Figure 3 shows the symbol for the nucleus of an atom of strontium-90 - Edexcel - GCSE Physics Combined Science - Question 3 - 2020 - Paper 1

To calculate the number of neutrons, we subtract the number of protons from the mass number. Thus, the number of neutrons is calculated as follows:

Number of neutrons = Mass number - Number of protons = 90 - 38 = 52. Therefore, there are 52 neutrons in the nucleus.

To complete the table, we recognize that the half-life of strontium-90 is 29 years, which means the mass of the strontium-90 sample will halve after each 29-year period. Therefore, after one half-life:

• Initial mass: 1600 g
• After 29 years: 800 g

Given the final mass is 400 g, this indicates two half-lives have occurred (29 years + 29 years = 58 years). Thus, the complete table should look as follows:

The scientific name for the radioactivity detector shown in Figure 5 is a Geiger-Müller counter.