Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

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elements the spectral distribution of background radiations shows a preponderance at low energies which is due to the degradation of γ photons by multiple Compton scattering in the shield. The interaction of natural radiation with Lead shield reduces background below 250 keV but adds lead fluorescence x rays of about 80 keV. To reduce this component further layers are used in decreasing order of Z (e.g. Lead, Cadmium and Copper) to absorb the characteristic x rays emitted by the preceding shield layer. Therefore a covering with Cadmium (Z=48) absorbs Lead x rays but add its own fluorescence x rays of about 22 keV. Thus, a final covering with Copper is used to absorb Cadmium fluorescence x rays. Copper fluorescence x rays of about 8 keV can be neglected because they fall below the energy region, even for low energy photon measurements [61]. Contributions to the natural background from gas and dust are due to 222 Rn and 220 Rn, daughters of Ra 226 and Th 232 , together with their progenies that can diffuse in the air from the building materials and the ground. This source of radioactivity is normally limited with ventilation system filtering the air introduced in the shielded rooms where the detection system is located. Table 2.3.1 Activity concentration in building materials for few common natural radionuclides. Material Country Average activity concentration [Bqkg -1 ] 48 226 Ra 232 Th Natural Origin granite Germany 100 80 1200 granite Russia 110 170 1500 tuff Italy 130 120 1500 pumice stone Germany 130 130 1100 concrete with alum Sweden 1500 70 850 Industrial Origin phosphorite chalk Germany 600 < 5 110 phosphate chalk Great Britain 800 20 70 calcium silicate Canada 2150 - - calcium silicate USA 1400 - - red mud brick Germany 280 230 330 ash Germany 210 130 700 aggregate of coal, ash and concrete 2.3.1.2 Detectors 40 K Finland 100 70 190 Different kinds of detectors are available for direct measurements of activity in human organs. For the particular case of detecting low energy photon emitters two kinds of detecting
systems were used in the frame of the present work: a phoswich scintillation detector system and a semiconductor detector system. The “phoswich” detector (from “phosphor sandwich”) is based on the scintillation mechanism occurring in some inorganic crystals when exposed to a field of ionizing radiations [128]. The luminescence of inorganic scintillators can be explained on the basis of allowed and forbidden energy bands of a crystal. In an atom the electronic energy states are composed by discrete energy levels that are usually represented with an energy level diagram composed by single lines. In a crystal composed by numerous atoms, the single atomic energy levels merge to form a band of allowed energy states. In the ground state of the crystal, the uppermost allowed band that contains electrons, called valence band, is completely filled whereas the next allowed band, called conduction band, is empty. The two bands are separated by a forbidden energy band where, in case of an ideal pure crystal, electrons can never be found. Absorption of energy produces the elevation of an electron from its normal position in the valence band into the conduction band, consequently forming a hole in the valence band. In case of a pure crystal the return of the electron from the conduction to the valence band is an inefficient mechanism of luminescence production. In fact the typical energy gap determines too high energetic photon to lie in the visible range, where the optoelectronic devices work more efficiently. In order to enhance the probability of visible photon emissions, small amounts of impurities are commonly added to inorganic scintillators forming energy states between valence and conduction band. These impurities are called activators and their energy states may exist at a ground and excited level. Transition among these levels can efficiently produce scintillation visible photons. An ionizing radiation crossing a crystal produces charged particles that will form a large number of electron-hole pairs by elevating electrons from the valence to the conduction band. The positive hole will drift to the location of an activator site ionizing it while the electron will migrate through the crystal until it encounters an ionized activator. The electron can so drop in the impurity site creating a neutral impurity configuration with its own energy states in the forbidden gap of the crystal. If the activator state is in an excited configuration a transition will occur quickly and with high probability with the emission of a photon in the visible range. The time gap between the absorption of the radiation and the photon emission depends on the decay time constant, specific for each scintillating material. The use of the scintillation detectors would be impossible without the availability of devices to convert the extremely weak light output of a scintillation pulse into the corresponding electrical signal [128]. This is carried out by a photomultiplier that can be considered a fast amplifier. It consists of an evacuated glass tube with a photocathode at its entrance and several dynodes in the interior part. The photocathode serves to convert the incident light photons produced in the scintillating material into low energy electrons. Because only few hundred electrons may be produced, their charge is still too small to be used as a detectable electrical signal. Therefore the electrons emitted by the photocathode are guided, with the help of an electric field, into the electron multiplier section of the photomultiplier. The electrons are guided to the first dynode that is a coated with a substance that emits secondary electrons when primary electrons impact on it. The secondary electrons emitted by the first dynode are then focused in direction to the successive dynode where they impact producing other electrons that will move to a third dynode and so on. The production of secondary electrons by the successive dynodes results in a final amplification of the number of electrons up to 10 7 -10 10 electrons for a typical scintillation pulse, sufficient to easily serve as a charge signal for the original scintillation event. This charge is normally collected at the anode of the multiplier section. 49
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Forschungszentrum Karlsruhe in der
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Für diesen Bericht behalten wir un
Page 7 and 8: i ABSTRACT The biokinetic model pre
Page 9 and 10: ZUSAMMENFASSUNG Das von der Interna
Page 11 and 12: 1 INDEX OF CONTENTS INDEX OF SYMBOL
Page 13 and 14: 3 INDEX OF SYMBOLS Here a short glo
Page 15: Chapter 1 Introduction 5
Page 18 and 19: the duties of the Department for Ra
Page 20 and 21: adionuclide. Therefore only isotope
Page 22 and 23: stabilise the +4 oxidation state [1
Page 24 and 25: techniques adopted in the early pha
Page 26 and 27: present in spent and MOX reactor fu
Page 28 and 29: INTRAVENOUS INJECTION skin WOUND bl
Page 30 and 31: functions, defined as retained and
Page 32 and 33: the contamination event, of such as
Page 34 and 35: Table 1.3.2 Indicative 239 Pu detec
Page 36 and 37: The kinetics of Plutonium in the ki
Page 38 and 39: 1.4.2 COMMENTS ON THE ICRP 67 MODEL
Page 41: Chapter 2 Data and measurements 31
Page 44 and 45: Therefore the radiolysis process, m
Page 46 and 47: Recent technologic developments in
Page 48 and 49: eu(t) = 0.19e −0.272t + 0.023e
Page 50 and 51: function for each of the considered
Page 52 and 53: the minimum detectable activity of
Page 54 and 55: 2.2.2 AVAILABLE MEASUREMENTS Immedi
Page 56 and 57: Table 2.2.4 Daily fecal excretion o
Page 60 and 61: The phoswich detector is based on t
Page 62 and 63: HPGe crystals are produced in cylin
Page 64 and 65: This quantity is normally expressed
Page 66 and 67: The peak is located in the region B
Page 68 and 69: To introduce the second quantity, t
Page 70 and 71: 117 cm 3 h -1 for the incoming and
Page 72 and 73: Figure 2.3.8 The Lawrence Livermore
Page 74 and 75: three detectors are used. Two detec
Page 76 and 77: Table 2.3.4 Efficiency factors of p
Page 78 and 79: • the necessity of performing mea
Page 80 and 81: Table 2.3.7 Impulses in the measure
Page 82 and 83: 2.4 ACTIVITY MEASUREMENTS IN BIOASS
Page 84 and 85: If more then one radionuclide is ma
Page 86 and 87: L A is the air layer in µgcm -2 ;
Page 88 and 89: The electrodeposition cell used for
Page 90 and 91: Table 2.4.1 238 Pu, 239 Pu and 241
Page 93 and 94: 3.1.1 MATHEMATICAL TOOLS 3.1.1.1 So
Page 95 and 96: calculating the amount of Plutonium
Page 97 and 98: 3.1.2 ANALYSIS OF THE ICRP 67 MODEL
Page 99 and 100: empirical curves given by Langham,
Page 101 and 102: the worst performance of the group.
Page 103 and 104: leave the total clearance from the
Page 105 and 106: Figure 3.1.4 shows that the use of
Page 107 and 108: 3.1.3 MODIFICATION OF ICRP 67 MODEL
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The structure of Polig’s skeleton
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Percentage daily urinary excretion
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of 0.693d -1 . The values of the F
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the basis of all the reference data
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Table 3.1.10 Transfer rates of the
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3.1.4 VERIFICATION OF THE OPTIMIZED
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Table 3.1.13 Intakes and percentage
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soft tissue ST2 soft tissue ST0 sof
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For the routine application of Mode
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excreted by individuals aged sixty
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Table 3.1.20 Exponents and coeffici
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tract [57] to consider a contaminat
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The sensitivity coefficients for th
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Sensitivity coefficients S i Figure
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transfer rates on the Plutonium uri
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Geometric standard deviations rangi
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3.2 APPLICATION OF THE OPTIMIZED MO
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lymph nodes, as in the LLNL phantom
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Americium in the lungs [Bq] 1000 10
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Daily urinary excretion [Bqd -1 ] 1
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long time is not yet described by t
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excretion that is one of the main i
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The comparison of model’s predict
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Americium in the lungs [Bq] 1000 10
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153 CONCLUSIONS The optimized model
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Annex Quantities used in Radiologic
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present. As the radiation weighting
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w R is the radiation weighting fact
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161 BIBLIOGRAPHY 1. Plutonium. W. K
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29. Nenot, J.-C. and Stather, J. W.
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55. International Atomic Energy Age
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81. Crowley, J., Lanz, H., Scott, K
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107. Hempelmann, L.H., Langham,W.H.
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137. Breitestein, B.D., Newton, C.E
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167. Harrison, J.D., Khursheed, A.,
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JOURNALS OWN PUBLICATIONS RELATED T
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177 ACKNOWLEDGEMENTS Special thanks
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Name: Andrea Luciani Date and place
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