3.63 Radioactive Half-life
3.63 Radioactive Half-life
- Define the half-life of a radioisotope.
- Explain variation in half-lives.
Assume that you cut a sheet of paper down the center to get two halves. Then you cut each half down the center to
get four pieces. If you keep cutting the pieces of paper in half, you would soon a reach a point where the pieces are
too small to cut again. A radioactive isotope is a little like that sheet of paper.
What Is a Radioactive Isotope?
A radioactive isotope, or radioisotope, has atoms with unstable nuclei. The unstable nuclei naturally decay, or break
down, by losing energy and particles of matter to become more stable. If they gain or lose protons as they decay,
they become different elements. Over time, as the nuclei continue to decay, less and less of the original radioisotope
remains.
Rate of Radioactive Decay
A radioisotope decays and changes to a different element at a constant rate. The rate is measured in a unit called
thehalf-life. This is the length of time it takes for half of a given amount of the radioisotope to decay. This rate is
always the same for a given radioisotope, regardless of temperature, pressure, or other conditions outside the nuclei
of its atoms.
Q:How is repeatedly cutting paper in half like the decay of a radioisotope?
A:As a radioisotope decays, the amount of the radioisotope decreases by half during each half-life, just as a piece
of paper decreases in size by half each time you cut it down the center. You can see a video of this half-life analogy
at the following URL. http://blip.tv/chemteam/an-analogy-for-half-life-4507204