Isotopes of mendelevium

Mendelevium (₁₀₁Md) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁵⁶Md (which was also the first isotope of any element produced one atom at a time) in 1955. There are 17 known radioisotopes, ranging in atomic mass from ²⁴⁴Md to ²⁶⁰Md, and 5 isomers. The longest-lived isotope is ²⁵⁸Md with a half-life of 51.3 days, and the longest-lived isomer is ^258mMd with a half-life of 57 minutes.

Isotopes of mendelevium (₁₀₁Md)

Main isotopes^[1] Decay abun­dance half-life (t1/2) mode pro­duct ^256Md synth 1.17 h ε ^256Fm ^257Md synth 5.52 h ε ^257Fm α ^253Es SF – ^258Md synth 51.5 d α ^254Es ε ^258Fm β^− ^258No ^259Md synth 1.60 h SF – α ^255Es ^260Md synth 31.8 d SF – α ^256Es ε ^260Fm β^− ^260No

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List of isotopes

Nuclide ^[n 1]	Z	N	Isotopic mass (Da) ^[n 2]^[n 3]	Half-life	Decay mode ^[n 4]	Daughter isotope	Spin and parity ^[n 5]^[n 6]
	Excitation energy^[n 6]
^244Md^[2]	101	143		0.30+0.19 −0.09 s	α	^240Es
^245Md^[2]	101	144	245.08081(33)#	0.33+0.15 −0.08 s	α	^241Es	7/2−#
					β^+ (rare)	^245Fm
^245mMd	200(100)# keV			0.90(25) ms	SF	(various)	1/2−#
^246Md^[3]	101	145	246.08171(28)#	0.9(2) s	α	^242Es
					β^+?	^246Fm
^246mMd				4.4(8) s	β^+ (>67%)	^246Fm
					α (<23%)	^242Es
					β^+, SF (>10%)	(various)
^247Md^[4]	101	146	247.08152(22)#	1.20(12) s	α (99.14%)	^243Es	(7/2−)
					SF (0.86%)	(various)
					β^+?	^247Fm
^247mMd	153 keV			0.23(3) s	α (80%)	^243Es	(1/2−)
					SF (20%)	(various)
^248Md	101	147	248.08282(26)#	7(3) s	β^+ (80%)	^248Fm
					α (20%)	^244Es
					β^+, SF (.05%)	(various)
^249Md^[5]	101	148	249.08291(22)#	26(1) s	α (75%)	^245Es	(7/2−)
					β^+ (25%)	^249Fm
^249mMd^[6]	100(100)# keV			1.5+1.2 −0.5 s	α	^245Es	(1/2−)
^250Md^[7]	101	149	250.08442(32)#	54(4) s	β^+ (93.0%)	^250Fm
					α (7.0%)	^246Es
					β^+, SF (0.026%)	(various)
^251Md^[8]	101	150	251.084774(20)	4.27(26) min	β^+ (90%)	^251Fm	(7/2−)
					α (10%)	^247Es
^252Md	101	151	252.08643(14)#	2.3(8) min	β^+	^252Fm
					α (rare)^[9]	^248Es
^253Md	101	152	253.08714(3)#	12(8) min [6.4+11.6 −3.6 min]	β^+ (~99%)^[10]	^253Fm	(7/2−)
					α (~1%)	^249Es
^254Md	101	153	254.08959(11)#	10(3) min	β^+	^254Fm	(0−)
					α (rare)	^250Es
^254mMd	50(100)# keV			28(8) min	β^+	^254Fm	(3−)
					α (rare)	^250Es
^255Md	101	154	255.091084(7)	27(2) min	β^+ (92%)	^255Fm	(7/2−)
					α (8%)	^251Es
					SF (.15%)	(various)
^256Md	101	155	256.09389(13)#	77(2) min	β^+ (89%)	^256Fm	(1−)
					α (11%)	^252Es
^257Md	101	156	257.0955424(29)	5.52(5) h	EC (84.8%)	^257Fm	(7/2−)
					α (15.2%)	^253Es
					SF (rare)	(various)
^258Md^[11]	101	157	258.098431(5)	51.59(29) d	α	^254Es	(8−)#
					β^− (<0.0015%)	^258No
					β^+ (<0.0015%)	^258Fm
^258mMd	0(200)# keV			57.0(9) min	EC	^258Fm	1−#
					SF (<15%)	(various)
					α (<1.2%)	^254Es
					β^− (rare)	^258No
^259Md^[n 7]^[12]	101	158	259.10051(22)#	1.60(6) h	SF	(various)	7/2−#
					α (rare)	^255Es
^260Md^[13]	101	159	260.10365(34)#	27.8(8) d	SF	(various)
					α (<5%)	^256Es
					EC (<5%)	^260Fm
					β^− (<3.5%)	^260No
This table header & footer: view

1. ^mMd – 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. Modes of decay:

   EC:	Electron capture
   SF:	Spontaneous fission

5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. Not directly synthesized, occurs as decay product of ²⁵⁹No

Chronology of isotope discovery

Isotope	Discovered	Reaction
^244Md	2020	^209Bi(^40Ar,5n)
^245Md	1996	^209Bi(^40Ar,4n)
^246Md	1996	^209Bi(^40Ar,3n)
^247Md	1981	^209Bi(^40Ar,2n)
^248Md	1973	^241Am(^12C,5n)
^249Md	1973	^241Am(^12C,4n)
^250Md	1973	^243Am(^12C,5n), ^243Am(^13C,6n)
^251Md	1973	^243Am(^12C,4n), ^243Am(^13C,5n)
^252Md	1973	^243Am(^13C,4n)
^253Md	1992	^243Am(^13C,3n)
^254Md	1970	^253Es(α,3n)
^255Md	1958	^253Es(α,2n)
^256Md	1955	^253Es(α,n)
^257Md	1964	^252Cf(^11B,α2n)
^258Md	1970	^255Es(α,n)
^259Md	1982	^248Cm(^18O,α3n)^[14]
^260Md	1989	^254Es+^18O, ^22Ne — transfer

References

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14. see nobelium

• Isotope masses from:
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• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.
  • M. Thoennessen (2012). "Discovery of Isotopes of Elements with Z≥100". Atomic Data and Nuclear Data Tables. 99 (3): 312–344. arXiv:1203.2105. Bibcode:2013ADNDT..99..312T. doi:10.1016/j.adt.2012.03.003. S2CID 94982856.