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Carbon-14 decays into nitrogen-14 with the release of a beta ($\beta^-$) particle and an antineutrino ($ar{ u}_e$) - AQA - A-Level Physics - Question 2 - 2022 - Paper 1
Question 2
Carbon-14 decays into nitrogen-14 with the release of a beta ($\beta^-$) particle and an antineutrino ($ar{ u}_e$). Figure 2 shows the distribution of kinetic ener... show full transcript
Worked Solution & Example Answer:Carbon-14 decays into nitrogen-14 with the release of a beta ($\beta^-$) particle and an antineutrino ($ar{ u}_e$) - AQA - A-Level Physics - Question 2 - 2022 - Paper 1
Step 1
Step 2
Explain how Figure 2 supports the existence of the antineutrino
Answer
Figure 2 shows a distribution of kinetic energies of particles that indicates they have a range of energies. The presence of an antineutrino is suggested because there should be more energy observed in the decay than what is accounted for by the particle and the nitrogen-14 produced. The missing energy, evidenced by the observed spectrum, implies that another particle (the antineutrino) carries away this excess energy.
Step 4
Deduce which of the three gamma photons could have been produced by positron annihilation
Answer
The minimum energy produced in the annihilation of the positron and the electron is calculated to be . Therefore, the gamma photons produced during annihilation must each have energies of at least . Referring to Table 1, only gamma photons G2 () and G3 () meet this criterion.