Radiation

For the nucleus of an atom to be stable, it must contain a suitable ratio of protons to neutrons. If this ratio is not suitable, i.e. th nucleus is unstable, the nucleus disintegrates, throwing out fragments and/or energy in an effort to achieve a stable ratio.

Radiation is the spontaneous breaking up of unstable nuclei resulting in the emission of radiation

DescriptionHENRI BECQUEREL exposed crystals of a uranium compound to sunlight and then placed the crystals on a photographic plate wrapped in black paper. When the plate was developed, an image of the crystals resulted. He thought that the absorbed energy of the sun was being released by the uranium compound in the form of X-rays, causing the image on the plate.He set up the experiment again, but the weather was overcast so he put his wrapped up photographic plates in a darkened drawer, along with some crystals of the uranium compound and left it for a few days.He developed the plates anyway and the results were identical to when the crystals had been exposed to sunlight. This meant that the uranium compound emitted radiation without an external source of energy like the sun. Becquerel went on to discover that the radiation ionised the air around it causing the air to conduct electricity. He also demonstrated that the radiation emitted by uranium compounds could be deflected by a magnetic field and therefore must contain charged particles.

Henri Becquerel - Discovered that uranium salts left on a photographic plate in the dark left a mark on the plate. He concluded that the uranium gave out 'rays'. He called these rays 'radiation'.

Marie and Pierre CurieThe Polish chemist Marie Curie and her husband Pierre carried out further research on uranium compounds and other substances that emitted the radiation discoverd by Becquerel. Marie called this newly discovered radiation, RADIOACTIVITY.She discovered that the amount of radiation depended on the proportion of uranium in the sample.The ore pitchblende emitted much more radiation than uranium. This suggested to Marie that it contained something more radioactive than uranium. Together with her husband they isolated the the elements polonium and radium from pitchblende (much more radioactive than uranium).

Types of radiation Alpha radiation ( positive charge). Beta radiation (negative charge). Gamma rays (neutral charge)

The Geiger - Müller tube can be used to detect radioactivity. In the tube, a gas is ionised by alpha, beta or gamma radiation, the resulting electric current is amplified and detected.

Alpha particlesThese particles consist of:2 protons2 neutrons(helium nucleus)Properties:A) Positive particlesB) Low penetrating ability (stopped by human skin and paper)C) Damage human cellsD) Deflected by magnetic and electrical fieldsUses:Americium - 241 isotope in smoke detectorsSmoke detectors contain a radioactive source - Am-241, and a detector. They sense a change in the amount of radiation (alpha particles) reaching the detector in the presence of smoke.Am has a half-life of over 400 years so it does not have to be replaced but the battery for the detector does.Harmful effects of alpha particles:Cause cancer e.g. radon-alpha emitter causes lung cancer.

Beta particlesBeta particles consist of:ElectronsThe neutron inside the nucleus changes into a proton and an electron. The electron is emitted from the nucleus. In this way the atomic number goes up and the mass number stays the same.Properties:A) Negative chargeB) Moderate penetrating ability (stopped by 5mm of aluminium) --> can penetrate the body causing cancerC) Deflected in magnetic / electrical fields.Uses:Carbon-14 isotope is used to date archaeological artefacts which were once living (plants + animals) up to age 10,000 years. All living organisms contain Carbon-14 and Carbon-12 When the organism dies, the carbon-14 will decay The ratio of Carbon-14 to Carbon-12 gives the age of the organism.

Gamma raysHigh energy electromagnetic radiation (no mass, charge, or particles) (no new element forms).Properties:A) No chargeB) High penetrating ability (stopped by lead)C) No effect in magnetic or electrical fields.Uses:Cobalt-60 used in the treatment of cancer. Cancer cells are more easily damaged by radiation than normal cells.Cobalt-60 is also used in preserving food by irridation. The gamma rays kill micro-organisms and insects present in the food that could cause to food to deteriorate quickly.

energy is emitted

Nucleur reactions involve changes in an unstable nucleus involving protons and neutrons. This causes elements to change into other elements.Chemical reactions only involve changes in the distribution of electrons. Chemical reactions cannot change one element into another element.

Radioisotopes are unstable radioactive isotopes

The half-life of a radioactive isotope is the time taken for half of the atoms in the sample to decay.

Background radiationA low level of radiation surrounds us all the timeSources:radon gas, formed from the decay of radioisotopes found in rocks in the groundcobalt-60 used in medicinemedical X-raysWeapons testsNuclear waste

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Radiation

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