72 research outputs found
Event layers in the Japanese Lake Suigetsu 'SG06' sediment core:Description, interpretation and climatic implications
Event layers in lake sediments are indicators of past extreme events, mostly the results of floods or earthquakes. Detailed characterisation of the layers allows the discrimination of the sedimentation processes involved, such as surface runoff, landslides or subaqueous slope failures. These processes can then be interpreted in terms of their triggering mechanisms. Here we present a 40 ka event layer chronology from Lake Suigetsu, Japan. The event layers were characterised using a multi-proxy approach, employing light microscopy and μXRF for microfacies analysis. The vast majority of event layers in Lake Suigetsu was produced by flood events (362 out of 369), allowing the construction of the first long-term, quantitative (with respect to recurrence) and well dated flood chronology from the region. The flood layer frequency shows a high variability over the last 40 ka, and it appears that extreme precipitation events were decoupled from the average long-term precipitation. For instance, the flood layer frequency is highest in the Glacial at around 25 ka BP, at which time Japan was experiencing a generally cold and dry climate. Other cold episodes, such as Heinrich Event 1 or the Late Glacial stadial, show a low flood layer frequency. Both observations together exclude a simple, straightforward relationship with average precipitation and temperature. We argue that, especially during Glacial times, changes in typhoon genesis/typhoon tracks are the most likely control on the flood layer frequency, rather than changes in the monsoon front or snow melts. Spectral analysis of the flood chronology revealed periodic variations on centennial and millennial time scales, with 220 yr, 450 yr and a 2000 yr cyclicity most pronounced. However, the flood layer frequency appears to have not only been influenced by climate changes, but also by changes in erosion rates due to, for instance, earthquakes
Feasibility studies of the polarization of photons beyond the optical wavelength regime with the J-PET detector
J-PET is a detector optimized for registration of photons from the
electron-positron annihilation via plastic scintillators where photons interact
predominantly via Compton scattering. Registration of both primary and
scattered photons enables to determinate the linear polarization of the primary
photon on the event by event basis with a certain probability. Here we present
quantitative results on the feasibility of such polarization measurements of
photons from the decay of positronium with the J-PET and explore the physical
limitations for the resolution of the polarization determination of 511 keV
photons via Compton scattering. For scattering angles of about 82 deg (where
the best contrast for polarization measurement is theoretically predicted) we
find that the single event resolution for the determination of the polarization
is about 40 deg (predominantly due to properties of the Compton effect).
However, for samples larger than ten thousand events the J-PET is capable of
determining relative average polarization of these photons with the precision
of about few degrees. The obtained results open new perspectives for studies of
various physics phenomena such as quantum entanglement and tests of discrete
symmetries in decays of positronium and extend the energy range of polarization
measurements by five orders of magnitude beyond the optical wavelength regime.Comment: 10 pages, 14 figures, submitted to EPJ
J-PET: a new technology for the whole-body PET imaging
The Jagiellonian Positron Emission Tomograph (J-PET) is the first PET built
from plastic scintillators. J-PET prototype consists of 192 detection modules
arranged axially in three layers forming a cylindrical diagnostic chamber with
the inner diameter of 85 cm and the axial field-of-view of 50 cm. An axial
arrangement of long strips of plastic scintillators, their small light
attenuation, superior timing properties, and relative ease of the increase of
the axial field-of-view opens promising perspectives for the cost effective
construction of the whole-body PET scanner, as well as construction of MR and
CT compatible PET inserts. Present status of the development of the J-PET
tomograph will be presented and discussed.Comment: Presented at the 2nd Jagiellonian Symposium on Fundamental and
Applied Subatomic Physics, Krak\'ow, Poland, June 4-9, 2017. To be published
in Acta Phys. Pol.
Commissioning of the J-PET detector for studies of decays of positronium atoms
The Jagiellonian Positron Emission Tomograph (J-PET) is a detector for
medical imaging of the whole human body as well as for physics studies
involving detection of electron-positron annihilation into photons. J-PET has
high angular and time resolution and allows for measurement of spin of the
positronium and the momenta and polarization vectors of annihilation quanta. In
this article, we present the potential of the J-PET system for background
rejection in the decays of positronium atoms.Comment: Presented at the 2nd Jagiellonian Symposium on Fundamental and
Applied Subatomic Physics, Krak\'ow, Poland, June 4-9, 2017. To be published
in Acta Phys. Pol.
Evaluation of Single-Chip, Real-Time Tomographic Data Processing on FPGA - SoC Devices
A novel approach to tomographic data processing has been developed and
evaluated using the Jagiellonian PET (J-PET) scanner as an example. We propose
a system in which there is no need for powerful, local to the scanner
processing facility, capable to reconstruct images on the fly. Instead we
introduce a Field Programmable Gate Array (FPGA) System-on-Chip (SoC) platform
connected directly to data streams coming from the scanner, which can perform
event building, filtering, coincidence search and Region-Of-Response (ROR)
reconstruction by the programmable logic and visualization by the integrated
processors. The platform significantly reduces data volume converting raw data
to a list-mode representation, while generating visualization on the fly.Comment: IEEE Transactions on Medical Imaging, 17 May 201
Three-dimensional image reconstruction in J-PET using Filtered Back Projection method
We present a method and preliminary results of the image reconstruction in
the Jagiellonian PET tomograph. Using GATE (Geant4 Application for Tomographic
Emission), interactions of the 511 keV photons with a cylindrical detector were
generated. Pairs of such photons, flying back-to-back, originate from e+e-
annihilations inside a 1-mm spherical source. Spatial and temporal coordinates
of hits were smeared using experimental resolutions of the detector. We
incorporated the algorithm of the 3D Filtered Back Projection, implemented in
the STIR and TomoPy software packages, which differ in approximation methods.
Consistent results for the Point Spread Functions of ~5/7,mm and ~9/20, mm were
obtained, using STIR, for transverse and longitudinal directions, respectively,
with no time of flight information included.Comment: Presented at the 2nd Jagiellonian Symposium on Fundamental and
Applied Subatomic Physics, Krak\'ow, Poland, June 4-9, 2017. To be published
in Acta Phys. Pol.
Simulation studies of annihilation-photon's polarisation via Compton scattering with the J-PET tomograph
J-PET is the first positron-emission tomograph (PET) constructed from plastic
scintillators. It was optimized for the detection of photons from
electron-positron annihilation. Such photons, having an energy of 511 keV,
interact with electrons in plastic scintillators predominantly via the Compton
effect. Compton scattering is at most probable at an angle orthogonal to the
electric field vector of the interacting photon. Thus registration of multiple
photon scatterings with J-PET enables to determine the polarization of the
annihilation photons. In this contribution we present estimates on the physical
limitation in the accuracy of the polarization determination of ~keV
photons with the J-PET detector.Comment: Submitted to Hyperfine Interaction
Determination of the 3\gamma fraction from positron annihilation in mesoporous materials for symmetry violation experiment with J-PET scanner
Various mesoporous materials were investigated to choose the best material
for experiments requiring high yield of long-lived positronium. We found that
the fraction of 3\gamma annihilation determined using \gamma-ray energy spectra
and positron annihilation lifetime spectra (PAL) changed from 20% to 25%. The
3gamma fraction and o-Ps formation probability in the polymer XAD-4 is found to
be the largest. Elemental analysis performed using scanning electron microscop
(SEM) equipped with energy-dispersive X-ray spectroscop EDS show high purity of
the investigated materials.Comment: 12 pages, 2 figure
Feasibility studies for imaging ee annihilation with modular multi-strip detectors
Studies based on imaging the annihilation of the electron (e) and its
antiparticle positron (e) open up several interesting applications in
nuclear medicine and fundamental research. The annihilation process involves
both the direct conversion of ee into photons and the formation of
their atomically bound state, the positronium atom (Ps), which can be used as a
probe for fundamental studies. With the ability to produce large quantities of
Ps, manipulate them in long-lived Ps states, and image their annihilations
after a free fall or after passing through atomic interferometers, this purely
leptonic antimatter system can be used to perform inertial sensing studies in
view of a direct test of Einstein equivalence principle. It is envisioned that
modular multistrip detectors can be exploited as potential detection units for
this kind of studies. In this work, we report the results of the first
feasibility study performed on a e beamline using two detection modules
to evaluate their reconstruction performance and spatial resolution for imaging
ee annihilations and thus their applicability for gravitational
studies of Ps
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