Lawrencium

iso	NA	half-life	DM	DE (MeV)	DP
²⁶²Lr	syn	3.6 h	EC		²⁶²No
²⁶¹Lr	syn	44 m	SF/EC?
²⁶⁰Lr	syn	2.7 m	alpha	8.04	²⁵⁶Md
²⁵⁹Lr	syn	6.2 s	78% alpha	8.44	²⁵⁵Md
²⁵⁹Lr	syn	6.2 s	22% SF
²⁵⁸Lr	syn	4.1 s	alpha	8.68,8.65,8.62,8.59	²⁵⁴Md
²⁵⁷Lr	syn	0.65 s	alpha	8.86,8.80	²⁵³Md
²⁵⁶Lr	syn	27 s	alpha	8.62,8.52,8.32...	²⁵²Md
²⁵⁵Lr	syn	21.5 s	alpha	8.43,8.37	²⁵¹Md
²⁵⁴Lr	syn	13 s	78% alpha	8.46,8.41	²⁵⁰Md
²⁵⁴Lr	syn	13 s	22% EC		²⁵⁴No
²⁵³Lr^m	syn	0.57 s	alpha	8.79	²⁴⁹Md
²⁵³Lr^g	syn	1.49 s	92% alpha	8.72	²⁴⁹Md
²⁵³Lr^g	syn	1.49 s	8% SF
²⁵²Lr	syn	0.36 s	alpha	9.02,8.97	²⁴⁸Md

Lawrencium (pronounced /ləˈrɛnsiəm/, lə-REN-see-əm) is a radioactive synthetic element with the symbol Lr (formerly Lw) and atomic number 103.

Its most stable known isotope is ²⁶²Lr, with a half-life of approximately 3.6 hours. Little is known of the chemistry but there is strong evidence for the formation of a trivalent ion in aqueous solution, confirming lawrencium's place as the final member of the actinide elements.

1 Official discovery
2 Naming
3 Electronic structure
4 Physical characteristics
5 Classification
6 Experimental chemistry
7 Isotopes
8 History of synthesis of isotopes by laboratory fusion reactions
9 History of synthesis of isotopes by hot fusion
10 Synthesis of isotopes as decay products
11 Chronology of isotope discovery
12 Isomerism in lawrencium nuclides
- 12.1 ²⁵⁵Lr
- 12.2 ²⁵³Lr
13 Chemical yields of isotopes
- 13.1 Cold fusion
14 References
15 Further reading
16 External links

Official discovery

Lawrencium was first synthesized by the nuclear-physics team of Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, Robert M. Latimer, and their co-workers on February 14, 1961, at the Lawrence Radiation Laboratory (now called the Lawrence Berkeley National Laboratory) at the University of California. The first atoms of lawrencium were produced by bombarding a three-milligram target consisting of three isotopes of the element californium with boron-10 and boron-11 nuclei from the Heavy Ion Linear Accelerator (HILAC).

The Berkeley team reported that the isotope ²⁵⁷103 was detected in this manner, and that it decayed by emitting an 8.6 MeV alpha particle with a half-life of about eight seconds. This identification was later corrected to be ²⁵⁸Lr.

25298Cf + 115B → 263–x103Lr → 258103Lr + 5 10n

The team at the University of California suggested the name lawrencium, and the symbol "Lw", for the new element, but "Lw" was not adopted, and "Lr" was officially accepted instead.

In 1967, nuclear-physics researchers in Dubna, Russia, reported that they were not able to confirm assignment of an alpha emitter with a half-life of eight seconds to ²⁵⁷103. This isotope was later deduced to be ²⁵⁸Lr. Instead, the Dubna team reported an isotope with a half-life of about 45 seconds as ²⁵⁶Lr.

24395Am + 188O → 261–x103Lr → 256103Lr + 5 10n

Further experiments in 1969, conducted by Travis Anselm and his colleagues, demonstrated an actinide chemistry for the new element. This placed lawrencium in row 8B of the periodic table. In 1971, the nuclear physics team at the University of California at Berkeley successfully performed a whole series of experiments aimed at measuring the nuclear decay properties of the lawrencium isotopes with mass numbers from 255 through 260.

In 1992, the IUPAC Trans-fermium Working Group (TWG) officially recognized the nuclear physics teams at Dubna and Berkeley as the co-discoverers of lawrencium.

Naming

The origin of the name,ratified by the American Chemical Society, is in reference to the nuclear-physicist Ernest O. Lawrence, of the University of California, who invented the cyclotron particle accelerator. The symbol Lw was used originally, but in 1963 this was changed to Lr. In August 1997, the International Union of Pure and Applied Chemistry (IUPAC) ratified the name lawrencium and the symbol Lr during a meeting in Geneva.

Electronic structure

Lawrencium is element 103 in the standard Periodic Table of the Elements. In the extended periodic table, it is the first member of the 6d-block, so in accordance with the Madelung rule, its electronic configuration should be [Rn]7s²5f¹⁴6d¹. However, results from quantum mechanical research have suggested that this configuration is incorrect, and is in fact [Rn]7s²5f¹⁴7p¹. A direct measurement of this is not possible. Though early calculations gave conflicting results^[1], more recent studies and calculations confirm the suggestion^[2] ^[3].

Physical characteristics

The gross appearance of lawrencium is unknown, however it is most likely to be a silvery-white or grey metal. If sufficient amounts of lawrencium were produced, it would pose a serious radiation hazard.

Classification

A strict correlation between the periodic table blocks and the orbital-shell configurations for neutral atoms would classify lawrencium as a transition metal because it could be classed as a d-block element. One could also argue that lawrencium belongs in the post-transition metal, or poor metal, category due to its predicted 7p orbital-shell electron and its lack of electrons in the 6d orbital shell. However, lawrencium is classified as an actinide element according to the IUPAC recommendations.^[4] In order of increasing atomic number, lawrencium is the final member of the actinide series of rare earth elements.

Experimental chemistry

Gaseous phase

The first gaseous-phase studies of lawrencium were reported in 1969 by a nuclear-physics team at the Flerov Laboratory of Nuclear Reactions (FLNR) in the Soviet Union. They used the nuclear reaction ²⁴³Am+¹⁸O to produce lawrencium nuclei, which they then exposed to a stream of chlorine gas, and a volatile chloride product was formed. This product was deduced to be ²⁵⁶LrCl₃, and this confirmed that lawrencium is a typical actinide element.

Aqueous phase

The first aqueous-phase studies of lawrencium were reported in 1970 by a nuclear-physics team at the Lawrence Berkeley National Laboratory in California. This team used the nuclear reaction ²⁴⁹Cf+¹¹B to produce lawrencium nuclei. They were able to show that lawrencium forms a trivalent ion, similar to those of the other actinide elements, but in contrast with that of nobelium. Further experiments in 1988 confirmed the formation of a trivalent lawrencium(III) ion using anion-exchange chromatography using α-hydroxyisobutyrate (α-HIB) complex. Comparison of the elution time with other actinides allowed a determination of 88.6 picometers for the ionic radius for Lr³⁺. Attempts to reduce lawrencium in the Lr(III) ionization state to Lr(I) using the potent reducing agent hydroxylamine hydrochloride were unsuccessful.

Summary of compounds

Formula	Names(s)
LrCl₃	lawrencium trichloride ; lawrencium(III) chloride

Isotopes

Twelve isotopes of lawrencium have been synthesized with ²⁶²Lr being the longest-lived and the heaviest, with a half-life of 216 minutes. ²⁵²Lr is the lightest isotope of lawrencium to be produced to date.

History of synthesis of isotopes by laboratory fusion reactions

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.

History of synthesis of isotopes by 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 to ²⁵⁶Lr 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 to ²⁵⁵Lr.

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 to ²⁶⁰Lr,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 to ²⁵⁷Lr.

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.

Synthesis of isotopes as decay products

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

Evaporation residue	Observed Lr isotope
²⁶⁷Bh, ²⁶³Db	²⁵⁹Lr
²⁷⁸Uut, 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

Chronology of isotope discovery

Isotope	Year discovered	discovery reaction
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

Isomerism in lawrencium nuclides

²⁵⁵Lr

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

²⁵³Lr

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 0.57s. 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.

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing lawrencium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.