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

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the duties of the Department for Radiation Protection of the Forschungszentrum Karlsruhe, which acts as official regional center for the monitoring of internal exposure from occupational activities. In order to correctly explain the bioassays from occupationally contaminated subjects, the available ICRP model for Plutonium metabolism in humans must be further developed. Particular care will be taken for the model’s ability to predict the activity in urine, because this is the most common and feasible technique in the radiation protection practice in case of Plutonium exposure. To this end all relevant data and investigations on Plutonium metabolism and excretion rates available in the scientific literature will be assembled and used in the analysis below. An occupationally exposed subject, characterized by a well documented scenario of contamination, will be also considered. Measurements on this subject have already been carried out since the first event of contamination, providing an extensive set of data on Plutonium metabolism, covering almost two decades. The data obtained in recent years show a significant enhancement of the urinary excretion compared to earlier assays. In the present work further measurements will be carried out providing simultaneously the amounts of activity both in bioassays and different organs. Starting from the available ICRP model, the final goal is to develop a biokinetic model that accurately describes the Plutonium metabolism by avoiding any assumption that can't be supported by known physiological processes. Also procedures such as sensitivity and uncertainty analysis, rarely applied in modeling projects of internal dosimetry, will be applied to interpret phenomena like urinary excretion enhancement at long times after exposure. As a by-product, a deeper and more complete understanding of the internal workings of the new model will be obtained. 8
1.2.1 PHYSICAL CHARACTERISTICS 9 1.2 PLUTONIUM Plutonium (Pu, Z = 94) belongs to the actinide series, which starts with Actinium (Ac, Z = 89) and ends with Lawrencium (Lr, Z = 103). It is a silvery-white metal that melts at 639.5 °C and boils at 3235 °C, and its density at 25 °C is 19.737 gcm -3 [3]. The first synthesized Plutonium isotope was 238 Pu, produced by bombarding Uranium with 16-MeV deuterons at the University of California cyclotron, and was identified on 23 February, 1941 [4]. The reaction was: 238 92U (d,2n) 93 238 Np − 238 ⎯ 94 Pu ⎯ → reaction 1.2.1 Later a second isotope was produced, 239 Pu, obtained by neutron capture of 238 U. The neutrons were generated from a (d,n) reaction using a cyclotron: 238 92U (n, ) 92 239 U − 239 ⎯ 93 Np ⎯ → − 239 ⎯ 94 Pu ⎯ → reaction 1.2.2 It was soon found that 239 Pu is more readily fissionable by slow neutrons than 235 U. This discovery stimulated intensive studies of the properties of Plutonium and its compounds. Prolonged irradiation of Uranium by slow neutrons, carried out during the years 1941-1943, made it possible to prepare and isolate in pure forms micrograms and later ever increasing amounts of the 239 Pu isotope. All the neutron deficient isotopes of Plutonium from 232 to 238 were produced by irradiation with charged particles. Some of the heavier isotopes were also produced in a similar way. At present Plutonium is mainly produced in nuclear reactors based on the Uranium- Plutonium cycle [5], normally as result of (n,γ) neutron captures in 238 U and to a lesser extent through (n,2n) reactions. The isotopes 240, 241, 242 and 243 are formed from successive neutron captures. The short half life of 243 Pu essentially limits the production of Plutonium isotopes in reactors with 242 Pu. Plutonium may be produced from 238 U in a reactor with any type of neutron energy spectrum, from thermal to fast. Indeed the yield of the various ratio of Plutonium isotopes differs according to the large variation of the neutron cross sections of the various Plutonium isotopes with neutron energies. Generally, fissions are more likely with fast neutrons than with intermediate or thermal neutrons [4]. Even if the Plutonium is regarded as one of the typically anthropogenic elements, it is constantly produced in nature in Uranium ores according to reaction 1.2.2. The neutrons necessary for the (n,γ) reaction of 238 U are provided by spontaneous fission and alpha-neutron reactions. The resulting 239 Pu was observed in pitchblende and monazite ores. Yet the concentrations due to this natural source are very small: The Uranium to Plutonium ratio is approximately 10 11 :1 [6]. The possibility of finding other Plutonium radioisotopes in nature due to the primordial processes of earth formation depends on the halftime of the
Page 1: Forschungszentrum Karlsruhe in der
Page 4 and 5: 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 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 64 and 65: This quantity is normally expressed
Page 66 and 67: The peak is located in the region B
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To introduce the second quantity, t
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117 cm 3 h -1 for the incoming and
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Figure 2.3.8 The Lawrence Livermore
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three detectors are used. Two detec
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Table 2.3.4 Efficiency factors of p
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• the necessity of performing mea
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Table 2.3.7 Impulses in the measure
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2.4 ACTIVITY MEASUREMENTS IN BIOASS
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If more then one radionuclide is ma
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L A is the air layer in µgcm -2 ;
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The electrodeposition cell used for
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Table 2.4.1 238 Pu, 239 Pu and 241
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3.1.1 MATHEMATICAL TOOLS 3.1.1.1 So
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calculating the amount of Plutonium
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3.1.2 ANALYSIS OF THE ICRP 67 MODEL
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empirical curves given by Langham,
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the worst performance of the group.
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leave the total clearance from the
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Figure 3.1.4 shows that the use of
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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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