Learning Outcomes

• Historical outline of radioactivity: work of Becquerel (discovery of radiation from uranium salts); Marie and Pierre Curie (discovery of polonium and radium).

• Widespread occurrence of radioactivity.

Antoine Henri Becquerel• In 1896, while investigating

uranium salts, Becquerel accidentally discovered radioactivity . Becquerel found that the photographic plates were fully exposed when in contact with radioactive salt.

Marie Curie• developed a theory of radioactivity techniques for isolating radioactive isotopes, and discovered two new elements, Polonium and Radium

Natural Radiation comes from

• Sources in the earth that contain radioactive isotopes.

• Sources from space in the form of cosmic rays

• Sources in the atmosphere, particularly from Radon gas that is released from the Earth's crust.

• About 15% of background radiation comes from medical X-rays and nuclear medicine.

• About 3% of background radiation comes from other man-made sources such as: nuclear testing, power plants, and smoke detectors.

Pierre Curie• Pierre discovered nuclear

energy, by identifying the continuous emission of heat from Radium particles. He also investigated the radiation emissions of radioactive substances, which lead to the discovery of Alpha, Beta and Gamma radiation.

Learning Outcomes

• Alpha, beta and gamma radiation (nature andpenetrating ability).One example each of:• an α-emitter, e.g. 241Am• a β-emitter, e.g. 14C• a γ-emitter, e.g. 60Co.

Radioactivity

• Is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation

• There are three types alpha, beta and gamma

Alpha particle

Alpha

• Made of 2 protons + 2 neutrons• Helium nucleus• From unstable nuclei• Low penetration; stopped by a sheet of

paper• Americum-241 [used in smoke detectors]

emits alpha particles

Alpha particle

Smoke detector

Beta

• Electrons• Formed when a neutron decays into a

proton and an electron• Penetrate 5mm of aluminum• Carbon-14 used in carbon-dating emits beta

particles

Neutron decay

Carbon 14

Learning Outcomes

• Uses of radioisotopes (three examples).• 14C age determination (calculations not

required).• 60Co for cancer treatment.• Food irradiation.

The animation below shows the decay of a radioactive sample of Carbon-14 to stable Nitrogen by the emission of beta particles.

Carbon-14 decays to nitrogen-14

Take in Carbon-14

• The percentage of carbon-14 in all of these living things is the same as the percentage of carbon-14 in the atmosphere.

Death

• The carbon-14 within every once-living thing will someday turn back into nitrogen-14

Carbon-14 detection

Gamma

• High energy electromagnetic radiation• Not deflected by magnetic or electric fields• Only stopped by several cms of lead.• Cobalt-60 [used to treat cancer] emits

gamma rays

Gamma Rays

Learning Outcomes

• Demonstration of properties –detection and penetrating power

Penetration

Penetration 2

Learning Outcomes

• Distinction between chemical reaction and nuclear reaction

• (simple equations required –confine examples to alpha and beta emissions).

Nuclear reactions

• Emission of radioactive radiation• In a nuclear reaction the nucleus forms a

new element,

Loss of an alpha particle

• Radium-226 Radon-222 + alpha particle

• 22688Ra222

86Rn +42He

• Mass decreases by 4 [226222]• Atomic number decreases by 2 [8886]

Beta loss

• Carbon-14 nitrogen-14 + beta

• 146C 14

7N + 0-1e

• Mass number stays the same• Atomic number increases by 1

Learning Outcomes

• Radioisotopes.• Half-life (non-mathematical treatment).• Uses of radioisotopes (three examples).

Radioisotopes

• A Radioisotope (radionuclide) is an atom with an unstable nucleus.

Transmutation

• Change of one element into another

• Rutherford confirmed the artificial transmutation of nitrogen. Alpha particles were allowed to pass through nitrogen gas; when one struck a nitrogen nucleus, a hydrogen nucleus was ejected, and an oxygen nucleus formed.

Half life

• Time taken for half of the nuclei in any given sample to decay

uses

• Medical—.gamma rays kill cancerous cells and sterilises equipment

• Archaeological—after a living thing dies the amount of C-14 decreases. Used to determine the age of a plant/animal

• Food—gamma rays kill disease causing organisms