# Calculate mass or number of atoms based on MBq?

1. Aug 2, 2017

### beany_bot

Trying to work out how many atoms of Technetium-99m there are in a 10 MBq dose?
Basically trying to work out if the actual weight of the Technetium-99m will affect the "flight" properties of an aerosol labeled with Technegas. Or would it be negligible?

Basically will using Technegas to radiolabel an aerosol affect it's properties due to the relatively high mass of the Technetium atoms relative to the existing dry power (e.g. lactose). Lets assume the powder is 20 micron sized particles and the Technetium will "coat" the surface.

2. Aug 2, 2017

### gmax137

3. Sep 27, 2017

### minerva

If you've got some nuclide of interest, say Tc99m, then you can look up the "specific activity" for that nuclide.
This gives you Bq per gram. (Then I'll let you convert grams to atoms, as an exercise for the reader.)
But this assumes that you've got nothing but pure 100% Tc-99m in your sample.

This assumes none of the nuclide has decayed, that it's 100% Tc-99m atoms, that it's not mixed in with any Tc-99 ground-state atoms or anything else, and it assumes that there's no other atoms attached to a molecule padding out the weight. The presence of all of those factors needs to be a correction factor, when you determine Bq per gram for your real-world radiochemical material.

In radiopharmacy, with a common nuclide such as Tc99m, this is often done with a dose calibrator machine which is counting in a known geometry - just put your hot vial inside, and it will tell you how many MBq are in it.