126 research outputs found
Potential of the J-PET detector for studies of discrete symmetries in decays of positronium atom - a purely leptonic system
The Jagiellonian Positron Emission Tomograph (J-PET) was constructed as a
prototype of the cost-effective scanner for the simultaneous metabolic imaging
of the whole human body. Being optimized for the detection of photons from the
electron-positron annihilation with high time- and high angular-resolution, it
constitutes a multi-purpose detector providing new opportunities for studying
the decays of positronium atoms. Positronium is the lightest purely leptonic
object decaying into photons. As an atom bound by a central potential it is a
parity eigenstate, and as an atom built out of an electron and an anti-electron
it is an eigenstate of the charge conjugation operator. Therefore, the
positronium is a unique laboratory to study discrete symmetries whose precision
is limited in principle by the effects due to the weak interactions expected at
the level of (~10) and photon-photon interactions expected at the level
of (~10). The J-PET detector enables to perform tests of discrete
symmetries in the leptonic sector via the determination of the expectation
values of the discrete-symmetries-odd operators, which may be constructed from
the spin of ortho-positronium atom and the momenta and polarization vectors of
photons originating from its annihilation. In this article we present the
potential of the J-PET detector to test the C, CP, T and CPT symmetries in the
decays of positronium atoms.Comment: 27 pages, 6 figure
A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators
We present a study of the application of the Jagiellonian Positron Emission
Tomograph (J-PET) for the registration of gamma quanta from decays of
ortho-positronium (o-Ps). The J-PET is the first positron emission tomography
scanner based on organic scintillators in contrast to all current PET scanners
based on inorganic crystals. Monte Carlo simulations show that the J-PET as an
axially symmetric and high acceptance scanner can be used as a multi-purpose
detector well suited to pursue research including e.g. tests of discrete
symmetries in decays of ortho-positronium in addition to the medical imaging.
The gamma quanta originating from o-Ps decay interact in the plastic
scintillators predominantly via the Compton effect, making the direct
measurement of their energy impossible. Nevertheless, it is shown in this paper
that the J-PET scanner will enable studies of the o-Ps decays with
angular and energy resolution equal to and
keV, respectively. An order of magnitude shorter decay
time of signals from plastic scintillators with respect to the inorganic
crystals results not only in better timing properties crucial for the reduction
of physical and instrumental background, but also suppresses significantly the
pileups, thus enabling compensation of the lower efficiency of the plastic
scintillators by performing measurements with higher positron source
activities
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.
Trilateration-based reconstruction of ortho-positronium decays into three photons with the J-PET detector
This work reports on a new reconstruction algorithm allowing to reconstruct
the decays of ortho-positronium atoms into three photons using the places and
times of photons recorded in the detector. The method is based on trilateration
and allows for a simultaneous reconstruction of both location and time of the
decay. Results of resolution tests of the new reconstruction in the J-PET
detector based on Monte Carlo simulations are presented, which yield a spatial
resolution at the level of 2 cm (FWHM) for X and Y and at the level of 1 cm
(FWHM) for Z available with the present resolution of J-PET after application
of a kinematic fit. Prospects of employment of this method for studying angular
correlations of photons in decays of polarized ortho-positronia for the needs
of tests of CP and CPT discrete symmetries are also discussed. The new
reconstruction method allows for discrimination of background from random
three-photon coincidences as well as for application of a novel method for
determination of the linear polarization of ortho-positronium atoms, which is
also introduced in this work.Comment: 18 pages, 5 figures. Accepted for publication in Nuclear
Instrumentation and Methods in Physics Research
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
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
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
Feasibility study of the positronium imaging with the J-PET tomograph
A detection system of the conventional PET tomograph is set-up to record data
from e+ e- annihilation into two photons with energy of 511 keV, and it gives
information on the density distribution of a radiopharmaceutical in the body of
the object. In this paper we explore the possibility of performing the three
gamma photons imaging based on ortho-positronium annihilation, as well as the
possibility of positronium mean lifetime imaging with the J-PET tomograph
constructed from plastic scintillators. For this purposes simulations of the
ortho-positronium formation and its annihilation into three photons were
performed taking into account distributions of photons' momenta as predicted by
the theory of quantum electrodynamics and the response of the J-PET tomograph.
In order to test the proposed ortho-positronium lifetime image reconstruction
method, we concentrate on the decay of the ortho-positronium into three photons
and applications of radiopharmaceuticals labeled with isotopes emitting a
prompt gamma quantum. The proposed method of imaging is based on the
determination of hit-times and hit-positions of registered photons which
enables the reconstruction of the time and position of the annihilation point
as well as the lifetime of the ortho-positronium on an event-by-event basis. We
have simulated the production of the positronium in a cylindrical phantom
composed of a set of different materials in which the ortho-positronium
lifetime varied from 2.0 ns to 3.0 ns, as expected for ortho-positronium
created in the human body. The presented reconstruction method for total-body
J-PET like detector allows to achieve a mean lifetime resolution of about 40
ps. Recent Positron Annihilation Lifetime Spectroscopy measurements of
cancerous and healthy uterine tissues show that this sensitivity may allow to
study the morphological changes in cell structures.Comment: accepted in PMB
(http://iopscience.iop.org/article/10.1088/1361-6560/aafe20
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
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