Nuclear Reactions

Explain isotope stability (4)

• The stability of an isotope is dependent on the ratio of protons and neutrons in the nucleus

• If the ratio does not lie in the belt of stability, the nucleus can undergo spontaneous radioactive decay

• An atom will usually go through a series of radioactive decay on its way to stability

• Each step in the decay process takes a different length of time, and different atoms within a sample will break down at different times

What is half-life?

• Time it takes for half of the sample to decay

  • n = time passed/half-life

  • mass remaining = initial mass*(1/2)ⁿ

What is radioactive decay?

A spontaneous natural process where an unstable atomic nucleus loses energy by emitting particles or waves to reach a more stable state

What are the 5 types of radioactive decay?

alpha decay, beta decay, gamma decay, positron emission, and electron capture

What is alpha decay? (4)

• Spontaneous emission of a helium nucleus from an atom

• Represented by ⁴₂He

• e.g. ²²⁶Ra → ²²²Rn + ⁴He

• A sheet of paper easily blocks alpha particles, but readily damages chromosomes if inhaled or ingested

What is beta decay? (3)

• A neutron is converted into a proton and a beta particle

• Represented by ⁰_-1β

  • ¹⁴C →¹⁴N + _-1β

What is gamma decay? (4)

• A gamma particle is a high-energy photon which is emitted when the nucleus is in an excited state

• Represented by ⁰₀ γ

• Often given off after other nuclear reactions (alpha, beta, etc…)

• Dangerous because it is hard to block them, but this also makes them useful for medical diagnostics

What is a positron emission? (2)

• A proton is converted into a neutron and a positron (a particle with the same mass as an electron but with a positive charge)

• Represented by ⁰₊₁e

What is electron capture? (2)

• A nucleus absorbs an orbital electron (usually from the innermost shell)

• Represented by ⁰_-1e

What is nuclear fusion? (3)

• Small light nuclei are combined to form a larger, heavier nucleus

• Releases a very large amount of energy

• The main source of energy is the sun (supernovae)

What is nuclear fission? (3)

• Large nuclei break apart into smaller ones

• Releases a large amount of energy

• Used in nuclear power plants to generate enegy energy

What is mass defect? (2)

• Refers to the difference between the mass of the nucleons (protons and neutrons) in a nucleus weighted separately and together

• This “missing mass” is converted into binding energy, using E = mc², which holds the nucleus together

Represent protons, neutrons, and electrons using nuclear notation (^A_ZX) (3)

• Proton - ¹₁p

• Neutron - ¹₀n

• Electron - ⁰_-1e