CK-12-Physics-Concepts - Intermediate

http://www.ck12.org Chapter 22. The Nucleus

Here is a reaction showing the fusion of a hydrogen-2 atom and a hydrogen-3 atom.

2

1 H+

3

1 H→

4

2 He+

1

0 n

The disintegration of unstable nuclei does not occur all at once. The rate of disintegration is a statistical process. The
most convenient way to consider it is by a concept known ashalf-life. The time required for half of the atoms in any
given quantity of a radioactive substance to decay is the half-life of that element. Each particular isotope has its own
half-life. For example, the half-life of radium-226 is 1600 years. That is, beginning with 1.00 gram of radium-226,
it would take 1600 years for half of it to decay and leave 0.50 gram remaining. After another 1600 years, only 0.25
gram would remain. In each half-life, exactly half of the beginning amount decays.

TABLE22.1: Half-lives of Various Substances

Element Isotope Half-life

Hydrogen^31 H 12.3 years

Carbon^146 C 5730 years

Polonium^19484 Po 0.7 seconds

Uranium^23892 U 4.5× 109 years

Example Problem:4.00 grams of tritium (hydrogen-3) are produced in the lab. How much of it will remain after
24.6 years?

Solution:24.6 years is two half-lives for hydrogen-3, so^14 of the original amount will remain. That would be 1.00
gram.

Summary

• In all nuclear reactions, the total of the atomic numbers are the left of the equation must equal the total of the
  atomic numbers on the right side of the equation.


• The sum of the mass numbers on the left of the equation must equal the sum of the mass numbers on the right
  of the equation.


• The breakup of a larger nucleus into two or more smaller nuclei is called fission.


• The joining together of two or more smaller nuclei to form a larger one is called fusion.


• The time required for half of the atoms in any given quantity of a radioactive substance to decay is the half-life
  of that element.

Practice

Questions

http://www.youtube.com/watch?v=eKXganH2uiY

MEDIA

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URL: http://www.ck12.org/flx/render/embeddedobject/63586

Follow up questions: