21 January 2010

Reference people

A couple of days ago, a rather malformed email with the subject "Reference man....bad? should it be changed?" arrived in my inbox:


I am and one of the cases is talking about how the nuclear clean-up sites standards should be changed from not only including the Reference Man...but other age groups as well.

Do you think this would be an effective policy to put in place? Or do you see places where they might have problems?



I am still baffled by the first half of the first sentence, but I attempted a coherent answer nonetheless, since I have the feeling that this individual is a grade schooler asking for information for a research report. Conceivably, my answer may be of use to some other fledgeling researcher, so I'm posting it here.

Dear Chrissy,

If I understand your question correctly, you're asking if the Reference Man model is too inaccurate to continue being used. In short, the answer is no; however, there are a number of applications where its use as model would be inappropriate. In fact, in the 35 years since ICRP 23 (which defined Reference Man) was released, a number of other reference individuals have been created. According to the book for my health physics class [James E. Turner, Atoms, Radiation, and Radiation Protection, 2nd ed., John Wiley & Sons, Inc., New York, 1995, pp. 487--489], "reference data have been compiled for an adult female and for children and infants of various ages." So, actually, part of what you're asking has already been done.

Reference Man's purpose is to simulate the effect of an internal radiation dose (i.e., inhaling radioactive dust that sticks inside the lungs) on the rest of a person's body. For the most part, these estimates for effective radiation doses are very rough, accurate to perhaps on the order of ten percent. Since Reference Man is primarily used to estimate values for workmen, it would usually approximate an average worker pretty well. (Children, for example, are not often radiation cleanup workers.) For other cases where more accurate doses to particular people need to be calculated, one of the other reference models can be used.

When high precision is needed, the models used are far more detailed. As an example, consider radiation therapy for cancer, where very high doses of radiation are needed to very specific areas of a person (the cancerous parts). Cancer tissue is more susceptible to radiation than healthy tissue, but healthy parts are still damaged by large amounts of radiation. Therefore, the medical physicists need to make very accurate representations of the person, which is usually done by taking a detailed scan of them with MRI or CT scans. Then, once they have determined the proper settings that will eliminate the cancer but not the person, they do the therapy. No professional would consider using a rough model like Reference Man for a one-shot, high-precision job like that.

In summary, Reference Man is only a tool. He is a model used as a good first-order approximation to the general public. As such, it's not necessary to impose extra policies: when more precision is needed, better models are used.

I hope this answers your question satisfactorily.

Seth Johnson


Post a Comment