Skip to main content
Hong Kong Observatory Brand Hong Kong - Asia's world city
GovHK Traditional Chinese Simplified Chinese Search
Search Site Map Contact Us
red dot
Print Version
Back
Print Version PDF Version

Exhibit 5
What is Half-Life?

What is Half-Life?

When a radioactive element decays, the number of radioactive nuclei decreases with time. The time it takes for the number of radioactive nuclei to decrease to half its original amount is called its half-life. Each radioactive element has a characteristic half-life. The half-lives of various radioactive elements may vary from millionths of a second to billions of years.

How to Protect Ourselves from Ionizing Radiation?Exhibit 4
Exhibit 6 What are the Sources of Ionizing Radiation?
Last revision date: <20 Dec 2012>