Radioactive decay and mass spectrometry are often used to date rocks after they have cooled from a magma 87 Rb has a half life of 4 88 x 10 10 years and follows the radioactive decay A rock was dated by assaying the product of this decay The mass spectrum of a homogenized sample of rock showed the ...

The Answer is in the image, click to view ...

Radioactive decay and mass spectrometry are often used to date rocks after they have cooled from a

Question:

Radioactive decay and mass spectrometry are often used to date rocks after they have cooled from a magma. ⁸⁷Rb has a half-life of 4.88 x 10¹⁰ years and follows the radioactive decay

A rock was dated by assaying the product of this decay. The mass spectrum of a homogenized sample of rock showed the ⁸⁷Sr/⁸⁶Sr ratio to be 2.25. Assume that the original ⁸⁷Sr/⁸⁶Sr ratio was 0.700 when the rock cooled. Chemical analysis of the rock gave 15.5 ppm Sr and 265.4 ppm Rb, using the average atomic masses from a periodic table. The other isotope ratios were ⁸⁶Sr/⁸⁸Sr = 0.119 and ⁸⁴Sr/⁸⁸Sr = 0.007. The isotopic ratio for ⁸⁷Rb/⁸⁵Rb is 0.330. The isotopic masses are as follows:

Isotope 87 Rb 85 Rb 885r 865r 845r 875r Sr Atomic Mass, u 86.909 84.912 87.906 85.909 83.913 86.909