5 (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 7 represents a decay that can happen inside the nucleus of an atom - Edexcel - GCSE Physics Combined Science - Question 5 - 2020 - Paper 1

Figure 7 depicts a process where a neutron is produced alongside a proton, a characteristic of beta minus decay. In this process, a neutron in the nucleus converts into a proton and emits a beta particle (electron) and an antineutrino.

The half-life of cobalt-60 is 5 years, which means after 5 years, the activity will reduce to half.

Starting with an initial activity of 38.5 kBq in the year 2000, we calculate:

• After 5 years (2005):

  $ext{Activity}_{2005} = \frac{38.5 ext{ kBq}}{2} = 19.25 ext{ kBq}$

• After 10 years (2010):

  $ext{Activity}_{2010} = \frac{19.25 ext{ kBq}}{2} = 9.625 ext{ kBq}$

• After 15 years (2015):

  $ext{Activity}_{2015} = \frac{9.625 ext{ kBq}}{2} = 4.8125 ext{ kBq}$

• After 20 years (2020):

  $ext{Activity}_{2020} = \frac{4.8125 ext{ kBq}}{2} = 2.40625 ext{ kBq}$

Thus, the estimated activity of the cobalt-60 source in the year 2020 is approximately 2.41 kBq.