Plutonium-242
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Plutonium-242
Actinides and fission products by half-life
Actinides[1] by decay chain Half-life
range (y)
Fission products of 235U by yield[2]
4n 4n+1 4n+2 4n+3
4.5-7% 0.04-1.25% <0.001%
228RaNo 4-6 + 155Euþ
244Cm? 241Pu? 250Cf 227AcNo 10-29 90Sr 85Kr 113mCdþ
232U? 238Pu? 243Cm? 29-97 137Cs 151Smþ 121mSn
248Bk[3] 249Cf? 242mAm? 141-351

No fission products
have a half-life
in the range of
100-210 k years ...

241Am? 251Cf?[4] 430-900
226RaNo 247Bk 1.3 k - 1.6 k
240Pu 229Th 246Cm? 243Am? 4.7 k - 7.4 k
245Cm? 250Cm 8.3 k - 8.5 k
239Pu? 24.1 k
230ThNo 231PaNo 32 k - 76 k
236Np? 233U? 234UNo ? 99Tc? 126Sn
248Cm 242Pu 327 k - 375 k 79Se?
1.53 M 93Zr
237Np? 2.1 M - 6.5 M 135Cs? 107Pd
236U 247Cm? 15 M - 24 M 129I?
244Pu 80 M

... nor beyond 15.7 M years[5]

232ThNo 238UNo 235U?No 0.7 G - 14.1 G

Legend for superscript symbols
?  has thermal neutron capture cross section in the range of 8-50 barns
fissile
metastable isomer
No  primarily a naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
+  range 4-97 y: Medium-lived fission product
?  over 200,000 y: Long-lived fission product

Plutonium-242 (242Pu) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 373,300 years. The half-life of 242Pu is about 15 times longer than that of 239Pu; therefore, it is one-fifteenth as radioactive, and not one of the larger contributors to nuclear waste radioactivity. 242Pu's gamma ray emissions are also weaker than those of the other isotopes.[6]

It is not fissile (though it is fissionable by fast neutrons) and its neutron capture cross section is also low.

In the nuclear fuel cycle

Transmutation flow in LWR

Plutonium-242 is produced by successive neutron capture 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 and about a 1/4 chance of retaining the neutron and becoming the following isotope. The proportion of 242Pu is low at low 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 curium-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 actinides like californium, 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 and would be better used in a fast reactor 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 primarily decays into uranium-238 via alpha decay, before continuing along the uranium series. Plutonium-242 will occasionally decay via spontaneous fission with a rate of 5.5 × 10-4%.[7]

References

  1. ^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
  2. ^ Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
  3. ^ Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
    "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248 with a half-life greater than 9 y. No growth of Cf248 was detected, and a lower limit for the ?- half-life can be set at about 104 y. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 y."
  4. ^ This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".
  5. ^ Excluding those "classically stable" nuclides with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is nearly eight quadrillion years.
  6. ^ "PLUTONIUM ISOTOPIC RESULTS OF KNOWN SAMPLES USING THE SNAP GAMMA SPECTROSCOPY ANALYSIS CODE AND THE ROBWIN SPECTRUM FITTING ROUTINE" (PDF).
  7. ^ Chart of all nuclei which includes half life and mode of decay

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

Plutonium-242
 



 



 
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