Lecture 5b- Nuclear Reactions

Introduction to Nuclear Reactions

• Nuclear Reactions: Focuses on predicting products of transmutation when nuclei undergo nuclear reactions.

• Transmutation: A radioactive nucleus changes due to decay, emitting particles (alpha or beta).

• Alpha Decay: When a parent nucleus emits an alpha particle, the atomic number changes, leading to the formation of a different element.

Nuclear Equations

• Writing nuclear equations requires:

  • Identifying starting isotope (e.g., uranium-238).

  • Representing the emitted particle (alpha or beta).

• Example of Alpha Decay:

  • Uranium-238 (represented as

    • Atomic number: 92 (protons)

    • Mass number: 238 (protons + neutrons)

  • Emits an alpha particle:

    • Resulting product: Thorium-234.

  • Balance:

    • Mass numbers: 238 (U) = 234 (Th) + 4 (alpha)

    • Atomic numbers: 92 (U) = 90 (Th) + 2 (alpha)

Predicting Products of Alpha Decay

• Example: Reactant undergoes alpha decay with mass number of 175.

  • Product includes an alpha particle: mass number = 4.

  • To balance:

    • Mass number of other product = 171 (175 - 4).

    • Atomic number of other product = 76 (78 - 2).

• Identifying Elements:

  • Atomic number 76 corresponds to Osmium on the periodic table.

Types of Nuclear Decay

Beta Decay

• In beta decay, a neutron is converted to a proton, emitting a beta particle (high-energy electron).

• Example:

  • Carbon-14 undergoes beta decay, resulting in mass number remaining the same (14). Atomic number changes from 6 (C) to 7 (N).

  • Product: Nitrogen-14.

Predicting Products of Beta Decay

• Example: Thorium undergoing beta decay.

  • Product includes a beta particle.

  • Balancing:

    • Mass number remains 234.

    • Atomic number = 91 (90 + 1).

  • Identifying Elements:

    • Element 91 corresponds to Protactinium (Pa).

Series of Nuclear Reactions

• Decay Series: Example shows Uranium-238 transforming through alpha and beta decay until reaching stable Lead-206.

• Alpha Decay: Decreases mass number by 4 and atomic number by 2.

• Beta Decay: Mass number stays the same, atomic number increases by 1.

Review Questions

1. Alpha Decay:

   • Atomic Number decreases by 2; Mass Number decreases by 4.

2. Beta Decay:

   • Mass Number remains the same; Atomic Number increases by 1.

3. Bismuth-213 emits an alpha particle:

   • Products:

     • Mass Number: 209

     • Atomic Number: 81 (element = Thallium).

4. Bismuth-213 emits a beta particle:

   • Products:

     • Mass Number: 213

     • Atomic Number: 84 (element = Polonium).

Conclusion

• Practice writing and balancing nuclear equations to reinforce understanding.

• Upcoming topic: Half-life concepts.