View source for Physics:Plutonium-242

{{Short description|Isotope of plutonium}}
{{Infobox isotope
 | alternate_names =
 | symbol =Pu
 | mass_number =242
 | mass = 242.059
 | num_neutrons =148
 | num_protons =94
 | abundance =
 | halflife = {{val|375,000|u=years}}
 | image =
 | decay_product = Uranium-238
 | decay_symbol = <sup>238</sup>U
 | decay_mass =
 | decay_mode1 = alpha decay
 | decay_energy1 =
 | decay_mode2 =
 | decay_energy2 =
 | decay_mode3 =
 | decay_energy3 =
 | decay_mode4 =
 | decay_energy4 =
 | parent =
 | parent_symbol =
 | parent_mass =
 | parent_decay =
 | parent2 =
 | parent2_symbol =
 | parent2_mass =
 | parent2_decay =
 | spin =
 | excess_energy =
 | binding_energy =

}}
{{Actinidesvsfissionproducts}}

'''Plutonium-242''' ('''<sup>242</sup>Pu''' or '''Pu-242''') is one of the [[Physics:Isotopes of plutonium|isotopes of plutonium]], the second longest-lived, with a [[Physics:Half-life|half-life]] of 375,000 years.
The half-life of <sup>242</sup>Pu is about 15 times that of <sup>239</sup>Pu; so it is one-fifteenth as radioactive, and not one of the larger contributors to [[Physics:Nuclear waste|nuclear waste]] radioactivity.
<sup>242</sup>Pu's [[Physics:Gamma ray|gamma ray]] emissions are also weaker than those of the other isotopes.<ref>{{cite web|url=http://www.wmsym.org/archives/2001/21B/21B-18.pdf|format=PDF|title=PLUTONIUM ISOTOPIC RESULTS OF KNOWN SAMPLES USING THE SNAP GAMMA SPECTROSCOPY ANALYSIS CODE AND THE ROBWIN SPECTRUM FITTING ROUTINE|access-date=2013-03-15|archive-date=2017-08-13|archive-url=https://web.archive.org/web/20170813191754/http://www.wmsym.org/archives/2001/21B/21B-18.pdf|url-status=dead}}</ref>

It is not fissile (but it is fissionable by fast neutrons) and its [[Physics:Neutron capture|neutron capture]] cross section is also low.

==In the nuclear fuel cycle==

[[Image:Sasahara.svg|thumb|right|400px|Transmutation flow in LWR]]
Plutonium-242 is produced by successive [[Physics:Neutron capture|neutron capture]] on <sup>239</sup>Pu, <sup>240</sup>Pu, and <sup>241</sup>Pu. The odd-mass isotopes <sup>239</sup>Pu and <sup>241</sup>Pu have about a 3/4 chance of undergoing [[Physics:Nuclear fission|fission]] on capture of a thermal neutron and about a 1/4 chance of retaining the [[Physics:Neutron|neutron]] and becoming the following isotope. The proportion of <sup>242</sup>Pu is low at low [[Engineering:Burnup|burnup]] but increases nonlinearly.

Plutonium-242 has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to become another fissile isotope (either [[Chemistry:Curium|curium]]-245 or plutonium-241) and then one more neutron to undergo [[Physics:Nuclear fission|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 [[Chemistry:Actinide|actinide]]s like [[Chemistry:Californium|californium]], which is a neutron emitter by spontaneous fission and difficult to handle) or becoming <sup>242</sup>Pu again, so the mean number of neutrons absorbed until fission is even higher than 4. Therefore, <sup>242</sup>Pu is particularly unsuited to recycling in a thermal reactor and would be better used in a [[Physics:Fast reactor|fast reactor]] where it can be fissioned directly. However, <sup>242</sup>Pu'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 [[Physics:Uranium-238|uranium-238]] via [[Physics:Alpha decay|alpha decay]], before continuing along the uranium series. Plutonium-242 decays via [[Physics:Spontaneous fission|spontaneous fission]] in about 5.5&nbsp;×&nbsp;10<sup>−4</sup>% of cases<ref>[https://web.archive.org/web/20000817205239/http://nucleardata.nuclear.lu.se/nucleardata/toi/pdf/chart.pdf Chart of all nuclei which includes half life and mode of decay]</ref>.

==References==
{{reflist}}
{{Isotopes of plutonium}}

[[Category:Actinides]]
[[Category:Nuclear materials]]
[[Category:Isotopes of plutonium]]

{{Sourceattribution|Plutonium-242}}