An unknown radioactive element decays into non-radioactive substances. In 700 days the radioactivity of a sample decreases by 47 percent. (a) What is the half-life of the element? half-life: [_____________] (days) (b) How long will it take for a sample of 100 mg to decay to 55 mg? time needed:[_____________] (days)

The half-life of 232Th is 1.4 x 10" yr. Find the number of disintegrations per hour emitted by 1.0 mol of 23TH.

The accompanying figure illustrates that after two half-lives, ____ percent of the parent radioisotope has decayed.   50   0   75   25   100

14.20 Round your answers to 6 decimal places. Box your final answers.

The half-life of 14C is 5730 years, and the current decay rate in living organisms is 14.3 disintegrations per minute per gram of carbon (d.p.m./g C). What is the age (in years BP) of an artifact found to have a decay rate of 4.75 d.p.m/g C in 2013? IMPORTANT: When entering your answer: • Enter the number only (no units) • Do not leave any spaces • Report your number to the tens column (regardless of the significant figures) Correctly round your answer to the tens column (margin of allowed error is only ± 10, so always use un-rounded numbers in your calculations) Examples: 12340 or 5670 (include the zero in the units column, Canvas will add a comma for you)

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The half-lives of different radioisotopes are given in the table. Half-life (min) Radioisotope argon-44 lead-196 time: potassium-44 indium-117 How long would it take, in minutes, for the amount of argon-44 to decrease from 64.0 mg to 8.00 mg? ADI 12 37 22 43 NOV 1 C min C 3:37 1 ()))

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