Isotopes of einsteinium

Einsteinium (₉₉Es) 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 discovered (in nuclear fallout from an H-bomb test) was ²⁵³Es in 1952. There are 18 known radioisotopes from ²⁴⁰Es to ²⁵⁷Es, and 3 nuclear isomers (^250mEs, ^254mEs, and ^256mEs). The longest-lived isotope is ²⁵²Es with a half-life of 471.7 days, or around 1.293 years.

Main isotopes of einsteinium (₉₉Es)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^252Es syn 471.7 d α ^248Bk ε ^252Cf β^− ^252Fm ^253Es syn 20.47 d SF – α ^249Bk ^254Es syn 275.7 d ε ^254Cf β^− ^254Fm α ^250Bk ^255Es syn 39.8 d β^− ^255Fm α ^251Bk SF –

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]
^240Es	99	141	240.06892(43)#	6(2) s[1]	α	^236Bk
					β^+ (rare)	^240Cf
^241Es	99	142	241.06854(24)#	10(5) s [8(+6−5) s]	α	^237Bk	(3/2−)
					β^+ (rare)	^241Cf
^242Es	99	143	242.06975(35)#	13.5(25) s	α (99.94%)	^238Bk
					β^+, SF (.6%)	(various)
					β^+ (rare)	^242Cf
^243Es	99	144	243.06955(25)#	21(2) s	β^+ (70%)	^243Cf	3/2−#
					α (30%)	^239Bk
^244Es	99	145	244.07088(20)#	37(4) s	β^+ (94.69%)	^244Cf
					α (5.3%)	^240Bk
					β^+, SF (.01%)	(various)
^245Es	99	146	245.07132(22)#	1.1(1) min	β^+ (60%)	^245Cf	(3/2−)
					α (40%)	^241Bk
^246Es	99	147	246.07290(24)#	7.7(5) min	β^+ (90.1%)	^246Cf	4−#
					α (9.9%)	^242Bk
					β^+, SF (.003%)	(various)
^247Es	99	148	247.07366(3)#	4.55(26) min	β^+ (93%)	^247Cf	7/2+#
					α (7%)	^243Bk
					SF (9×10^−5%)	(various)
^248Es	99	149	248.07547(6)#	27(5) min	β^+ (99.75%)	^248Cf	2−#, 0+#
					α (.25%)	^244Bk
					β^+, SF (3×10^−5%)	(various)
^249Es	99	150	249.07641(3)#	102.2(6) min	β^+ (99.43%)	^249Cf	7/2+
					α (.57%)	^245Bk
^250Es	99	151	250.07861(11)#	8.6(1) h	β^+ (97%)	^250Cf	(6+)
					α (3%)	^246Bk
^250mEs	200(150)# keV			2.22(5) h	EC (99%)	^250Cf	1(−)
					α (1%)	^246Bk
^251Es	99	152	251.079992(7)	33(1) h	EC (99.51%)	^251Cf	(3/2−)
					α (.49%)	^247Bk
^252Es	99	153	252.08298(5)	471.7(19) d	α (76%)	^248Bk	(5−)
					EC (24%)	^252Cf
					β^− (.01%)	^252Fm
^253Es[n 7]	99	154	253.0848247(28)	20.47(3) d	α	^249Bk	7/2+
					SF (8.7×10^−6%)	(various)
^254Es	99	155	254.088022(5)	275.7(5) d	α	^250Bk	(7+)
					EC (10^−4%)	^254Cf
					SF (3×10^−6%)	(various)
					β^− (1.74×10^−6%)	^254Fm
^254mEs	84.2(25) keV			39.3(2) h	β^− (98%)	^254Fm	2+
					IT (3%)	^254Es
					α (.33%)	^250Bk
					EC (.078%)	^254Cf
					SF (.0045%)	(various)
^255Es	99	156	255.090273(12)	39.8(12) d	β^− (92%)	^255Fm	(7/2+)
					α (8%)	^251Bk
					SF (.0041%)	(various)
^256Es	99	157	256.09360(11)#	25.4(24) min	β^−	^256Fm	(1+, 0−)
^256mEs	0(100)# keV			7.6 h	β^− (99.99%)	^256Fm	(8+)
					β^−, SF (.002%)	(various)
^257Es	99	158	257.09598(44)#	7.7(2) d	β^−	^257Fm	7/2+#
					α	^253Bk

1. ^mEs – 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
   IT:	Isomeric transition
   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. Most common isotope

References

1. Konki, J.; et al. (10 Jan 2017). "Towards saturation of the electron-capture delayed fission probability: The new isotopes ²⁴⁰Es and ²³⁶Bk". Physics Letters B. 764: 265–270. Bibcode:2017PhLB..764..265K. doi:10.1016/j.physletb.2016.11.038. ISSN 0370-2693.

• Isotope masses from:
  • 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
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• 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.