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Nuclear Fission and Fusion

Akoranga 9 Ngā Whāinga Ako


There are three types of nuclear reactions

  1. Radioactive decay ($\alpha$, $\beta$, $\gamma$)
  2. Nuclear fission
  3. Nuclear fusion



If the protons are positively charged, why don’t they repel each other and the nucleus break apart?

Electrostatic Force vs. Nuclear Force

Radioactive Isotopes

Absorption of a Nucleon

Pātai: Write 2x nuclear equations to express this reaction


\begin{align*} & {}^{1}_{0}n + {}^{235}_{92}U \rightarrow {}^{236}_{92}U \newline & {}^{236}_{92}U \rightarrow {}^{92}_{36}Kr + {}^{141}_{56}Ba + 3{}^{1}_{0}n \end{align*}

Extra pātai: What do you think the three neutrons produced do?

Nuclear Fusion


\begin{align*} & {}^{3}_{1}H + {}^{2}_{1}H \rightarrow {}^{4}_{2}He + {}^{1}_{0}n \end{align*}

Producing Energy: Mass Balance

\begin{align*} & {}^{3}_{1}H + {}^{2}_{1}H \rightarrow {}^{4}_{2}He + {}^{1}_{0}n \end{align*}

  1. Calculate the total mass of the reactants.
  2. Calculate the total mass of the products.

Theory of Relativity, $E = mc^{2}$

During the fusion process, the total mass is not conserved because some of the mass of the fusing nuclei is converted to energy.

\begin{align*} & E = mc^{2} \end{align*}

Pātai: Smoke Detector

Pātai: Nuclear Fission

Pātai: Nuclear Reactor

Tips for the Assessment

  1. EXPLAIN your answers.
  2. Watch out for the numbers NOT in standard forms (e.g. $\times 10^{-27}$)
  3. Half-life – Draw a graph!!!
    • Don’t forget about the shape of the exponential curve
  4. Nuclear Equations – double check the atomic numbers and the mass numbers
  5. $E = mc^{2}$ – SHOW CLEAR WORKING