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Nuclear Fission and Fusion


Akoranga 9 Ngā Whāinga Ako


Recall

There are three types of nuclear reactions

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

Fission


Question

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


Whakatika

\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


Whakatika

\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