Astronomy quiz question: radioactive decay age

Astronomy 210 Quiz 7, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

Consider two samples with differing amounts of radioactive elements, embedded gaseous daughter elements, and inert material (which is not involved in the decay process). Which sample is older, as determined by radioactive dating?
(A) Sample A.
(B) Sample B.
(C) (There is a tie.)
(D) (Cannot be determined, as they have different amounts of inert material.)

Correct answer: (C)

The solidification age of a sample (how long ago has it been since it was last molten) is determined by the ratio of decay products to its unstable isotopes. A larger ratio of decay products to unstable isotopes corresponds to a sample with a very old solidification age, but since both samples have the same ratio of decay products to unstable isotopes, they must have the same solidification age.

Section 30676
Exam code: quiz07Sq5h
(A) : 10 students
(B) : 13 students
(C) : 13 students
(D) : 2 students

"Success level": 39% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55

Compare to an older version of this question from Fall 2010.

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