Using python, write code for the problem.

21. Radioactive Decay Strontium 90, a radioactive element that is part of the fallout from nuclear explosions, has a half life of 28 years. This means that a given quantity of strontium-90 will emit radioactive particles and decay to one-half its size every 28 years. How many years are required for 100 grams of strontium 90 to decay to less than 1 gram? See Fig. 3.33