Radioactivity

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Radioactivity

Ionising radiation

Emitted from unstable nuclei

α Alpha particles: - helium nuclei ejected from unstable nuclei

     - heavily ionising

     - short range, 10cm in air

     - stopped by thin card

β Beta particles: - fast moving electrons from unstable nuclei 

           - less ionising

           - long distances in air

           - stopped by 1-2mm of aluminium

           - charge of -1

γ Gamma rays: - photons of high energy EM waves

          - extremely penetrating

          - interact with atoms which then may emit ionising radiation

          - stopped by 10s of cm of lead

          - massless and without charge

Nuclear transformations

Radioactive forms of elements: isotopes

Decay randomly over time

Emit combinations of αβ and γ radiation

γ rays have no effect on the mass or charge of a decaying atom

αβ emissions cause a change in the atomic number

Original element ---> another element

Radiation and half-life

Detecting ionisation radiation

Nuclear radiation: produced by radioactive isotopes and the processes in stars

Ionises atoms that is reacts with

Detected by: - photographic film: becomes fogged when exposed to ionising radiation

                    - Geiger-Muller tube: radiation ionises the gases inside allowing a pulse of      current to pass between the electrodes, this is fed to a rate meter.

Sources of background radiation

Earth's rocks: Slow decay of isotopes of uranium produces radon and thoron gases. Radon      is highly radioactive

Cosmic rays: When stars explode, violent reactions produce cosmic rays that shower     Earth.

Medical: Radioactive materials are used in diagnosis and treatments

Nuclear power and weapons: Testing weapons and leaks from stations

Radioactive decay

- Random process, not possible to predict

- It is possible to predict the percentage of unstable atoms in a sample will decay in a given time.

- Rate of decay: 1 becquerel (Bq) is one decay per second

- Process of decay…

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