*•58 Two radioactive materials that alpha decay, 238U and 232Th, and one that beta decays, "K, are sufficiently abundant in granite to contribute significantly to the heating of Earth through the de- cay energy produced. The alpha-decay isotopes give rise to decay chains that stop when stable lead isotopes are formed. The isotope 4"K has a single beta decay. (Assume this is the only possible decay of that isotope.) Here is the information: Stable Decay Half-Life End Parent Mode (y) Point (MeV) (ppm) 238U 232Th 4.47 x 10° 206рЬ 51.7 1.41 x 1010 208Pb 42.7 13 1.28 x 10° 40Ca 1.31 4 In the table Q is the total energy released in the decay of one par- ent nucleus to the final stable end point and f is the abundance of the isotope in kilograms per kilogram of granite; ppm means parts per million. (a) Show that these materials produce energy as heat at the rate of 1.0 x 10-9 W for each kilogram of granite. (b) Assuming that there is 2.7 x 102 kg of granite in a 20-km-thick spherical shell at the surface of Earth, estimate the power of this decay process over all of Earth. Compare this power with the total solar power intercepted by Earth, 1.7 x 1017 W.
*•58 Two radioactive materials that alpha decay, 238U and 232Th, and one that beta decays, "K, are sufficiently abundant in granite to contribute significantly to the heating of Earth through the de- cay energy produced. The alpha-decay isotopes give rise to decay chains that stop when stable lead isotopes are formed. The isotope 4"K has a single beta decay. (Assume this is the only possible decay of that isotope.) Here is the information: Stable Decay Half-Life End Parent Mode (y) Point (MeV) (ppm) 238U 232Th 4.47 x 10° 206рЬ 51.7 1.41 x 1010 208Pb 42.7 13 1.28 x 10° 40Ca 1.31 4 In the table Q is the total energy released in the decay of one par- ent nucleus to the final stable end point and f is the abundance of the isotope in kilograms per kilogram of granite; ppm means parts per million. (a) Show that these materials produce energy as heat at the rate of 1.0 x 10-9 W for each kilogram of granite. (b) Assuming that there is 2.7 x 102 kg of granite in a 20-km-thick spherical shell at the surface of Earth, estimate the power of this decay process over all of Earth. Compare this power with the total solar power intercepted by Earth, 1.7 x 1017 W.
College Physics
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ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
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Transcribed Image Text:*•58 Two radioactive materials that alpha decay, 238U and 232Th,
and one that beta decays, "K, are sufficiently abundant in granite
to contribute significantly to the heating of Earth through the de-
cay energy produced. The alpha-decay isotopes give rise to decay
chains that stop when stable lead isotopes are formed. The isotope
4"K has a single beta decay. (Assume this is the only possible decay of
that isotope.) Here is the information:
Stable
Decay
Half-Life
End
Parent Mode
(y)
Point
(MeV) (ppm)
238U
232Th
4.47 x 10°
206рЬ
51.7
1.41 x 1010
208Pb
42.7
13
1.28 x 10°
40Ca
1.31
4
In the table Q is the total energy released in the decay of one par-
ent nucleus to the final stable end point and f is the abundance of
the isotope in kilograms per kilogram of granite; ppm means parts
per million. (a) Show that these materials produce energy as heat
at the rate of 1.0 x 10-9 W for each kilogram of granite. (b)
Assuming that there is 2.7 x 102 kg of granite in a 20-km-thick
spherical shell at the surface of Earth, estimate the power of this
decay process over all of Earth. Compare this power with the total
solar power intercepted by Earth, 1.7 x 1017 W.
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