The term radioactive is applied to substances which aren't stable and break down into lighter elements. You probably know this, but it really answers your question. A radioactive sample emits the most radiation as soon as it is formed or isolated. The reason is that that is when the concentration of the radioactive material is the greatest. It begins to decay immediately and as it does, the concentration of radioactive material in the sample gets less. This process can take milliseconds or millions of years depending upon the rate at which the substance breaks down. The reason it's important is that we need to know how long a radioactive material will take to decay to the point that there is so little left that it no longer poses a threat to life. One of the problems with nuclear plants as they are currently designed is that they produce a lot of radioactive waste products. The problem is what do you do with this stuff which can be deadly for thousands of years. You've probably heard of Yucca Mountain. It's a place in Utah where the U.S. has built a storage facility for radioactive waste. They burrowed deep into the mountain and planned to deposit nuclear waste there. The thing is Utah doesn't want to become a garbage dump for radioactive material, so we have a problem. Meanwhile radioactive waste keeps building up and being temporarily stored, usually at the nuclear plant where it was made.......Just one piece of trivia which you can skip. You. and everyone else born after 1945 have a radioactive isotope in your bones which didn't exist on earth before the first nuclear explosions were produced. The substance is Strontium 90. Strontium resembles calcium and when its ingested (in cows milk or plant food ) the body uses it like calcium to build bones and teeth. The isotope strontium 90 has a half life of 25,000 years. That means that 25,000 years after it was produced in the first above ground nuclear explosions half of it will have decayed and no longer be a threat. After another 25,000 years only one quarter of it will remain....and so on. The reason knowing such things is important is that knowing the length of time a radioactive substance will exist is a factor which should be considered in making the stuff.
