A monitoring instrument will be installed at a remote site for 12 years. It will work correctly only if the activity of its sealed radioactive source is at least 250 Bq250\ \mathrm{Bq}250 Bq at the end of this time.
The four available sources have the following properties.
| source | starting activity / Bq\mathrm{Bq}Bq | half-life / years |
|---|---|---|
| P | 3200 | 3 |
| Q | 2400 | 4 |
| R | 800 | 6 |
| S | 300 | 12 |
Which source should be selected?
Source Q
Source R
Source S
Source P