Chapter 20, Problem 44E

Isotopes such as ²⁶Al (half-life: $7.2\times {10}^5$ years) are believed to have been present in our solar system as it Formed, but have since decayed and are now called extinct nuclides.

(a) ²⁶Al decays by ${\text{β}}^{\text{+}}$ emission or electron capture. Write the equations for these two nuclear transformations.

(b) The earth was formed about . $4.7\times {10}^9$ (4.7 billion) years ago. How old was the earth when 99.999999% of the ²⁶Al originally present had decayed?