Plutonium-242 (²⁴²Pu or Pu-242) is one of the

isotopes of plutonium Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long b ...

, the second longest-lived, with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of 375,000 years. The half-life of ²⁴²Pu is about 15 times that of ²³⁹Pu; so it is one-fifteenth as radioactive, and not one of the larger contributors to

nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons re ...

radioactivity. ²⁴²Pu's

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

emissions are also weaker than those of the other isotopes. It is not

fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typi ...

(but it is

fissionable In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typi ...

fast neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

s) and its

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...

cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...

is also low.

In the nuclear fuel cycle

Plutonium-242 is produced by successive

on ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu. The odd-mass isotopes ²³⁹Pu and ²⁴¹Pu have about a 3/4 chance of undergoing fission on capture of a

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...

and about a 1/4 chance of retaining the

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

and becoming the following isotope. The proportion of ²⁴²Pu is low at low

burnup In nuclear power technology, burnup (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per initi ...

but increases nonlinearly. Plutonium-242 has a particularly low

for

capture; and it takes three neutron absorptions to become another

isotope (either

curium Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...

-245 or plutonium-241) and then one more neutron to undergo fission. Even then, there is a chance either of those two fissile isotopes will absorb the fourth neutron instead of fissioning, becoming curium-246 (on the way to even heavier

actinide The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The info ...

s like

californium Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding cur ...

, which is a neutron emitter by spontaneous fission and difficult to handle) or becoming ²⁴²Pu again, so the mean number of neutrons absorbed until fission is even higher than 4. Therefore, ²⁴²Pu is particularly unsuited to recycling in a

thermal reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and stru ...

and would be better used in a

fast reactor A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as opposed ...

where it can be fissioned directly. However, ²⁴²Pu's low cross section means that relatively little of it will be transmuted during one cycle in a thermal reactor.

Decay

Plutonium-242 mainly decays into

uranium-238 Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it ...

via

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an ato ...

, before continuing along the

uranium series In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directl ...

. Plutonium-242 decays via

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdow ...

in about 5.5 × 10⁻⁴% of casesChart of all nuclei which includes half life and mode of decay
/ref>

References

{{Isotopes of plutonium Actinides Nuclear materials Isotopes of plutonium