Is a Half-life Better Than No Life?

How can something have half a life? In biology, something is either dead or alive. In the world of rocks and other non-living things, there is such a thing as having a half-life; elements that are radioactive have half-lives. 

An atom is the smallest form of an element such as gold, iodine or uranium. An atom is like a tiny solar system with a centre called a "nucleus" and tiny planets called "electrons" flying around it. Radioactive atoms change into other atoms; the rate at which they change is called a “half-life”. When there is a bunch of radioactive atoms together, the speed at which the element becomes something else is always the same for that particular element. 

The most common iodine released from a nuclear power plant accident, iodine-131, has a half-life of about eight days - 8.0197 days to be exact. Half of its radioactivity will be gone as half of the iodine changes into xenon in eight days. Half of the remaining iodine-131 changes in the next eight days and so on; it takes ten half-lives before the radioactive element is gone – so, for iodine-131, it takes eighty days (10 x 8.0197 = 80.197 days) before it has all changed into xenon-131. Xenon-131 cannot change back to Iodine-131.
In fact, since the change always involves the loss of atomic energy, however small, it is called "decay".

Half lives can be extremely short - iodine-109 has a half-life of 93.5 microseconds. That's short! One microsecond is one millionth of a second. On the other hand, iodine-129 has a half life of 15.7 million years.

Iodine-109 and iodine-129 are different isotopes of iodine. Isotopes are different kinds of the same element just as a terrier and a German shepherd are different kinds of dogs. There are 37 known isotopes of iodine; almost all of them products of nuclear nuclear reactors. Iodine-127 is the only iodine that is not radioactive. It is the one that is essential for healthy thyroids for healthy people. It is the one that should be taken immediately after a nuclear accident. The only other natural iodine is iodine-129, found normally in nature in very small amounts.

If iodine has an atomic weight of 131 and xenon has an atomic weight of 131, how do we know which is which? The atomic number, based on the number of protons in the nucleus, is different. Iodine’s atomic number is 53 while xenon has 54 protons in its nucleus. 
Each proton has a positive electrical charge. To maintain neutrality, the number of electrons in orbit around the nucleus will be the same.  All of the characteristics – colour, chemical reactivity, boiling point, freezing point and so on – of an element depend upon the number of protons in the nucleus. The atomic number is another way to name an element.

All of the iodines have 53 protons in their nuclei. The electrons flying around the nucleus are considered to be weightless. What makes the weights different (109, 131, 127, etc) are the number of neutrons in the nucleus. A neutron is "glue" to hold the nucleus together - it is made up of an electron and a proton so has the same weight as a proton. When iodine decays into xenon, it loses one of the electrons from the nucleus (and some energy). This leaves one more proton in the nucleus than before the decay. The atomic number goes from 53 to 54. Iodine has become a different element!

So, is a half life better than no life? Half lives are useful for dating the age of the universe, dead bodies, and for some industrial and medical purposes. In those cases, a half-life is a good thing. However, the vast majority of radioactive elements have entered the world through atomic bomb testing and nuclear power plant emissions (or accidents). Their half-lives are part of environmental pollution. Half-lives are not good things.