Topic 9. Specific Activity & Concentration. Definition:. Activity Mass. Specific Activity =. (SA). Mass may designate mass of the radionuclide or labeled compound.
Specific Activity & Concentration
Specific Activity =
Massmay designate mass of the radionuclide or labeled compound.
A defining equation such as this can be solved for several types of useful information:
activity = mass x SA
mCi/gm, Ci/mg, kBq/mcg, etc.
Any convenient units of activity/mass.
A 150 mCi sample of 131I is chemically bound to 60 mg of NaI. What is the SA of the sample?
SA = activity/mass
= 150 mCi/60 mg
= 2.5 mCi/mg
Using the previous sample, where SA was found to be 2.5 mCi/mg, how much NaI would be contained in a 100 mCi sample?
mass = activity/SA
= 100mCi/(2.5 mCi/mg)
= 40 mg of NaI
Units: mCi/cc, Ci/ml, kBq/cc, etc.
This defining equation may also be solved for either volume or activity to yield:
activity = volume x concentration
A liquid radioactive sample of 51Cr has a concentration of 220 Ci/cc. What volume must be drawn up to have an activity of 1.5 mCi?
= 1.5 mCi/( 0.22mCi/cc)
= 6.8 cc
A 14C sample has a concentration of 2.1 mCi /cc. What activity is contained in a volume of 3.25 cc?
activity = concentration x volume
= 2.1 mCi/cc x 3.25 cc
= 6.825 mCi