elapsed time = 87.51 * (log (100 / 10) / .30103)
elapsed time = 87.51 * (1 / .30103)
elapsed time = 290.70 days
Half life = (120 * .30103) / log (1 / .54821)
Half life = 36.1236 / log (1.8241)
Half life = 36.1236 / .26105
Half life = 138.38 days
3) Your professor tells you to measure a sample of phosphorus-32 (half life = 14.263 days). You forget about this until 7 days later, you measure its mass to be 37 grams.
(Luckily, in that intervening week, the sample was safely isolated and all safety rules and regulations regarding the proper handling of radioactive materials were strictly enforced.)
What was the mass of phosphorus-32 one week before, when you were supposed to measure it?
Beginning amount = 37 * 2(7 / 14.263)
Beginning amount = 37 * 2(.49078)
Beginning amount = 37 * 1.4052
Beginning amount = 51.993 grams
4) Hydrogen-3 or tritium as it is commonly called, has a half life of 12.32 years. If you start with 20 grams of it, how much will remain after 25 years?
Ending Amount = 20 / 2(25 / 12.32)
Ending Amount = 20 / 2(2.0292)
Ending Amount = 20 / 4.0818
Ending Amount = 4.8997 grams
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