HEALTH PHYSICS AND RADIATION DOSIMETRY
Helping Set Guidelines for Radiation Protection

Jim Bogard tests dosimeter responses to radiation from nearby sources.

In December 1942 when the first controlled chain reaction was achieved in Chicago, some physicists measured radiation levels in the workplace. As the Manhattan Project began, "health physics" methods were needed to measure radiation emitted by manmade radionuclides and control radioactive contamination of the workplace.

In the 1940s Oak Ridge health physicists Karl Morgan, Herbert Parker, Ernest Wollan, and others developed instrumentation for measuring radiation to help protect worker health. With Elda Anderson, Myron Fair, and Doc Emerson, Morgan spearheaded the formation of the national Health Physics Society and became its first president. Morgan and Jim Turner wrote the first textbook on health physics.

In Oak Ridge, programs of theoretical and applied research were carried out to foster the development of health physics instruments and dosimeters for monitoring radiation levels and worker exposures. In the mid-1950s ORNL health physicists developed neutron dosimetry techniques and portable personnel monitors for alpha and gamma radiation that have since been used worldwide.

Before the Manhattan Project, radiation protection was largely concerned with controlling medical uses of radiation, principally X-ray machines. Also, radionuclides for medical and industrial use were largely limited to members of the naturally occurring uranium series, such as radium-226. The development of fission reactors (e.g., the Oak Ridge Graphite Reactor) resulted in the generation of a variety of new radionuclides with important applications in research, industry, and medicine. Guidance was needed to ensure the beneficial uses of these radioisotopes, while protecting those who used them. Under Morgan's direction, the first formal report on permissible concentrations of radionuclides in the workplace was issued in 1959 as Publication 2 of the International Commission on Radiological Protection (ICRP).

The calculations underlying that report were carried out by ORNL's dosimetry research group, headed by Walter Snyder, with the able assistance of Mary Rose Ford. This group helped establish ORNL as an international center for dose calculations. At the time, workers were the focus of radiation protection. To establish guidance that would achieve international consensus, it was necessary to agree on typical characteristics of a radiation worker. Under Snyder's leadership, Mary Jane Cook and others assembled ICRP Publication 23, a massive collection of anatomical and physiological data that defined ICRP's "Reference Man," a model that has served as an international standard for decades.

Using this information, Snyder and co-workers formulated a 3D model of the body, incorporating Monte Carlo methods for modeling radiation transport, to calculate radiation dose. The resulting model was developed with the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine and is referred to worldwide as the "MIRD Phantom."

Since the late 1970s ORNL's dosimetry research has been guided by Keith Eckerman, a member of ICRP's committee on dose limits and chairman of its dose calculations group. Recognizing the growing need to address intakes of radionuclides by the public (e.g., by inhalation, ingestion, or injection), Eckerman refocused ORNL's dosimetry research toward developing age- and gender-specific dose estimates. As a first step, Eckerman and Mark Cristy extended the radiation transport models and mathematical phantoms from a reference adult male to children and adult females.

Next came a long-term project to identify and model changes with age in the biological behavior ("biokinetics") of radio-nuclides. This required the introduction of biologically realistic models that incorporate physiological changes common during human maturation. The effort, led by Rich Leggett, provided not only the needed models for children but also yielded improvements in predictions of the fate of radionuclides in adults. These physiologically based models, which form the core of ICRP's recent publications on doses to the public, also have replaced ICRP's traditional biokinetic models for the radiation worker. The information collected during this work provided a valuable starting point for a new ICRP publication on anatomical and physiological characteristics of a "Reference Family," soon to replace "Reference Man."

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