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This Concept Map, created with IHMC CmapTools, has information related to: wee loo kang radioactivity, Radioactive isotopes emit particles or radiation from the nucleus spontaneously and randomly From _dN_ = A = -λ N dt to get -λ t Formula: N = No e radioactive substances can decay in another radioactive substance that in turn redecay into even more stable necleus what are these particles or radiation? In radioactive decay or disintegration, an alpha particle or beta particle or gamma ray may be emitted, 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 symbol: t 1/2 Formula: _ln2_ = λ t 1/2 can be used in Real life application Radioactivity therapy in medicine able to calculate dose if substance is a few years older by assume dose = time x count rate -λ t Formula: N = No e, Radioactive isotopes emit particles or radiation from the nucleus spontaneously and randomly From _dN_ = A = -λ N dt to get -λ t Formula: N = No e radioactive substances can decay in another radioactive substance that in turn redecay into even more stable necleus 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 symbol: t 1/2 Formula: _ln2_ = λ t 1/2, 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 symbol: t 1/2 Formula: _ln2_ = λ t 1/2 can be used in Real life application 14 C carbon dating t 1/2 = 5700 years Formula: -λ t Formula: N = No e can be used to find age of an old object, 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, 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, Different proton number results in different elements formed what is meant by isotopes of an element? Isotopes are atoms of the same element having the same proton number but different nucleon number, Unstable nucleus are radioactive what does radioactive mean? Radioactive isotopes emit particles or radiation from the nucleus spontaneously and randomly From _dN_ = A = -λ N dt to get -λ t Formula: N = No e radioactive substances can decay in another radioactive substance that in turn redecay into even more stable necleus, 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, Structure of Nucleus some nucleus are unstable Unstable nucleus are radioactive, Structure of Nucleus what can be found inside the nucleus? protons and neutrons, Radioactive isotopes emit particles or radiation from the nucleus spontaneously and randomly From _dN_ = A = -λ N dt to get -λ t Formula: N = No e radioactive substances can decay in another radioactive substance that in turn redecay into even more stable necleus what does spontaneous mean? Spontaneous means - happens by itself - cannot be changed by any physical or chemical means, 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, Radioactive isotopes emit particles or radiation from the nucleus spontaneously and randomly From _dN_ = A = -λ N dt to get -λ t Formula: N = No e radioactive substances can decay in another radioactive substance that in turn redecay into even more stable necleus 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, protons and neutrons what scientists know about neutrons? No charge 1 unit mass, Nucleus & Radioactivity what do scientists know about nucleus? Structure of Nucleus, 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? Different proton number results in different elements formed, protons and neutrons what scientists know about protons? 1 unit +ve charge 1 unit mass, 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