27.3 Alpha, Beta & Gamma Rays

Rutherford classified the three types of naturally occurring nuclear radiation according to penetrating ability.  Listed from least to greatest penetrating ability, the three types are alpha, beta, and gamma rays.

When americium-241 decays, it releases alpha particles energetic enough to ionize gas molecules.  This property is used in the ionizing smoke detector where ionized gas molecules are used as conductors between two electrodes, establishing a current in the detector.  When smoke particles enter the detector they block the alpha particles, which stops the ionization of the air causing the current in the gas to drop, triggering the alarm.

You can explore the effect that smoke and other barriers have on radiation using a Geiger counter, a device that measures the number of alpha particles, beta particles, and gamma radiation emitted by an isotope.  Either the type of barrier or the radioactive isotope can be manipulated.  The responding variable is the amount (per unit time) of each type of radiation reaching the Geiger counter.

Try This Read the description of each particle below, and explain why Rutherford's ranking of emitted radiation particles by penetrating power makes sense in terms of the structure of each particle.

• alpha ( α ) particle: a helium nucleus made up of 2 neutrons and 2 protons;  symbol or
  
  

• beta ( β ) particle: a very high-speed electron; symbol or
  
  

• gamma ( ) particle: a high-energy photon (higher energy than X-rays);  symbol

 

The Process of Nuclear Decay

The decay process must obey the following laws of physics:

1. conservation of charge
   

2. conservation of nucleons
   

3. conservation of mass-energy

The first two laws will be used to complete and balance nuclear decay equations while the third will be applied later when you investigate the concept of mass defect and binding energy.

Simulation: Nuclear Decay There are several types of decay that can be simulated with the Nuclear Decay  Gizmo  .  Use the gizmo to study alpha and beta decay.  Watch for the concepts of conservation of charge and nucleon number as you use the Gizmo. Note: This Gizmo may be used in Assignment 18.

Answer the following self-check questions then click the "Check your work" bar to assess your responses.

SC 2. The following questions relate to the alpha decay of americium-241.

a. What is the alpha decay equation?

b. What is the parent element and what are the daughter elements?

c. How does this decay equation obey the law of conservation of charge?

d. How does this decay equation obey the law of conservation of nucleons?