Answer to Question #9498 Submitted to "Ask the Experts"

Category: Radiation Basics

The following question was answered by an expert in the appropriate field:

Are there any methods that would allow one to model the pathway of particles emitted from a radioactive source, whether it's in the body or in the open?

Yes, there has been considerable work done in the modeling of the migration/translocation of radioactive materials, both gases and particulate matter, in the environment and in the human body. The methods that apply to the environmental transport of materials involve pathway analyses that trace movement through various media to a desired endpoint. Often the endpoint is a human being. The mathematical models that apply to transport in the external environment are different from the models that apply to intake and distribution of the same radioactive species in the human body, although some conceptual aspects are similar. We are not able here to provide details about the mathematical models involved, but I will try to provide some information to assist you.

Environmental transport models include such elements as atmospheric dispersion, transport in surface and groundwater, transfer to soil and vegetation, and uptake by land and sea/freshwater animals, including man.  The models can be quite complicated and some require rather sophisticated mathematics to describe and solve the transport equations.

One of the better-known and useful references in this regard is a book edited by John Till and H. Robert Meyer, Radiological Assessment: A Textbook on Environmental Dose Analysis, published in 1983 as NUREG/CR-3332 for the U.S. Nuclear Regulatory Commission. This large volume is available online through this NRC link. A revised edition of this reference is available as a book by John Till and Helen Grogan, Radiological Risk Assessment and Environmental Analysis, Oxford, 2008. It is available on as well as other places.

The RESRAD group of computer codes, available free through Argonne National Laboratory, is extremely popular and widely used for assessing dose consequences associated with the transport of radioactive materials in environmental media and in specialized situations. Perhaps the major application of RESRAD codes has been in assessing the dose impacts of residual ground and/or building contamination at sites undergoing decommissioning activities.

If you are a member of the Health Physics Society, you can find additional related resources on the Members Only page; click on the Toolbox for Health Physicists, and look at the listings under Atmospheric Dispersion and Decontamination and Decommissioning. There are many other sources of information on this topic and much information and assistance available through government agencies, such as the Environmental Protection Agency (EPA).

Most of the best known and widely used work related to intake, uptake, distribution, retention, and excretion of radioactive materials in the human body has been published by the International Commission on Radiological Protection (ICRP). The work includes consideration of intakes of particulate activity (as well as gases) primarily through inhalation and ingestion. Regulations, specifying intake limits for radionuclides in current use by the U.S. Nuclear Regulatory Commission (NRC) or agreement state licensees in the United States, are based on results obtained from internal dosimetry models described in ICRP Publication 30, Limits of Intakes of Radionuclides by Workers (published in four parts and supplements from 1972 to 1978).

In later years, the ICRP updated its recommendations and made changes to many of the intake and metabolic models that had been in use. The respiratory tract model became considerably more sophisticated than that used in generating ICRP-30 results, and metabolic models that had earlier included primarily one-way transport through tissue compartments in the body were modified to allow recycling of material between blood and organs.

The major relevant ICRP publications that document the ICRP efforts and results are ICRP Publications 61, 66, 67, 68, 69, 71, and 72, all of which you can find described among the publications listed on the ICRP Web site.

There are naturally many other sources of information about the transport of radioactive material within the human body. The EPA and the NRC have published various documents relating to internal dosimetry and some of the modeling considerations. You can search for some of these online. Again, if you have access to the Health Physics Toolbox, you can find some useful Web pages by searching the listings under Dosimetry – Internal Dosimetry. 

I hope this is helpful. Good luck.

George Chabot, PhD, CHP

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