Radioactivity
5 marks · NormalAn isotope of sodium, , is unstable and decays by emitting a beta minus () particle.
Write the balanced nuclear equation for this decay, including the correct atomic and mass numbers for the product nucleus and the beta particle.
Explain what happens to the atomic number and mass number of the nucleus during beta minus decay.
Is the product nucleus more stable after the decay? With reference to neutrons and protons, explain your answer briefly.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) ^{24}_{11}\mathrm{Na} \rightarrow ^{24}_{12}\mathrm{Mg} + ^{0}_{-1}\mathrm{e} · must show sodium-24 changes to magnesium-24; beta particle shown as ^{0}_{-1}e
(b) Atomic number increases by 1, mass number stays the same. · must show Atomic number increases by 1, Mass number stays the same
(c) Yes; Beta decay converts a neutron to a proton, improving the neutron-to-proton ratio if nucleus was neutron-rich, so it becomes more stable. · must show Stability increases if beta decay corrects neutron-to-proton ratio, Refers to neutron-proton change
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Marking points
A1 (a) · 1 mark · Correct balancing of the equation for atomic number and mass number.
A2 (a) · 1 mark · Correct symbols for all particles ().
B1 (b) · 1 mark · States atomic number increases by 1 and mass number unchanged during beta minus decay.
B1 (c) · 1 mark · States product is more stable or explains stability in terms of neutron-to-proton ratio.
B2 (c) · 1 mark · Links beta emission to conversion of neutron to proton or balancing the ratio for stability.
Worked solution
a) The balanced nuclear equation is:
b) In beta minus decay, a neutron in the nucleus changes into a proton and emits a beta particle (an electron). The atomic number increases by 1 (from 11 to 12), the mass number stays the same (24).
c) Yes, the product nucleus is more stable if it was neutron-rich before. Beta minus decay converts a neutron to a proton, making the neutron-to-proton ratio closer to that needed for nuclear stability.