Comparison of electromagnetic and nuclear dissociation of 17Ne^{17}\mathrm{Ne}

The Borromean drip-line nucleus ¹⁷Ne has been suggested to possess a two-proton halo structure in its ground state. In the astrophysical rp-process, where the two-proton capture reaction ¹⁵O(2p,γ) ¹⁷Ne plays an important role, the calculated reaction rate differs by several orders of magnitude between different theoretical approaches. To add to the understanding of the ¹⁷Ne structure we have studied nuclear and electromagnetic dissociation. A 500 MeV/u¹⁷Ne beam was directed toward lead, carbon, and polyethylene targets. Oxygen isotopes in the final state were measured in coincidence with one or two protons. Different reaction branches in the dissociation of ¹⁷Ne were disentangled. The relative populations of s and d states in ¹⁶F were determined for light and heavy targets. The differential cross section for electromagnetic dissociation (EMD) shows a continuous internal energy spectrum in the three-body system ¹⁵O + 2p. The ¹⁷Ne EMD data were compared to current theoretical models. None of them, however, yields satisfactory agreement with the experimental data presented here. These new data may facilitate future development of adequate models for description of the fragmentation process

Detecting solar chameleons through radiation pressure

Light scalar elds can drive the accelerated expansion of the universe. Hence, they are obvious dark energy candidates. To make such models compatible with tests of General Relativity in the solar system and \fth force" searches on Earth, one needs to screen them. One possibility is the so-called \chameleon" mechanism, which renders an eective mass depending on the local matter density. If chameleon particles exist, they can be produced in the sun and detected on Earth exploiting the equivalent of a radiation pressure. Since their eective mass scales with the local matter density, chameleons can be re ected by a dense medium if their eective mass becomes greater than their total energy. Thus, under appropriate conditions, a ux of solar chameleons may be sensed by detecting the total instantaneous momentum transferred to a suitable opto-mechanical force/pressure sensor. We calculate the solar chameleon spectrum and the reach in the chameleon parameter space of an experiment using the preliminary results from a force/pressure sensor, currently under development at INFN Trieste, to be mounted in the focal plane of one of the X-Ray telescopes of the CAST experiment at CERN. We show, that such an experiment signies a pioneering eort probing uncharted chameleon parameter space.1661sciescopu

Observation of two-electron transitions in dense non-Maxwellian laser-produced plasmas and their use as diagnostic reference lines

International audienceTwo-electron satellite transitions near He-beta, 1s2s3s-1s(2)2P and 1s2s3d-1s(2)2p, have been identified in dense laser-produced plasmas. Space resolved high-resolution spectra indicate that their existence is confined to the area of the laser spot thereby providing a localized emission source of the highest density plasma region. Detailed modeling with the MARIA-code verifies their advantageous use as diagnostic reference lines in dense optically thick plasmas. Close to the target surface, anomalous high emission is encountered for the Li-like two-electron transitions op = 1s2s(2)-1s(2)2p. The high resolution data taken with spherically bent mica crystals indicates that there is an intensity correlation with higher order intercombination satellite transitions 1s2l3l ` -1s(2)2 `` near He-alpha. An important finding is the very good agreement between the data and the simulations, when considering forbidden transitions only and when using two-electron transitions as reference lines. Based on these reference lines space resolved non-Maxwellian signatures could be determined. (C) 2001 Elsevier Science Ltd. All rights reserved

A study of highly charged ions interacting with a plasma target at the Institute of Modern Physics

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">A new experimental area for the investigation of ion beam matter interaction and ion beam plasma interaction was completed at the Institute of Modern Physics (Lanzhou, China). We report the details of this low-energy setup and first results on ion beam matter interaction, where we measured the charge state of O5+ ions at 1 MeV passing through a hydrogen gas target. The data were compared with the Monte-Carlo simulation results for cold hydrogen gas and hydrogen plasma.</span

Investigation on the energy loss in low energy protons interacting with hydrogen plasma

<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Energy loss of protons with energy 100 keV penetrating the partially ionized hydrogen plasma target was measured. The plasma target was created by electric discharge in the hydrogen gas, the state of the plasma target was diagnosed by using the laser interferometry method: the free electron density is up to 10(16) cm(-3), temperature is about 1-2 eV, and the plasma target may exist at the microsecond level. It is found that the energy loss of protons is closely related to the free electron density, and the energy loss data enable us to infer the value of the Coulomb logarithm (10.8) for the stopping power of the free electrons. This agrees well with the theoretical prediction which is 4.3 times higher than that given by the Bethe formula for neutral hydrogen, which is a little bigger than Hoffmann&#39;s result but much smaller than Jacoby&#39;s result. Comparing our result with Hoffmann&#39;s, the energy we used is only 100 keV, much lower than 1.4 MeV/u, and the low-energy regime we applied could be the cause of the increase in the enhancement factor. However, in the comparison between our result and the Jacoby&#39;s, the effective charge for protons is almost constant, unlike the Kr+ impact in wihch the enhanced ion charge state induces the giant enhancement factor. Compared to the gas target, the energy loss enhancement factor in plasma target is 2.9.</span