Radioactivity
History of Radioactivity
Henry Becquerel: wrapped crystals of uranium salt in black pepper and left them lying in the dark on a photographic plate, which became partially darkened indicating some form of radiation was being emitted by the salt and penetrating the paper. This emission became known as radioactivity
Pierre and Marie Curie: By purifying uranium called pitchblende, they discovered two highly radioactive elements, polonium and radium
Pierre and Marie Curie: By purifying uranium called pitchblende, they discovered two highly radioactive elements, polonium and radium
Nature of Radioactivity
RADIOACTIVITY: is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation
Radiation
Type |
What is
it? |
Examples |
Effect of
Electircal Field |
Penetrating
Power |
Uses |
Alpha Particles |
Helium Nucleus (two
protons and two neutrons emitted from the nucleus |
Americium-241 |
Attracted to negative
electrode |
Stopped by sheet of paper |
Smoke detectors |
Beta Particles |
Neutron turns into proton
and electron. Only electron is emitted |
Carbon-14 |
Attracted to positive
electrode |
Stopped by 5mm of aluminium |
Dating archaeo-logical
artefacts |
Gamma Ray |
High energy electromag- netic radiation (no
particles) |
Cobalt-60 |
None |
Stopped by thick block of
lead |
Radioth-eraphy (kills cancer) |
Nuclear Reactions
When either alpha or beta particles are emitted, a new element is formed. This is called Transmutation
Alpha Emission (loss of two protons and two neutrons)
Beta emission (neutron becomes a proton and an electron
Alpha Emission (loss of two protons and two neutrons)
- The atomic number decreases by two
- The mass number decreases by four
Beta emission (neutron becomes a proton and an electron
- The atomic number increases by one
- The mass number remains the same
- An electron is emitted
Nuclear Reactions:
|
Chemical Reactions:
|
Half-Life
HALF-LIFE: of an element is the time taken for half the nuclei in any given sample to decay
Carbon-14 dating has a half life of about 5700 years, which allows the age of ancient materials to be determined. Plants take in small amounts of carbon-14 during photosynthesis which becomes incorporated into its tissues. When is dies it stops taking in CO2 and the level of carbon-14 falls. Therefore the age of an artefact can be estimated by measuring the ratio of C-12 to C-14 present in the artefact.
Carbon-14 dating has a half life of about 5700 years, which allows the age of ancient materials to be determined. Plants take in small amounts of carbon-14 during photosynthesis which becomes incorporated into its tissues. When is dies it stops taking in CO2 and the level of carbon-14 falls. Therefore the age of an artefact can be estimated by measuring the ratio of C-12 to C-14 present in the artefact.
Radioactivity Around Us
There is always a certain amount of radiation in our environment (known as background radiation). Most occurs naturally e.g. radon gas from ground, and cosmic rays from space, but some is man-made e.g. medical uses