7. (a) Which of these describes isotopes of an element? A same atomic number different number of neutrons B same atomic number different number of protons C same mass number different number of neutrons D same mass number different number of protons (b) Figure 9 represents a decay that can happen inside the nucleus of an atom - Edexcel - GCSE Physics - Question 7 - 2020 - Paper 1

The decay represented in Figure 9 shows a proton transforming into a neutron, which characterizes beta plus decay. Therefore, the correct answer is:

C beta plus.

To estimate the activity of the cobalt-60 source in the year 2020, we need to calculate the number of half-lives that have passed from 2000 to 2020. This is a span of 20 years, which accounts for:

ext{Number of Half-Lives} = rac{20 ext{ years}}{5 ext{ years/half-life}} = 4 ext{ half-lives}

Next, since each half-life reduces the activity by half, the fraction of the activity remaining after 4 half-lives can be expressed as:

ext{Remaining Activity} = rac{1}{2^4} = rac{1}{16}

So, the activity in 2020 would be:

38.5 ext{ kBq} imes rac{1}{16} = 2.40625 ext{ kBq} ext{ (approximately } 2.4 ext{ kBq)}

Thus, the estimated activity of the source in the year 2020 is approximately 2.4 kBq.