Isotopes of einsteinium

Einsteinium (99Es) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be discovered (in nuclear fallout from the Ivy Mike H-bomb test) was 253Es in 1952. There are 18 known radioisotopes, from 240Es to 257Es, and 8 nuclear isomers. The longest-lived isotope is 252Es with a half-life of 471.7 days or 1.291 years; the second longest, 254Es with half-life of 275.7 days is more available.

List of isotopes

Nuclide	Z	N	Isotopic mass (Da)	Discovery year	Half-life	Decay mode	Daughter isotope	Spin and parity
Excitation energy
240Es	99	141	240.06895(39)#		6.0(17)s	α (70%)	236Bk	4−#
β+ (30%)	240Cf
β+, SF (0.16%)	(various)
241Es	99	142	241.06859(25)#		4.3+2.4 −1.2s	α	237Bk	3/2−#
242Es	99	143	242.06957(28)#		16.9(8)s	β+	242Cf	2+#
α (41%)	238Bk
β+, SF (1.5%)	(various)
243Es	99	144	243.06951(22)#		22.1(14)s	α (61%)	239Bk	(7/2+)
β+? (39%)	243Cf
243mEs	50(50)#keV		>50#μs	IT?	243Es	3/2−#
α?	239Bk
β+?	243Cf
244Es	99	145	244.07088(20)#		37(4)s	β+ (95%)	244Cf	6+#
α (5%)	240Bk
β+, SF (0.011%)	(various)
245Es	99	146	245.07119(18)#		1.11(6)min	β+ (51%)	245Cf	(3/2−)
α (49%)	241Bk
245mEs	30(15)#keV	(1967)	>50#μs	IT?	245Es	7/2+#
α?	241Bk
β+?	245Cf
246Es	99	147	246.07281(10)		7.5(5)min	β+ (90.1%)	246Cf	4−#
α (9.9%)	242Bk
β+, SF (0.003%)	(various)
247Es	99	148	247.073622(21)		4.55(26)min	β+ (93%)	247Cf	(7/2+)
α (7%)	243Bk
247mEs	50(50)#keV	(2001)	>20#μs	IT?	247Es	(3/2−)
α?	243Bk
β+	247Cf
248Es	99	149	248.07547(6)#		24(3)min	β+ (99.75%)	248Cf	2−#
α (0.25%)	244Bk
β+, SF (3.5×10−4%)	(various)
249Es	99	150	249.07641(3)#		102.2(6)min	β+ (99.43%)	249Cf	7/2+
α (0.57%)	245Bk
250Es	99	151	250.07861(11)#		8.6(1)h	β+	250Cf	6(+)
250mEs	200(150)#keV		2.22(5)h	β+	250Cf	1(−)
251Es	99	152	251.079991(6)		33(1)h	EC (99.5%)	251Cf	3/2−
α (0.5%)	247Bk
251mEs	8.4(10)keV	----	>200#μs	IT?	251Es	(7/2+)
EC?	251Cf
252Es	99	153	252.08298(5)		471.7(19)d	α (78%)	248Bk	(4+)
EC (22%)	252Cf
253Es	99	154	253.0848212(13)		20.47(3)d	α	249Bk	7/2+
SF (8.7×10−6%)	(various)
253mEs	106(4)keV	(1993)	>10#μs	IT?	253Es	3/2−#
254Es	99	155	254.088024(3)		275.7(5)d	α	250Bk	7+
β− (1.74×10−4%)	254Fm
SF (<3×10−6%)	(various)
254mEs	80.4(11)keV		39.3(2)h	β− (98%)	254Fm	2+
IT (<3%)	254Es
α (0.32%)	250Bk
EC (0.076%)	254Cf
SF (<0.045%)	(various)
255Es	99	156	255.090274(12)		39.8(12)d	β− (92.0%)	255Fm	(7/2+)
α (8.0%)	251Bk
SF (0.0041%)	(various)
256Es	99	157	256.09360(11)#		7.6h	β−	256Fm	7+#
β−, SF (0.002%)	(various)
256mEs	0(100)#keV		25.4(12)min	β−	256Fm	0+#
257Es	99	158	257.09598(44)#		7.7(2)d	β−	257Fm	7/2+#
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