4,051 research outputs found
Performances of multi-gap timing RPCs for relativistic ions in the range Z=1-6
We present the performance of Multi-gap timing RPCs under irradiation by
fully stripped relativistic ions (gamma*beta=2.7, Z=1-6). A time resolution of
80 ps at high efficiency has been obtained by just using standard `off the
shelf' 4-gap timing RPCs from the new HADES ToF wall. The resolution worsened
to 100 ps for ~ 1 kHz/cm2 proton flux and for ~ 100 Hz/cm2 Carbon flux. The
chambers were operated at a standard field of E=100 kV/cm and showed a high
stability during the experiment, supporting the fact that RPCs are a convenient
choice when accommodating a very broad range of ionizing particles is needed.
The data provides insight in the region of very highly ionizing particles (up
to x 36 mips) and can be used to constrain the existing avalanche and
Space-Charge models far from the usual `mip valley'. The implications of these
results for the general case of detection based on secondary processes (n,
gamma) resulting in highly ionizing particles with characteristic energy
distributions will be discussed, together with the nature of the time-charge
correlation curve.Comment: 31 pages, 19 figures, submitted to JINS
Compressive Sensing of Signals Generated in Plastic Scintillators in a Novel J-PET Instrument
The J-PET scanner, which allows for single bed imaging of the whole human
body, is currently under development at the Jagiellonian University. The dis-
cussed detector offers improvement of the Time of Flight (TOF) resolution due
to the use of fast plastic scintillators and dedicated electronics allowing for
sam- pling in the voltage domain of signals with durations of few nanoseconds.
In this paper we show that recovery of the whole signal, based on only a few
samples, is possible. In order to do that, we incorporate the training signals
into the Tikhonov regularization framework and we perform the Principal
Component Analysis decomposition, which is well known for its compaction
properties. The method yields a simple closed form analytical solution that
does not require iter- ative processing. Moreover, from the Bayes theory the
properties of regularized solution, especially its covariance matrix, may be
easily derived. This is the key to introduce and prove the formula for
calculations of the signal recovery error. In this paper we show that an
average recovery error is approximately inversely proportional to the number of
acquired samples
Application of the Compress Sensing Theory for Improvement of the TOF Resolution in a Novel J-PET Instrument
Nowadays, in Positron Emission Tomography (PET) systems, a Time of Flight
information is used to improve the image reconstruction process. In Time of
Flight PET (TOF-PET), fast detectors are able to measure the difference in the
arrival time of the two gamma rays, with the precision enabling to shorten
significantly a range along the line-of-response (LOR) where the annihilation
occurred. In the new concept, called J-PET scanner, gamma rays are detected in
plastic scintillators. In a single strip of J-PET system, time values are
obtained by probing signals in the amplitude domain. Owing to Compress Sensing
theory, information about the shape and amplitude of the signals is recovered.
In this paper we demonstrate that based on the acquired signals parameters, a
better signal normalization may be provided in order to improve the TOF
resolution. The procedure was tested using large sample of data registered by a
dedicated detection setup enabling sampling of signals with 50 ps intervals.
Experimental setup provided irradiation of a chosen position in the plastic
scintillator strip with annihilation gamma quanta
Novel method for hit-position reconstruction using voltage signals in plastic scintillators and its application to Positron Emission Tomography
Currently inorganic scintillator detectors are used in all commercial Time of
Flight Positron Emission Tomograph (TOF-PET) devices. The J-PET collaboration
investigates a possibility of construction of a PET scanner from plastic
scintillators which would allow for single bed imaging of the whole human body.
This paper describes a novel method of hit-position reconstruction based on
sampled signals and an example of an application of the method for a single
module with a 30 cm long plastic strip, read out on both ends by Hamamatsu
R4998 photomultipliers. The sampling scheme to generate a vector with samples
of a PET event waveform with respect to four user-defined amplitudes is
introduced. The experimental setup provides irradiation of a chosen position in
the plastic scintillator strip with an annihilation gamma quanta of energy
511~keV. The statistical test for a multivariate normal (MVN) distribution of
measured vectors at a given position is developed, and it is shown that signals
sampled at four thresholds in a voltage domain are approximately normally
distributed variables. With the presented method of a vector analysis made out
of waveform samples acquired with four thresholds, we obtain a spatial
resolution of about 1 cm and a timing resolution of about 80 p
The Straw Tube Trackers of the PANDA Experiment
The PANDA experiment will be built at the FAIR facility at Darmstadt
(Germany) to perform accurate tests of the strong interaction through bar pp
and bar pA annihilation's studies. To track charged particles, two systems
consisting of a set of planar, closed-packed, self-supporting straw tube layers
are under construction. The PANDA straw tubes will have also unique
characteristics in term of material budget and performance. They consist of
very thin mylar-aluminized cathodes which are made self-supporting by means of
the operation gas-mixture over-pressure. This solution allows to reduce at
maximum the weight of the mechanical support frame and hence the detector
material budget. The PANDA straw tube central tracker will not only reconstruct
charged particle trajectories, but also will help in low momentum (< 1 GeV)
particle identification via dE/dx measurements. This is a quite new approach
that PANDA tracking group has first tested with detailed Monte Carlo
simulations, and then with experimental tests of detector prototypes. This
paper addresses the design issues of the PANDA straw tube trackers and the
performance obtained in prototype tests.Comment: 7 pages,16 figure
High prevalence of BRCA1 deletions in BRCAPRO-positive patients with high carrier probability.
Mutation screening of the BRCA1 and BRCA2 genes in probands with familial breast/ovarian cancer has been
greatly improved by the multiplex ligation-dependent probe amplification (MLPA) assay able to evidence gene
rearrangements not detectable by standard screening methods. However, no criteria for selection of cases to
be submitted to the MLPA test have been reported yet. We used the BRCAPro software for the selection of
familial breast/ovarian cancer probands investigated with the MLPA approach after negative BRCA1/2
conventional mutation screening. One hundred and seventy-seven probands were investigated for germline
BRCA1/2 mutations after assessment of genetic risk using BRCAPro. Probands were classified as BRCAPro
positive (n = 67) when the carrier probability (CP) was >10% and as BRCAPro negative (n = 110), when the CP
was <10%. Conventional mutational analyses of the BRCA1/2 genes and, in one case, of p53 identified 22
pathogenetic germline mutations, 12 in BRCA1, 9 in BRCA2 and 1 in p53, in 22/177 (12.4%) probands. All the
mutations except one were detected in BRCAPro-positive patients. In the 46 BRCAPro-positive cases that
resulted negative by BRCA1/2 mutation, screening analysis of rearrangements within BRCA1/2 by MLPA was
carried out. Three patients with a very high CP showed BRCA1 deletions, consisting of deletions of exons 1–2 in
two probands and of exon 24 in the third proband. In one case, the exons 1–2 deletion was shown to
cosegregate with disease in the family. No BRCA2 rearrangements were detected, but one patient showed the
1100delC of the CHEK2 gene, whose probe is present in the BRCA2 kit. In our series, the highest carrier
detection rate of mutation screening plus MLPA analysis (52.3%) was in patients with a BRCAPro CP >50%
Measurement of the production of the four-fermion final states mediated by neutral current processes
Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph
Recent tests of a single module of the Jagiellonian Positron Emission
Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips
have proven its applicability for the detection of annihilation quanta (0.511
MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved
resolution is almost by a factor of two better with respect to the current
TOF-PET detectors and it can still be improved since, as it is shown in this
article, the intrinsic limit of time resolution for the determination of time
of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much
lower. As the major point of the article, a method allowing to record
timestamps of several photons, at two ends of the scintillator strip, by means
of matrix of silicon photomultipliers (SiPM) is introduced. As a result of
simulations, conducted with the number of SiPM varying from 4 to 42, it is
shown that the improvement of timing resolution saturates with the growing
number of photomultipliers, and that the 2 x 5 configuration at two ends
allowing to read twenty timestamps, constitutes an optimal solution. The
conducted simulations accounted for the emission time distribution, photon
transport and absorption inside the scintillator, as well as quantum efficiency
and transit time spread of photosensors, and were checked based on the
experimental results. Application of the 2 x 5 matrix of SiPM allows for
achieving the coincidence resolving time in positron emission tomography of
0.170 ns for 15 cm axial field-of-view (AFOV) and 0.365 ns
for 100 cm AFOV. The results open perspectives for construction of a
cost-effective TOF-PET scanner with significantly better TOF resolution and
larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures
Measurement of the production of the four-fermion final states mediated by neutral current processes
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