radioactivity

• Radioactivity


  The spontaneous emission of radiation from unstable atomic nuclei

  
• Radioactive decay


  1. Transformation of one nuclide into another by emitting a particle

  2. Rate of decay is proportional to the number of nuclei

  3. N = N0e-λt

  4. Half-life is the time for the population to fall to half of its initial value

  
• Decay constant (λ)


  Characterises the rate of radioactive decay

  
• Most nuclides are radioactive
• We cannot determine which individual nuclei will decay, only that some will decay

  
• As temperature increases


  The rate of radioactive decay increases
• Decay rate (R)


  The strength of a radioactive substance, measured in becquerels (Bq) or curies (Ci)

  
• R = λN = λN0e-λt
• 1 Ci = 3.7x10^10 Bq
• Alpha decay


  Emission of a helium-4 nucleus from an atomic nucleus

  
• Disintegration energy (Q)


  Energy released in an alpha decay, typically around 5 MeV
• Alpha particle tunnelling


  The alpha particle can tunnel through the potential energy barrier due to quantum mechanical effects

  
• Beta decay


  Radioactive decay that results in a change in the atomic number by ±1, emitting an electron (β-) or positron (β+)

  
• Beta decay does not conserve energy, linear momentum or angular momentum
• Neutrino


  A neutral, weakly interacting particle introduced to satisfy conservation laws in beta decay

  
• Beta decay can be viewed as the conversion of a neutron to a proton (β-) or a proton to a neutron (β+)

  
• Disintegration energy for β- decay


  Q = Mp - Ms - me
• Disintegration energy for β+ decay


  Q = Mp - Ms - 2me
• Radiocarbon dating


  Determining the age of an organism by measuring the ratio of 14C to 12C
• The 14C in the atmosphere is constantly replenished by cosmic ray induced processes
• Gamma decay


  Emission of a high-energy photon from an excited nuclear state

  
• Gamma ray emission often follows alpha or beta decay