I discovered a cool website that lets you type in equations and it takes car of looking up data and unit conversions. I'm sure it does much much more, but I don't have the need to pay for the Pro subscription. I am not a mathematician or expert in nuclear engineering, so feel free to let me know if I've made any mistakes.

An example of half-life:

100(.5^(300 years/cesium-137 half life)

http://www.wolframalpha.com/input/?i=10 ... lf+life%29The 100 can be any number in Bq or grams or other units. Time can be entered in years, days or seconds, and any other isotopes can be used.

In the example above, no matter what number is entered, only about 1% cesium-137 remains after 300 year. In other words, if man stopped making Cs-137 today all but 1% will be gone in 300 years. That's good, but 1% of a really big number is still a really big number.

Another example of half-life:

120 Curies .5^(100 days/Iodine-131 half life)

http://www.wolframalpha.com/input/?i=12 ... lf+life%29To convert form amount of radiation to grams:

100 TBq/cesium-137 specific activity

http://www.wolframalpha.com/input/?i=10 ... c+activityThe radiation amount can be entered as Becquerels or Cures and again any isotope can be entered and the software will look up its specific activity.

To convert from grams to amount of radiation:

(100 grams)(cesium-137 specific activity)

http://www.wolframalpha.com/input/?i=%2 ... ctivity%29Finally, I made an equations to show how much Cs-137 from nuclear weapons test fallout is decaying in upper layers of the North Pacific ocean every day.:

(Please don't take these numbers too seriously, since estimates very widely as to the actual amount of radiation.)

69 PBq - 69 PBq(.5^(1 day/cesium-137 half life))

http://www.wolframalpha.com/input/?i=69 ... life%29%29My result came out to 4.356 TBq per day, which wasn't that far off from the article I read that got me interested in trying to figure this out in the first place.