Y Schutz

Identification of photons and particles in the segmented electromagnetic calorimeter TAPS

Abstract The algorithms devellped for the identification of one and two hard-photon events detected with TAPS are presented. After a presentation of the energy and time calibrations, the identification of single module events and the shower reconstruction, special emphasis is given to the rejection of the background generated by cosmic rays, π 0 decay and e ± conversion pairs. The effect of discontinuous showers is also discussed. The method was tested on data taken with TAPS at GANIL for heavy-ion collisions at energies of several tens of A MeV.

Evidence for thermal equilibration in multifragmentation reactions probed with bremsstrahlung photons

The production of nuclear bremsstrahlung photons (E{sub {gamma}}>30 MeV) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at 60A MeV . The measured photon spectra, angular distributions, and multiplicities indicate that a significant fraction of the hard photons is emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multifragment {sup 36}Ar+{sup 197}Au reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time scale.

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 quasifree 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.

TOPOLOGY ANALYSIS FOR THE IDENTIFICATION OF ENERGETIC PHOTONS IN A SEGMENTED ELECTROMAGNETIC CALORIMETER

Abstract We present a novel method to identify energetic photons detected in a segmented electromagnetic calorimeter. It is based on topology analysis of electromagnetic showers which develop in the detector following the impact of photons. This approach supplements standard methods for the most energetic photons detected in a given experiment and for which the limited statistics does not permit to define the parameters of the pulse-shape analysis. The method is tested on photons with energies above Eγ>250 MeV produced in the reaction Ar+Ca at 180 A MeV and detected with the TAPS multidetector.

Identification of hydrogen isotopes with the BaF2 electromagnetic calorimeter TAPS

Abstract The mass spectrum of hydrogen isotope was deduced from the kinetic energy and time-of-flight (TOF) measured with the segmented electromagnetic calorimeter TAPS. The reactions studied were Kr + Ni at 60 A MeV and Ar + Ca at 180 A MeV. Proper corrections for the energy lost by charged particles in passive absorbers between the target and the scintillator are essential to improve greatly the mass resolution. Extension of the capabilities of TAPS to identify light charged particles allows one to study correlations between photons or neutral pions and charged particles.

Thermal bremsstrahlung probing the thermodynamical state of multifragmenting systems

Inclusive and exclusive hard-photon (E-gamma > 30 MeV) production in five different heavy-ion reactions (Ar-36+Au-197, Ag-107, Ni-58, C-12 at 60A MeV and Xe-129+Sn-120 at 50A MeV) has been studied coupling the TAPS photon spectrometer with several charged-particle multidetectors covering more than 80% of 4 pi. 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.

Transverse momentum distributions of neutral pions produced at deep subthreshold energies

We present in this paper transverse momentum distributions of π0-mesons measured in 36Ar+197Au reactions at 25A and 35A MeV beam energies with the spectrometer TAPS at the KVI AGOR accelerator. Our data are consistent with thermal-like emission of π0-mesons with temperature parameters much lower than in earlier measurements.