nobelium ← lawrencium → rutherfordium Lu
↑
Lr
↓
(Upt) 103Lr Periodic table Appearance unknown, probably silvery, white or metallic gray General properties Name, symbol, number lawrencium, Lr, 103 Element category actinide Category notes Sometimes considered a transition metal Group, period, block n/a, 7, d Standard atomic weight [262] g·mol−1 Electron configuration [Rn] 5f14 7s2 7p1 Electrons per shell 2, 8, 18, 32, 32, 8, 3 (Image) Physical properties Phase solid (presumably) Atomic properties Oxidation states 3 Ionization energies 1st: 443.8 kJ·mol−1 2nd: 1428.0 kJ·mol−1 3rd: 2219.1 kJ·mol−1 Miscellanea CAS registry number 22537-19-5 Most stable isotopes Main article: Isotopes of 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 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 22% EC 254No 253Lrm syn 0.57 s alpha 8.79 249Md 253Lrg syn 1.49 s 92% alpha 8.72 249Md 8% SF 252Lr syn 0.36 s alpha 9.02,8.97 248Md This box: view • talk • edit Lawrencium Common English pronunciation of lawrencium Problems listening to this file? See media help.
↑
Lr
↓
(Upt) 103Lr Periodic table Appearance unknown, probably silvery, white or metallic gray General properties Name, symbol, number lawrencium, Lr, 103 Element category actinide Category notes Sometimes considered a transition metal Group, period, block n/a, 7, d Standard atomic weight [262] g·mol−1 Electron configuration [Rn] 5f14 7s2 7p1 Electrons per shell 2, 8, 18, 32, 32, 8, 3 (Image) Physical properties Phase solid (presumably) Atomic properties Oxidation states 3 Ionization energies 1st: 443.8 kJ·mol−1 2nd: 1428.0 kJ·mol−1 3rd: 2219.1 kJ·mol−1 Miscellanea CAS registry number 22537-19-5 Most stable isotopes Main article: Isotopes of 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 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 22% EC 254No 253Lrm syn 0.57 s alpha 8.79 249Md 253Lrg syn 1.49 s 92% alpha 8.72 249Md 8% SF 252Lr syn 0.36 s alpha 9.02,8.97 248Md This box: view • talk • edit Lawrencium Common English pronunciation of lawrencium Problems listening to this file? See media help.
Official discovery Lawrencium was made by Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, and Robert M. Latimer on February 14, 1961 at the Lawrence Radiation Laboratory (now called Lawrence Berkeley National Laboratory) on the University of California, Berkeley campus. It was produced by bombarding a three milligram target composed of three isotopes of californium with boron-10 and B-11 ions in the Heavy Ion Linear Accelerator (HILAC).
The Berkeley team reported that the isotope 257103 was detected in this manner and decayed by emitting an 8.6 MeV alpha particle with a half-life of ~8 seconds. The assignment was later corrected to 258Lr.
25298Cf + 115B → 263−x103Lr → 258103Lr + 5 10n The team suggested the name lawrencium (Lw) for the new element.
In 1967, researchers in Dubna, Russia reported that they were not able to confirm an alpha emitter with a half-life of 8 seconds as 257103. This assignment has since been changed to 258Lr. Instead, they reported a 45s activity assigned to 256Lr.
24395Am + 188O → 261−x103Lr → 256103Lr + 5 10n Further work in 1969 indicated an actinoid chemistry for the new element founded by Travis Anselm in 8B. In 1971, the team at the University of California performed a whole series of experiments aimed at measuring the decay properties of lawrencium isotopes with mass numbers from 255-260.
In 1992, The IUPAC/IUPAP Transfermium Working Group (TWG) officially recognised the Dubna and Berkeley teams as co-discoverers of lawrencium.
[edit] Naming The origin of the name, preferred by the American Chemical Society, is in reference to Ernest O. Lawrence, inventor of the cyclotron. The symbol Lw originally was used but in 1963 it was changed to Lr. In August 1997 the International Union of Pure and Applied Chemistry (IUPAC) ratified the name lawrencium and symbol Lr during a meeting in Geneva.
Lawrencium has also been referred to as eka-lutetium.[citation needed]
[edit] Electronic structure Lawrencium is element 103 in the Periodic Table. The two forms of the projected electronic structure are:
Bohr model 2, 8, 18, 32, 32, 9, 2 Quantum mechanical model 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f146d1 There has been a suggestion that the electron configuration could be [Rn]7s25f147p1 instead. Direct measurement is impossible, however, and calculations have given conflicting results.[1]
[edit] Physical characteristics The appearance of this element is unknown, however it is most likely silvery-white or gray and metallic. If sufficient amounts of lawrencium were produced, it would pose a radiation hazard. Contrary to some sources, bulk properties of this element, such as the melting point, have not been possible to measure to date. However, the 1st, 2nd and 3rd ionization energies have been measured[citation needed].
[edit] Periodic classification A strict correlation between periodic table blocks and electron configuration for neutral atoms would describe lawrencium as a transition metal because it should be classed as a d-block element. However, it is classified as an actinoid according to IUPAC recommendations.[2]
[edit] Experimental chemistry [edit] Gas phase chemistry The first gas phase studies were reported in 1969 by a team at the Flerov Laboratory of Nuclear Reactions (FLNR). They used the reaction 243Am+18O to produce lawrencium nuclei which reacted with a stream of chlorine gas to form a volatile chloride component. The product was assigned to 256LrCl3 and confirmed that lawrencium was a typical actinide.
[edit] Aqueous phase chemistry The first liquid phase studies were reported in 1970 by the team at the LBNL. They used the reaction 249Cf+11B to produce lawrencium nuclei. They were able to show that lawrencium formed a trivalent ion, similar to other actinides but in stark contrast to nobelium. Further work 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 pm for the ionic radius for Lr3+. Attempts to reduce Lr(III) to Lr(I) using the potent reducing agent hydroxylamine hydrochloride were unsuccessful.
[edit] Summary of compounds and complex ions Formula Names(s) LrCl3 lawrencium trichloride ; lawrencium(III) chloride [edit] Isotopes Main article: Isotopes of lawrencium Twelve isotopes of lawrencium have been synthesized with 262Lr being the longest-lived and heaviest, with a half-life of 216 minutes. 252Lr is the lightest isotope known to date.
[edit] History of synthesis of isotopes by cold fusion [edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] History of synthesis of isotopes by hot fusion [edit] 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 a 45s activity 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 35s. This activity was also initially assigned to 256Lr or 257Lr and later to solely 256Lr.
[edit] 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.
[edit] 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.
[edit] 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 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% EC 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 EC branch of 261mRf was therefore suggested.
[edit] 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
[edit] 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.
[edit] 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.
[edit] 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 MeV, 8.4 MeV and 8.2 MeV, with half-lives of ~8s and 15s, 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.
[edit] 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 MeV, 8.4 MeV and 8.2 MeV, with half-lives of ~8s and 15s, 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 254Es + 22Ne - transfer This reaction was studied in 1987 at the LLNL. They were able to detect new 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 X-rays and was assigned to 262No, resulting from the EC of 262Lr.
[edit] 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, 257Dbg,m 253Lrg,m 260Bh , 256Db 252Lr [edit] Chronology of isotope discovery Isotope Year discovered discovery reaction 252Lr 2001 209Bi(50Ti,3n) 253Lrg 1985 209Bi(50Ti,2n) 253Lrm 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 [edit] Isomerism in lawrencium nuclides [edit] 255Lr Recent work on the spectroscopy of 255Lr formed in the reaction 209Bi(48Ca,2n)255Lr has provided evidence for an isomeric level.
[edit] 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 1.49s.
[edit] Chemical yields of isotopes [edit] Cold fusion The table below provides cross-sections and excitation energies for cold fusion reactions producing rutherfordium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
Projectile Target CN 1n 2n 3n 48Ca 209Bi 257Lr
The Berkeley team reported that the isotope 257103 was detected in this manner and decayed by emitting an 8.6 MeV alpha particle with a half-life of ~8 seconds. The assignment was later corrected to 258Lr.
25298Cf + 115B → 263−x103Lr → 258103Lr + 5 10n The team suggested the name lawrencium (Lw) for the new element.
In 1967, researchers in Dubna, Russia reported that they were not able to confirm an alpha emitter with a half-life of 8 seconds as 257103. This assignment has since been changed to 258Lr. Instead, they reported a 45s activity assigned to 256Lr.
24395Am + 188O → 261−x103Lr → 256103Lr + 5 10n Further work in 1969 indicated an actinoid chemistry for the new element founded by Travis Anselm in 8B. In 1971, the team at the University of California performed a whole series of experiments aimed at measuring the decay properties of lawrencium isotopes with mass numbers from 255-260.
In 1992, The IUPAC/IUPAP Transfermium Working Group (TWG) officially recognised the Dubna and Berkeley teams as co-discoverers of lawrencium.
[edit] Naming The origin of the name, preferred by the American Chemical Society, is in reference to Ernest O. Lawrence, inventor of the cyclotron. The symbol Lw originally was used but in 1963 it was changed to Lr. In August 1997 the International Union of Pure and Applied Chemistry (IUPAC) ratified the name lawrencium and symbol Lr during a meeting in Geneva.
Lawrencium has also been referred to as eka-lutetium.[citation needed]
[edit] Electronic structure Lawrencium is element 103 in the Periodic Table. The two forms of the projected electronic structure are:
Bohr model 2, 8, 18, 32, 32, 9, 2 Quantum mechanical model 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f146d1 There has been a suggestion that the electron configuration could be [Rn]7s25f147p1 instead. Direct measurement is impossible, however, and calculations have given conflicting results.[1]
[edit] Physical characteristics The appearance of this element is unknown, however it is most likely silvery-white or gray and metallic. If sufficient amounts of lawrencium were produced, it would pose a radiation hazard. Contrary to some sources, bulk properties of this element, such as the melting point, have not been possible to measure to date. However, the 1st, 2nd and 3rd ionization energies have been measured[citation needed].
[edit] Periodic classification A strict correlation between periodic table blocks and electron configuration for neutral atoms would describe lawrencium as a transition metal because it should be classed as a d-block element. However, it is classified as an actinoid according to IUPAC recommendations.[2]
[edit] Experimental chemistry [edit] Gas phase chemistry The first gas phase studies were reported in 1969 by a team at the Flerov Laboratory of Nuclear Reactions (FLNR). They used the reaction 243Am+18O to produce lawrencium nuclei which reacted with a stream of chlorine gas to form a volatile chloride component. The product was assigned to 256LrCl3 and confirmed that lawrencium was a typical actinide.
[edit] Aqueous phase chemistry The first liquid phase studies were reported in 1970 by the team at the LBNL. They used the reaction 249Cf+11B to produce lawrencium nuclei. They were able to show that lawrencium formed a trivalent ion, similar to other actinides but in stark contrast to nobelium. Further work 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 pm for the ionic radius for Lr3+. Attempts to reduce Lr(III) to Lr(I) using the potent reducing agent hydroxylamine hydrochloride were unsuccessful.
[edit] Summary of compounds and complex ions Formula Names(s) LrCl3 lawrencium trichloride ; lawrencium(III) chloride [edit] Isotopes Main article: Isotopes of lawrencium Twelve isotopes of lawrencium have been synthesized with 262Lr being the longest-lived and heaviest, with a half-life of 216 minutes. 252Lr is the lightest isotope known to date.
[edit] History of synthesis of isotopes by cold fusion [edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] History of synthesis of isotopes by hot fusion [edit] 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 a 45s activity 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 35s. This activity was also initially assigned to 256Lr or 257Lr and later to solely 256Lr.
[edit] 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.
[edit] 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.
[edit] 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 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% EC 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 EC branch of 261mRf was therefore suggested.
[edit] 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
[edit] 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.
[edit] 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.
[edit] 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 MeV, 8.4 MeV and 8.2 MeV, with half-lives of ~8s and 15s, 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.
[edit] 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 MeV, 8.4 MeV and 8.2 MeV, with half-lives of ~8s and 15s, 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 254Es + 22Ne - transfer This reaction was studied in 1987 at the LLNL. They were able to detect new 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 X-rays and was assigned to 262No, resulting from the EC of 262Lr.
[edit] 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, 257Dbg,m 253Lrg,m 260Bh , 256Db 252Lr [edit] Chronology of isotope discovery Isotope Year discovered discovery reaction 252Lr 2001 209Bi(50Ti,3n) 253Lrg 1985 209Bi(50Ti,2n) 253Lrm 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 [edit] Isomerism in lawrencium nuclides [edit] 255Lr Recent work on the spectroscopy of 255Lr formed in the reaction 209Bi(48Ca,2n)255Lr has provided evidence for an isomeric level.
[edit] 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 1.49s.
[edit] Chemical yields of isotopes [edit] Cold fusion The table below provides cross-sections and excitation energies for cold fusion reactions producing rutherfordium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.
Projectile Target CN 1n 2n 3n 48Ca 209Bi 257Lr
