2. 21.1 Nuclear Stability and Radioactive Decay
A. Radioactive Decay
1. Decomposition of nucleus.
a. Total mass number and atomic number must be conserved in any
nuclear change.

3. B. Zone of Stability 1. Of 2000 nuclides, only 279 are stable
2. Nuclides more than 83 protons are unstable
3. Light nuclides stable when neutron/proton ratio = 1
4. Heavier nuclides stable when t neutron/proton ratio > 1
5. Magic numbers
a. Special stability p+ or n is: 2, 8, 20, 28, 50, 82, 126

4. C. Types of Radioactive Decay
1. Alpha Emission
a. Alpha particle (α) is a helium nucleus ( 4He ), so it has a 2+ charge.
b. Alpha emission is restricted almost entirely to very heavy nuclei.
238U 4He Th 2 92 90 2

5. 2. Beta Emission
a. Beta particle (β) is an electron emitted from the nucleus.
b. Beta particles are emitted when a n --> a p+ and an e-
Lowers n/p+ ratio
234Th Pa + 0e 90 91 -1

6. 3. Positron Emission
a. Positrons the same mass as an electron, but a “+” charge.
b. Positron emission arises from the conversion of a p+ --> n and a positron.
Increases n/p+ ratio.
22Na 0e Ne 1 10 11

7. 4. Electron Capture
a. Inner orbital electron is captured by the nucleus.
b. e- combines with a p+ and a n is formed.
n/p+ ratio increases
201Hg + 0e Au + 0 79 80 -1

8. 5. Gamma Emission
a. Gamma rays () are high-energy electromagnetic waves emitted when it changes from an excited state to a ground state.
b. Usually follows other types of decay.
238U He Th  90 92 2

9. D. Decay Series
1. Multiple decays are needed to produce a stable nuclide
a. Original - "Parent" nuclide
b. Ensuing decay nuclides are called "daughter" nuclides

10. 21.3 Nuclear Transformations
A. Nuclear Transformation
1. The change of one element into another
B. Methods of Transformation
1. Particle accelerators overcome the repulsive forces of the target nucleus
a. Cyclotron-Particle is accelerated in a spiral path to the target.
b. Linear Accelerator - Particle is accelerated down a linear track.

11. C. Transuranium Elements
1. Elements beyond Uranium
, 114, 116, 118 (as of May, 1999)
*** notice the absence of odd atomic numbers in the heavy nuclides