Posted on July 2, 2015
Today is the 183nd day of the year – so it is the halfway mark, with 182 days of 2015 before today, and 182 days of 2015 after today.
(Of course, on Leap Years, the end of July 1 is the halfway mark of the 366-day year.)
Second Half of the Year Day is a perfect time to look back at 2015, so far, and figure out how things are going. Maybe make some adjustments. Remind yourself of your goals, or decide to cross out or rededicate yourself to your New Year's resolutions.
- Do you know what an element's half-life is? It is the amount of time it takes for half of its unstable atoms to undergo radioactive decay.
Most elements are stable, not radioactive. But some elements (and some isotopes) are radioactive and spontaneously emit energy or particles.
For example, atoms of the radioactive element radium can “decay” by emitting either alpha particles or carbon-14 nuclei – and thus become another element (either radon or lead). We can never predict exactly which particular radium atom will decay, exactly when, but the the decay rate for a bunch of radium atoms is predictable; radium's half-life is the amount of time it takes for half of the atoms in a sample of radium to decay.
Radium-226 has a half-life of about 1,600 years.
Learn more about radioactivity by watching this video. The Second Half of the video talks about half-life.
- Read Give Me Half!, by Stuart J. Murphy, and then try the trick of how to share food fairly: one person cuts the food in half, and the other person chooses his or her half.
- Read Half Magic, by Edward Eager.
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