This preview shows page 1. Sign up to view the full content.
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 ...
View
Full
Document
This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.
 Fall '08
 SPRUNGER
 Physics, Mass

Click to edit the document details