Decay Heat and Fission Properties
Plutonium isotopes undergo radioactive decay, which produces decay heat. Different isotopes produce different amounts of heat per mass. The decay heat is usually listed as watt/kilogram, or milliwatt/gram. In case of larger pieces of plutonium (e.g. a weapon pit) and inadequate heat removal the resulting self-heating may be significant. All isotopes produce weak gamma on decay.
| Isotope | Decay mode | Half-life (years) | Decay heat (W/kg) | Spontaneous fission neutrons (1/(g·s)) | Comment |
|---|---|---|---|---|---|
| 238Pu | alpha to 234U | 87.74 | 560 | 2600 | Very high decay heat. Even in small amounts can cause significant self-heating. Used on its own in radioisotope thermoelectric generators. |
| 239Pu | alpha to 235U | 24100 | 1.9 | 0.022 | The principal fissile isotope in use. |
| 240Pu | alpha to 236U, spontaneous fission | 6560 | 6.8 | 910 | The principal impurity in samples of the 239Pu isotope. The plutonium grade is usually listed as percentage of 240Pu. High spontaneous fission hinders use in nuclear weapons. |
| 241Pu | beta-minus, to 241Am | 14.4 | 4.2 | 0.049 | Decays to americium-241; its buildup presents a radiation hazard in older samples. |
| 242Pu | alpha to 238U | 376000 | 0.1 | 1700 |
Americium-241, the decay product of plutonium-241, has half-life of 430 years, 1.2 spontaneous fissions per gram per second, and decay heat of 114 watts per kilogram. As its decay produces highly penetrative gamma rays, its presence in plutonium, determined by the original concentration of plutonium-241 and the sample age, increases the radiation exposure of surrounding structures and personnel.
Read more about this topic: Plutonium, Characteristics
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