11 research outputs found
Positronium signature in organic liquid scintillators for neutrino experiments
Electron anti-neutrinos are commonly detected in liquid scintillator
experiments via inverse beta decay, by looking at the coincidence between the
reaction products, neutron and positron. Prior to positron annihilation, an
electron-positron pair may form an orthopositronium (o-Ps) state, with a mean
life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off
effects, it may introduce distortions in the photon emission time distribution,
crucial for position reconstruction and pulse shape discrimination algorithms
in anti-neutrino experiments. Reversing the problem, the o-Ps induced time
distortion represents a new signature for tagging anti-neutrinos in liquid
scintillator.
In this paper, we report the results of measurements of the o-Ps formation
probability and lifetime, for the most used solvents for organic liquid
scintillators in neutrino physics (pseudocumene, linear alkyl benzene,
phenylxylylethane, and dodecane). We characterize also a mixture of
pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength
shifter.
In the second part of the paper, we demonstrate that the o-Ps induced
distortion of the scintillation photon emission time distributions represent an
optimal signature for tagging positrons on an event by event basis, potentially
enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure
A feasibility study of the time reversal violation test based on polarization of annihilation photons from the decay of ortho-Positronium with the J-PET detector
The Jagiellonian Positron Emission Tomograph (J-PET) is a novel de- vice
being developed at Jagiellonian University in Krakow, Poland based on or- ganic
scintillators. J-PET is an axially symmetric and high acceptance scanner that
can be used as a multi-purpose detector system. It is well suited to pur- sue
tests of discrete symmetries in decays of positronium in addition to medical
imaging. J-PET enables the measurement of both momenta and the polarization
vectors of annihilation photons. The latter is a unique feature of the J-PET
detector which allows the study of time reversal symmetry violation operator
which can be constructed solely from the annihilation photons momenta before
and after the scattering in the detector
Hit-Time and Hit-Position Reconstruction in Strips of Plastic Scintillators Using Multithreshold Readouts
In this article, a new method for the reconstruction of hit-position and
hit-time of photons in long scintillator detectors is investigated. This
research is motivated by the recent development of the positron emission
tomography scanners based on plastic scintillators. The proposed method
constitutes a new way of signal processing in Multi-Voltage-Technique. It is
based on the determination of the degree of similarity between the registered
signals and the synchronized model signals stored in a library. The library was
established for a set of well defined hit-positions along the length of the
scintillator. The Mahalanobis distance was used as a measure of similarity
between the two compared signals. The method was validated on the experimental
data measured using two-strips J-PET prototype with dimensions of 5x9x300
mm. The obtained Time-of-Flight (TOF) and spatial resolutions amount to
325~ps (FWHM) and 25~mm (FWHM), respectively. The TOF resolution was also
compared to the results of an analogous study done using Linear Fitting method.
The best TOF resolution was obtained with this method at four pre-defined
threshold levels which was comparable to the resolution achieved from the
Mahalanobis distance at two pre-defined threshold levels. Although the
algorithm of Linear Fitting method is much simpler to apply than the
Mahalanobis method, the application of the Mahalanobis distance requires a
lower number of applied threshold levels and, hence, decreases the costs of
electronics used in PET scanner