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Application of the compress sensing theory for improvement of the TOF resolution in a novel J-PET instrument

100%

Raczyński L. , Moskal P. , Kowalski P. , Wiślicki W. , Bednarski T. , Białas P. , Czerwiński E. , Gajos A. , Kapłon Ł. , Kochanowski A. , Korcyl G. , Kowal J. , Kozik T. , Krzemień W. , Kubicz E. , Niedźwiecki S. , Pałka M. , Rudy Z. , Salabura P. , Gupta-Sharma N. , Silarski M. , Słomski A. , Smyrski J. , Strzelecki A. , Wieczorek A. , Zieliński M. , Zoń N.

2016

tom Vol. 61, No. 1

35--39

Nowadays, in positron emission tomography (PET) systems, a time of fl ight (TOF) information is used to improve the image reconstruction process. In 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 signifi cantly 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 compressive sensing (CS) 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.

Laser-induced ablation: physics and diagnostics of ion emission

100%

Torrisi L.

tom Vol. 56, No. 2

113-117

Pulsed lasers generating beams of different intensities may be used to produce ablation of solid targets placed in high vacuum and to generate pulsed plasma and ion acceleration. The plasma is in a non-equilibrium condition and in the first instant the particles being generated are subject to thermal interactions, to a supersonic gas expansion in vacuum and to a Coulomb acceleration due to the high electric field developed along the normal to the target surface. The ion diagnostics, based on time-of-flight technique, allow us to measure the mean ion energy, the total number of ions, as well as the ion energy and charge state distributions. The ion energy distributions may be described by the Coulomb- -Boltzmann-Shifted (CBS) function, which after fitting to the experimental data may be used to determine the equivalent ion temperature and the accelerating voltage. Given the equivalent acceleration voltage and the plasma Debye length, it is possible to estimate the magnitude of the electric field developed in the plasma. Measurements of the ablation yield, plasma dimension and optical spectroscopy allow us to calculate the atomic and electronic plasma density and to evaluate the coronal plasma temperature. Some applications of the laser-induced ablation consist in the realization of laser ion sources (LIS), generation of multi-energetic ion beams by using a post-accelerating voltage, use of ultra-intense fs lasers to accelerate ions to energies of the order of tens MeV/nucleon. Other special applications include the pulsed laser deposition (PLD) of thin films, the laser ablation coupled to mass quadrupole spectrometry (LAMQS) probes, ablation of biological tissues, and generation of plasma for astrophysical and nuclear investigations.

Three methods for photon migration measurements in pulp

88%

Saarela J. , Tormanen M. , Myllyla R.

tom Vol. 12, No. 2

193-197

This paper gives an overview of three promising optical techniques for conducting laser pulses time-of-flight measurements in pulp. The oscilloscope method and time-of-flight lidar method are especially good for fast in-line measurements while a streak camera is superior in the laboratory.