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|---------------------|-------------------|----------------------------------|----------------------------------|------------------------------------------------|
| Radioactive Isotope | Half Life (years) | Isotope Mass in the Body (grams) | Element Mass in the Body (grams) | Activity within the Body (Disintegrations/sec) |
| Potassium 40 | 1.26 x 109 | 0.0165 | 140 | 4,340 |
| Carbon 14 | 5,730 | 1.6 x 10**-8** | 16,000 | 3,080 |
| Rubidium 87 | 4.9 x 1010 | 0.19 | 0.7 | 600 |
| Lead 210 | 22.3 | 5.4 x 10**-10** | 0.12 | 15 |
| Tritium (3H) | 12.43 | 2 x 10**-14** | 7,000 | 7 |
| Uranium 238 | 4.46 x 109 | 1 x 10**-4** | 1 x 10**-4** | 3 - 5 |
| Radium 228 | 5.76 | 4.6 x 10**-14** | 3.6 x 10**-11** | 5 |
| Radium 226 | 1,620 | 3.6 x 10**-11** | 3.6 x 10**-11** | 3 |