John Harkett, aged 12, of Miami, Okla. For his question‑,

What causes radioactivity?

Sixty years ago, scientists were dust about certain that nothing could change an atom. An atom of iron, like every other atom of iron, stayed that way for all eternity. An atom of gold, the smallest possible particle of gold, remained what it was, For the most part, this is true. But certain atoms were discovered which did not stay as they were. Far from it.

The first hint came with the discovery of uranium. This strange ore was constantly shooting forth strange rays. Then radium was purified from pitchblend, an ore of uranium. Certainly the atoms of radium were up to something unusual. Radium was over a million times morn radioactive than ordinary uranium. Slowly, surely and with great to‑do, its atoms were changing into atoms of lead.

So the old idea. that an atom cannot change was tossed aside. Certain atoms since time on earth began have been busy changing themselves into atoms of something else. It was calculated that the change is taken in easy stages over billions of years. In four and a half billion years, half of any lump of ordinary uranium will become lead. In the meantime, the changing atoms have passed through 14 different stages.

There are a limited number of different atoms and they come in different sizes. The uranium atom is one of the big ones. Its central core contains 238 proton end neutron particles. We do not know for sure what causes an atom to be radioactive. But we call them unstable atoms. For some reason they seem unable to hold the balance which keeps an ordinary atom whole. A number of radioactive atoms have been discovered in the past sixty years. All of them ors large atoms. It may be that atoms of over a certain size are gust too big to hold their particles together,

What’s more, each atom is a chain of radioactivity is smaller than the one before it. The big atom breaks apart by shooting off tiny particles. It releases tremendous energy as it does so. Experiments show that there are three types of rays shooting off from a radioactive substance.

One stream of particles shoots out at the rate, of 10,000 miles a second. It is made of alpha particles. These are sizable particles as large as helium atoms. Beta particles are thousands of times smaller. However, they travel almost at the speed of light. Their charge is about half that of the alpha particles. Also rushing forth from the radioactive substance are gamma particles.

Each time one of these minute particles leaves an atom, that atom becomes an atom of something else. No one can change or stop the process of radioactivity. In 1620 years, half the present supply of radium will be lead. This lead is made of staple atoms and is radioactive no longer. In nature many radioactive substances exist in rocks and ores. There they are safe from any damage to the world. After, all, ten tons of the very best pitchblend yield only one tiny gram of precious radium.