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# Topic 9 - PowerPoint PPT Presentation

Topic 9. Specific Activity &amp; Concentration. Definition:. Activity Mass. Specific Activity =. (SA). Mass may designate mass of the radionuclide or labeled compound.

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Topic 9

Specific Activity & Concentration

Definition:

Activity

Mass

Specific Activity =

(SA)

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

SA

mass =

or

activity = mass x SA

Units of Specific Activity:

mCi/gm, Ci/mg, kBq/mcg, etc.

Any convenient units of activity/mass.

Sample Problem:

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

Sample Problem #2:

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

Definition:

activity

Concentration =

volume

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

or

activity

volume =

concentration

Sample Problem:

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?

activity

volume =

concentration

= 1.5 mCi/( 0.22mCi/cc)

= 6.8 cc

Sample Problem #2:

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