Part A : URANIUM AND RADIOACTIVITY

A.1. What is uranium?
A.2. What is radioactivity?
A.3. How far can atomic radiation penetrate?
A.4. Is radioactivity dangerous?
A.5. How do radioactive elements produce other radioactive elements?

---

A.1. What is uranium?

Uranium is the heaviest metal that occurs in nature. It is an unstable material which gradually breaks apart or "decays" at the atomic level, as described in the next section. Any such material is said to be "radioactive".

As uranium slowly decays, it gives off invisible bursts of penetrating energy called "atomic radiation". It also produces more than a dozen other radioactive substances as by-products.

These unstable by-products, having little or no commercial value, are called "uranium decay products". They are discarded as waste when uranium is mined. One of them is a toxic radioactive gas called radon. The others are radioactive solids.

A.2. What is radioactivity?

Science teaches us that everything is made of tiny little particles called atoms. They are too small to be seen even under a powerful microscope. When a substance is radioactive, it means that its atoms are exploding (sub-microscopically) and throwing off pieces of themselves with great force. This process is called "radioactive decay".

During radioactive decay, two types of tiny electrically charged particles are given off, travelling very fast. They are called alpha and beta particles. Some radioactive materials are alpha emitters, and others are beta emitters. In addition, highly energetic rays called gamma rays are often emitted. Gamma rays are not material particles at all, but a form of pure energy very similar to x-rays, travelling at the speed of light.

A.3. How far can atomic radiation penetrate?

Gamma rays penetrate through soft tissue just as light shines through a window. Beta particles have less penetrating power, travelling less than two centimeters in soft tissue. Alpha particles have the least penetrating power, travelling just a few micrometers in soft tissue, equivalent to a few cell diameters.

A.4. Is radioactivity dangerous?

Alpha particles, beta particles and gamma rays can do great harm to a living cell by breaking its chemical bonds at random and disrupting the cell's genetic instructions.

Massive exposure to atomic radiation can cause death within a few days or weeks. Smaller doses can cause burns, loss of hair, nausea, loss of fertility and pronounced changes in the blood. Still smaller doses, too small to cause any immediate visible damage, can result in cancer or leukemia in the person exposed, congenital abnormalities in his or her children (including physical deformities, diseases and mental retardation), and possible genetic defects in future generations.

Outside the body, alpha emitters are the least harmful, and gamma emitters are more dangerous than beta emitters.

Inside the body, however, alpha emitters are the most dangerous. They are about 20 times more damaging than beta emitters or gamma emitters. Thus, although alpha radiation cannot penetrate through a sheet of paper or a dead layer of skin, alpha emitters are extremely hazardous when taken into the body by inhalation or ingestion, or through a cut or open sore.

A.5. How do radioactive elements produce other radioactive elements?

When atoms undergo radioactive decay, they change into new substances, because they have lost something of themselves. These by-products of radioactive decay are called "decay products" or "progeny". In many cases, the decay products are also radioactive. If so, they too will disintegrate, producing even more decay products and giving off even more atomic radiation.

Click on small image to view the full scale image.

Thus uranium-238 changes into thorium-230 (in three stages), which then changes into radium-226, and thence into radon-222. The numbers keep getting smaller because the atoms are losing a part of themselves.