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A nucleus of polonium Po may decay to the stable isotope of lead ^{208}_{82}Pb through a chain of emissions following the sequence eta o eta o ext{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 ^{208}_{82}Pb through a chain of emissions following the sequence eta o eta o ext{α}. Figur... show full transcript
Worked Solution & Example Answer:A nucleus of polonium Po may decay to the stable isotope of lead ^{208}_{82}Pb through a chain of emissions following the sequence eta o eta o ext{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 ^{208}_{82}Pb.
Answer
To show the decay sequence from polonium to lead in Figure 13, draw four arrows indicating the following changes:
- An arrow moving down 2 units to represent the loss of neutrons due to beta decay (one neutron changes to one proton).
- An arrow moving right 1 unit to represent the gain of one proton as a result of the same beta decay.
- Another arrow moving down 2 units to indicate a further decrease in neutrons during the second beta decay.
- Finally, an arrow moving right 1 unit to signify the gain of another proton, leading to the stable ^{208}_{82}Pb.
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 in proton and neutron numbers in nuclei like ^{208}_{82}Pb can be primarily attributed to the strong nuclear force (SNF) and electromagnetic repulsion.
- The strong nuclear force is a fundamental force that acts between nucleons (protons and neutrons) and helps hold the nucleus together. Its range is about 3 fm, which is sufficient to bind nucleons when they are in close proximity.
- Protons repel each other due to electromagnetic force as they have the same charge, which tends to destabilize the nucleus if too many protons are present.
- Neutrons help to counteract this repulsion by adding attractive strong nuclear force without contributing to electromagnetic repulsion.
- Thus, having more neutrons than protons stabilizes the nucleus by minimizing repulsive forces among protons while maintaining strong interaction.
Step 3
Step 4
Explain the origin and nature of two sources of this radiation.
Answer
The electromagnetic radiation emitted from the thallium nucleus following its formation comes from:
- Transition from an excited state to a lower energy state: When the thallium nucleus is formed, it is usually in an excited state. As it transitions to a more stable state, it releases energy in the form of gamma radiation.
- Decay of isotopes: Other isotopes of thallium or decay products may also emit gamma radiation as they transition to stable forms, thereby contributing further to electromagnetic emissions.
Step 5
Explain why the metastable form of the isotope of technetium ^{99m}_{43}Tc is a radioactive source suitable for use in medical diagnosis.
Answer
The metastable form of technetium ^{99m}_{43}Tc is particularly useful in medical diagnosis due to:
- Short half-life: It decays relatively quickly (approximately 6 hours), which is ideal for medical applications as it minimizes radiation exposure to patients while providing enough time to perform diagnostic imaging.
- Gamma emission: During its decay, it emits gamma rays which can easily penetrate body tissues, allowing for effective imaging using gamma cameras. This ability to produce clear images while minimizing harmful effects makes it suitable for diagnostic procedures.