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 ...

(₉₆Cm) is an

artificial element A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; ...

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, is ...

cannot be given, and it has no stable isotopes. The first

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

synthesized was ²⁴²Cm 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 nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s ranging from ²³³Cm to ²⁵¹Cm. 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, higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited ...

s. The longest-lived isotope is ²⁴⁷Cm, with

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 ...

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 nucl ...

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 the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", ...

. The longest-lived isomer is ^246mCm with a half-life of 1.12 seconds.

List of isotopes

, - , rowspan=2, ²³³Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 233.05077(8) , rowspan=2, 27(10) s , β⁺ (80%) , ²³³Am , rowspan=2, 3/2+# , - , α (20%) , ²²⁹Pu , - , rowspan=3, ²³⁴Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 138 , rowspan=3, 234.05016(2) , rowspan=3, 52(9) s , β⁺ (71%) , ²³⁴Am , rowspan=3, 0+ , - , α (27%) , ²³⁰Pu , - , SF (2%) , (various) , - , rowspan=2, ²³⁵Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 139 , rowspan=2, 235.05143(22)# , rowspan=2, 300(+250−100) s , β⁺ , ²³⁵Am , rowspan=2, 5/2+# , - , α , ²³¹Pu , - , rowspan=2, ²³⁶Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 140 , rowspan=2, 236.05141(22)# , rowspan=2, 6.8(0.8) min , β⁺ (82%) , ²³⁶Am , rowspan=2, 0+ , - , α (18%) , ²³²Pu , - , rowspan=2, ²³⁷Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 141 , rowspan=2, 237.05290(22)# , rowspan=2, 20# min , β⁺ , ²³⁷Am , rowspan=2, 5/2+# , - , α , ²³³Pu , - , rowspan=2, ²³⁸Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 142 , rowspan=2, 238.05303(4) , rowspan=2, 2.4(1) h , EC (90%) , ²³⁸Am , rowspan=2, 0+ , - , α (10%) , ²³⁴Pu , - , rowspan=2, ²³⁹Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 239.05496(11)# , rowspan=2, 2.5(0.4) h , β⁺ (99.9%) , ²³⁹Am , rowspan=2, (7/2−) , - , α (.1%) , ²³⁵Pu , - , rowspan=3, ²⁴⁰Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 144 , rowspan=3, 240.0555295(25) , rowspan=3, 27(1) d , α (99.5%) , ²³⁶Pu , rowspan=3, 0+ , - , EC (.5%) , ²⁴⁰Am , - , SF (3.9×10⁻⁶%) , (various) , - , rowspan=2, ²⁴¹Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 241.0576530(23) , rowspan=2, 32.8(2) d , EC (99%) , ²⁴¹Am , rowspan=2, 1/2+ , - , α (1%) , ²³⁷Pu , - , rowspan=4, ²⁴²CmMost common isotopes , rowspan=4 style="text-align:right" , 96 , rowspan=4 style="text-align:right" , 146 , rowspan=4, 242.0588358(20) , rowspan=4, 162.8(2) d , α , ²³⁸Pu , rowspan=4, 0+ , - , SF (6.33×10⁻⁶%) , (various) , - , CD (10⁻¹⁴%)Heaviest known nuclide to undergo

cluster decay Cluster decay, also named heavy particle radioactivity or heavy ion radioactivity, 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, but less than a typic ...

, ²⁰⁸Pb
³⁴Si , - , β⁺β⁺ (rare) , ²⁴²Pu , - , style="text-indent:1em" , ^242mCm , colspan="3" style="text-indent:2em" , 2800(100) keV , 180(70) ns , , , , - , rowspan=3, ²⁴³Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 147 , rowspan=3, 243.0613891(22) , rowspan=3, 29.1(1) y , α (99.71%) , ²³⁹Pu , rowspan=3, 5/2+ , - , EC (.29%) , ²⁴³Am , - , SF (5.3×10⁻⁹%) , (various) , - , style="text-indent:1em" , ^243mCm , colspan="3" style="text-indent:2em" , 87.4(1) keV , 1.08(3) μs , IT , ²⁴³Cm , 1/2+ , - , rowspan=2, ²⁴⁴Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 244.0627526(20) , rowspan=2, 18.10(2) y , α , ²⁴⁰Pu , rowspan=2, 0+ , - , SF (1.34×10⁻⁴%) , (various) , - , style="text-indent:1em" , ^244m1Cm , colspan="3" style="text-indent:2em" , 1040.188(12) keV , 34(2) ms , IT , ²⁴⁴Cm , 6+ , - , style="text-indent:1em" , ^244m2Cm , colspan="3" style="text-indent:2em" , 1100(900)# keV , >500 ns , SF , (various) , , - , rowspan=2, ²⁴⁵Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 149 , rowspan=2, 245.0654912(22) , rowspan=2, 8.5(1)×10³ y , α , ²⁴¹Pu , rowspan=2, 7/2+ , - , SF (6.1×10⁻⁷%) , (various) , - , style="text-indent:1em" , ^245mCm , colspan="3" style="text-indent:2em" , 355.92(10) keV , 290(20) ns , IT , ²⁴⁵Cm , 1/2+ , - , rowspan=2, ²⁴⁶Cm , rowspan=2 style="text-align:right" , 96 , rowspan=2 style="text-align:right" , 150 , rowspan=2, 246.0672237(22) , rowspan=2, 4.76(4)×10³ y , α (99.97%) , ²⁴²Pu , rowspan=2, 0+ , - , SF (.0261%) , (various) , - , style="text-indent:1em" , ^246mCm , colspan="3" style="text-indent:2em" , 1179.66(13) keV , 1.12(0.24) s , IT , ²⁴⁶Cm , 8- , - , ²⁴⁷Cm , style="text-align:right" , 96 , style="text-align:right" , 151 , 247.070354(5) , 1.56(5)×10⁷ y , α , ²⁴³Pu , 9/2− , - , style="text-indent:1em" , ^247m1Cm , colspan="3" style="text-indent:2em" , 227.38(19) keV , 26.3(0.3) μs , IT , ²⁴⁷Cm , 5/2+ , - , style="text-indent:1em" , ^247m2Cm , colspan="3" style="text-indent:2em" , 404.90(3) keV , 100.6(0.6) ns , IT , ²⁴⁷Cm , 1/2+ , - , rowspan=3, ²⁴⁸Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 152 , rowspan=3, 248.072349(5) , rowspan=3, 3.48(6)×10⁵ y , α (91.74%) , ²⁴⁴Pu , rowspan=3, 0+ , - , SF (8.26%) , (various) , - , β⁻β⁻ (rare) , ²⁴⁸Cf , - , style="text-indent:1em" , ^248mCm , colspan="3" style="text-indent:2em" , 1458.1(1) keV , 146(18) μs , IT , ²⁴⁸Cm , (8-) , - , ²⁴⁹Cm , style="text-align:right" , 96 , style="text-align:right" , 153 , 249.075953(5) , 64.15(3) min , β⁻ , ²⁴⁹Bk , 1/2(+) , - , style="text-indent:1em" , ^249mCm , colspan="3" style="text-indent:2em" , 48.758(17) keV , 23 μs , α , ²⁴⁵Pu , (7/2+) , - , rowspan=3, ²⁵⁰Cm , rowspan=3 style="text-align:right" , 96 , rowspan=3 style="text-align:right" , 154 , rowspan=3, 250.078357(12) , rowspan=3, 8300# y , SF (74%)The nuclide with the lowest

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...

known to undergo

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 breakdo ...

as the main decay mode , (various) , rowspan=3, 0+ , - , α (18%) , ²⁴⁶Pu , - , β⁻ (8%) , ²⁵⁰Bk , - , ²⁵¹Cm , style="text-align:right" , 96 , style="text-align:right" , 155 , 251.082285(24) , 16.8(2) min , β⁻ , ²⁵¹Bk , (1/2+)

Actinides vs fission products

References

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