A sample of a radioisotope shows an activity of 999 disintegrations per minute due to beta decay. If after 1.10 years the activity is 952 disintegrations per minute, what is the half-life of this radioisotope?
1. 4.38 × 10-2 yr
2. 11.4 yr
3. 0.25 yr
4. 15.8 yr
5. 9.1 yr