33 research outputs found
New Preshower detector for DIRAC Experiment
The Preshower (PSh) detector is a component of the DIRAC setup. It is
designed to improve rejection efficiency of e-e+ pairs background in the
{\pi}{\pi} and K{\pi} pair measurement. To increase the overall efficiency, a
new two-layer structure scintillator Preshower detector has been realized in
the region where the Nitrogen Cherenkov detector has been shortened to
introduce new detectors. The new Preshower-Cherenkov combination ensures the
electron rejection efficiency better than 99.9% in momentum region 1-7 GeV/c.Comment: to be published in NIM
The SrTiO displacive transition revisited by Coherent X-ray Diffraction
We present a Coherent X-ray Diffraction study of the antiferrodistortive
displacive transition of SrTiO, a prototypical example of a phase
transition for which the critical fluctuations exhibit two length scales and
two time scales. From the microbeam x-ray coherent diffraction patterns, we
show that the broad (short-length scale) and the narrow (long-length scale)
components can be spatially disentangled, due to 100 m-scale spatial
variations of the latter. Moreover, both components exhibit a speckle pattern,
which is static on a 10 mn time-scale. This gives evidence that the
narrow component corresponds to static ordered domains. We interpret the
speckles in the broad component as due to a very slow dynamical process,
corresponding to the well-known \emph{central} peak seen in inelastic neutron
scattering.Comment: 4 pages, 3 figures, accepted in PR
X-ray fluorescence from the element with atomic number Z = 120
Accepted for publication in Physical Review LettersAn atomic clock based on X-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by X-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the X-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K X-rays from the element with Z = 120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time _f$ = 2.5×10−18s has been deduced for Z=120 from the measured X-ray multiplicity
First atom lifetime and scattering length measurements
The results of a search for hydrogen-like atoms consisting of
mesons are presented. Evidence for atom production
by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen
in terms of characteristic pairs from their breakup in the same target
() and from Coulomb final state interaction (). Using
these results the analysis yields a first value for the atom lifetime
of fs and a first model-independent measurement of
the S-wave isospin-odd scattering length
( for isospin ).Comment: 14 pages, 8 figure
Spatio-temporal channel characterization: theoretical framework and applications in MIMO system design
Standardless PIXE analysis of thick biomineral structures
The particle-induced X-ray emission (PIXE) of thick biomineral targets provides pertinent surface analysis, but if good reference materials are missing then complementary approaches are required to handle the matrix effects. This is illustrated by our results from qualitative and semiquantitative analysis of biomaterials and calcified tissues in which PIXE usually detected up to 20 elements with Z > 14 per sample, many at trace levels. Relative concentrations allow the classification of dental composites according to the mean Z and by multivariate statistics. In femur bones from streptozotocin-induced diabetic rats, trace element changes showed high individual variability but correlated to each other, and multivariate statistics improved discrimination of abnormal pathology. Changes on the in vitro demineralization of dental enamel suggested that a dissolution of Ca compounds in the outermost layer results in the uncovering of deeper layers containing higher trace element levels. Thus, in spite of significant limitations, standardless PIXE analysis of thick biomineral samples together with proper additional procedures can provide relevant information in biomedical research
Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy
First experimental feasibility study of VIPIC: a custom-made detector for X-ray speckle measurements
exterior, view of the north elevation, from the Loire Rive