Hi,

It is rather simple calculation exercise. All you need to do is to calculate specific activity for each Ra isotope you mentioned. Specific activity is, by definition, the activity of 1g of pure radionuclide. If you know nuclides half-life (T1/2) you can calculate the decay constatnt (dec) as:

dec=ln2/T1/2.

Activity is related to mass or number of atoms (N) as:

A=dec x N

Using the Avogadro number (approx. 6.02x10^23) you can calculate the amount of atoms you have in 1 g of your isotope.

The rest is simple conversion of units from Ci or pCi to Bq and then from g to ug.

Good luck!

Pawel

Dear Professor,

Thank you so much for your reply. 

It's very elementary; by definition,

1 Ci Ra-226 is equvalent of 1g Ra226;

then, 1 pCi is equivalent of 1 pg (0.001 ug ) Ra226.

Regards!

- Activity = decay constant x number of atoms

number of atoms = Activity /decay constant (1)

- but Number of atoms = (mass of element x Avogadro s number)/ mass number. (2)

- from this mass of element = (number of atoms x mass number)/ Avogadro number. (3)

- from equation (2) = (1) we get on :

Activity / decay constant= (mass of element x Avogadro s number)/ mass number. (4)

- From equ. 4 we get on :

Mass of element (g) = (Activity .mass number) / (decay constant x Avogadro s number)

1 pg =0.000001 ug = 1e-12 g

1 Ci Ra-226 is equal or equivalent to 1gm of Ra-226

that is mean 1pCi is equal to (0.001ug) of Ra-226

Andras Sarkadi , you are absolutly true...

1pCi/l = 0.037 Bq/l - (1)

1 Bq/l = 39 µg/l - (2)

So, 1 pCi/l = 0.037 * 39 µgl-1

=> 1pCi/l = 1.443 µgl-1

Check https://wikipedi.org/wiki/Becquerel. Thanks