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

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This quantity is normally expressed as a percentage. The main important factors affecting the energy resolution are: • the statistical fluctuations in the number of charge carriers (i.e. electron-hole pair) produced in the detector; • the electronic noise in the detector itself, the preamplifier and the amplifier; • the incomplete collection of the charge carriers. Such factors are generally present in any kind of detecting system. For a scintillation detector further factors affect the energy resolution because the initial electric sign is firstly converted into light and then converted again into an electric one. Such further factors are the emission of the luminescence, the collection of photons on the photocathode and the emission of photoelectrons. The energy (w) spent by a radiation interacting with a detecting materials to create one electron-hole pair (as in the semiconductor detectors) is actually greater than the energy gap (E g) between valence and conduction bands. For instance for a Germanium detector the mean energy required for creating a pair is 2.96 eV whereas the energy gap is only about 0.67 eV at 300 K. This difference between w and E g reveals that part of the energy is dissipated into processes that don’t generate charge carriers. Therefore if the energy E is deposited in the detector, the average number of charge carriers is given by E/w and in case of a pure Poisson statistical process the standard deviation of the number of pairs should be just the square root of such ratio. Yet, the experience has shown that the fluctuations are smaller. A factor, called Fano factor (F), is therefore introduced and the standard deviation of the number of charged carriers is more realistically given by: σ = FE w 54 equation 2.3.2 The two extreme values of F are 0 and 1. The former means there are no statistical fluctuations and all the energy is spent for generating charged carriers. The latter means that the number of produced pairs is governed by Poisson statistics. If the distribution of an energy spectrum relating to a monoenergetic source with energy E is described with a Gaussian function, the FWHM results as following [129]: FWHM = 2 2ln(2)w = 2 2ln(2)wFE equation 2.3.3 It results that the FWHM and so the energy resolution decreases with decreasing values of w. On the basis of such considerations a semiconductor detector is expected to have the best energy resolution, thanks to its low energy threshold for an electron-hole pair production. Single full energy peaks even separated by few keV energies can be easily identified in the spectrum. In case of scintillation detectors full energy peaks can be still located and the centroid calculated, but the lower energy resolution doesn’t allow sometimes to distinguish photons with energy closer than some ten keV. When single full energy peaks are present energy calibration is easily performed. The centroids of the full energy peaks are associated to the energy of the emitted radiations, known from the decay characteristics of the radionuclides. A fitting is normally performed using a polynomial function to calculate the energy value of each channel of the MCA. On the basis of the energy calibration the energy of any further full energy peak can be evaluated and the relative radionuclide identified.
2.3.1.5 Efficiency calibration The purpose of the efficiency calibration of a direct measurement system is to evaluate the fraction of photons from a radioactive source located within the body that are actually detected and thus converted in pulses. The efficiency will depend on several factors such as: • source-detector geometry due to source distribution and source-detector distance; • elemental composition and density of all the materials traversed by the photons • photons attenuation coefficients of these materials; • energy and angle-dependent cross sections of the detector material for the various photon interactions. In principle the detector efficiency for a certain radionuclide distributed in the human body could be typically calculated by means of Monte Carlo simulations. Yet, this procedure is time expensive and often not all the input information necessary for simulating the sourcedetector configuration is likely available. Therefore efficiency calibration is normally performed by measuring known amounts of activity of a radionuclide. The radionuclide is present in a source characterized by materials and geometry simulating the actual conditions of measurement on contaminated subjects. Therefore the source used for efficiency calibration of in vivo detecting system, named phantom, is given by one or more radionuclides dispersed throughout a volume of materials simulating in elemental composition, density and shape the whole human body or some particular organs. For radionuclides that are roughly uniformly distributed in human body as Caesium or Cobalt and for which whole body counters are used, the phantom is easily built by assembling bottles filled by aqueous solution with known amount of activity. The bottles are then arranged for simulating a human body. A famous example of such phantom is the so-called BOMAB (Bottle Manikin Absorption) [131]. For low energy photons emitters that concentrate in specific organs or tissue of human body and that are detected with partial body counters, the physical and geometric characteristics of the part of the body where the radionuclide is deposited must be accurately reproduced in calibration phase. Therefore anthropomorphic phantoms are used with tissue equivalent materials for the different organs and tissues. This is the case of Iodine that accumulates in thyroid, transuranium elements as Americium and Plutonium that accumulate in liver and skeleton, or other radionuclides inhaled in insoluble form that concentrate in lung. The efficiency is normally calculated according to Deutsches Institut für Normung (DIN) methodology [132]. A spectrum of a certain calibration phantom is acquired and the full energy absorption peak is separated for each radionuclide within the phantom. The spectrum region around the peak is divided in five parts, as in Figure 2.3.3. A 1 A 2 z 0 4 z 0 4 B z b 55 A 3 A 4 Figure 2.3.3 Partitioning of the full energy peak area for efficiency calculation purposes according to DIN methodology (see the text for the meaning of the symbols). z 0 4 z 0 4
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Forschungszentrum Karlsruhe in der
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Für diesen Bericht behalten wir un
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i ABSTRACT The biokinetic model pre
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ZUSAMMENFASSUNG Das von der Interna
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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 58 and 59: elements the spectral distribution
Page 60 and 61: The phoswich detector is based on t
Page 62 and 63: HPGe crystals are produced in cylin
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
Page 109 and 110: The structure of Polig’s skeleton
Page 111 and 112: Percentage daily urinary excretion
Page 113 and 114: of 0.693d -1 . The values of the F
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Percentage daily urinary excretion
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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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Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

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