Answer to Question #3878 Submitted to "Ask the Experts"

I am trying to calculate the probability of a primary gamma interaction for several different gamma emission energies with a Ludlum 44-10 2" x 2" NaI gamma scintillator, pursuant to Section 6.7.2 of the Nuclear Regulatory Commission’s NUREG 1507. One of the pieces of information that is needed is absorption coefficients for NaI at the relevant energies. While the National Institute of Standards and Technology's absorption coefficient resource is useful for pure elements and common shielding materials, it doesn't include detector materials, such as an NaI crystal. Can you recommend a good resource for NaI absorption coefficients at various energies?

The January 1970 edition of the Radiological Health Handbook (published by the US Department of Health, Education and Welfare, the Food and Drug Administration, and the Bureau of Radiological Health), page 139, has the mass attenuation coefficients (in the units of square centimeters per gram) for pure elements and several other materials, such as sodium iodide from 10 keV to 100 MeV.

Should you ever need the mass attenuation coefficient for a molecular substance, one can sum the mass attenuation coefficients of the constituent atomic species, once each is multiplied by the fraction (by the weight) of the i^th element in the molecule.

David J. Allard, CHP