Mathematical and Physical Journal
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Problem P. 4579. (November 2013)

P. 4579. Traces of Argon were found in one of the most ancient stone of the Earth. The stone was powdered in vacuum, and it was found that the number of Argon atoms is 1/10000 of the number of Potassium atoms. The {}^{40}\mathrm{K} atoms are radioactive and their half-life is 1.18.109 years. 11% of the daughter elements are {}^{40}\!\mathrm{Ar} atoms which are stable. Now 0.0118% of all the potassium atoms is {}^{40}\mathrm{K} isotopes. How old is the stone?

(5 pont)

Deadline expired on December 10, 2013.

Sorry, the solution is available only in Hungarian. Google translation

Megoldásvázlat. 3,68 milliárd éves.


75 students sent a solution.
5 points:58 students.
4 points:12 students.
3 points:1 student.
1 point:2 students.
Unfair, not evaluated:2 solutions.

Problems in Physics of KöMaL, November 2013