Question

10. A rock contains 270 micromoles of U-238 and 110 Micromoles of Pb-206. Assuming that all the Pb-206 comes from decay of the U-238, estimate the rock's age.

Answer 1

sal. Given, Present U-238 = 270 Mmoles. decayed U-238 (present Pb-200) = 1 10 u moles. Halb-life of U-238, Trg = 4,468x10 year. Rate law for nuclear reaction, In [A] = k t - ( CA) k = ln (2) The — (33 I > It = Tira en 22 x ln [A [A ] where, [A ] = initial present U-238 CA] = Present U-238 Tua = Half-life of U-238 t = time when [A ] U.238 O present. Scanned with CamScanner

Initial U-238, [A] = Present 0-238 + decayed U-238 270 lumolt llo ll mol = 380 lmod. so, Rocks age, t = 4.468x10 year los ca xoln 380 lmol 1 (270 umsi = t= 2.20 x doº years. 8.20 billion years (Ang). Scanned with CamScanner