At a remote monitoring station, a sealed radioactive source is used to check a radiation detector. The source is prepared immediately before a journey that takes 16 hours16\ \text{hours}16 hours. The detector check then takes a further 8 hours8\ \text{hours}8 hours.
The source has an initial activity of 640 kBq640\ \text{kBq}640 kBq and a half-life of 8.0 hours8.0\ \text{hours}8.0 hours.
For safe handling, the activity of the source must be no greater than 250 kBq250\ \text{kBq}250 kBq when it arrives. The detector gives usable readings only while the activity of the source is at least 75 kBq75\ \text{kBq}75 kBq.
Calculate the activity of the source when it arrives and at the end of the detector check.
Explain whether this source can be used for the detector check.