157 research outputs found
Beam profile investigation of the new collimator system for the J-PET detector
Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector
which will be used for search for discrete symmetries violations in the decays
of positronium atoms and for investigations with positronium atoms in
life-sciences and medical diagnostics. In this article we present three methods
for determination of the beam profile of collimated annihilation gamma quanta.
Precise monitoring of this profile is essential for time and energy calibration
of the J-PET detector and for the determination of the library of model signals
used in the hit-time and hit-position reconstruction. We have we have shown
that usage of two lead bricks with dimensions of 5x10x20 cm^3 enables to form a
beam of annihilation quanta with Gaussian profile characterized by 1 mm FWHM.
Determination of this characteristic is essential for designing and
construction the collimator system for the 24-module J-PET prototype.
Simulations of the beam profile for different collimator dimensions were
performed. This allowed us to choose optimal collimation system in terms of the
beam profile parameters, dimensions and weight of the collimator taking into
account the design of the 24 module J-PET detector.Comment: 14 pages, 9 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
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
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.
Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector
In this paper we present prospects for using the J-PET detector to search for
discrete symmetries violations in a purely leptonic system of the positronium
atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium
decays into three photons. No zero expectation values for chosen correlations
between ortho-positronium spin and momentum vectors of photons would imply the
existence of physics phenomena beyond the Standard Model. Previous measurements
resulted in violation amplitude parameters for CP and CPT symmetries consistent
with zero, with an uncertainty of about 10-3. The J-PET detector allows to
determine those values with better precision thanks to a unique time and
angular esolution combined with a high geometrical acceptance. Achieving the
aforementioned is possible due to application of polymer scintillators instead
of crystals as detectors of annihilation quanta.Comment: in Nukleonika 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.
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.
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
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