Isotopes of lawrencium

Lawrencium (₁₀₃Lr) 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 synthesized was ²⁵⁸Lr in 1961. There are thirteen known radioisotopes from ²⁵¹Lr to ²⁶⁶Lr, and 1 isomer (^253mLr). The longest-lived isotope is ²⁶⁶Lr with a half-life of 11 hours. Heavier isotopes are expected to have longer half-lives.

Main isotopes of lawrencium (₁₀₃Lr)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^254Lr syn 13 s 78% α ^250Md 22% ε ^254No ^255Lr syn 21.5 s α ^251Md ^256Lr syn 27 s α ^252Md ^259Lr syn 6.2 s 78% α ^255Md 22% SF ^260Lr syn 2.7 min α ^256Md ^261Lr syn 44 min SF/ε? ^262Lr syn 3.6 h ε ^262No ^266Lr syn 10 h 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]
^251Lr[1]	103	148	251.09418(32)#	27(+118-13) ms	SF	(various)
^252Lr[n 7]	103	149	252.09526(26)#	390(90) ms [0.36(+11−7) s]	α (90%)	^248Md
					β^+ (10%)	^252No
					SF (1%)	(various)
^253Lr[n 8]	103	150	253.09509(22)#	580(70) ms [0.57(+7−6) s]	α (90%)	^249Md	(7/2−)
					SF (9%)	(various)
					β^+ (1%)	^253No
^253mLr[n 8]	30(100)# keV			1.5(3) s [1.5(+3−2) s]			(1/2−)
^254Lr[n 9]	103	151	254.09648(32)#	13(3) s	α (78%)	^250Md
					β^+ (22%)	^254No
					SF (.1%)	(various)
^255Lr	103	152	255.096562(19)	22(4) s	α (69%)	^251Md	7/2−#
					β^+ (30%)	^255No
					SF (1%)	(various)
^256Lr	103	153	256.09849(9)	27(3) s	α (80%)	^252Md
					β^+ (20%)	^256No
					SF (.01%)	(various)
^257Lr	103	154	257.09942(5)#	646(25) ms	α (99.99%)	^253Md	9/2+#
					β^+ (.01%)	^257No
					SF (.001%)	(various)
^258Lr	103	155	258.10176(11)#	4.1(3) s	α (95%)	^254Md
					β^+ (5%)	^258No
^259Lr	103	156	259.10290(8)#	6.2(3) s	α (77%)	^255Md	9/2+#
					SF (23%)	(various)
					β^+ (.5%)	^259No
^260Lr	103	157	260.10551(13)#	2.7 min	α (75%)	^256Md
					β^+ (15%)	^260No
					SF (10%)	(various)
^261Lr	103	158	261.10688(22)#	44 min	SF	(various)
					α (rare)	^257Md
^262Lr	103	159	262.10961(22)#	216 min	β^+	^262No
					α (rare)	^258Md
^266Lr[n 10]	103	163	266.11983(56)#	11 h	SF	(various)

1. ^mLr – 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:

   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 a decay product of ²⁵⁶Db
8. Not directly synthesized, occurs as a decay product of ²⁵⁷Db
9. Not directly synthesized, occurs as a decay product of ²⁵⁸Db
10. Not directly synthesized, occurs as a decay product of ²⁹⁴Ts

Nucleosynthesis

Cold fusion

²⁰⁵Tl(⁵⁰Ti,xn)^255−xLr (x=2?)

This reaction was studied in a series of experiments in 1976 by Yuri Oganessian and his team at the FLNR. Evidence was provided for the formation of ²⁵³Lr in the 2n exit channel.

²⁰³Tl(⁵⁰Ti,xn)^253−xLr

This reaction was studied in a series of experiments in 1976 by Yuri Oganessian and his team at the FLNR.

²⁰⁸Pb(⁴⁸Ti,pxn)^255−xLr (x=1?)

This reaction was reported in 1984 by Yuri Oganessian at the FLNR. The team was able to detect decays of ²⁴⁶Cf, a descendant of ²⁵⁴Lr.

²⁰⁸Pb(⁴⁵Sc,xn)^253−xLr

This reaction was studied in a series of experiments in 1976 by Yuri Oganessian and his team at the FLNR. Results are not readily available.

²⁰⁹Bi(⁴⁸Ca,xn)^257−xLr (x=2)

This reaction has been used to study the spectroscopic properties of ²⁵⁵Lr. The team at GANIL used the reaction in 2003 and the team at the FLNR used it between 2004–2006 to provide further information for the decay scheme of ²⁵⁵Lr. The work provided evidence for an isomeric level in ²⁵⁵Lr.

Hot fusion

²⁴³Am(¹⁸O,xn)^261−xLr (x=5)

This reaction was first studied in 1965 by the team at the FLNR. They were able to detect activity with a characteristic decay of 45 seconds, which was assigned to²⁵⁶Lr or ²⁵⁷Lr. Later work suggests an assignment to ²⁵⁶Lr. Further studies in 1968 produced an 8.35–8.60 MeV alpha activity with a half-life of 35 seconds. This activity was also initially assigned to ²⁵⁶Lr or ²⁵⁷Lr and later to solely ²⁵⁶Lr.

²⁴³Am(¹⁶O,xn)^259−xLr (x=4)

This reaction was studied in 1970 by the team at the FLNR. They were able to detect an 8.38 MeV alpha activity with a half-life of 20s. This was assigned to²⁵⁵Lr.

²⁴⁸Cm(¹⁵N,xn)^263−xLr (x=3,4,5)

This reaction was studied in 1971 by the team at the LBNL in their large study of lawrencium isotopes. They were able to assign alpha activities to²⁶⁰Lr,²⁵⁹Lr and ²⁵⁸Lr from the 3-5n exit channels.

²⁴⁸Cm(¹⁸O,pxn)^265−xLr (x=3,4)

This reaction was studied in 1988 at the LBNL in order to assess the possibility of producing ²⁶²Lr and ²⁶¹Lr without using the exotic ²⁵⁴Es target. It was also used to attempt to measure an electron capture (EC) branch in ^261mRf from the 5n exit channel. After extraction of the Lr(III) component, they were able to measure the spontaneous fission of ²⁶¹Lr with an improved half-life of 44 minutes. The production cross-section was 700 pb. On this basis, a 14% electron capture branch was calculated if this isotope was produced via the 5n channel rather than the p4n channel. A lower bombarding energy (93 MeV c.f. 97 MeV) was then used to measure the production of ²⁶²Lr in the p3n channel. The isotope was successfully detected and a yield of 240 pb was measured. The yield was lower than expected compared to the p4n channel. However, the results were judged to indicate that the ²⁶¹Lr was most likely produced by a p3n channel and an upper limit of 14% for the electron capture branch of ^261mRf was therefore suggested.

²⁴⁶Cm(¹⁴N,xn)^260−xLr (x=3?)

This reaction was studied briefly in 1958 at the LBNL using an enriched ²⁴⁴Cm target (5% ²⁴⁶Cm). They observed a ~9 MeV alpha activity with a half-life of ~0.25 seconds. Later results suggest a tentative assignment to ²⁵⁷Lr from the 3n channel

²⁴⁴Cm(¹⁴N,xn)^258−xLr

This reaction was studied briefly in 1958 at the LBNL using an enriched ²⁴⁴Cm target (5% ²⁴⁶Cm). They observed a ~9 MeV alpha activity with a half-life of ~0.25s. Later results suggest a tentative assignment to ²⁵⁷Lr from the 3n channel with the ²⁴⁶Cm component. No activities assigned to reaction with the ²⁴⁴Cm component have been reported.

²⁴⁹Bk(¹⁸O,αxn)^263−xLr (x=3)

This reaction was studied in 1971 by the team at the LBNL in their large study of lawrencium isotopes. They were able to detect an activity assigned to ²⁶⁰Lr. The reaction was further studied in 1988 to study the aqueous chemistry of lawrencium. A total of 23 alpha decays were measured for ²⁶⁰Lr, with a mean energy of 8.03 MeV and an improved half-life of 2.7 minutes. The calculated cross-section was 8.7 nb.

²⁵²Cf(¹¹B,xn)^263−xLr (x=5,7??)

This reaction was first studied in 1961 at the University of California by Albert Ghiorso by using a californium target (52% ²⁵²Cf). They observed three alpha activities of 8.6, 8.4 and 8.2 MeV, with half-lives of about 8 and 15 seconds, respectively. The 8.6 MeV activity was tentatively assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁸Lr, resulting from the 5n exit channel. The 8.4 MeV activity was also assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁶Lr. This is most likely from the 33% ²⁵⁰Cf component in the target rather than from the 7n channel. The 8.2 MeV was subsequently associated with nobelium.

²⁵²Cf(¹⁰B,xn)^262−xLr (x=4,6)

This reaction was first studied in 1961 at the University of California by Albert Ghiorso by using a californium target (52% ²⁵²Cf). They observed three alpha activities of 8.6, 8.4 and 8.2 MeV, with half-lives of about 8 and 15 seconds, respectively. The 8.6 MeV activity was tentatively assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁸Lr. The 8.4 MeV activity was also assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁶Lr. The 8.2 MeV was subsequently associated with nobelium.

²⁵⁰Cf(¹⁴N,αxn)^260−xLr (x=3)

This reaction was studied in 1971 at the LBNL. They were able to identify a 0.7s alpha activity with two alpha lines at 8.87 and 8.82 MeV. This was assigned to²⁵⁷Lr.

²⁴⁹Cf(¹¹B,xn)^260−xLr (x=4)

This reaction was first studied in 1970 at the LBNL in an attempt to study the aqueous chemistry of lawrencium. They were able to measure a Lr³⁺ activity. The reaction was repeated in 1976 at Oak Ridge and 26s ²⁵⁶Lr was confirmed by measurement of coincident X-rays.

²⁴⁹Cf(¹²C,pxn)^260−xLr (x=2)

This reaction was studied in 1971 by the team at the LBNL. They were able to detect an activity assigned to ²⁵⁸Lr from the p2n channel.

²⁴⁹Cf(¹⁵N,αxn)^260−xLr (x=2,3)

This reaction was studied in 1971 by the team at the LBNL. They were able to detect an activities assigned to ²⁵⁸Lr and ²⁵⁷Lr from the α2n and α3n and channels. The reaction was repeated in 1976 at Oak Ridge and the synthesis of ²⁵⁸Lr was confirmed.

²⁵⁴Es + ²²Ne – transfer

This reaction was studied in 1987 at the LLNL. They were able to detect new spontaneous fission (SF) activities assigned to ²⁶¹Lr and ²⁶²Lr, resulting from transfer from the ²²Ne nuclei to the ²⁵⁴Es target. In addition, a 5 ms SF activity was detected in delayed coincidence with nobelium K-shell X-rays and was assigned to ²⁶²No, resulting from the electron capture of ²⁶²Lr.

Decay products

Isotopes of lawrencium have also been identified in the decay of heavier elements. Observations to date are summarised in the table below:

List of lawrencium isotopes produced as other nuclei decay products

Parent nuclide	Observed lawrencium isotope
^294Ts, ^290Mc, ^286Nh, ^282Rg, ^278Mt, ^274Bh, ^270Db	^266Lr
^267Bh, ^263Db	^259Lr
^278Nh, ^274Rg, ^270Mt, ^266Bh, ^262Db	^258Lr
^261Db	^257Lr
^272Rg, ^268Mt, ^264Bh, ^260Db	^256Lr
^259Db	^255Lr
^266Mt, ^262Bh, ^258Db	^254Lr
^261Bh, ^257Db^g,m	^253Lr^g,m
^260Bh, ^256Db	^252Lr
^255Db	^251Lr

Isotopes

Summary of all lawrencium isotopes known

Isotope	Year discovered	discovery reaction
^251Lr	2005	^209Bi(^48Ti,2n)
^252Lr	2001	^209Bi(^50Ti,3n)
^253Lr^g	1985	^209Bi(^50Ti,2n)
^253Lr^m	2001	^209Bi(^50Ti,2n)
^254Lr	1985	^209Bi(^50Ti,n)
^255Lr	1970	^243Am(^16O,4n)
^256Lr	1961? 1965? 1968? 1971	^252Cf(^10B,6n)
^257Lr	1958? 1971	^249Cf(^15N,α3n)
^258Lr	1961? 1971	^249Cf(^15N,α2n)
^259Lr	1971	^248Cm(^15N,4n)
^260Lr	1971	^248Cm(^15N,3n)
^261Lr	1987	^254Es + ^22Ne
^262Lr	1987	^254Es + ^22Ne
^266Lr	2014	^249Bk(^48Ca,7α3n)

Thirteen isotopes of lawrencium plus one isomer have been synthesized with ²⁶⁶Lr being the longest-lived and the heaviest, with a half-life of 11 hours. ²⁵¹Lr is the lightest isotope of lawrencium to be produced to date.

Lawrencium-253 isomers

A study of the decay properties of ²⁵⁷Db (see dubnium) in 2001 by Hessberger et al. at the GSI provided some data for the decay of ²⁵³Lr. Analysis of the data indicated the population of two isomeric levels in ²⁵³Lr from the decay of the corresponding isomers in ²⁵⁷Db. The ground state was assigned spin and parity of 7/2−, decaying by emission of an 8794 keV alpha particle with a half-life of 0.57 s. The isomeric level was assigned spin and parity of 1/2−, decaying by emission of an 8722 keV alpha particle with a half-life of 1.49 s.

Lawrencium-255 isomers

Recent work on the spectroscopy of ²⁵⁵Lr formed in the reaction ²⁰⁹Bi(⁴⁸Ca,2n)²⁵⁵Lr has provided evidence for an isomeric level.

References

1. Leppänen, A.-P. (2005). Alpha-decay and decay-tagging studies of heavy elements using the RITU separator (PDF) (Thesis). University of Jyväskylä. pp. 83–100. ISBN 978-951-39-3162-9. ISSN 0075-465X.

• Isotope masses from:
  • M. Wang; G. Audi; A. H. Wapstra; F. G. Kondev; M. MacCormick; X. Xu; et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references" (PDF). Chinese Physics C. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003.
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• 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.
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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
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  • 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.