arXiv subjects

J. -C. Poizat

Publications and source records attributed to J. -C. Poizat.

3 recordsLinked to original sources

arXiv2008

Monitoring the Bragg peak location of 73 MeV/u carbon ions by means of prompt $γ$-ray measurements

By means of a time-of-flight technique, we measured the longitudinal profile of prompt $γ$-rays emitted by 73 MeV/u $^{13}$C ions irradiating a PMMA target. This technique allowed us to minimize the shielding against neutrons and scattered $γ$-rays, and to correlate prompt gamma emission to the ion path. This correlation, together with a high counting rate, paves the way toward real-time monitoring of the longitudinal dose profile during ion therapy treatments. Moreover, the time correlation between the prompt gamma detection and the transverse position of the incident ions measured by a beam monitor can provide real-time 3D control of the irradiation.

physics.atom-ph↗

arXiv2005

Electron gas polarization effect induced by heavy H-like ions of moderate velocities channeled in a silicon crystal

We report on the observation of a strong perturbation of the electron gas induced by 20 MeV/u U$^{91+}$ ions and 13 MeV/u Pb$^{81+}$ ions channeled in silicon crystals. This collective response (wake effect) in-duces a shift of the continuum energy level by more than 100 eV, which is observed by means of Radiative Electron Capture into the K and L-shells of the projectiles. We also observe an increase of the REC probability by 20-50% relative to the probability in a non-perturbed electron gas. The energy shift is in agreement with calculations using the linear response theory, whereas the local electron density enhancement is much smaller than predicted by the same model. This shows that, for the small values of the adiabaticity parameter achieved in our experiments, the density fluctuations are not strongly localized at the vicinity of the heavy ions.

physics.atom-ph↗

arXiv2005

Summary of experimental studies at CERN on a positron source using crystal effects

New kind of positron sources for future linear colliders, where the converter is a tungsten crystal oriented on the <111> axis, has been studied at CERN in the WA103 experiment. In such sources the photons which create the $e^+ e^-$ pairs result from channeling radiation and coherent bremsstrahlung. In this experiment electron beams of 6 and 10 GeV were sent on different kinds of targets: a 4 mm thick crystal, a 8 mm thick crystal and a compound taraget (4 mm crystal + 4 mm amorphous disk). An amorphous tungsten target 20 mm thick was also used for comparison with the 8 mm crystal. Tracks of outgoing charged particles were detected and analyzed by a drift chamber in a magnetic field. The energy and angle spectra of the positrons were obtained for energies up to 150 MeV and angles up to 30 degrees. The measured positron distribution in momentum space (longitudinal versus transverse) is also presented, giving a full momentum space description of the source. Results on outgoing photons are also presented. A significant enhancement of both photon and positron production is clearly observed. At 10 GeV incident energy, the positron enhancement factor is 4 for the 4 mm crystal, about 2 for the 8 mm crystal. Besides, the simulation code for the crystal processes is validated by a quite good agreement between the simulated and experimental spectra, both for positrons and photons.

physics.ins-det↗