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Studies of unicellular microorganisms Saccharomyces cerevisiae by means of positron annihilation lifetime spectroscopy

Kubicz E., Jasińska B., Zgardzińska B., Bednarski T., Białas P., Czerwiński E., Gajos A., Gorgol M., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowalski P., Kozik T., Krzemień W., Niedźwiecki S., Pałka M., Raczyński L., Rajfur Z., Rudy Z., Rundel O., Sharma N. G., Silarski M., Słomski A., Strzelecki A., Wieczorek A., Wiślicki W., Zieliński M., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

749--753

EN

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 lyophilized 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 lyophilized, 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 me mbrane were observed in ESEM images.

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Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector

Kamińska D., Gajos A., Czerwiński E., Bednarski T., Białas P., Gorgol M., Jasińska B., Kapłon Ł., Korcyl G., Kowalski P., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Sharma N. G., Silarski M., Słomski A., Strzelecki A., Wieczorek A., Wiślicki W., Zieliński M., Zgardzińska B., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

729--732

EN

In this paper, we present prospects for using the Jagiellonian positron emission tomograph (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 the unique time and angular resolution combined with a high geometrical acceptance. Achieving the aforementioned is possible because of the application of polymer scintillators instead of crystals as detectors of annihilation quanta.

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Reconstruction of hit time and hit position of annihilation quanta in the J-PET detector using the Mahalanobis distance

Sharma N. G., Silarski M., Bednarski T., Białas P., Czerwiński E., Gajos A., Gorgol M., Jasińska B., Kamińska D., Kapłon Ł., Korcyl G., Kowalski P., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Słomski A., Strzelecki A., Wieczorek A., Wiślicki W., Zieliński M., Zgardzińska B., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

765--769

EN

The J-PET detector being developed at the Jagiellonian University is a positron emission tomograph composed of the long strips of polymer scintillators. At the same time, it is a detector system that will be used for studies of the decays of positronium atoms. The shape of photomultiplier signals depends on the hit time and hit position of the gamma quantum. In order to take advantage of this fact, a dedicated sampling front-end electronics that enables to sample signals in voltage domain with the time precision of about 20 ps and novel reconstruction method based on the comparison of examined signal with the model signals stored in the library has been developed. As a measure of the similarity, we use the Mahalanobis distance. The achievable position and time resolution depend on the number and values of the threshold levels at which the signal is sampled. A reconstruction method as well as preliminary results are presented and discussed.

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Processing optimization with parallel computing for the J-PET scanner

Krzemień W., Bała M., Bednarski T., Białas P., Czerwiński E., Gajos A., Gorgol M., Jasińska B., Kamińska D., Kapłon Ł., Korcyl G., Kowalski P., Kozik T., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Sharma N. G., Silarski M., Słomski A., Stola K., Strzelecki A., Trybek D., Wieczorek A., Wiślicki W., Zieliński M., Zgardzińska B., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

745--748

EN

The Jagiellonian Positron Emission Tomograph (J-PET) collaboration is developing a prototype time of flight (TOF)-positron emission tomograph (PET) detector based on long polymer scintillators. This novel approach exploits the excellent time properties of the plastic scintillators, which permit very precise time measurements. The very fast fi eld programmable gate array (FPGA)-based front-end electronics and the data acquisition system, as well as low- and high-level reconstruction algorithms were specially developed to be used with the J-PET scanner. The TOF-PET data processing and reconstruction are time and resource demanding operations, especially in the case of a large acceptance detector that works in triggerless data acquisition mode. In this article, we discuss the parallel computing methods applied to optimize the data processing for the J-PET detector. We begin with general concepts of parallel computing and then we discuss several applications of those techniques in the J-PET data processing.

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Preface

Zgardzińska B.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

701

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PALS investigations of free volumes thermal expansion of J-PET plastic scintillator synthesized in polystyrene matrix

Wieczorek A., Zgardzińska B., Jasińska B., Gorgol M., Bednarski T., Białas P., Czerwiński E., Gajos A., Kamińska D., Kapłon Ł., Kochanowski A., Korcyl G., Kowalski P., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Sharma N. G., Silarski M., Silarski A., Strzelecki A., Wiślicki W., Zieliński M., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

777--781

EN

The polystyrene doped with 2,5-diphenyloxazole as a primary fluor and 2-(4-styrylphenyl)benzoxazole as a wavelength shifter prepared as a plastic scintillator was investigated using positronium probe in wide range of temperatures from 123 to 423 K. Three structural transitions at 260, 283, and 370 K were found in the material. In the o-Ps intensity dependence on temperature, the significant hysteresis is observed. Heated to 370 K, the material exhibits the o-Ps intensity variations in time.

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Ortho-para spin conversion of Ps by paramagnetic O2 dissolved in organic compounds

Zgardzińska B., Białko W., Jasińska B.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

801--804

EN

The o-Ps mean lifetime value in liquids decreases in the presence of the paramagnetic oxygen molecules via the ortho-para conversion process. This effect was observed for several organic samples composed of carbon and hydrogen atoms differing in the arrangement of atoms forming the molecule, e.g. n-alkanes, alcohols, branched isomer of alkane, cycloalkane. The usually observed tendency of the o-Ps lifetime value to be an increasing function of temperature (in the case of measurements performed in vacuum) changes to a decreasing one in the presence of O2 dissolved in the sample. The difference between the o-Ps lifetimes measured in samples in vacuum and in the presence of O2 increases with the distance from the melting point. The ortho-para constant rate λconv was estimated to be ~130 μs–1 at 300 K for three compounds investigated.

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Positrons in naphthalene : critical remarks on the relation between o-Ps lifetime and void size

Goworek T., Zgardzińska B., Wawryszczuk J.

Nukleonika

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2013

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Vol. 58, No. 1

183-187

EN

Lowering the temperature or applying high pressure leads to elimination of positronium component in the e+ lifetime spectrum in solid naphthalene. Disappearance of positronium means reaching the free volume size limit at which there is no energy level in the potential well. It allows to estimate that size, which is found inconsistent with predictions of the popular Tao-Eldrup model. The range of applicability of that model is discussed. The dependence of the free e+ decay constant on pressure indicates that positronium is formed not only in the blob processes, but during the whole free positron life. The lifetime of free positrons begins to rise with temperature earlier than Ps intensity.

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Positron study of the structure of nonadecane-tricosane mixed solid

Zgardzińska B., Goworek T.

Nukleonika

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2010

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Vol. 55, No. 1

47-49

EN

Positron annihilation lifetime and intensity were measured as a function of temperature for a binary mixture of two normal alkanes. The rotator phase is preceded by the range of about 7 K, in which one observes instability of spectrum parameters. In that range the mixed solid, being initially introduced into rotator phase, transforms to a rigid one in the time scale of several hours.

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Ortho-positronium in liquid alkanes

Zgardzińska B.

Nukleonika

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2010

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Vol. 55, No. 1

41-46

EN

Positron lifetime spectra were measured for a series of odd-numbered liquid n-alkanes (C7H16, C9H20, C13H28 and C19H40) in a broad range of temperature. According to the “bubble model” the ortho-positronium (o-Ps) lifetime is determined by surface tension. Bubble radius was calculated using the Tao-Eldrup model and compared to the radius expected from the surface tension of liquid. The radii are not identical, their difference rises with temperature. If one assumes the difference of radii as constant, the o-Ps lifetime calculated from the Tao-Eldrup model rises faster than the experimental one. The distinct rise of the difference of radii has no physical explanation in the accepted o-Ps annihilation model. This effect can be the result of radiation chemistry processes not taken into account so far in the bubble model.