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Radioactivity 2

Radioactivity 2. Ionizing Power and Penetrating Power. Recap. Alpha a radiation consists of helium nuclei, particles are made up of two protons and two neutrons.

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Radioactivity 2

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  1. Radioactivity 2 Ionizing Power and Penetrating Power

  2. Recap... • Alpha a radiation consists of helium nuclei, particles are made up of two protons and two neutrons. • Beta b radiation consists of high-energy electrons emitted from the nuclei of atoms. (For each electron emitted, a neutron in the nucleus becomes a proton.) • Gamma g radiation is very short wavelength electromagnetic radiation.

  3. Ionizing Power and Penetrating Power • These are linked. • The penetrating power ofnuclear radiation depends upon the ionizing power of the radiation. • The radiation continues to penetrate matter until it has lost all of its energy.

  4. Ionizing Power and Penetrating Power • The further it can penetrate into the substance the more spread out the ionization it causes will be, • So….. the more localized the ionization the less penetrating power it will possess.

  5. Alpha Particles • are the least penetrating as they are • the most densely ionizing. • They are completely absorbed by 10 cm of air, 0.01 mm lead or a sheet of paper.

  6. Alpha Particles • This means that if a given number of alphas are fired at a target they will all cause ionization near the surface of the material, resulting in the effects of the radiation being concentrated in a small volume. • The double charge and considerable mass of the alpha in comparison with the other nuclear radiation forms explains why the impact on matter is so great.

  7. Beta Particles • A beta particle can penetrate quite deeply into matter before its energy has been used up. • Its penetrating power is therefore moderate (absorbed by 1m air, 0.1 mm lead or 3mm aluminium sheet).

  8. Beta Particles • Betas have only about 1/8000 of the mass of an alpha particle and only half of the charge. • Therefore their interaction with matter as they passes through is far less severe. • So the effects of interaction (ionization) are much more spread out.

  9. Gamma Rays • have an ionizing power so low that they penetrate very deeply into matter before most of the energy has been used up. • Their penetrating power is therefore very high (about 99.9% is absorbed by 1 km of air or 10 cm lead).

  10. Gamma Rays • Gamma rays are pure energy - no charge and no mass - therefore their interaction with matter is much less than the other two forms of nuclear radiation.

  11. Absorption of radiation alpha (a) radiation - is easily absorbed by a few centimetres of air or a thin sheet of paper; beta (b) radiation - easily passes through air or paper but is mostly absorbed by a few millimetres of metal; gamma (g) radiation - is very penetrating and requires many centimetres of lead or metres of concrete to absorb most of it.

  12. Penetration Power

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