Browsing by Author "Ali, Yusuf"

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    Accumulation of 63Ni, 106Ru and 125Sb in phytoplankton
    (2022-08-22) Ali, Yusuf; University of Gothenburg/Institute of Clinical Sciences; Göteborgs universitet/Institutionen för kliniska vetenskaper
    Background: Nuclear Power Plants (NPPs) release small amounts of radionuclides which contribute with a low radiation dose to the environment as well as humans and animals. In this context, marine ecosystems are critical, since most NPPs in Sweden are located by the sea. The Concentration Factor (CF) is a model parame ter that is used to study the transport and uptake of these radionuclides. However, the published CF values for many elements range across several orders of magnitude. Aims: The aim of this project was to experimentally determine phytoplankton CF for some of the radionuclides released from various nuclear facilities in Sweden, in order to improve their uncertainties and to enable a more realistic dose assessment. The elements analyzed in this study were nickel, ruthenium and antimony. Materials and Methods: Seawater samples from two separate stations (Anholt E and Karlsödjupet) near NPP in Sweden, were collected by SMHI. Phytoplankton were then cultured in these seawater samples with addition of relevant radionuclides and nutrients. The cultures were filtered when the phytoplankton concentration reached around 1·106 cells/mL. A HPGe-detector was used to measure the activity of the filtrates and filters from 106Ru and 125Sb. Likewise, a liquid scintillation counter (LSC) was used to measure the activity of the samples containing 63Ni. Results and Discussion: The mean calculated phytoplankton dry weight were 33 ± 8 and 26 ± 4 pg for Anholt E and Karlsödjupet, respectively. The phytoplankton growth rates and dry weights in the different seawater samples were not significantly different. The mean calculated phytoplankton CF for the respective elements were as follows: 4000 and 3800 L/kg for Ni; 15000 and 20000 L/kg for Ru and 250 and 700 L/kg for Sb. The obtained values are in good agreement with published data. Conclusion: The phytoplankton CF for the elements studied were as follows: 4000 and 3800 L/kg for Ni; 15000 and 20000 L/kg for Ru and 250 and 700 L/kg for Sb. The CF obtained in this study, had a smaller variation compared to the literature data, thus the uncertainties in the CF have been improved considerably. These CF will therefore provide a more realistic dose assessment. Keywords: concentration factor (CF), phytoplankton, phaeodactylum tricornutum, uptake, radioactive releases, nickel, ruthenium, antimony, gamma spectroscopy, liquid scintillation counting.
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    Characterizing CEPA, a phoswich array
    (2019-08-01) Ali, Yusuf; Bergentall, Valdemar; Dahlgren, Erik; University of Gothenburg/Department of physics; Göteborgs universitet/Institutionen för fysik
    The structure of unstable nuclei is studied at the international facility FAIR, Darmstadt, Germany. One experimental setup at FAIR is called R3B where radioactive beams at relativistic energies impinge on a specific target which allows to collect data on the reactions taking place. For these experiments, different detectors have been built and CEPA is one of them. CEPA is the detector that will be characterized in this thesis. This detector consists of 24 sectors, where each sector has four tightly packed scintillator detectors, each a combination of LaBr3 and LaCl3, making up a phoswich crystal unit. Each phoswich crystal unit is made out of 7 cm LaBr3 and 8 cm LaCl3, respectively. Previous CEPA prototypes have been characterized at Chalmers, but the latest CEPA crystals have a new geometrical shape, the shape of a frustum. The three characteristics of CEPA that are investigated are their energy calibration, their energy resolution and the dependence of the detected energy on the position of the interaction. It was found that the energy resolution for the four LaBr3 parts of the tested sector did not meet the requirements [5]. Crystal one was the closest to meet the requirements, but still did not met the requirements with a factor 1.73 times higher (resolution) compared with the prototype, the other crystals were approximately a factor 2.5 higher. On the LaCl3 part none of the crystals met the requirements. The calibration measurements were also not successful since the characterized peak positions for different -sources did not end up on the expected place for all the sources. Unfortunately the sector that was investigated exhibited a significant position dependence.