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In radioactive decay or disintegration, an alpha particle or beta particle or gamma ray may be emitted what are gamma rays? Gamma rays are - high frequency electromagnetic waves - have no mass - have no charge - have low ionisation power - have high penetrating power - travel very long distance in air - stopped by few cm thick lead or 30 cm thick high density concrete - can be detected by GM-tube or film-badge Gamma decay A A *X ==> X + Gamma ray Z Z excited normal - Excited nucleus returns to normal ground state but no transmutation takes place, Proton number or atomic number, Z Nucleon number or mass number, A A X Z where X represents a nuclide what makes an element different from another element? All atoms of the same element have the same proton number, Radioactive isotopes emit particles or radiation from the nucleus sponteneously and randomly what does sponteneous mean? Sponteneous means - happens by itself - cannot be changed by any physical or chemical means, All atoms of the same element have the same proton number what is meant by isotopes of an element? Isotopes are atoms of the same element having the same proton number but different nucleon number, Radioactive isotopes emit particles or radiation from the nucleus sponteneously and randomly what are these particles or radiation? In radioactive decay or disintegration, an alpha particle or beta particle or gamma ray may be emitted, Radioactive isotopes emit particles or radiation from the nucleus sponteneously and randomly what does half-life mean? Half-life means the time taken for half the number of radioactive atoms to have undergone decay or the time taken for the number of radioactive atoms to reduce to half the number before, Unstable nucleus are radioactive what does radioactive mean? Radioactive isotopes emit particles or radiation from the nucleus sponteneously and randomly, In radioactive decay or disintegration, an alpha particle or beta particle or gamma ray may be emitted what are beta particles? Beta particles are - fast speed electrons - have 1 unit negative charge - have negligible mass - have moderate ionisation power - have moderate penetrating power - stopped by few mm aluminium foil - travel few m in air - can be detected by GM-tube Beta decay A A 0 X ==> Y + e (Beta) Z Z+1 -1 - Element X transmuted to another element Y with nucleon number unchanged but proton number is increased by 1, In radioactive decay or disintegration, an alpha particle or beta particle or gamma ray may be emitted what are alpha particles? Alpha particles are - helium nucleus - have 4 units mass - have 2 units positive charge - have high ionisation power - very low penetrating power - stopped by skin and paper - travel about 10 cm in air - can be detected by cloud-chamber Alpha decay A A-4 4 X ==> Y + He (alpha) Z Z-2 2 - Element X transmuted to another element Y with nucleon number less by 4 & proton number less by 2, protons and neutrons what scientists know about protons? 1 unit +ve charge 1 unit mass, Structure of Nucleus some nucleus are unstable Unstable nucleus are radioactive, protons and neutrons what scientists know about neutrons? No charge 1 unit mass, Structure of Nucleus how scientists represent a nucleus? Proton number or atomic number, Z Nucleon number or mass number, A A X Z where X represents a nuclide, Nucleus & Radioactivity what do scientists know about nucleus? Structure of Nucleus, Structure of Nucleus what can be found inside the nucleus? protons and neutrons, Radioactive isotopes emit particles or radiation from the nucleus sponteneously and randomly what does random mean? Random in space means decay takes place equally likely in all directions or no preferred direction Random in time means each and every radioactive isotope has equal chance of undergoing decay independent of each other, Proton number or atomic number, Z Nucleon number or mass number, A A X Z where X represents a nuclide what is meant by a nuclide? A nuclide is just an atom of an element that has a specific nucleon number