Absorption of plutonium compounds in the respiratory tract
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In order to optimise the monitoring of potentially exposed workers, it is desirable to determine specific values of absorption for the compounds handled. This study derives specific values of absorption rates for different chemical forms of plutonium from in vitro and animal (monkeys, dogs, mice, rats) experiments, and from human contamination cases. Different published experimental data have been reinterpreted here to derive values for the absorption parameters, f(r), s(r) and s(s), used in the human respiratory tract model currently adopted by the International Commission on Radiological Protection (ICRP). The consequences of the use of these values were investigated by calculating related committed effective doses per unit intake. Average and median estimates were calculated for f(r), s(r), and s(s) for each plutonium compound, that can be used as default values for specific chemical forms instead of the current reference types. Nevertheless, it was shown that the use of the current ICRP reference absorption types provides reasonable approximations. Moreover, this work provides estimates of the variability in pulmonary absorption and, therefore, facilitates analyses of the uncertainties associated with assessments, either from bioassay measurements or from prospective calculations, of intake and dose.Keywords:
Respiratory tract
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One of the perspective way to calculate absorbed (equivalent) dose and their rate is numerical simulation. GEANT4 is one of the software toolkit for the simulation of the passage of particles through matter. The article is devoted to define correct way of dose and dose rate calculation as dose rate should be calculated at the point; correct way of dose conversion coefficient approximation by piecwise continuous function. Calculation method of the absorbed (equivalent) dose and absorbed (equivalent) dose rate of ionizing radiation (gamma, neutron and electron radiation) at the point is proposed in the article. Approximating functions are proposed and the corresponding coefficients are calculated. Figures with coefficients dependencies of particles fluence and particle fluence energy depending on the energy of the particles are given. These coefficients are needed for calculations of absorbed (equivalent) dose. The absorbed dose rate calculation method which is used in GEANT4 can not be used for dose rate calculation. Proper mathematical method for absorbed dose rate calculation was chosen and was described in the article. Also, the method of absorbed (equivalent) dose rate calculation are given. Proposed calculation method of the absorbed (equivalent) dose and absorbed (equivalent) dose rate of the ionizing radiation may be used for numerical simulation of ionization radiation passage through the matter, for example, with the use of GEANT4
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We have calculated the absorbed dose in tissue-equivalent medium(polyethylene) from radioactive filter paper with beta dose point kernels, and then elicited the dose-density curve with autoradiography. There is a linear relationship between density and absorbed dose within the range of 0-68.84mGy. So the absorbed dose from the radiaoactive filter paper in non tissue-equivalent medium could be calculated inversely: the absorbed dose rate from 1MBq/cm2 radiaoactive filter paper on the other side of glass bottom of the culture bottle is 21.9 cGy/h. The method is simple and can be used to inspect the radio-uniformity of radioactive filter paper at the same time.
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Nucleon-meson cascade calculations have been carried out for monoenergetic neutrons and protons in the energy range from 3.5 GeV to 1.0 TeV normally incident on a semi-infinite slab of tissue 30 cm thick. The absorbed dose and dose equivalent as a function of tissue depth are presented, and analytic expressions for the resulting maximum and average fluence-to-absorbed-dose and fluence-to-dose-equivalent factors are given as a function of incident neutron or proton energy. The calculations were performed by using Monte Carlo methods in conjunction with theoretical nuclear-interaction models.
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For photon energies most frequently encountered in radiation protection the determination of absorbed dose in a phantom still presents considerable difficulties. This applied equally, or even more so, to the evaluation of the dose equivalent distribution in the ICRU sphere. Based on the experience and results obtained in the course of the realisation of the unit of water absorbed dose in a water phantom the distribution in the sphere could be deduced exerimentally. Preliminary investigations with TL dosemeters were followed by measurements with an ionisation chamber calibrated against the primary national standard for determining water absorbed dose in a phantom in the conventional X ray energy range. In order to ensure a high degree of tissue equivalence of the sphere phantom material, the results of attenuation and backscatter measurements were used to select appropriate materials. Monte Carlo calculations using a specifically developed code were also employed for the determination of the dose equivalent distribution inside the sphere for a wide range of energies of incident photons. From the dose equivalent distribution produced by a given spectral fluence of the incident beam, the various dose equivalent quantities discussed hitherto can be derived and some of their properties assessed. In addition, these calculations yielded information on the spectral photon fluence distribution at various depths in the sphere. On the other hand, this knowledge enabled the experimental data to be evaluated with improved accuracy. Furthermore, the dose equivalent in the surface layer of the sphere was approximately determined via measurements of the backscatter factor as the results of the Monte Carlo calculations showed fluctuations which are increased in comparison with the results for deep lying locations. With these data, conversion factors between receptor-free quantities (e.g., air kerma and exposure) and dose equivalent quantities in the sphere were deduced for a wide variety of irradiation geometries and energies.
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Monte Carlo conversion factors from absorbed dose in air to dose equivalent index, depth dose and mean dose equivalent are given for a 30 cm ICRU sphere and compared with various experimentally determined values.
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The quality factor (Q) is intended to relate the biological effectiveness of a radiation to the absorbed dose delivered in tissue. Quality factors are defined as a function of the unrestricted linear energy transfer (L) relationship in water and are used with operational quantities. Radiation weighting factors (wR) are used in protection quantities to take into account total radiation detriment. While the International Commission on Radiological Protection (ICRP) defines the Q(L) relationship, the International Commission on Radiation Units and Measurements (ICRU) recommends the charged particle stopping power and range data. If either of these data recommendations change, the quality factors must be recomputed. The latest guidance from both organisations applicable to neutron quality factors are the ICRP Publication 60 (Q(L) relationship) and the ICRU Report 49 (stopping power and range data). In the present study, absorbed dose conversion coefficients (pGy cm2) were calculated for two operational quantities defined by the ICRU--the ambient absorbed dose and the personal absorbed dose. Dose-equivalent (pSv cm2) conversion coefficients were also computed using mean quality factors based on ICRP 60 and ICRU 49 recommendations. Effective quality factors were then calculated from the ratio of the dose-equivalent to the absorbed dose conversion coefficients for both the personal dose-equivalent and ambient dose-equivalent and compared to values reported in the literature.
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