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RADAR - The Kinetic Models Here's the really hard part. Conceptually,
it's not too hard to explain the part of the system. You understand
the basics already if you understand N Here, A(t) is the activity as a function of
time (t), a
We have 0.75 Bq being removed with the first exponential term and 0.25 Bq being removed with the second term. This would apply to any isotope of iodine. To calculate the number of disintegrations specifically for I-131 (assuming that we are integrating from zero to infinity) one needs only to calculate the following simple ratios: where l
Intestine: 5400 disintegrations Liver: 4150 disintegrations Stomach: 4800 disintegrations Thyroid: 219,000 disintegrations Total Body: 264,000 disintegrations This is easy stuff - drag the a 's and l's into a spreadsheet and try it yourself. Just remember to apply the physical decay constant for I-131 and the value to convert hours to seconds. The hard part is deciding on the actual values of the a 's and l 's for every compound. We've put in the database (see the Internal Sources resource page) what we believe are the best available for many pharmaceuticals in nuclear medicine and other compounds for the occupational radionuclide situations. In this table, we give you fractions (a 's) and, instead of l 's, we give the corresponding biological half-times, as this is usually better understood by more people. The model for I-131 NaI is just slightly different than what is shown above - these kinetic models normally change over time as new information is gained about a pharmaceutical. Most of our kinetic models (but not all) come from the ICRP 53/ICRP 80 documents, and their model for NaI was a little different than the MIRD model from 1975. We intend to keep the database current and to use the latest and most accurate values for any compound. If you know of some data we haven't considered, or think one of the models is off, let us know. <Rant Mode On> In our table, we continue to show the value given in the ICRP reports
of Ã/A <Rant Mode Off>
In addition to models for the biokinetics of various compounds within the body, there are a few standardized models that have been developed for modeling the kinetics of activity as it passes through the respiratory and digestive systems (which are common routes of entry into the body for radioactive materials). Two such models were presented in 1979 in ICRP Publication 30. The model for the digestive system is a relatively simple four compartment model with first order kinetics linking the compartments and unidirectional movement of material. The respiratory tract model was a bit more complicated, consisting of 10 compartments linked by first order kinetics, with some material recycling. However, this model was updated in a later publication (ICRP Publication 66), with a model with more compartments and many more complexities. To work with this model, one needs to purchase special software called LUDEP (available from the National Radiological Protection Board of the UK). Solutions employing this more complicated model have formed the basis for the newest recommendations of the ICRP for worker DCFs. Let's see those phantoms Overview of the External Dose Assessment System |