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A nucleus of polonium Po may decay to the stable isotope of lead 20882Pb through a chain of emissions following the sequence α → β → α - AQA - A-Level Physics - Question 7 - 2018 - Paper 2
Question 7
A nucleus of polonium Po may decay to the stable isotope of lead 20882Pb through a chain of emissions following the sequence α → β → α . Figure 13 shows the posit... show full transcript
Worked Solution & Example Answer:A nucleus of polonium Po may decay to the stable isotope of lead 20882Pb through a chain of emissions following the sequence α → β → α - AQA - A-Level Physics - Question 7 - 2018 - Paper 2
Step 1
Draw four arrows on Figure 13 to show the sequence of changes to N and Z that occur as the polonium nucleus is transformed into 20882Pb.
Answer
- Begin at the position for polonium on the grid.
- Draw an arrow down-left (to indicate an alpha decay which reduces both N and Z).
- Then, draw an arrow to the right (to indicate a beta decay which increases Z by 1 while keeping N constant).
- Finally, draw another arrow down-left (for another alpha decay) to arrive at the position of 20882Pb.
Step 2
Explain why there is this imbalance between proton and neutron numbers by referring to the forces that operate within the nucleus.
Answer
The imbalance between proton and neutron numbers in nuclei is primarily due to the strong nuclear force (SNF) that acts to hold nucleons (protons and neutrons) together. The SNF operates at ranges up to around 3 fm and is responsible for binding nucleons together, but it only acts on very short distances (approximately 0.8 fm).
Protons experience electrostatic repulsion due to their positive charge, which tends to destabilize the nucleus.
Neutrons contribute to the strong nuclear force without adding to the repulsive forces experienced by protons, allowing for some flexibility in the ratio of neutrons to protons for stability. Therefore, a higher number of neutrons compared to protons can enhance stability by dampening repulsive forces while still contributing to attractive interactions.
Step 3
Step 4
Explain the origin and location of the sources of this radiation.
Answer
The electromagnetic radiation emitted from the thallium atom originates from transitions of electrons between energy levels as the atom relaxes from an excited state to a lower energy state. This radiation can include gamma rays, which are emitted from the nucleus during these transitions.
Radiation sources in general are varied; they can originate from nuclear decay processes, such as those seen in metastable states, where an unstable nucleus releases energy through gamma emission following decay.
Step 5
Explain why the metastable form of the isotope of technetium 99Tc is a radioactive source suitable for use in medical diagnosis.
Answer
The metastable form of technetium-99, known as Tc-99m, is particularly suitable for medical diagnosis due to its ideal characteristics. It has a relatively short half-life of about 6 hours, which minimizes patient exposure to radiation while still allowing sufficient time for diagnostic procedures.
Additionally, Tc-99m emits gamma radiation that can be easily detected by imaging equipment, providing high-resolution images of internal organs. These properties make it an excellent choice for a wide range of medical diagnostic applications.