放射性是不稳定原子核因辐射失去能量的过程。它以Becquerels（BQ）进行测量。
1 t½ = 100 rem
1 rem = 0.01 t½
例子:
将15 半衰期转换为REM：
15 t½ = 1,500 rem
| 半衰期 | REM |
|---|---|
| 0.01 t½ | 1 rem |
| 0.1 t½ | 10 rem |
| 1 t½ | 100 rem |
| 2 t½ | 200 rem |
| 3 t½ | 300 rem |
| 5 t½ | 500 rem |
| 10 t½ | 1,000 rem |
| 20 t½ | 2,000 rem |
| 30 t½ | 3,000 rem |
| 40 t½ | 4,000 rem |
| 50 t½ | 5,000 rem |
| 60 t½ | 6,000 rem |
| 70 t½ | 7,000 rem |
| 80 t½ | 8,000 rem |
| 90 t½ | 9,000 rem |
| 100 t½ | 10,000 rem |
| 250 t½ | 25,000 rem |
| 500 t½ | 50,000 rem |
| 750 t½ | 75,000 rem |
| 1000 t½ | 100,000 rem |
| 10000 t½ | 1,000,000 rem |
| 100000 t½ | 10,000,000 rem |
规则