Curium-245
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Curium-245
Main isotopes of curium (96Cm)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
242Cm syn 160 d ? 238Pu
SF -
243Cm syn 29.1 y ? 239Pu
? 243Am
SF -
244Cm syn 18.1 y ? 240Pu
SF -
245Cm syn 8500 y ? 241Pu
SF -
246Cm syn 4730 y ? 242Pu
SF -
247Cm syn 1.56×107 y ? 243Pu
248Cm syn 3.40×105 y ? 244Pu
SF -
250Cm syn 9000 y SF -
? 246Pu
?- 250Bk

Curium (96Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutrons.

There are 19 known radioisotopes ranging from 233Cm to 251Cm. There are also ten known nuclear isomers. The longest-lived isotope is 247Cm, with a half-life of 15.6 million years - several orders of magnitude longer than the half-life of all known nuclei of elements beyond curium in the periodic table. The longest-lived isomer is 246mCm with a half-life of 1.12 seconds.

List of isotopes

Nuclide
[n 1]
Z N Isotopic mass (u)
[n 2][n 3]
Half-life
[n 4]
Decay
mode

[n 5]
Daughter
isotope

Spin and
parity
[n 6][n 4]
Excitation energy[n 4]
233Cm 96 137 233.05077(8) 27(10) s ?+ (80%) 233Am 3/2+#
? (20%) 229Pu
234Cm 96 138 234.05016(2) 52(9) s ?+ (71%) 234Am 0+
? (27%) 230Pu
SF (2%) (various)
235Cm 96 139 235.05143(22)# 5# min ?+ 235Am 5/2+#
? 231Pu
236Cm 96 140 236.05141(22)# 6.8(0.8) min ?+ (82%) 236Am 0+
? (18%) 232Pu
237Cm 96 141 237.05290(22)# 20# min ?+ 237Am 5/2+#
? 233Pu
238Cm 96 142 238.05303(4) 2.4(1) h EC (90%) 238Am 0+
? (10%) 234Pu
239Cm 96 143 239.05496(11)# 2.5(0.4) h ?+ (99.9%) 239Am (7/2-)
? (.1%) 235Pu
240Cm 96 144 240.0555295(25) 27(1) d ? (99.5%) 236Pu 0+
EC (.5%) 240Am
SF (3.9×10-6%) (various)
241Cm 96 145 241.0576530(23) 32.8(2) d EC (99%) 241Am 1/2+
? (1%) 237Pu
242Cm[n 7] 96 146 242.0588358(20) 162.8(2) d ? 238Pu 0+
SF (6.33×10-6%) (various)
CD (10-14%)[n 8] 208Pb
34Si
?+?+ (rare) 242Pu
242mCm 2800(100) keV 180(70) ns
243Cm 96 147 243.0613891(22) 29.1(1) y ? (99.71%) 239Pu 5/2+
EC (.29%) 243Am
SF (5.3×10-9%) (various)
243mCm 87.4(1) keV 1.08(3) µs IT 243Cm 1/2+
244Cm[n 7] 96 148 244.0627526(20) 18.10(2) y ? 240Pu 0+
SF (1.34×10-4%) (various)
244m1Cm 1040.188(12) keV 34(2) ms IT 244Cm 6+
244m2Cm 1100(900)# keV >500 ns SF (various)
245Cm 96 149 245.0654912(22) 8.5(1)×103 y ? 241Pu 7/2+
SF (6.1×10-7%) (various)
245mCm 355.92(10) keV 290(20) ns IT 245Cm 1/2+
246Cm 96 150 246.0672237(22) 4.76(4)×103 y ? (99.97%) 242Pu 0+
SF (.0261%) (various)
246mCm 1179.66(13) keV 1.12(0.24) s IT 246Cm 8-
247Cm 96 151 247.070354(5) 1.56(5)×107 y ? 243Pu 9/2-
247m1Cm 227.38(19) keV 26.3(0.3) µs IT 247Cm 5/2+
247m2Cm 404.90(3) keV 100.6(0.6) ns IT 247Cm 1/2+
248Cm 96 152 248.072349(5) 3.48(6)×105 y ? (91.74%) 244Pu 0+
SF (8.26%) (various)
?-?- (rare) 248Cf
248mCm 1458.1(1) keV 146(18) µs IT 248Cm (8-)
249Cm 96 153 249.075953(5) 64.15(3) min ?- 249Bk 1/2(+)
249mCm 48.758(17) keV 23 µs ? 245Pu (7/2+)
250Cm 96 154 250.078357(12) 8300# y SF (74%)[n 9] (various) 0+
? (18%) 246Pu
?- (8%) 250Bk
251Cm 96 155 251.082285(24) 16.8(2) min ?- 251Bk (1/2+)
  1. ^ mCm – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ a b c # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. ^ Modes of decay:
  6. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  7. ^ a b Most common isotopes
  8. ^ Heaviest known nuclide to undergo cluster decay
  9. ^ The nuclide with the lowest atomic number known to undergo spontaneous fission as the main decay mode

Actinides vs fission products

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

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.

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