CK-12 Physical Science Concepts - For Middle School

3.61. Beta Decay http://www.ck12.org

Q:Try to balance the following nuclear equation for beta-minus decay by filling in the missing subscript and
superscript.

131

53 I→

?

?Xe +

0

− 1 e + energy

A:The subscript of Xe is 54, and the superscript is 131.

Dangers of Beta Decay

Beta particles can travel about a meter through air. They can pass through a sheet of paper or a layer of cloth but not
through a sheet of aluminum or a few centimeters of wood. They can also penetrate the skin and damage underlying
tissues. They are even more harmful if they are ingested or inhaled.

Summary

• Beta decay occurs when a nucleus is unstable because it has too many or too few neutrons relative to protons.
  The nucleus emits a beta particle and energy. A beta particle is either an electron (beta-minus decay) or a
  positron (beta-plus decay).


• In beta-minus decay, a neutron breaks down to a proton and an electron, and the electron is emitted from the
  nucleus. In beta-plus decay, a proton breaks down to a neutron and a positron, and the positron is emitted from
  the nucleus.


• Balanced nuclear equations show how the numbers of protons and neutrons change in beta decay.


• Beta radiation is harmful to living things.

Vocabulary

• beta decay: Type of radioactive decay in which an unstable atomic nucleus emits a beta particle (electron or
  positron) and energy.

Explore More

Read the article about beta decay at the following URL. Be sure to watch the short video at the bottom of the page.
Then answer the questions below.

http://teachnuclear.ca/contents/cna_radiation/nuclear-decay/beta_decay/

1. Write a balanced nuclear equation for the beta-minus decay of cesium-137. Identify the new element that
   results from the reaction. How many neutrons does this element have?


2. What are beta emitters? Give three examples.

Review

1. Compare and contrast beta-minus and beta-plus decay.


2. Fill in the missing subscript and superscript in this nuclear equation to balance it:

14
?C→
?
7 N +
0
− 1 e + energy

Does the equation represent beta-minus or beta-plus decay? How do you know?