Isotopes of mendelevium

Mendelevium (Md) is a synthetic element, and thus a standard atomic mass 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 16 known radioisotopes, ranging in atomic mass from ²⁴⁵Md 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 58.0 minutes.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin
	excitation energy
245Md	101	144	245.08081(33)#	0.90(25) ms	SF	(various)	(1/2−)#
					α (rare)	241Es
245mMd	200(100)# keV			400(200) ms [0.35(+23−16) s]	α	241Es	(7/2+)
					β+ (rare)	245Fm
246Md	101	145	246.08171(28)#	1.0(4) s	α	242Es
					β+ (rare)	246Fm
247Md	101	146	247.08152(22)#	1.12(22) s	SF	(various)	1/2−#
					α (rare)	243Es
247mMd				~0.2 s	α (99.99%)	243Es
					SF (10−4%)	(various)
248Md	101	147	248.08282(26)#	7(3) s	β+ (80%)	248Fm
					α (20%)	244Es
					β+, SF (.05%)	(various)
249Md	101	148	249.08291(22)#	24(4) s	α (60%)	245Es	(7/2−)
					β+ (40%)	249Fm
249mMd	100(100)# keV			1.9(9) s			(1/2−)
250Md	101	149	250.08442(32)#	52(6) s	β+ (93%)	250Fm
					α (7%)	246Es
					β+, SF (.02%)	(various)
251Md	101	150	251.084774(20)	4.0(5) min	β+ (90%)	251Fm	7/2−#
					α (10%)	247Es
252Md	101	151	252.08643(14)#	2.3(8) min	β+ (50%)	252Fm
					α (50%)	248Es
253Md	101	152	253.08714(3)#	12(8) min [6(+12−3) min]	β+	253Fm	7/2−#
					α	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 (1%)	(various)
258Md	101	157	258.098431(5)	51.5(3) d	α (99.99%)	254Es	(8−)#
					β− (.0015%)	258No
					β+ (.0015%)	258Fm
258mMd	0(200)# keV			57.0(9) min	EC (70%)	258Fm	1−#
					SF (20%)	(various)
					β− (10%)	258No
					α (1.2%)	254Es
259Md	101	158	259.10051(22)#	1.60(6) h	SF (98.7%)	(various)	7/2−#
					α (1.3%)	255Es
260Md	101	159	260.10365(34)#	27.8(8) d	SF (85%)	(various)
					α (5%)	256Es
					EC (5%)	260Fm
					β− (3.5%)	260No

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

Chronology of isotope discovery

Isotope	Discovered	Reaction
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)
260Md	1989	254Es+18O, 22Ne — transfer

References

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Isotopes of fermium	Isotopes of mendelevium	Isotopes of nobelium
Table of nuclides