CK-12 Physical Science Concepts - For Middle School

3.56. Radioactivity http://www.ck12.org

the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won
two Nobel Prizes for her discoveries. You can learn more about Marie Curie at this URL: http://nobelprize.org/no
bel_prizes/physics/laureates/1903/marie-curie-bio.html

Summary

• Radioactivity is the ability of an atom to emit charged particles and energy from its nucleus. The charged
  particles and energy are called by the general term radiation.


• Radioactivity was discovered in 1896 by Antoine Henri Becquerel when he found that uranium leaves an
  image like an X-ray on a photographic plate. Besides uranium, radioactive elements include radium and
  polonium, both of which were discovered by Marie Curie.

Vocabulary

• radiation: Energy emitted by the nucleus of a radioisotope or an accelerating particle; transfer of energy by
  electromagnetic waves that can travel across space as well as through matter.


• radioactivity: Ability of an atom to emit charged particles and energy from the nucleus.

Explore More

Watch the video about radioactivity at the following URL, and then answer the questions below. http://www.youtu
be.com/watch?v=q1pMDMXLSBI

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/82374

1. If a nucleus is unstable, it eventually breaks apart. This process is called __.


2. The element polonium has 84 protons. What can you infer about polonium, based on this information?


3. One type of radioactivity is alpha emission. What is an alpha particle? What happens to an alpha particle after
   it is emitted from an unstable nucleus?


4. Why is the element called uranium-238 radioactive? What products form when its nuclei break apart?

Review

1. What is radioactivity?


2. Define radiation.


3. Identify some radioactive elements.


4. Explain how radioactivity was discovered.