Question

99mTc is the most widely used radioisotope in nuclear medicine. It emits two (2) 142.6 keV and ninety eight (98) 140.5 keV photons for every 100 disintegrations. Determine the exposure rate in mR/min (thats milliRoentgen/min) at 50 cm from a 20 mCi (thats milliCurie) 99mTc source, assuming no shielding.

Answer 1

The exposure rate constant for Tc-99m is 0.720

The units of exposure rate constant are:

where, R stands for Roentgen.

The relation between the activity (A) of a radionuclide and its exposure rate (E) at a distance r from it is given by:

Note that, the energy of the photons is required for absorbed dose calculation. It is not required for exposure rate calculation. So, the given energies are an extra information.

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