What was the mass of phosphorus-32 one week before, when you were supposed to measure it?īeginning amount = ending amount * 2 (time / half-life)Ĥ) Hydrogen-3 or tritium as it is commonly called, has a half life of 12.32 years. (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.) You forget about this until 7 days later, you measure its mass to be 37 grams. 54821)ģ) Your professor tells you to measure a sample of phosphorus-32 (half life = 14.263 days). Half life = (time * log 2) / log (beginning amount / ending amount) 30103)Ģ) You measure the radioactivity of a substance, then when measuring it 120 days later, you find that it only has 54.821 % of the radioactivity it had when you first measured it. How much time will it take until only 10 grams remain?Įlapsed time = half life * log (beginning amount / ending amount) / log 2Įlapsed time = 87.51 * (log (100 / 10) /.
There are four half life problems further down this page.ġ) You start with 100 grams of sulfur-35, which has a half life of 87.51 days. This calculator can solve half life problems whenever three of the four variables are known: The above formulas are used in calculations involving the exponential decay