21. Nuclear Chemistry
Radioactive Half-Life
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Practice this topic
- Multiple Choice
The half-life of arsenic-74 is about 18 days. If a sample initially contains 5.13 x 104 mg arsenic-74, what mass (in mg) would be left after 80 days?
866views1rank - Multiple Choice
What percentage of carbon – 14 ( t1/2 = 5715 years) remains in a sample estimated to be 18,315 years old?
972views1rank - Textbook QuestionFluorine-18 undergoes positron emission with a half-life of 1.10 x 10^2 minutes. If a patient is given a 250 mg dose for a PET scan, how long will it take for the amount of fluorine-18 to drop to 75 mg?(a) 56 minutes(b) 96 minutes (c) 132 minutes (d) 191 minutes783views
- Textbook QuestionIn a cave in Oregon, archaeologists found bones, plant remains, and fossilized feces. DNA remaining in the feces indi-cates their human origin but not their age. To date the remains, the decay rate was measured and found to be 2.71 disinte-grations/min per gram of carbon. Currently living organisms have a decay rate of 15.3 disintegrations/min per gram of carbon, and the half-life of 14C is 5715 years. How old are the remains? (a) 1460 years(b) 9900 years(c) 14300 years(d) 18600 years319views
- Textbook Question
Some watch dials are coated with a phosphor, like ZnS, and a polymer in which some of the 1H atoms have been replaced by 3H atoms, tritium. The phosphor emits light when struck by the beta particle from the tritium decay, causing the dials to glow in the dark. The half-life of tritium is 12.3 yr. If the light given off is assumed to be directly proportional to the amount of tritium, by how much will a dial be dimmed in a watch that is 50 yr old?
940views - Textbook Question
Cobalt-60 is a strong gamma emitter that has a half-life of 5.26 yr. The cobalt-60 in a radiotherapy unit must be replaced when its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2016, when will it be necessary to replace the cobalt-60?
2317views - Multiple ChoiceA 2.00 mg sample of the radioisotope phosphorus-32 is found to contain 0.400 mg of phosphorus-32 after 33.3 days. Calculate the half-life (in days).646views
- Multiple ChoiceCarbon-14, which is present in all living tissue, radioactively decays via a first-order process. A one-gram sample of wood taken from a living tree gives a rate for carbon-14 decay of 13.6 counts per minute (CPM). If the half-life for carbon-14 is 5720 years, calculate the time it would take for the count rate to decrease to 6.8 CPM.735views