IB Physics SL E 3 4 Mass Energy Equivalence Questions

Apply SL mass-energy equivalence to nuclear decay and binding-energy data, calculating released energy from mass or energy differences.

Exam points

apply E=mc^2 to relate nuclear mass differences to released or absorbed energy
calculate decay energy from nuclear masses or binding energies, including beta-minus examples and electronvolt conversions
compare initial and final nuclear energies to determine the Q-value and report an appropriate unit and precision

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Study E.3.4—Mass-energy equivalence conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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Tritium may be produced by bombarding a nucleus of the isotope lithium-7 with a high-energy neutron. The reaction equation for this interaction is

{ }_{3}^{7} \mathrm{Li}+{ }_{0}^{1} \mathrm{n} \rightarrow{ }_{1}^{3} \mathrm{H}+{ }_{Z}^{4} \mathrm{X}+{ }_{0}^{1} \mathrm{n} .

Use the following data to show that the minimum energy that a neutron must have to initiate the reaction in (b)(i) is about 2.5 MeV .

\begin{array}{ll} \text { Rest mass of lithium-7 nucleus } & =7.0160 \mathrm{u} \\ \text { Rest mass of tritium nucleus } & =3.0161 \mathrm{u} \\ \text { Rest mass of X nucleus } & =4.0026 \mathrm{u} \end{array}

(mass difference $=) 7.0160-[3.0161+4.0026]=(-) 2.7 \times 10^{-3} \mathrm{u}$ ;
( energy required $=)(-) 2.7 \times 10^{-3} \times 931.5$ or 2.5151 MeV ;
( $\approx 2.5 \mathrm{MeV}$ )

Marking guidance:

Allow unit conversions via mass and $m c^{2}$ .

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IB Physics SL E 3 4 Mass Energy Equivalence Questions question 1