000 (to be published in Nuc.
Phys. A
Proton-deuteron radiative capture cross sections at intermediate energies
Differential cross sections of the reaction have been
measured at deuteron laboratory energies of 110, 133 and 180 MeV. The data were
obtained with a coincidence setup measuring both the outgoing He and the
photon. The data are compared with modern calculations including all possible
meson-exchange currents and two- and three- nucleon forces in the potential.
The data clearly show a preference for one of the models, although the shape of
the angular distribution cannot be reproduced by any of the presented models.Comment: 6 pages, 6 figures, accepted for publication in EPJ
Hard photon and neutral pion production in cold nuclear matter
The production of hard photons and neutral pions in 190 MeV proton induced
reactions on C, Ca, Ni, and W targets has been for the first time concurrently
studied. Angular distributions and energy spectra up to the kinematical limit
are discussed and the production cross-sections are presented. From the target
mass dependence of the cross-sections the propagation of pions through nuclear
matter is analyzed and the production mechanisms of hard photons and primordial
pions are derived. It is found that the production of subthreshold particles
proceeds mainly through first chance nucleon-nucleon collisions. For the most
energetic particles the mass scaling evidences the effect of multiple
collisions.Comment: submitted to Phys. Lett.
Evidence for Thermal Equilibration in Multifragmentation Reactions probed with Bremsstrahlung Photons
The production of nuclear bremsstrahlung photons (E 30 MeV) has
been studied in inclusive and exclusive measurements in four heavy-ion
reactions at 60{\it A} MeV. The measured photon spectra, angular distributions
and multiplicities indicate that a significant part of the hard-photons are
emitted in secondary nucleon-nucleon collisions from a thermally equilibrated
system. The observation of the thermal component in multi-fragment
Ar+Au reactions suggests that the breakup of the thermalized
source produced in this system occurs on a rather long time-scale.Comment: Revised version, accepted for publication in Physical Review Letters.
4 pages, 4 fig
Compressional-mode giant resonances in deformed nuclei
AbstractBackground-free inelastic scattering spectra have been obtained for the Sm isotopes with 400 MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the isoscalar giant resonances (L⩽3) have been extracted for the spherical nucleus 144Sm and the deformed nucleus 154Sm. We have observed that the effects of deformation are different for the low- and high-excitation-energy components of the isoscalar giant dipole resonance in 154Sm. Evidence for the theoretically predicted coupling between the isoscalar dipole resonance and the high-energy octupole resonance is reported
Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions
Photon energy spectra up to the kinematic limit have been measured in 190 MeV
proton reactions with light and heavy nuclei to investigate the influence of
the multiple-scattering process on the photon production. Relative to the
predictions of models based on a quasi-free production mechanism a strong
suppression of bremsstrahlung is observed in the low-energy region of the
photon spectrum. We attribute this effect to the interference of photon
amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let
Dynamical effects in proton-proton bremsstrahlung for non-coplanar geometries
The proton-proton bremsstrahlung process, including both coplanar and non-coplanar kinematics, has been measured with polarized protons of 190 MeV. High-precision cross sections and analyzing powers have been obtained. Cross sections as a function of non-coplanarity angle are presented and show large variations of dynamical origin. Non-coplanar analyzing powers have been measured for the first time and are compared to theoretical predictions. (C) 2000 Elsevier Science B.V. All rights reserved
Cross sections and electromagnetic response functions for radiative proton capture in pd -> He-3+e(+)e(-)
Exclusive differential cross sections of virtual-photon radiative proton capture in pd --> He-3 + e(+)e(-) at a proton energy of 190 MeV have been measured for the first time. The leptonic-angle dependence of the measured cross section is exploited in order to determine the electromagnetic response functions in the time-like region. The data are compared to a relativistic gauge-invariant impulse approximation and a Faddeev calculation. Differences between theoretical predictions and data are discussed in terms of enhanced magnetic radiation possibly originating from virtual Delta excitations
Methylphenidate significantly improves declarative memory functioning of adults with ADHD
Contains fulltext :
87790.pdf (publisher's version ) (Closed access)BACKGROUND: Declarative memory deficits are common in untreated adults with attention-deficit hyperactivity disorder (ADHD), but limited evidence exists to support improvement after treatment with methylphenidate. The objective of this study was to examine the effects of methylphenidate on memory functioning of adults with ADHD. METHODS: Eighteen adults with ADHD who were clinical responders to methylphenidate participated in this randomized crossover trial. After 3 days of no treatment, patients received in random order either their usual methylphenidate dose (mean: 14.7 mg; range: 10-30 mg) or placebo, separated by a 6-7-day washout period. Patients performed an immediate word recall test 1 h after treatment administration. Three hours after intake, patients performed the second part of the memory test (delayed word recall and a recognition test). RESULTS: Delayed recognition and immediate recall was similar on treatment and on placebo. Delayed word recall was significantly better in the methylphenidate than in the placebo condition (F (1, 17) = 7.0, p < 0.017). A significant correlation was found between prestudy CES-D depression scores and difference scores on delayed recall (r = 0.602, p < 0.008). CONCLUSION: Methylphenidate improves declarative memory functioning in patients with ADHD. New studies should further examine whether subclinical depressive symptoms mediate the effect of methylphenidate on declarative memory.1 oktober 201
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