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A student does an experiment with radioactive materials - OCR Gateway - GCSE Physics - Question 24 - 2021 - Paper 4
Question 24
A student does an experiment with radioactive materials. He investigates how the activity of radiation changes with distance. The radiation moves from the radioacti... show full transcript
Worked Solution & Example Answer:A student does an experiment with radioactive materials - OCR Gateway - GCSE Physics - Question 24 - 2021 - Paper 4
Step 1
Describe, using these results, how the count rate changes as the detector is moved away from the source.
Answer
As the detector is moved away from the radioactive source, the count rate observed decreases significantly. From the data presented in the table, when the detector is at 10 cm, the count rate is 1024 counts per minute. At a distance of 20 cm, the count rate drops to 256 counts per minute, and at 80 cm, it further decreases to 64 counts per minute. This demonstrates an exponential decline in count rate with increasing distance, indicative of the inverse square law of radiation, where intensity decreases as the distance from the source increases.
Step 2
Predict what these last two results should have been and explain the anomalies in the last two results.
Answer
If we follow the trend established in the earlier data, one might predict the count rates for 160 cm and 320 cm to continue decreasing exponentially. Given the pattern, the expected results could be around 4 counts per minute for 160 cm and close to 0 counts per minute for 320 cm. The anomalies in the last two results may be attributed to the geometric dispersion of radiation, where at greater distances the radiation intensity diminishes rapidly and also the absorption characteristics of the medium between the source and detector might play a role in attenuating the radiation. Therefore, at 320 cm, the measure could be extremely low, potentially zero, due to complete absorption or scattering.
Step 3
Explain how this treatment reduces damage to healthy cells.
Answer
The rotation of the gamma radiation source around the patient during treatment minimizes exposure of healthy cells by distributing the radiation dose over a larger area and reducing the dose concentration on any single point. This technique allows for the tumor to receive the necessary amount of radiation to effectively kill cancer cells while protecting surrounding healthy tissues. Moreover, the scheduled intervals of treatment every four days further help in allowing healthy cells to recover and repair themselves between treatments, thereby enhancing the effectiveness of the treatment while reducing collateral damage to non-cancerous tissues.