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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 position o... 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
- First Arrow: From the polonium nucleus, draw an arrow to the left and down (indicating the emission of an alpha particle). This decreases both the neutron and proton numbers.
- Second Arrow: From the new nucleus, draw an arrow to the left (indicating another alpha emission), which again decreases both N and Z.
- Third Arrow: From the resultant nucleus, draw an arrow pointing upwards (indicating beta decay), which increases the proton number by 1 while maintaining the same neutron count.
- Fourth Arrow: Finally, from this nucleus, draw another arrow pointing upwards (indicating a subsequent beta decay), which increases the proton number again by 1 and maintains the neutron count.
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 is primarily due to the strong nuclear force (SNF) and electromagnetic forces. The SNF, which acts between nucleons (protons and neutrons), is effective over very short distances (around 1 fm to 3 fm). It binds protons and neutrons together to form stable nuclei. However, protons repel each other due to their positive charge, which creates a necessity for neutrons to provide additional binding without causing repulsion. Neutrons thus serve to stabilize the nucleus, balancing the electrostatic forces resulting from the protons.
Additionally, a nucleus with too many neutrons may become unstable, leading to radioactive decay as it adjusts proton and neutron ratios towards stability.
Step 3
Step 4
Explain the origin and roadmap to other sources of this radiation.
Answer
The electromagnetic radiation emitted from the thallium atom following its formation is caused by the transition of electrons between energy levels. When thallium is formed in an excited state, the excess energy is released as electromagnetic radiation when an electron drops to a lower energy level. This can occur in many other isotopes, where excited nuclear states result in the emission of gamma radiation as the nucleus transitions to a lower energy state.
Step 5
Explain why the metastable form of the isotope of technetium 99743Tc is a radioactive source suitable for use in medical diagnosis.
Answer
The metastable form of technetium-99m () is ideal for medical diagnosis because it emits gamma radiation, which can penetrate human tissue without causing significant harm. Its relatively short half-life allows for rapid decay, minimizing patient exposure to radiation while providing sufficient time to conduct imaging procedures. This property makes an effective tracer in various diagnostic techniques, particularly in nuclear medicine.