Curium Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inten ...

(Cm) is an

artificial element A synthetic element is a known chemical element that does not occur naturally on Earth: it has been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, it i ...

with an atomic number of 96. Because it is an artificial element, a

standard atomic weight The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, ...

cannot be given, and it has no

stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundan ...

. The first

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

synthesized was Cm in 1944, which has 146 neutrons. There are 19 known

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s ranging from Cm to Cm. There are also ten known

nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). "Metastable" describes nuclei whose excited states have Half-life, half-lives of ...

s. The longest-lived isotope is Cm, with

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

15.6 million years – orders of magnitude longer than that of any known isotope beyond curium, and long enough to study as a possible

extinct radionuclide An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, but has since decayed to virtually zero abundance and is no longer detectable as a primordial nu ...

that would be produced by the

r-process In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for nucleosynthesis, the creation of approximately half of the Atomic nucleus, atomic nuclei Heavy meta ...

. The longest-lived known isomer is Cm with a half-life of 1.12 seconds.

List of isotopes

, -id=Curium-233 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 233.050771(87) , rowspan=2, 27(10) s , β (80%) , Am , rowspan=2, 3/2+# , - , α (20%) , Pu , -id=Curium-234 , rowspan=3, Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 138 , rowspan=3, 234.050159(18) , rowspan=3, 52(9) s , β (71%) , Am , rowspan=3, 0+ , - , α (27%) , Pu , - , SF (2%) , (various) , -id=Curium-235 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 139 , rowspan=2, 235.05155(11)# , rowspan=2, 7(3) min , β (96%) , Am , rowspan=2, 5/2+# , - , α (4%) , Pu , -id=Curium-236 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 140 , rowspan=2, 236.051372(19) , rowspan=2, 6.8(8) min , β (82%) , Am , rowspan=2, 0+ , - , α (18%) , Pu , -id=Curium-237 , Cm , style="text-align:right" , 96 , style="text-align:right" , 141 , 237.052869(80) , >10# min , α (?%) , Pu , 5/2+# , -id=Curium-238 , rowspan=3, Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 142 , rowspan=3, 238.053082(13) , rowspan=3, 2.2(4) h , EC (96.11%) , Am , rowspan=3, 0+ , - , α (3.84%) , Pu , - , SF (0.048%) , (various) , -id=Curium-239 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 239.05491(16) , rowspan=2, 2.5(4) h , β , Am , rowspan=2, 7/2−# , - , α (6.2x10%) , Pu , -id=Curium-240 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 144 , rowspan=2, 240.0555282(20) , rowspan=2, 30.4(37) d , α , Pu , rowspan=2, 0+ , - , SF (3.9×10%) , (various) , -id=Curium-241 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 241.0576512(17) , rowspan=2, 32.8(2) d , EC (99.0%) , Am , rowspan=2, 1/2+ , - , α (1.0%) , Pu , -id=Curium-242 , rowspan=3, Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 146 , rowspan=3, 242.0588342(12) , rowspan=3, 162.8(2) d , α , Pu , rowspan=3, 0+ , - , SF (6.2×10%) , (various) , - , CD (1.1×10%)Heaviest known nuclide to undergo

cluster decay Cluster decay, also named heavy particle radioactivity, heavy ion radioactivity or heavy cluster decay," is a rare type of nuclear decay in which an atomic nucleus emits a small "cluster" of neutrons and protons, more than in an alpha particle, ...

, Pb
Si , -id=Curium-242m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 2800(100) keV , 180(70) ns , , , , -id=Curium-243 , rowspan=3, Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 243.0613873(16) , rowspan=3, 29.1(1) y , α (99.71%) , Pu , rowspan=3, 5/2+ , - , EC (0.29%) , Am , - , SF (5.3×10%) , (various) , -id=Curium-243m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 87.4(1) keV , 1.08(3) μs , IT , Cm , 1/2+ , -id=Curium-244 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 244.0627506(12) , rowspan=2, 18.11(3) y , α , Pu , rowspan=2, 0+ , - , SF (1.37×10%) , (various) , -id=Curium-244m1 , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 1040.181(11) keV , 34(2) ms , IT , Cm , 6+ , -id=Curium-244m2 , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 1100(900)# keV , >500 ns , SF , (various) , , -id=Curium-245 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 149 , rowspan=2, 245.0654910(12) , rowspan=2, 8250(70) y , α , Pu , rowspan=2, 7/2+ , - , SF (6.1×10%) , (various) , -id=Curium-245m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 355.92(10) keV , 290(20) ns , IT , Cm , 1/2+ , -id=Curium-246 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 150 , rowspan=2, 246.0672220(16) , rowspan=2, 4706(40) y , α (99.97%) , Pu , rowspan=2, 0+ , - , SF (0.02615%) , (various) , -id=Curium-246m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 1179.66(13) keV , 1.12(24) s , IT , Cm , 8− , -id=Curium-247 , Cm , style="text-align:right" , 96 , style="text-align:right" , 151 , 247.0703527(41) , 1.56(5)×10 y , α , Pu , 9/2− , -id=Curium-247m1 , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 227.38(19) keV , 26.3(3) μs , IT , Cm , 5/2+ , -id=Curium-247m2 , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 404.90(3) keV , 100.6(6) ns , IT , Cm , 1/2+ , -id=Curium-248 , rowspan=2, Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 152 , rowspan=2, 248.0723491(25) , rowspan=2, 3.48(6)×10 y , α (91.61%) , Pu , rowspan=2, 0+ , - , SF (8.39%) , (various) , -id=Curium-248m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 1458.1(10) keV , 146(18) μs , IT , Cm , 8−# , -id=Curium-249 , Cm , style="text-align:right" , 96 , style="text-align:right" , 153 , 249.0759540(25) , 64.15(3) min , β , Bk , 1/2+ , -id=Curium-249m , style="text-indent:1em" , Cm , colspan="3" style="text-indent:2em" , 48.76(4) keV , 23 μs , , -id=Curium-250 , rowspan=3, Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 154 , rowspan=3, 250.078358(11) , rowspan=3, 8300# y , SFThe nuclide with the lowest

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...

known (almost surely) to undergo

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...

as the main decay mode , (various) , rowspan=3, 0+ , - , α (?%) , Pu , - , β (?%) , Bk , -id=Curium-251 , Cm , style="text-align:right" , 96 , style="text-align:right" , 155 , 251.082285(24) , 16.8(2) min , β , Bk , (3/2+)

Actinides vs fission products

References

* Isotope masses from: ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Curium