Suggest, with a reason, which type of radiation is likely to be the most appropriate for the sterilisation of metallic surgical instruments - AQA - A-Level Physics - Question 5 - 2018 - Paper 2

The public need not worry because the energy of the radiation used for sterilisation is insufficient to induce radioactivity in the instruments. Typically, ionising radiation only affects the outer electrons of atoms and does not alter the nuclei.

To analyze the data, we can use the inverse square law, which states that intensity (count rate) is inversely proportional to the square of the distance (d). Calculate the expected rates:

• For d = 0.20 m, $I_1 = C_0 / (0.20^2)$
• For d = 0.50 m, $I_2 = C_0 / (0.50^2)$
• For d = 1.00 m, $I_3 = C_0 / (1.00^2)$

Using actual values from Table 1:

• At 0.20 m: count rate = 9013 counts/min
• At 0.50 m: count rate = 1395 counts/min
• At 1.00 m: count rate = 242 counts/min

Calculating values based on expected inverse-square relationships does not match the data. For instance, the ratio of count rates should show a constant factor (i.e., both should decrease proportional to $1/d^2$), which is not observed with the obtained counts.

1. The G-M detector may have a dead time that causes inaccuracies in measurement at higher radiation levels.
2. There may be other sources of radiation or environmental factors that affect the count rate independent of the distance from the source.