For those needing portability, Rad Pro for Desktop works with Windows 8.1 tablets (just tested). Will not work with Surface tablets running Windows RT.
Select Activity Units
Select Calculation Direction
Uranium and Plutonium Grams Calculator
Activity to Grams
Grams to Activity
Select Isotope Group
Select Number of Isotopes
UK Radiation Adviser
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UK Radiation Protection Society
NRRPT Study Kit and Classic RP College Textbook
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Utilizing the specific activities of the uranium and plutonium isotopes, calculate the grams of PU and U from known activities or calculate the activities from know masses. If you select multiple isotopes, the total uranium and total plutonium are also calculated for you.