ch42-p063 - 63. We can find the age t of the rock from the...

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() U 9 1/2 UP b U 9 238/ 206 4.47 10 y 238 0.15mg ln ln 1 ln2 ln 2 206 0.86mg 1.18 10 y. T mm t m ⎛⎞ + × == + ⎜⎟ ⎝⎠ For the β decay of 40 K, the initial mass of 40 K is m m m KK A r K A r 0 40 40 = + = + /, b g so e e tt 0 K KA r K + −− λλ b g . We solve for m K : K 99 Ar Ar K ln2 1 .1810 y/1 .2510 y 1.6mg 1.7mg. 11 1 t me m m ee e λ ×× = = 63. We can find the age t of the rock from the masses of 238
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