Physics: Atoms and Radioactivity

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  • Created by: Charlotte
  • Created on: 22-02-13 13:38

Atoms are made up of electrons, protons and neutron.

Electrons: charge = -1, relative mass = 1/1836. Light particle, little mass, negative charge, orbit the nucleus of the atom

Protons: charge = + 1, relative mass = 1. Protons carry positive electric charge

Neutrons = charge = 0, relative mass = 1. Electricially neutral (uncharged)

Atomic number = number of protons

Mass number (nucleon number) = number of protons + neutrons

(Number of electrons = number of protons) - need to cancel each other out.

Isotopes = atom with the same number of protons but a different number of neutrons, resulting in a diferent MASS number. Stability of te nucleus in isotopes differ: as protons have positive charges they repel each other, and the neutrons affects this balance (either positively or negatively), too many/too few neutrons make it UNSTABLE, and an UNSTABLE NUCLEUS LEADS TO DECAY, and may give out alpha/beta particles.

When an unstable nuclei decay they give out IONISING RADIATION, causing atoms to lose or gain electric charge, which FORMS IONS, remember, decay is RANDOM - meaning it is not possible for it to predict when decay will happen.

Three basic types of radiation which is natural/spontaneous (first 2 formed FROM DECAY): 

  • Alpha: (, made up of 'helium nuclei' -  two neutrons, two proton -, but not actually helium, thrown out of unstable nuclei when they decay, it is strongly ionising, charge of +2, relative mass of 4, (weakly penetrating) stopped by skin/paper/few cm of air, weakly deflects magnetic fields, and can be dangerous if CONSUMED as they can change DNA (mutations). * New elements are formed from alpha decay because protons are lost.

forms a daughter nucleus and alpha particle, mass number decreases by 4, atomic number decreases by 2 (loses 2 protons & neutrons)

  • Beta: (, high energy electron that is ejected by a decaying nucleus, very weakly ionising, charge of -1, mass of 1/1836, stopped by a few mm of aluminium, strongly deflects magnetic fields, (medium penetrating) not stopped by skin and causes cancer. * Beta decay involves a neutron in the nucleus spllitting INTO a proton AND electron, the proton remains in the nucleus but the ELECTRON is ejected at high speed.

forms a daughter nucleus and a high energy electron, mass number stays the same (conserved), atomic number adds 1 (neutron splits, turning into a proton which adds 1 to the mass, and the electron is released).

  • Gamma: (, they are ELECTROMAGNETIC WAVES (travels at the speed of light and short wavelength), weakly ionising, charge of 0, mass of 0, very penetrating as it passes through the very densest materials - takes several cms of lead or a metre of concrete to stop it, doesnt delfect magnetic fields, causes cancer. * Emitted in 'packets' of energy called PHOTONS.

when an unstable nucleus emits a beta or alpha particle it may have surplus energy, which is the emition of gamma rays. They are PURE ENERGY, so no change to the atomic number of mass


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