Isotopes of seaborgium

Isotopes of seaborgium  (₁₀₆Sg)

Main isotopes [1] Decay abun­dance half-life (t1/2) mode pro­duct 265Sg synth 8.5 s α 261Rf 265mSg synth 14.4 s α 261mRf 267Sg synth 80 s α17% 263Rf SF 83% – 268Sg synth 13 s [2] SF 269Sg synth 14 min [3] α 265Rf 271Sg synth 31 s [4] α73% 267Rf SF27%

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Seaborgium (₁₀₆Sg) is a synthetic element and so has no stable isotopes. A standard atomic weight cannot be given. The first isotope to be synthesized was ²⁶³Sg in 1974. There are 13 known radioisotopes from ²⁵⁸Sg to ²⁷¹Sg and 4 known isomers (^259mSg, ^261mSg, ^263mSg, and ^265mSg). The longest-lived isotope is ²⁶⁹Sg with a half-life of 14 minutes.

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]
	Excitation energy [n 5]
258Sg [1]	106	152	258.11298(44)#	2.7(5) ms [2.6+0.6 −0.4 ms]	SF	(various)	0+
259Sg [5]	106	153	259.11440(13)#	402(56) ms	α	255Rf	(11/2−)
					β+ (<1%)	259Db
					SF (rare)	(various)
259mSg	87 keV			226(27) ms	α (97%)	261Sg	(1/2+)
					SF (3%)	(various)
					β+ (<1%)	259Db
260Sg [1]	106	154	260.114384(22)	4.95(33) ms	SF (71%)	(various)	0+
					α (29%)	256Rf
261Sg [1]	106	155	261.115949(20)	183(5) ms	α (98.1%)	257Rf	(3/2+)
					β+ (1.3%)	261Db
					SF (0.6%)	(various)
261mSg	100(50)# keV			9.3(1.8) µs [9.0+2.0 −1.5 μs]	IT	261Sg	7/2+#
262Sg [1]	106	156	262.11634(4)	10.3(1.7) ms	SF (94%)	(various)	0+
					α (6%)	258Rf
263Sg [1]	106	157	263.11829(10)#	940(140) ms	α (87%)	259Rf	9/2+#
					SF (13%)	(various)
263mSg	51(19)# keV			420(100) ms	α	259Rf	3/2+#
264Sg	106	158	264.11893(30)#	37 ms	SF	(various)	0+
265Sg [6]	106	159	265.12109(13)#	8.5+2.6 −1.6 s	α	261Rf
265mSg				14.4+3.7 −2.5 s	α	261mRf
266Sg [n 6] [1]	106	160	266.12198(26)#	390(110) ms	SF	(various)	0+
267Sg [n 7] [7]	106	161	267.12436(30)#	80+60 −20 s	SF (83%)	(various)
					α (17%)	263Rf
268Sg [n 8] [2]	106	162	268.12539(50)#	13+17 −4 s	SF	(various)	0+
269Sg [n 9]	106	163	269.12863(39)#	14+10 −4 min [3]	α	265Rf
271Sg [n 10]	106	165	271.13393(63)#	31+13 −7 s [4]	α (73%)	267Rf	3/2+#
					SF (27%)	(various)
This table header & footer: view

1. ^mSg – 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
   SF:	Spontaneous fission

5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Not directly synthesized, occurs as decay product of ²⁷⁰Hs
7. Not directly synthesized, occurs as decay product of ²⁷¹Hs
8. Not directly synthesized, occurs as decay product of ²⁷⁶Ds
9. Not directly synthesized, occurs in the decay chain of ²⁸⁵Fl
10. Not directly synthesized, occurs in the decay chain of ²⁸⁷Fl

Nucleosynthesis

Target	Projectile	CN	Attempt result
208Pb	54Cr	262Sg	Successful reaction
207Pb	54Cr	261Sg	Successful reaction
206Pb	54Cr	260Sg	Failure to date
208Pb	52Cr	260Sg	Successful reaction
209Bi	51V	260Sg	Successful reaction
238U	30Si	268Sg	Successful reaction
244Pu	26Mg	270Sg	Reaction yet to be attempted
248Cm	22Ne	270Sg	Successful reaction
249Cf	18O	267Sg	Successful reaction

Cold fusion

This section deals with the synthesis of nuclei of seaborgium by so-called "cold" fusion reactions. These are processes that create compound nuclei at low excitation energy (~10–20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.

²⁰⁸Pb(⁵⁴Cr,xn)^262−xSg (x=1,2,3)

The first attempt to synthesise seaborgium in cold fusion reactions was performed in September 1974 by a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna. They reported producing a 0.48 s spontaneous fission (SF) activity, which they assigned to the isotope ²⁵⁹Sg. Based on later evidence it was suggested that the team most likely measured the decay of ²⁶⁰Sg and its daughter ²⁵⁶Rf. The TWG concluded that, at the time, the results were insufficiently convincing. ^[8]

The Dubna team revisited this problem in 1983–1984 and were able to detect a 5 ms SF activity assigned directly to ²⁶⁰Sg. ^[8]

The team at GSI studied this reaction for the first time in 1985 using the improved method of correlation of genetic parent-daughter decays. They were able to detect ²⁶¹Sg (x=1) and ²⁶⁰Sg and measured a partial 1n neutron evaporation excitation function. ^[9]

In December 2000, the reaction was studied by a team at GANIL, France; they were able to detect 10 atoms of ²⁶¹Sg and 2 atoms of ²⁶⁰Sg to add to previous data on the reaction.

After a facility upgrade, the GSI team measured the 1n excitation function in 2003 using a metallic lead target. Of significance, in May 2003, the team successfully replaced the lead-208 target with more resistant lead(II) sulfide targets (PbS), which will allow more intense beams to be used in the future. They were able to measure the 1n,2n and 3n excitation functions and performed the first detailed alpha-gamma spectroscopy on the isotope ²⁶¹Sg. They detected ~1600 atoms of the isotope and identified new alpha lines as well as measuring a more accurate half-life and new EC and SF branchings. Furthermore, they were able to detect the K X-rays from the daughter rutherfordium isotope for the first time. They were also able to provide improved data for ²⁶⁰Sg, including the tentative observation of an isomeric level. The study was continued in September 2005 and March 2006. The accumulated work on ²⁶¹Sg was published in 2007. ^[10] Work in September 2005 also aimed to begin spectroscopic studies on ²⁶⁰Sg.

The team at the LBNL recently restudied this reaction in an effort to look at the spectroscopy of the isotope ²⁶¹Sg. They were able to detect a new isomer, ^261mSg, decaying by internal conversion into the ground state. In the same experiment, they were also able to confirm a K-isomer in the daughter ²⁵⁷Rf, namely ^257m2Rf. ^[11]

²⁰⁷Pb(⁵⁴Cr,xn)^261−xSg (x=1,2)

The team at Dubna also studied this reaction in 1974 with identical results as for their first experiments with a lead-208 target. The SF activities were first assigned to ²⁵⁹Sg and later to ²⁶⁰Sg and/or ²⁵⁶Rf. Further work in 1983–1984 also detected a 5 ms SF activity assigned to the parent ²⁶⁰Sg. ^[8]

The GSI team studied this reaction for the first time in 1985 using the method of correlation of genetic parent-daughter decays. They were able to positively identify ²⁵⁹Sg as a product from the 2n neutron evaporation channel. ^[9]

The reaction was further used in March 2005 using PbS targets to begin a spectroscopic study of the even-even isotope ²⁶⁰Sg.

²⁰⁶Pb(⁵⁴Cr,xn)^260−xSg

This reaction was studied in 1974 by the team at Dubna. It was used to assist them in their assignment of the observed SF activities in reactions using Pb-207 and Pb-208 targets. They were unable to detect any SF, indicating the formation of isotopes decaying primarily by alpha decay. ^[8]

²⁰⁸Pb(⁵²Cr,xn)^260−xSg (x=1,2)

The team at Dubna also studied this reaction in their series of cold fusion reactions performed in 1974. Once again they were unable to detect any SF activities. ^[8] The reaction was revisited in 2006 by the team at LBNL as part of their studies on the effect of the isospin of the projectile and hence the mass number of the compound nucleus on the yield of evaporation residues. They were able to identify ²⁵⁹Sg and ²⁵⁸Sg in their measurement of the 1n excitation function. ^[12]

²⁰⁹Bi(⁵¹V,xn)^260−xSg (x=2)

The team at Dubna also studied this reaction in their series of cold fusion reactions performed in 1974. Once again they were unable to detect any SF activities. ^[8] In 1994, the synthesis of seaborgium was revisited using this reaction by the GSI team, in order to study the new even-even isotope ²⁵⁸Sg. Ten atoms of ²⁵⁸Sg were detected and decayed by spontaneous fission.

Hot fusion

This section deals with the synthesis of nuclei of seaborgium by so-called "hot" fusion reactions. These are processes that create compound nuclei at high excitation energy (~40–50 MeV, hence "hot"), leading to a reduced probability of survival from fission and quasi-fission. The excited nucleus then decays to the ground state via the emission of 3–5 neutrons.

²³⁸U(³⁰Si,xn)^268−xSg (x=3,4,5,6)

This reaction was first studied by Japanese scientists at the Japan Atomic Energy Research Institute (JAERI) in 1998. They detected a spontaneous fission activity, which they tentatively assigned to the new isotope ²⁶⁴Sg or ²⁶³Db, formed by EC of ²⁶³Sg. ^[13] In 2006, the teams at GSI and LBNL both studied this reaction using the method of correlation of genetic parent-daughter decays. The LBNL team measured an excitation function for the 4n,5n and 6n channels, whilst the GSI team were able to observe an additional 3n activity. ^{[14] [15] [16]} Both teams were able to identify the new isotope ²⁶⁴Sg, which decayed with a short lifetime by spontaneous fission.

²⁴⁸Cm(²²Ne,xn)^270−xSg (x=4?,5)

In 1993, at Dubna, Yuri Lazarev and his team announced the discovery of long-lived ²⁶⁶Sg and ²⁶⁵Sg produced in the 4n and 5n channels of this nuclear reaction following the search for seaborgium isotopes suitable for a first chemical study. It was announced that ²⁶⁶Sg decayed by 8.57 MeV alpha-particle emission with a projected half-life of ~20 s, lending strong support to the stabilising effect of the Z = 108, N = 162 closed shells. ^[17] This reaction was studied further in 1997 by a team at GSI and the yield, decay mode and half-lives for ²⁶⁶Sg and ²⁶⁵Sg have been confirmed, although there are still some discrepancies. In the synthesis of ²⁷⁰Hs (see hassium), ²⁶⁶Sg was found to undergo exclusively SF with a short half-life (T_SF = 360 ms). It is possible that this is the ground state, (^266gSg) and that the other activity, produced directly, belongs to a high spin K-isomer, ^266mSg, but further results are required to confirm this.

A recent re-evaluation of the decay characteristics of ²⁶⁵Sg and ²⁶⁶Sg has suggested that all decays to date in this reaction were in fact from ²⁶⁵Sg, which exists in two isomeric forms. The first, ^265aSg has a principal alpha-line at 8.85 MeV and a calculated half-life of 8.9 s, while ^265bSg has a decay energy of 8.70 MeV and a half-life of 16.2 s. Both isomeric levels are populated when produced directly. Data from the decay of ²⁶⁹Hs indicates that ^265bSg is produced during the decay of ²⁶⁹Hs and that ^265bSg decays into the shorter-lived ^261gRf isotope. This contradicts the assignment of the long-lived alpha activity to ²⁶⁶Sg, instead suggesting that ²⁶⁶Sg undergoes fission in a short time.

Regardless of these assignments, the reaction has been successfully used in the recent attempts to study the chemistry of seaborgium (see below).

²⁴⁹Cf(¹⁸O,xn)^267−xSg (x=4)

The synthesis of seaborgium was first realized in 1974 by the LBNL/LLNL team. ^[18] In their discovery experiment, they were able to apply the new method of correlation of genetic parent-daughter decays to identify the new isotope ²⁶³Sg. In 1975, the team at Oak Ridge were able to confirm the decay data but were unable to identify coincident X-rays in order to prove that seaborgium was produced. In 1979, the team at Dubna studied the reaction by detection of SF activities. In comparison with data from Berkeley, they calculated a 70% SF branching for ²⁶³Sg. The original synthesis and discovery reaction was confirmed in 1994 by a different team at LBNL. ^[19]

Decay products

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

Evaporation Residue	Observed Sg isotope
291Lv, 287Fl, 283Cn	271Sg
285Fl	269Sg
276Ds, 272Hs	268Sg
271Hs	267Sg
270Hs	266Sg
277Cn, 273Ds, 269Hs	265Sg
271Ds, 267Ds	263Sg
270Ds	262Sg
269Ds, 265Hs	261Sg
264Hs	260Sg

Chronology of isotope discovery

Isotope	Year discovered	discovery reaction
258Sg	1994	209Bi(51V,2n)
259Sg	1985	207Pb(54Cr,2n)
260Sg	1985	208Pb(54Cr,2n)
261gSg	1985	208Pb(54Cr,n)
261mSg	2009	208Pb(54Cr,n)
262Sg	2001	207Pb(64Ni,n)
263Sgm	1974	249Cf(18O,4n) [18]
263Sgg	1994	208Pb(64Ni,n)
264Sg	2006	238U(30Si,4n)
265Sga, b	1993	248Cm(22Ne,5n)
266Sg	2004	248Cm(26Mg,4n)
267Sg	2004	248Cm(26Mg,3n)
268Sg	2022	232Th(48Ca,4n) [2]
269Sg	2010	242Pu(48Ca,5n)
270Sg	unknown
271Sg	2003	242Pu(48Ca,3n)

Isomerism

²⁶⁶Sg

Initial work identified an 8.63 MeV alpha-decaying activity with a half-life of ~21 s and assigned to the ground state of ²⁶⁶Sg. Later work identified a nuclide decaying by 8.52 and 8.77 MeV alpha emission with a half-life of ~21 s, which is unusual for an even-even nuclide. Recent work on the synthesis of ²⁷⁰Hs identified ²⁶⁶Sg decaying by SF with a short 360 ms half-life. The recent work on ²⁷⁷Cn and ²⁶⁹Hs has provided new information on the decay of ²⁶⁵Sg and ²⁶¹Rf. This work suggested that the initial 8.77 MeV activity should be reassigned to ²⁶⁵Sg. Therefore, the current information suggests that the SF activity is the ground state and the 8.52 MeV activity is a high spin K-isomer. Further work is required to confirm these assignments. A recent re-evaluation of the data has suggested that the 8.52 MeV activity should be associated with ²⁶⁵Sg and that ²⁶⁶Sg only undergoes fission.

²⁶⁵Sg

The recent direct synthesis of ²⁶⁵Sg resulted in four alpha-lines at 8.94, 8.84, 8.76 and 8.69 MeV with a half-life of 7.4 seconds. The observation of the decay of ²⁶⁵Sg from the decay of ²⁷⁷Cn and ²⁶⁹Hs indicated that the 8.69 MeV line may be associated with an isomeric level with an associated half-life of ~ 20 s. It is plausible that this level is causing confusion between assignments of ²⁶⁶Sg and ²⁶⁵Sg since both can decay to fissioning rutherfordium isotopes.

A recent re-evaluation of the data has indicated that there are indeed two isomers, one with a principal decay energy of 8.85 MeV with a half-life of 8.9 s, and a second isomer that decays with energy 8.70 MeV with a half-life of 16.2 s.

²⁶³Sg

The discovery synthesis of ²⁶³Sg resulted in an alpha-line at 9.06 MeV. ^[18] Observation of this nuclide by decay of ^271gDs,^271mDs and ²⁶⁷Hs has confirmed an isomer decaying by 9.25 MeV alpha emission. The 9.06 MeV decay was also confirmed. The 9.06 MeV activity has been assigned to the ground state isomer with an associated half-life of 0.3 s. The 9.25 MeV activity has been assigned to an isomeric level decaying with a half-life of 0.9 s.

Recent work on the synthesis of ^271g,mDs was resulted in some confusing data regarding the decay of ²⁶⁷Hs. In one such decay, ²⁶⁷Hs decayed to ²⁶³Sg, which decayed by alpha emission with a half-life of ~ 6 s. This activity has not yet been positively assigned to an isomer and further research is required.

Spectroscopic decay schemes

²⁶¹Sg

This is the currently accepted decay scheme for Sg from the study by Streicher et al. at GSI in 2003–2006

Retracted isotopes

²⁶⁹Sg

In the claimed synthesis of ²⁹³Og in 1999 the isotope ²⁶⁹Sg was identified as a daughter product. It decayed by 8.74 MeV alpha emission with a half-life of 22 s. The claim was retracted in 2001. This isotope was finally created in 2010.

Chemical yields of isotopes

Cold fusion

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

Projectile	Target	CN	1n	2n	3n
54Cr	207Pb	261Sg
54Cr	208Pb	262Sg	4.23 nb, 13.0 MeV	500 pb	10 pb
51V	209Bi	260Sg		38 pb, 21.5 MeV
52Cr	208Pb	260Sg	281 pb, 11.0 MeV

Hot fusion

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

Projectile	Target	CN	3n	4n	5n	6n
30Si	238U	268Sg	+	9 pb, 40.0	~ 80 pb, 51.0 MeV	~30 pb, 58.0 MeV
22Ne	248Cm	270Sg		~25 pb	~250 pb
18O	249Cf	267Sg		+

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• 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. hdl:11858/00-001M-0000-0010-23E8-5. S2CID   250839471.
  • 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 .
• "News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
• 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.
  • GSI (2011). "Superheavy Element Research at GSI" (PDF). GSI. Retrieved 24 August 2012.