The Nature of Radioactivity
What is radioactivity? Well, for those of you who have seen any of our other pages, you know the drill. For the newcomers, let's define some terms that you'll need to know for this page.
Radioactivity- the spontaneous breakdown of an unstable atomic nucleus with the emission of particles and rays.
Spontaneous- happens all by itself
Nucleus- the center of an atom
Emission- to give out
Fluorescent- the emission of light during the absorption of radiation from another source
Half-life- length of time during which half of a given number of atoms of a radioactive nuclide decays.
Nuclide- an atom of a particular mass and element
All radioactive nuclides have certain things in common.
1. Their radiation affects the emulsion on a photographic film. Even though photographic film is wrapped in heavy black paper and kept in the dark, some of the radiation from radioactive nuclides penetrate the wrapping and affect the film. When the film is developed, there's a black spot where the radiation's hit it. Some of the radiation penetrates paper, wood, flesh, thin metal sheets and thick glass.
2. Their radiation ionizes the surrounding air. A molecule with a charge is called an ion. When the radiation flies through the air they knock off electrons from the gas molecules around them. This causes the gas molecules to have a positive charge. That's ionizing the air.
3. Their radiation makes certain compounds fluoresce. The radiation from radioactive nuclides make bright flashes of light when they hit certain compounds. Since these flashes happen so often and rapidly, the flash is a constant glow.
4. Their radiation has special physiological effects. Radiation is very harmful. It can stop plants from reproducing, kill bacteria, and even kill large animals, like humans. Radiation burns take a long time to heal if ever, and can be fatal.
5. They undergo radioactive decay. All atoms eventually decay into simpler atoms, and start to emit nuclei. The only problem is we don't know how long it will take a specific atom to decay. But, we can figure out how long it will take half a sample of atoms to decay. That number in years, is called a half-life.
Types of Radioactivity
There was a scientist named Rutherford who did many experiments in radioactivity. He discovered that radiation from radioactive materials could be separated into 3 distinct types by a magnet.
1. a (alpha) particles. These are made of 2 protons and 2 neutrons; this is helium. Alpha particles have 2 positive electrical charges, speeds about 1/10 the speed of light, and masses about four times that of hydrogen. They are deflected only slightly by a magnetic field. Their penetrating power isn't very great. They can be stopped by tinfoil or a piece of paper.
2. b (beta) particles. These guys are electrons. They have single negative charges and may travel at nearly the speed of light. Their mass is only a small part of an alpha particle. Even though they have half as much charge, they are deflected quite a bit by a magnetic field and in the opposite direction. The high speed of the beta particle makes it much more penetrating than the alpha.
3. g (gamma) particles. These bad boys are high energy photons. They are the same kind of radiation as visible light, but of a much shorter wavelegnth and higher frequency. Gamma rays are produced by energy fluctuations in the nucleus that don't change the nuclide. They are the most penetrating radiation given off by radioactive elements. They are not electrically charged and aren't deflected by a magnetic field.
Fission occurs when you ram a neutron into a heavy nucleus. You end up with a neuron and two not-so-heavy nuclei. When this happens a large amount of energy is given up. The machines used to do this are called particle accelerators. What a particle accelerator does, is speed up the neutron then propel it into the other atom. They can be in the form of a straight line or a circle. Linear accelerators are built in a line. Cyclotrons and synchrotrons are circular in shape.
Now with fusion, the opposite happens. You have two light particles, meld them together, and end up with one heavy particles, along with a lot of energy. Because you can only do this under extreme temperatures, the process is also called a thermonuclear reaction.
This type of energy is the kind used in thermonuclear bombs, sometimes called a hydrogen bomb. The formation of alpha particles and tremendous amounts of energy from a compound of lithium and deuterium, is one possible reaction in a hydrogen bomb. This reaction is started by subjecting the compound to extremely high temperature and pressure and using a fission reactor as a detonator.