Program History

Keith Eckerman and Rich Leggett of ORNL’s Environmental Sciences Division led the effort to establish the CRPK, with the goal of preserving national expertise in radiation dosimetry, the science of assessing radiation doses to people. The MOU remains a key mechanism for ensuring that U.S. radiation protection programs are based on the best available scientific information and that this technical knowledge is maintained across federal agencies.

Today, CRPK continues to advance ORNL’s 70-year history of excellence in developing and applying radiation protection models and methods used worldwide.

ORNL Dosimetry Research Program

The Dosimetry Research Program at ORNL began in the 1950s under K. Z. Morgan, one of the early leaders in radiation protection. Morgan served as the Director of ORNL’s Health Physics Division and was an early recipient of the Gold Medal for Radiation Protection, awarded by the Royal Swedish Academy of Sciences in 1962. From 1979 to 2013, the program was led by Keith Eckerman, who earned the same honor in 2012.

The program developed the models and data needed to estimate how much radiation people receive from various sources and to set safe exposure limits. Many of these models became international standards, and are used by organizations around the world, such as the International Commission on Radiological Protection (ICRP). 

The program has traditionally served as a key resource for storing and updating computer-based dosimetry and biokinetic models, which are essential tools for understanding how radiation interacts with the human body. 

Dosimetric Model Development

In the 1960s, ORNL developed its first anatomical phantom: a computational model that represents the approximate size, shape, and position of human organs and tissues. This model made it possible to calculate radiation doses to specific body parts for both men and women.

For early computer-based simulations, ORNL scientists used combinations of regular geometric shapes such as ellipsoids and cylinders to represent the body and its organs. This approach allowed for Monte Carlo calculations, a statistical method used to model cross-irradiation of tissues.

The Medical Internal Radiation Dose (MIRD) Committee, representing the nuclear medicine community, adopted ORNL’s phantom to improve the accuracy of dose estimates. The ICRP later incorporated the same framework into a series of guidance reports on worker radiation exposure (ICRP Publications 30 and 68).

In the late 1970s and 1980s, ORNL expanded its phantom series to represent children at different ages — from infants through adolescents — and later developed a dedicated adult female phantom. These models were used by the ICRP to refine dose estimates for members of the public (ICRP Publications 56, 67, 69, 71, and 72).

More recent ICRP reports (Publications 133 and 155) and MIRD Pamphlet No. 28 continue to incorporate and build on ORNL and CRPK’s dosimetric model contributions.

Biokinetic Model Development

ORNL's biokinetic models have evolved considerably over the years, reflecting major advances in biology, physiology, and computing. These models describe how radionuclides behave within the human body, including how they move through organs, are retained in tissues, and are eventually excreted.

Early biokinetic models, developed from the 1950s through the early 1980s, relied on simple mathematical functions that described how elements were retained and eliminated based on data from human and animal studies. These early models typically represented a reference adult, without accounting for differences by age or sex.

By the early 1980s, ORNL researchers began creating age-specific biokinetic models to better represent the behavior of radionuclides in children. Because limited biological data existed for younger populations, scientists adopted a new physiological systems approach that modeled how biological processes change as humans grow. This innovation made it possible to estimate radiation doses for people of all ages more accurately.

Since then, ORNL has developed two main types of physiologically based biokinetic models:

1. System-level models, which describe basic physiological processes such as blood circulation or the movement of material through the digestive system.
2. Element-specific models, which describe how individual chemical elements behave within the body.

One foundational example of a basic physiological model is ORNL’s dynamic blood flow model, which uses age- and sex-specific parameters to describe how blood — and therefore radionuclides — circulates through tissues. This model incorporates data on cardiac output, blood perfusion rates, and tissue blood volumes, gathered from extensive literature reviews.

The blood flow model allows researchers to track how a radioactive material moves immediately after entering the bloodstream. It has been applied to estimate doses for short-lived medical radionuclides and to develop element-specific models for substances whose distribution depends largely on blood flow, such as potassium, cesium, and radon.

An example of a physiologically-based, element specific biokinetic model is the age-specific biokinetic model for lead, developed by ORNL to describe how lead moves through and is retained in the human body. This model incorporates extensive data on the time-dependent distribution and excretion of lead and has been used in several important applications:

• The ICRP uses it to calculate radiation doses from radioactive isotopes of lead.
• The EPA applies it to assess potential chemical toxicity in children.
• The State of California uses it to establish occupational exposure standards for lead.

The ICRP has now adopted ORNL’s element-specific models for many elements across the periodic table. CRPK leads ongoing efforts to develop and refine these systemic models for occupational and environmental exposure assessments, published in the ICRP’s Occupational Intake of Radionuclides and Public Intake of Radionuclides series.

Beyond radiation safety, these models have been used in nutrition research, toxicology, and even forensic science. In one notable criminal case, ORNL’s biokinetic model for polonium was used to estimate the amount of polonium-210 involved in the poisoning of a former Russian spy.

Nuclear Decay Data Evaluation

In the early 1970s, ORNL scientists began compiling decay data for radionuclides used in nuclear medicine. This work was part of a long-term collaboration with the MIRD Committee, a group focused on improving dose calculations for medical applications.

A radionuclide’s decay data describe key physical properties: its half-life, the types of radiation it emits (such as alpha particles, beta particles, or gamma rays), and the energy and frequency of those emissions. These details are essential for calculating accurate dose estimates and ensuring safe use of radioactive materials.

Between the mid-1970s and early 1980s, ORNL expanded this effort, compiling decay data for more than 800 radionuclides important to occupational and environmental exposure studies. The work culminated in ICRP Publication 38 (1983), which became an international reference for radiation safety.

In the 2000s, ORNL led the development of ICRP Publication 107 (2008), an updated and expanded database that includes 1,252 radionuclides. This work modernized decay data for current research and applications, supporting both medical and industrial radiation practices.

Compilation of Human Anatomical and Physiological Data

From the mid-1960s to the mid-1970s, ORNL led an effort through the ICRP to define the anatomical and physiological features of a “Reference Man.” This model represented a typical adult male and provided a consistent international basis for developing biokinetic and dosimetric models. The work helped standardize radiation protection assessments and allowed researchers worldwide to compare dose estimates using a common framework.

Building on that foundation, ORNL coordinated a second major ICRP initiative from the early 1990s to the early 2000s to establish a “Reference Family.” This new framework included anatomical and physiological data for males and females across a range of ages — from infants to adults — and enabled the creation of age-specific models that more accurately reflected how interacts with the human body throughout different stages of life, improving dose estimates for the public.