III.A.122.     In order to calculate the exposure rate that a visitor might receive from a patient with a therapeutic dose of a radionuclide you would need to know the:

    a.     Name of the nuclide.    Yes

    b.     Activity.    Yes

    c.     Exposure time.    No

    d.     Distance.    Yes

   Discussion:    You do not need to know either the half-life or the exposure time to determine the exposure rate.   For the specific nuclide you would look up the value for the gamma constant, multiply it by the activity (which was not listed here) and then use the distance in an inverse square relationship.

   Reference:    Physical Principles of Medical Imaging, 2nd Edition. p. 612