1,816 research outputs found
Electron irradiation effects on superconductivity in PdTe: an application of a generalized Anderson theorem
Low temperature ( 20~K) electron irradiation with 2.5 MeV relativistic
electrons was used to study the effect of controlled non-magnetic disorder on
the normal and superconducting properties of the type-II Dirac semimetal
PdTe. We report measurements of longitudinal and Hall resistivity, thermal
conductivity and London penetration depth using tunnel-diode resonator
technique for various irradiation doses. The normal state electrical
resistivity follows Matthiessen rule with an increase of the residual
resistivity at a rate of 0.77cm/. London penetration depth and thermal
conductivity results show that the superconducting state remains fully gapped.
The superconducting transition temperature is suppressed at a non-zero rate
that is about sixteen times slower than described by the Abrikosov-Gor'kov
dependence, applicable to magnetic impurity scattering in isotropic,
single-band -wave superconductors. To gain information about the gap
structure and symmetry of the pairing state, we perform a detailed analysis of
these experimental results based on insight from a generalized Anderson theorem
for multi-band superconductors. This imposes quantitative constraints on the
gap anisotropies for each of the possible pairing candidate states. We conclude
that the most likely pairing candidate is an unconventional
state. While we cannot exclude the conventional and the triplet
, we demonstrate that these states require additional assumptions about
the orbital structure of the disorder potential to be consistent with our
experimental results, e.g., a ratio of inter- to intra-band scattering for the
singlet state significantly larger than one. Due to the generality of our
theoretical framework, we think that it will also be useful for irradiation
studies in other spin-orbit-coupled multi-orbital systems.Comment: 22 pages, 12 figure
Thermal and Chemical Freeze-out in Spectator Fragmentation
Isotope temperatures from double ratios of hydrogen, helium, lithium,
beryllium, and carbon isotopic yields, and excited-state temperatures from
yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were
determined for spectator fragmentation, following collisions of 197Au with
targets ranging from C to Au at incident energies of 600 and 1000 MeV per
nucleon. A deviation of the isotopic from the excited-state temperatures is
observed which coincides with the transition from residue formation to
multi-fragment production, suggesting a chemical freeze-out prior to thermal
freeze-out in bulk disintegrations.Comment: 14 pages, 10 figures, submitted to Phys. Rev. C, small changes as
suggested by the editors and referee
Isospin dependent multifragmentation of relativistic projectiles
The N/Z dependence of projectile fragmentation at relativistic energies has
been studied with the ALADIN forward spectrometer at the GSI Schwerionen
Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident
energy of 600 MeV per nucleon have been used in order to explore a wide range
of isotopic compositions. For the interpretation of the data, calculations with
the statistical multifragmentation model for a properly chosen ensemble of
excited sources were performed. The parameters of the ensemble, representing
the variety of excited spectator nuclei expected in a participant-spectator
scenario, are determined empirically by searching for an optimum reproduction
of the measured fragment-charge distributions and correlations. An overall very
good agreement is obtained. The possible modification of the liquid-drop
parameters of the fragment description in the hot freeze-out environment is
studied, and a significant reduction of the symmetry-term coefficient is found
necessary to reproduce the mean neutron-to-proton ratios /Z and the
isoscaling parameters of Z<=10 fragments. The calculations are, furthermore,
used to address open questions regarding the modification of the surface-term
coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and
the isotopic evolution of the spectator system between its formation during the
initial cascade stage of the reaction and its subsequent breakup.Comment: 23 pages, 29 figures, published in Physical Review
Isotopic Dependence of the Nuclear Caloric Curve
The A/Z dependence of projectile fragmentation at relativistic energies has
been studied with the ALADIN forward spectrometer at SIS. A stable beam of
124Sn and radioactive beams of 124La and 107Sn at 600 MeV per nucleon have been
used in order to explore a wide range of isotopic compositions. Chemical
freeze-out temperatures are found to be nearly invariant with respect to the
A/Z of the produced spectator sources, consistent with predictions for expanded
systems. Small Coulomb effects (\Delta T \approx 0.6 MeV) appear for residue
production near the onset of multifragmentation.Comment: 11 pages, 3 figures, accepted for publ. in Phys. Rev. Let
Tracing a phase transition with fluctuations of the largest fragment size: Statistical multifragmentation models and the ALADIN S254 data
A phase transition signature associated with cumulants of the largest
fragment size distribution has been identified in statistical
multifragmentation models and examined in analysis of the ALADIN S254 data on
fragmentation of neutron-poor and neutron-rich projectiles. Characteristics of
the transition point indicated by this signature are weakly dependent on the
A/Z ratio of the fragmenting spectator source. In particular, chemical
freeze-out temperatures are estimated within the range 5.9 to 6.5 MeV. The
experimental results are well reproduced by the SMM model.Comment: 7 pages, 3 figures, Proceedings of the International Workshop on
Multifragmentation and Related Topics (IWM2009), Catania, Italy, November
2009
OC-0441: Genomic amplification of FancA in HNSCC: mechanisms of radioresistance and clinical relevance
Discriminant Analysis and Secondary-Beam Charge Recognition
The discriminant-analysis method has been applied to optimize the exotic-beam
charge recognition in a projectile fragmentation experiment. The experiment was
carried out at the GSI using the fragment separator (FRS) to produce and select
the relativistic secondary beams, and the ALADIN setup to measure their
fragmentation products following collisions with Sn target nuclei. The beams of
neutron poor isotopes around 124La and 107Sn were selected to study the isospin
dependence of the limiting temperature of heavy nuclei by comparing with
results for stable 124Sn projectiles. A dedicated detector to measure the
projectile charge upstream of the reaction target was not used, and alternative
methods had to be developed. The presented method, based on the multivariate
discriminant analysis, allowed to increase the efficacy of charge recognition
up to about 90%, which was about 20% more than achieved with the simple scalar
methods.Comment: 6 pages, 7 eps figures, elsart, submitted to Nucl. Instr. and Meth.
Gross Properties and Isotopic Phenomena in Spectator Fragmentation
A systematic study of isotopic effects in the break-up of projectile
spectators at relativistic energies has been performed with the ALADiN
spectrometer at the GSI laboratory. Searching for signals of criticality in the
fragment production we have applied the model independent universal
fluctuations theory already proposed to track criticality signals in
multifragmentation to our data. The fluctuation of the largest fragment charge
and of the asymmetry of the two and three largest fragments and their bimodal
distribution have also been analysed.Comment: 6 pages, 4 figures, IX International Conference on Nucleus-Nucleus
Collisions, Rio de Janeiro, Brazil, August 28 - September 1, 200
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