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Kalweit A.,TU Darmstadt | Ivanov M.,Gesellschaft fur Schwerionenforschung mbH
Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications - Proceedings of the 11th Conference | Year: 2010

In a Time Projection Chamber like the ALICE TPC, the simultaneous measurement of momentum and ionization along the trajectory of a charged particle allows excellent particle identification over a wide momentum range. Real data results from cosmic runs are shown. The latter allow a measurement of the energy loss signal of muons over several orders of magnitude in momentum. The obtained distributions are compared with Bethe-Bloch parameterizations. Influences of the detector calibration, e.g. the gain equalization with radioactive krypton gas, on the dE/dx resolution are discussed. The achieved performance is compared with theoretical expectations and shows that the detector is working according to specifications. © 2010 by World Scientific Publishing Co. Pte. Ltd.

Pangon V.,Gesellschaft fur Schwerionenforschung MbH | Pangon V.,Goethe University Frankfurt | Nagy S.,Debrecen University | Polonyi J.,University of Strasbourg | Sailer K.,Debrecen University
International Journal of Modern Physics A | Year: 2011

A numerical algorithm is used to solve the bare and the effective potential for the scalar φ4 model in the local potential approximation. An approximate dynamical Maxwell-cut is found which reveals itself in the degeneracy of the action for modes at some scale. This result indicates that the potential develop singular field dependence as far as one can see it by an algorithm of limited numerical accuracy. © 2011 World Scientific Publishing Company.

Rzadkiewicz J.,Andrzej Soltan Institute for Nuclear Studies | Rzadkiewicz J.,Poland Institute of Plasma Physics and Laser Microfusion | Gojska A.,Andrzej Soltan Institute for Nuclear Studies | Rosmej O.,Gesellschaft fur Schwerionenforschung MbH | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

This article presents a detailed analysis of the Kα x-ray spectra of Si induced by 11.4 MeV/u Ca projectiles penetrating a low-density SiO2 aerogel target measured with high spectral and spatial resolution at the UNILAC accelerator at GSI-Darmstadt. The low-density material used in the experiment was crucial for the space-resolved studies of the Si x-ray radiation (for different energies of stopping Ca ions). The stopping length of the 11 MeV/u Ca ions reaches up to 10 mm in the low-density SiO2 aerogel, whereas in regular quartz solid targets it is about 100 times shorter. The analysis of the x-ray spectra emitted by the stopping medium has shown a high level of the L-shell ionization, especially in the later considered phase (Ep∼5 MeV/u) of the stopping process. It has been further demonstrated that the population of the highly ionized states produced in the ion-atom collisions can be substantially reduced in the time between the collision and the x-ray emission due to the very intense rearrangement processes occurring in Si situated in the chemical environment of oxygen atoms. Moreover, comparison of the experimental values of the Kα L-shell satellite energy shifts with the results of the multiconfiguration Dirac-Fock calculations allows us to find that Si valence electron configuration is enriched due to electron transfer from valence-electron-rich oxygen atoms into highly ionized silicon atoms. Our results indicate that the Coulomb explosion in a highly ionized track core is prevented by rapid neutralization in the femtosecond time scale. © 2010 The American Physical Society.

Levai P.,KFKI Research Institute | Skokov V.,Gesellschaft fur Schwerionenforschung MbH
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Nonperturbative charm and bottom quark-pair production is investigated in the early stage of heavy-ion collisions. The time-dependent study is based on a kinetic description of fermion-pair production in strong non-Abelian fields. We introduce a time-dependent chromo-electric external field with a pulselike time evolution to simulate the overlap of two colliding heavy ions. The calculations is performed in a SU(2) color model with finite current quark masses. Yields of heavy quark pairs are compared to the ones of light and strange quark pairs. We show that the small inverse duration time of the field pulse determines the efficiency of the quark-pair production. The expected suppression for heavy quark production, as follows from the Schwinger formula for a constant field, is not seen, but rather an enhanced heavy quark production appears at ultrarelativistic energies. © 2010 The American Physical Society.

Block M.,Gesellschaft fur Schwerionenforschung mbH | Block M.,Johannes Gutenberg University Mainz
International Journal of Mass Spectrometry | Year: 2013

Penning-trap mass spectrometry (PTMS) has become the method of choice for direct high-precision mass measurements of radionuclides in recent years. This has opened up many new possibilities for the study of the nuclear structure evolution in nuclides far away from stability. The introduction of buffer-gas stopping along with advanced ion-manipulation techniques has extended the reach of PTMS to radionuclides produced in fusion-evaporation reactions. Thus, the elements heavier than fermium that can only be produced in this way are now also accessible to PTMS. This contribution reviews the present status of direct mass measurements of the heaviest elements taking the pioneering measurements with SHIPTRAP at GSI as an example. Novel approaches that can be realized combining PTMS with other techniques are addressed and the future perspectives for experiments on superheavy elements are discussed. © 2013 Elsevier B.V. All rights reserved.

Schwiening J.,Gesellschaft fur Schwerionenforschung MbH
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

The P̄ANDA experiment at FAIR will perform high precision experiments in the charmed quark sector using cooled antiproton beams of unprecedented intensities of L=2×1032 cm-2 s-1 in the momentum range of 115 GeV/c. The charged particle identification in the barrel region needs a thin detector operating in a strong magnetic field. A ring imaging Cherenkov detector using the DIRC principle is an excellent match to those requirements. This article describes aspects of the design and R&D for the P̄ANDA barrel DIRC detector. The availability of highly pixelated fast photon detectors allows several key improvements compared to the successful BaBar-DIRC detector, some of which were tested in a proton beam at GSI. The optical properties of the radiator bars, made from synthetic fused silica, are critical to the success of the DIRC. Measurements of the attenuation length and reflection coefficient allow the determination of the surface roughness of prototype radiator bars. © 2010 Elsevier B.V. All rights reserved.

Pangon V.,Gesellschaft fur Schwerionenforschung MbH | Pangon V.,Goethe University Frankfurt
International Journal of Modern Physics A | Year: 2012

We study in this paper the sine-Gordon model using functional renormalization group at local potential approximation using different renormalization group (RG) schemes. In d = 2, using WegnerHoughton RG we demonstrate that the location of the phase boundary is entirely driven by the relative position to the Coleman fixed point even for strongly coupled bare theories. We show the existence of a set of IR fixed points in the broken phase that are reached independently of the bare coupling. The bad convergence of the Fourier series in the broken phase is discussed and we demonstrate that these fixed points can be found only using a global resolution of the effective potential. We then introduce the methodology for the use of average action method where the regulator breaks periodicity and show that it provides the same conclusions for various regulators. The behavior of the model is then discussed in d≠2 and the absence of the previous fixed points is interpreted. © 2012 World Scientific Publishing Company.

Kratz J.V.,Gesellschaft fur Schwerionenforschung MbH | Schadel M.,Gesellschaft fur Schwerionenforschung MbH | Gaggeler H.W.,Gesellschaft fur Schwerionenforschung MbH
Physical Review C - Nuclear Physics | Year: 2013

Recent theoretical work has renewed interest in radiochemically determined isotope distributions in reactions of 238U projectiles with heavy targets that had previously been published only in parts. These data are being reexamined. The cross sections σ(Z) below the uranium target have been determined as a function of incident energy in thick-target bombardments. These are compared to predictions by a diffusion model whereby consistency with the experimental data is found in the energy intervals 7.65-8.30 MeV/u and 6.06-7.50 MeV/u. In the energy interval 6.06-6.49 MeV/u, the experimental data are lower by a factor of 5 compared to the diffusion model prediction indicating a threshold behavior for massive charge and mass transfer close to the barrier. For the intermediate energy interval, the missing mass between the primary fragment masses deduced from the generalized Qgg systematics including neutron pair-breaking corrections and the centroid of the experimental isotope distributions as a function of Z have been used to determine the average excitation energy as a function of Z. From this, the Z dependence of the average total kinetic-energy loss (TKEL̄) has been determined. This is compared to that measured in a thin-target counter experiment at 7.42 MeV/u. For small charge transfers, the values of TKEL̄ of this work are typically about 30 MeV lower than in the thin-target experiment. This difference is decreasing with increasing charge transfer developing into even slightly larger values in the thick-target experiment for the largest charge transfers. This is the expected behavior which is also found in a comparison of the partial cross sections for quasielastic and deep-inelastic reactions in both experiments. The cross sections for surviving heavy actinides, e.g., 98Cf, 99Es, and 100Fm indicate that these are produced in the low-energy tails of the dissipated energy distributions, however, with a low-energy cutoff at about 35 MeV. Excitation functions show that identical isotope distributions are populated independent of the bombarding energy indicating that the same bins of excitation energy are responsible for the production of these fissile isotopes. A comparison of the survival probabilities of the residues of equal charge and neutron transfers in the reactions of 238U projectiles with either 238U or 248Cm targets is consistent with such a cutoff as evaporation calculations assign the surviving heavy actinides to the 3n and/or 4n evaporation channels. © 2013 American Physical Society.

Block M.,Gesellschaft fur Schwerionenforschung mbH
Springer Tracts in Modern Physics | Year: 2014

The mass of an atom is directly related to the binding energy of all its constituents. Thus, it provides information about all the interactions inside the atom. High-precision mass measurements hence allow studies of fundamental interactions and are of great importance in many different fields in physics. Themasses of radionuclides provide information on their stability and their structure and are therefore of particular interest for nuclear structure investigations and as input for nucleosynthesis models in nuclear astrophysics. Penning trap mass spectrometry provides masses of radionuclides with unprecedented accuracies on the order of 10-8 and can nowadays be applied even to nuclides with short half-lives and low production rates. Utilizing advanced ion manipulation techniques radionuclides from essentially all elements produced in a broad range of nuclear reactions can be accessed. In this chapter the standard procedures of on-line Penning trap mass spectrometry are introduced and some representative examples of recent mass measurements are given. © Springer-Verlag Berlin Heidelberg 2014.

Reifarth R.,Gesellschaft fur Schwerionenforschung MbH | Reifarth R.,Goethe University Frankfurt
Journal of Physics: Conference Series | Year: 2010

Almost all of the heavy elements are produced via neutron capture reactions in a multitude of stellar production sites. The predictive power of the underlying stellar models is currently limited because they contain poorly constrained physics components such as convection, rotation or magnetic fields. Neutron captures measurements on heavy radioactive isotopes provide a unique opportunity to largely improve these physics components, and thereby address important questions of nuclear astrophysics. Such species are branch-points in the otherwise uniquely defined path of subsequent neutron captures along the s-process path in the valley of stability. These branch points reveal themselves through unmistakable signatures recovered from pre-solar meteoritic grains that originate in individual element producing stars. Measurements on radioactive isotopes for neutron energies in the keV region represent a stringent challenge for further improvements of experimental techniques. This holds true for the neutron sources, the detection systems and the technology to handle radioactive material. © 2010 IOP Publishing Ltd.

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