This question is about radioactivity - Edexcel - GCSE Physics Combined Science - Question 2 - 2021 - Paper 1

Similarity: Both fluorine-19 and its radioactive isotopes contain the same number of protons, which is 9.

Difference: The number of neutrons differs; fluorine-19 has 10 neutrons, while a radioactive isotope (e.g., fluorine-18) may have 9 neutrons.

The new count is greater than 268 because removing the aluminium sheet allows more beta particles to reach the G-M tube. The aluminium sheet absorbs some beta radiation, and without it, the detector can register a higher count.

There would be a reading on the counter due to the presence of background radiation. Even after the beta source is removed, the counter can detect natural radiation in the environment.

The SI unit for the activity of a radioactive source is the becquerel (Bq).

The SI unit for the activity of a radioactive source is the becquerel (Bq).

The number of remaining nuclei after 33 days can be calculated using the formula:

$N = N_0 imes (0.5)^{t/T_{1/2}}$

where:

• $N_0 = 1.7 imes 10^{23}$ (initial nuclei)
• $t = 33$ days
• $T_{1/2} = 11$ days

Substituting the values, we have:

N = 1.7 imes 10^{23} imes (0.5)^{33/11} = 1.7 imes 10^{23} imes (0.5)^3 = 1.7 imes 10^{23} imes rac{1}{8} = 2.125 imes 10^{22}

Thus, approximately $2.1 imes 10^{22}$ nuclei of radium-223 remain after 33 days.