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M. Pučetaitė et al. / Medical Physics in the Baltic States 7 (2009) 96 - 99 reflection technique exhibit absorptions resembling the first-derivative of a conventional absorption spectrum. The bands of such spectra are called restrahlen bands and their intensity grows proportionally to the absorption. For the first time in this work it is shown that there can be two types of mixed calcium oxalate and calcium phosphate stones. The stones of the first type do not have any domain structure, while the stones of the second type have one domain of calcium phosphate located close to the edge of the stone surrounded by calcium oxalate. This finding brings to conclusion that the stones with calcium oxalate as a main component can be formed in two ways: (I) loose calcium oxalate stone grows in urinary system from oversaturated salt solution without fixation to the walls of the system (II) calcium oxalate stone, which was initiated on the walls. In this case the grow starts from formation of calcium phosphate crystal on the wall of the system. Later this crystal is covered by calcium oxalate. We believe, that having larger set of calcium oxalate/calcium phosphate mixed stones we will be able to clarify if covering of calcium phosphate crystal by calcium oxalate takes place on the walls of urinary system, or the process starts when calcium phosphate for some reason (naturally, with aid of medicines or ultrasound treatment) will become loose. Such studies are now underway in our laboratory 99 5.References 1. Laurence Estepa, Michel Daudon. Contribution of Fourier Transform Infrared Spectroscopy to the Identification of Urinary Stones and Kidney Crystal Deposits. John Wiley & Sons, Inc. Biospectroscopy 3, 1997. p. 347-369. 2. Jennifer C. Anderson, James C. Williams Jr., Andrew P. Evan, Keith W. Condon, Andre J. Sommer. Analysis of Urinary Calculi Using an Infrared Microspectroscopic Surface Reflectance Imaging Technique. Urol Res., 35, 2007. p. 41-48. 3. C. Paluszkiewicz, M. Galka, W. Kwiatek, A. Parczewski, S. Walas. Renal Stone Studies Using Vibrational Spectroscopy and Trace Element Analysis. John Wiley & Sons, Inc. Biospectroscopy 3, 1997. p. 403-407. 4. Iqbal Singh. Renal Geology (Quantitative Renal Stone Analysis) by ‘Fourier Transform Infrared Spectroscopy’. Int Urol Nephrol, 40, 2008. p. 595- 602. 5. V. Hendrixson, V. Šablinskas, D. Leščiūtė, A. Želvys, F. Jankevičius, Z. Kučinskienė. Infrared spectroscoplcal approach in kidney stones research // Laboratorinė medicina. t. 10, nr. 2, 2008. p. 99- 105.
MEDICAL PHYSICS IN <strong>THE</strong> BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania HEALTH PHYSICS ASPECTS <strong>OF</strong> TRITIUM IN NUCLEAR SECTOR Irma GAJAUSKAITĖ*, Tatjana ZYK**, Gediminas ADLYS*, Edvardas KIELIUS* *Kaunas University of Technology, **Ignalina Nuclear Power Plant Abstract: Radiological effects of tritium are discussed, characterization of natural and manmade sources of tritium including nuclear sector is provided, dependence of tritium discharges upon reactor type is analyzed and tritium monitoring system in Ignalina NPP is presented in this article. Keywords: environmental radioactivity, tritium, nuclear reactors, RBMK reactor, liquid scintillation counter 1. Introduction Tritium is a radioactive form of hydrogen, which is found naturally in air and water. Naturally occurring tritium is produced in the upper atmosphere by interaction of cosmic rays with the nuclei of the atmospheric gases, principally by induced reactions. Maximum contribution has the interaction between a fast neutron and atmospheric nitrogen. Products of this reaction are tritium and carbon: 14 1 3 12 7 N + 0n → 1H + 6 C Very small fraction of natural tritium is produced by neutron capture by 6 Li in the earth’s crust [1]. The third way is cosmic deuteron reaction with deuterium 2 2 3 1 1 H + 1 H → 1H + 1p These are primarily interactions that happen in the upper atmosphere and the tritium falls to earth as rain. The man made tritium is released into environment by different sources. A large source was the stratosphere that accumulated tritium from the past thermonuclear testing [2]. Because of the atmospheric nuclear test conducted from 1945 until 1963, natural levels of 3 H in environmental samples were enhanced. After stoppage of atmosphere nuclear weapon tests at 1963 the released activity of 3 H has decayed with a half-life of 12.33 year. At present, the level of tritium in the atmosphere is close to natural origin before the nuclear tests [3]. The main source of the released tritium to-day are nuclear reactors and uranium fuel reprocessing plants. Other possible sources include consumer products and medical wastes [2]. New tritium sources are research units for nuclear fusion and neutrons generation. At present, natural tritium production remains far higher than manmade sources. 2. Radiological effects of tritium The tritium nucleus has extra neutrons, deficit in protons and excess amount of energy to be stable. 100 Because of this phenomenon the nucleus 3 H will undergo a nuclear transformation (radioactive decay) and one neutron converts to proton. This reduces the energy in the nucleus and new helium nucleus is left more stable. During transformation tritium nucleus emits a beta minus particle and antineutrino. 3 1 − H → He + β + ~ ν 3 2 The antineutrino ν ~ has no biological significance because it practically does not interact with matter. The maximum energy of emitted beta particle is of 18,6 keV with an average energy is of 5,7 keV. This is low energy beta radiation compared to most naturally occurring radioactive beta emitters. It is considered that relative biological effectiveness (RBE) of tritium is the same as of standard X-ray or gamma radiation. In this case, radiation weighting factor equal to 1 is applied to all Low Energy Transfer radiation (LET). The justification is that in general the greater values my not apply to cancer induction in humans (ICRP, 2007). Tritium is pure beta emitter of low energy. The maximum energy of 18,6 keV corresponds to maximum range of 6 μm in water or biological tissue. For comparison, the thickness of the epidermis and dermis of human skin is 20-100 μm and 1-3 mm respectively [1]. So the outer layer of skin is enough to stop external beta radiation of tritium. For this reason tritium could produce most internal exposure if it is taken into the body. It can happene by two main ways: inhalation and ingestion. The three major forms of tritium are present in the environment: tritiated water vapor (HTO), molecular tritium (HT) and tritiated methane (CH3T) [4]. These can be incorporated as a tissue free-water tritium into living organisms as organically bound tritium (OBT). Organically bound tritium has longer retention time in body than tritiated water. In the case of tritiated water tritium is expelled with a biological half life of approximately 10 days. For organic tritium inside the body the half life is approximately 30 days [1].
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2009 PROCEEDINGS OF THE 7 th INTERN
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