4 (a) Radioactive tracers can be used when scanning a person’s kidneys - Edexcel - GCSE Physics - Question 4 - 2022 - Paper 1

An isotope with a half-life of about 6 minutes is not suitable because it decays too quickly to give a reading. The technician would not be able to obtain sufficient data within such a short time frame.

An isotope with a half-life of about 6 days is not suitable because it remains in the body for too long, increasing the radiation dose to the patient and potentially causing harm.

1. Time limiting exposure: Reducing the time spent near the radiation source minimizes exposure.
2. Wearing Personal Protective Equipment (PPE): This includes lead aprons or goggles to shield against radiation.

Pushing the control rods further into the reactor absorbs more neutrons, which are necessary for sustaining the nuclear fission chain reaction. By absorbing these neutrons, the reaction slows down due to a lower probability of further fission events occurring.

To calculate the average speed of slow neutrons as a percentage of fast neutrons:

1. Average speed of fast neutrons: $3.0 \times 10^7 \text{ m/s}$

2. Average speed of slow neutrons: $4.0 \times 10^6 \text{ m/s}$

3. Percentage calculation:

   $\left( \frac{4.0 \times 10^6}{3.0 \times 10^7} \right) \times 100 = \frac{4.0 \times 100}{30} = \frac{400}{30} \approx 13.33\%$

Thus, the average speed of the slow neutrons is approximately 13.33% of the average speed of the fast neutrons.

Energy from the nuclear reaction is transferred to the heat exchanger, where the heat produced from fission is used to produce steam. This steam then drives turbines connected to generators, thus converting nuclear energy into electrical energy.