Physics - Section G: Radioactivity and Particles

Atoms and Radioactivity

Electrons, Protons and Neutrons

Atoms are made up of electrons, protons and neutrons:

• an electron is an extremely small particle with a negative charge which orbits the nucleus of an atom, making up the outer shells of the atom.
• a proton is a positvely charged particle found in the nucleous of an atom and
• a neutron is an uncharged particle found in the nucleous of an atom.

Atomic Number = No. of Protons in the nucleous

Atomic Mass = No. of nucleons (protons and neutrons) in the nucleus

Atomic Number = No, of electrons

Group Number = No. of Electrons in outer shell

Ionising Radiation

Alpha particles are helium nuclei ejected from unstable nuclei. They are heavily ionising and have only a short range - travelling only 10cm (appozimately) in air. Alpha particles can be stopped by thn card.

Beta particles are fast movng electrons ejected from unstable nuclei. They are less ionising than alpah particles and can travel long distances in the air. They are stopped by 1-2mm of aluminium.

Gamma rays are photons of high energy electromagnetic waves. They are extremely penetrating and interact with stoms which may then emit ionising radiation. They are only stopped by very thick lead (often tens of cm).

Nuclear Transformations

Radioactive forms (isotopes) of elements decay randomly over time emitting combinations of the different types of ionsing radiation. The emission of gamma rays has no effect on the atomic mass or charge of the decaying atom but gamma ray emission occurs with other types of radiation.

Both alpha and beta emissions cause a change in the atomic number of the original decaying element - in both processes the original element turns into another element.

Decay euations must balance - the sum of atomic masses before and after must be the same. The sum of the atomc numbers must be the same before and after.

Radiation and Half-Life

Detecting Ionising Radiation

Nuclear radiation can ionise atoms that it interacts with. This can be detected in a variety of ways:

• Photographic film - This is used in badges worn by workers at frisk from continous exposure to radiation. THe badge becomes fogged when exposed to ionising radiation. The badges are checked regularly to ensure safety limits are not exceeded.
• The Geiger-Muller tube - When ionising radiation enters the GM tube, it ioises the gases within allowing a pulse of current to pass between the electrodes. This is then fed to either a counter or rate metre.

Sources of Background Radiation

• Rocks - The slow decay of isotopes of uranium produces radon and thoron gases. Radon is highly radioactive and is a particular problem in certain parts of the UK, such…