| 1 | A | B | C | D | E |
| --- | --- | --- | --- | --- | --- |
| 2 | Isotopes of plutonium - Pu-240, Pu-241 and Pu-242 |  |  |  |  |
| 3 | Isotope | Thermal neutron cross section (barns) | Thermal neutron cross section (barns) | Decay Mode | Half-life |
| 4 | Isotope | Capture | Fission | Decay Mode | Half-life |
| 5 | 238U | 2.683 | 0.000 | α | 4.468 x 109 years |
| 6 | 239U | 20.57 | 14.11 | β | 23.45 minutes |
| 7 | 239Np | 77.03 | – | β | 2.356 days |
| 8 | 239Pu | 270.7 | 747.9 | α | 24,110 years |
| 9 | 240Pu | 287.5 | 0.064 | α | 6,561 years |
| 10 | 241Pu | 363.0 | 1012 | β | 14.325 years |
| 11 | 242Pu | 19.16 | 0.001 | α | 373,300 years |

Question: Which two isotopes of plutonium have the longest half-lives?
Answer: Pu-242, with a half-life of 373,300 years, and Pu-239, with a half-life of 24,110 years.