1. Unstable Nuclei and Radioactive Decay
Section 4.4
Unstable Nuclei and Radioactive Decay

2. Objectives
Explain relationship between unstable nuclei and radioactive decay
Characterize alpha, beta, and gamma radiation in terms of mass and change

3. Review Recall chemical reactions Are new substances formed?
Were atoms affected/changed?
Chemical reactions only involve electrons
Nucleus is NOT affected in CHEMICAL REACTIONS

4. Nuclear Reactions DO change the nucleus
Atoms of one element change into atoms of another

5. Radioactivity Substance spontaneously emits radiation
Rays and particles are called radiation
Atoms change into other elements

6. Unstable Systems
Radioactivity occurs when an atom’s nucleus is unstable
Unstable systems gain stability by losing energy

7. Radioactive Decay
Unstable nucleus loses energy by emitting radiation spontaneously
Radiates until stable
New atom forms

8. Types of Radiation
Alpha
Beta
Gamma

9. Alpha Radiation Deflects toward a negative charge Alpha particles
2 protons & 2 neutrons
42He or 
Blocked by only a thin sheet of paper

10. Nuclear Equation
22688 Ra  Rn He
Radium Radon

11. Beta Radiation Deflect toward positive charge Beta particles, 
Electron (-1 charge)
Aluminum blocks beta radiation
146C  147N 

12. Gamma Radiation High energy radiation No mass No charge Most dangerous
Accompany  or  particles
Account for energy lost
CANNOT form new atom on its own
00

13. Characteristics of Radiation Types
Symbol
Mass (amu)
Charge
Alpha  4 2+
Beta 
1/1840 1-
Gamma 

17. Practice
6027Co  6028Ni + ____
24195Am  ____ + 42He

18. Practice Solution 6027Co  6028Ni + 0-1 24195Am  23793Np + 42He
Complete the following nuclear reactions:
6027Co  6028Ni + 0-1
24195Am  Np + 42He