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A nucleus of polonium P0 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 P0 may decay to the stable isotope of lead 20882Pb through a chain of emissions following the sequence α → β− → α. Figure 13 shows the positio... show full transcript
Worked Solution & Example Answer:A nucleus of polonium P0 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
- Start by plotting the initial position of the polonium nucleus on the graph.
- The first change is an alpha emission (α), which decreases the proton number (Z) by 2 and the neutron number (N) by 2. Draw the first arrow down-left.
- The next step is a beta emission (β−), which increases the proton number (Z) by 1 and keeps the neutron number (N) the same. Draw the second arrow right.
- Finally, a second alpha emission (α) decreases both the proton number (Z) by 2 and the neutron number (N) by 2 again. Draw the last arrow down-left. These four movements show the path from polonium to the stable lead isotope.
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 the number of protons and neutrons in a nucleus can be explained by the forces that govern nuclear stability.
- The strong nuclear force (SNF) acts between nucleons (protons and neutrons) to bind them together, providing stability to the nucleus.
- This force is effective at very short ranges (up to about 0.8 fm) and overcomes the electrostatic repulsion expended by like-charged protons.
- However, as the number of protons increases, the repulsive forces between them also increase, necessitating more neutrons to help stabilize the nucleus against this repulsion.
- Thus, heavier nuclei require more neutrons than protons to maintain stability, leading to the observed imbalance.
Step 3
Step 4
Explain the origin and know the consequences of this radiation.
Answer
When the thallium nucleus is formed in an excited state after the decay process, it has excess energy.
- This energy can be released in the form of electromagnetic radiation, specifically gamma rays, as the nucleus transitions to a lower energy state.
- This release of energy is necessary for the atom to achieve stability.
- The emitted gamma radiation can have applications in medical diagnostics, as it can be used to image biological processes non-invasively.
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 (99mTc) is widely used in medical diagnostics due to several key reasons:
- Short Half-life: 99mTc has a half-life of about 6 hours, which minimizes radiation exposure to patients while providing sufficient time for imaging procedures.
- Gamma Emission: It emits gamma radiation, which is highly penetrating and can be detected using Gamma cameras, providing detailed images of tissues, organs, and regions of interest in the body.
- Chemistry Versatility: 99mTc can be easily incorporated into various pharmaceuticals for targeted imaging of specific organs or tissues, making it extremely useful in a range of diagnostic applications.