Induced Fission

• What occurs during induced fission?

  A stable nucleus splits into smaller nuclei
• What happens when uranium-235 absorbs a neutron?

  It becomes uranium-236
• Why is uranium-236 not usually shown in decay equations?

  It decays into smaller nuclei almost immediately
• What are the products of uranium-235 decay after neutron absorption?

  Two smaller daughter nuclei
• What are neutrons involved in induced fission called?

  Thermal neutrons
• What is the kinetic energy characteristic of thermal neutrons?

  They have low kinetic energy
• What happens if a fast-moving neutron hits a uranium-235 nucleus?

  It will rebound from the nucleus
• How is a thermal neutron defined?

  A neutron in thermal equilibrium with surroundings
• What is the core reactor temperature for thermal equilibrium?

  About 300 K
• What is the average kinetic energy of a thermal neutron?

  $6.21 \times 10^{-21} \text{ J}$
• How is the energy of a thermal neutron expressed in electronvolts?

  $0.04 \text{ eV}$
• What is the formula to calculate the speed of a thermal neutron?

  $v =$$\sqrt{\frac{2E}{m}}$
• What is the speed of a typical thermal neutron?

  $2700 \text{ m/s}$
• What are the products of fission reactions?

  Two daughter nuclei and two or three neutrons
• What leads to a chain reaction in fission?

  Neutrons released cause more fission reactions

  
• How many thermal neutrons are used in a controlled chain reaction?

  Only one thermal neutron
• What is critical mass in nuclear reactions?

  The minimum mass to maintain a steady chain reaction
• What happens if the mass is less than critical mass?

  The reaction will eventually stop
• What occurs with more than critical mass?

  It leads to a runaway reaction and explosion
• What are the three types of mass in nuclear reactions?

  • Subcritical mass: Less than critical mass, reaction stops
  • Critical mass: Minimum mass for steady reaction
  • Supercritical mass: More than critical mass, runaway reaction