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General Chemistry Principles, Patterns, and Applications, 2011

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particles with an energy of 0.545 MeV <strong>and</strong> undergoes 2.7 × 10 13 decays/s. How many watts of power are<br />

available from this RTG (1 watt = 1 J/s)?<br />

11. Potassium consists of three isotopes (potassium-39, potassium-40, <strong>and</strong> potassium-41). Potassium-40 is the<br />

least abundant, <strong>and</strong> it is radioactive, decaying to argon-40, a stable, nonradioactive isotope, by the emission<br />

of a β particle with a half-life of precisely 1.25 × 10 9 yr. Thus the ratio of potassium-40 to argon-40 in any<br />

potassium-40–containing material can be used to date the sample. In 1952, fragments of an early<br />

hominid, Meganthropus, were discovered near Modjokerto in Java. The bone fragments were lying on<br />

volcanic rock that was believed to be the same age as the bones. Potassium–argon dating on samples of the<br />

volcanic material showed that the argon-40-to-potassium-40 molar ratio was 0.00281:1. How old were the<br />

rock fragments? Could the bones also be the same age? Could radiocarbon dating have been used to date the<br />

fragments?<br />

A N S W E R S<br />

1. 6.6 × 10 −3 rad; 0.13 rem<br />

2.<br />

3.<br />

U92235 + n01®U92236 +g<br />

U92238 + n01®U92239 +g<br />

4.<br />

5.<br />

6.<br />

7.<br />

8.<br />

9.<br />

10.<br />

U92239 ® N93239 p + b -10<br />

N93239 p ® P94239u + b -10<br />

P94239u ® A95239m + b -10<br />

A95239m ® C96239m + b -10<br />

a. 7.1 × 10 18 atoms of Pu<br />

b. 0.35 J<br />

c. 0.49 rad<br />

d. 9.8 rem; this dose is unlikely to be fatal.<br />

11.<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1913

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