Radioactivity

1
Radioactivity

• Radioactive nuclei
• Radioactive nuclei are nuclei that undergo
  spontaneous changes and emit energy in the form
  of radiation.
• The emission of radiation by radioactive nuclei
  is often called radioactive decay.
• Types of emitted radiation
• Numerous types of emitted radiation have been
  identified. Five that are common and will be
  focused on are alpha, beta, gamma, neutron, and
  positron

2

• Alpha Radiation
• Alpha radiation consists of a stream of particles
  called alpha particles. Alpha particles are
  identical to helium nuclei they consist of two
  protons and two neutrons.
• Beta Radiation
• Beta radiation consists of a stream of beta
  particles that are identical to electrons. They
  are created in the nucleus of radioactive atoms
  when a neutron is converted into a proton and an
  electron.
• Gamma Radiation
• Gamma radiation consists of high energy rays
  similar to X rays, but with a higher energy.
• Neutron Radiation
• Neutron radiation consists of a stream of high
  energy neutrons emitted from the nuclei of
  radioactive nuclei.

3

• Positron Radiation
• Positron radiation consists of a stream of
  positrons which are identical to electrons except
  they have a positive electrical charge.
  Positrons are created in the nucleus of
  radioactive atoms when a proton is converted into
  a neutron and a positron.

4
Nuclear reactions

• where X is the symbol for the particle, A is
  the particle mass number and Z is the particle
  atomic number or electrical charge.
• Balanced nuclear reaction equation
• Sum of atomic numbers on left Sum of the
  atomic numbers on right
• Sum mass numbers on left Sum of the mass
  numbers on right
• When an unstable nucleus undergoes radioactive
  decay and the nucleus of a new element is
  produced as a product, the nucleus of new element
  that is produced is called a daughter nucleus.
• Example 10.2

5
Isotope half-life

• The half-life of an isotope is the time required
  for one-half of the radioactive nuclei in a
  sample of the isotope to undergo radioactive
  decay.
• The half-life of an isotope is used to indicate
  stability. The longer the half-life, the more
  stable is the isotope.

6

• Half-lives can be determined by measuring the
  number of times a sample of radioactive material
  is reduced by 1/2 in a measured amount of time.
• The fraction of original sample remaining as a
  function of time is shown graphically in the
  following diagram.