radioactive

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Artificial radiation You should know some of the sources of artificial background radiation.

Sources There is little we can do about natural background radiation. After all, we cannot stop eating, drinking or breathing to avoid it! However, human activity has added to background radiation by creating and using artificial sources of radiation. These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical X-rays. Move your mouse over the diagram to check your understanding of this.The experiment is known as Rutherford's alpha particle scattering experiment. In it, a beam of alpha particles is aimed at a thin foil of gold. In the experiment:

about 99% of the alpha particles pass straight through the foil

some of the alpha particles are deflected through small angles

a very small number of the alpha particles rebound off the gold foil

Because of the results of this experiment, Rutherford showed that:

the nucleus of an atom has a relatively small diameter compared with that of the atom

most of the mass of the atom is concentrated in the nucleus

atoms are made up of protons, neutrons (nucleus) and then surrounded by electrons

The atomic number of an element (Z) is the number of protons in a nucleus. This determines what the element is.

The mass number of an element (A) is the number of nucleons in a nucleus. The number of neutrons in a nucleus is A-Z.

Atoms of elements can contain different numbers of neutrons. Different forms are known as isotopes. The nucleus of an isotope is called a nuclide.

Radioisotopes and radionuclides refer to radioactive forms of elements.

A particular isotope of an element is defined by giving the name of the element and the mass number of the isotope. An example of this would be uranium-235.

The symbol is used for the nucleus of an element that has the chemical symbol X, a mass number A, and atomic number Z.

Question

The symbol is used for a particular isotope. If A = 14 and Z = 6,

How many protons does the isotope have in its nucleus?

How many neutrons does the isotope have in its nucleus?

What is the element X?

The number of protons in the nucleus of an atom is called its atomic number:

The atoms of a particular element all have the same number of protons

The atoms of different elements have different numbers of protons

The total number of protons and neutrons in an atom is called its mass number.

This is the full chemical symbol for chlorine-35.

The proton number is shown below the chemical symbol, and the mass number is shown above. In the example below, the atomic number is 17 and the mass number is 35. This means that each of these atoms has:

17 protons

17 electrons

35 - 17 = 18 neutrons

Isotopes are the atoms of an element with different numbers of neutrons. They have the same proton number, but different mass numbers. Fission is another word for splitting. The process of splitting a nucleus is called nuclear fission. Uranium or plutonium isotopes are normally used as the fuel in nuclear reactors, because their atoms have relatively large nuclei that are easy to split, especially when hit by neutrons.

When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following happens:

the nucleus splits into two smaller nuclei, which are radioactive

two or three more neutrons are released

some energy is released

The additional neutrons released may also hit other uranium or plutonium nuclei and cause them to split. Even more neutrons are then released, which in turn can split more nuclei. This is called a chain reaction. The chain reaction in nuclear reactors is controlled to stop it going too fast.

Background radiation is all around us. We can do little to avoid it. Most background radiation comes from natural sources, while most artificial radiation comes from medical examinations, such as X-ray photographs.

background radiation comes from animals, rocks, soil and plants and lastly cosmic rays.

Artificial radiation You should know some of the sources of artificial background radiation.

Sources There is little we can do about natural background radiation. After all, we cannot stop eating, drinking or breathing to avoid it! However, human activity has added to background radiation by creating and using artificial sources of radiation. These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical X-rays.

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