p43_065 - 65. We can find the age t of the rock from the...

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Unformatted text preview: 65. We can find the age t of the rock from the masses of mU0 = mU + 238 U and 206 Pb. The initial mass of 238 mPb . 206 Therefore, mU = mU0 e−λU t = (mU + m238 Pb /206)e−(t ln 2)/T1/2 U . We solve for t: t = = = For the β decay of 40 T1/2 U mU + (238/206)mPb ln ln 2 mU 9 4.47 × 10 y 238 0.15 mg ln 1 + ln 2 206 0.86 mg 1.18 × 109 y . K, the initial mass of 40 K is mK0 = mK + (40/40)mAr = mK + mAr , so mK = mK0 e−λK t = (mK + mAr )e−λK t . We solve for mK : mK = = mAr e−λK t mAr = λK t 1 − e− λK t e −1 1.6 mg = 1.7 mg . e(ln 2)(1.18×109 y)/(1.25×109 y) − 1 238 U is ...
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This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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