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 fourteen known isotopes from ²⁵¹Lr to ²⁶⁶Lr, except ²⁶³Lr and ²⁶⁵Lr, and seven isomers. The longest-lived known isotope is ²⁶⁶Lr with a half-life of 11 hours.

List of isotopes

|-id=Lawrencium-251 | rowspan=2|²⁵¹Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 148 | rowspan=2|251.09429(22)# | rowspan=2| | α | ²⁴⁷Md | rowspan=2|7/2− |- | SF | (various) |-id=Lawrencium-251m | style="text-indent:1em" | ^251mLr | colspan="3" style="text-indent:2em" | 117(27)&nbsp;keV | | α | ²⁴⁷Md | 1/2− |-id=Lawrencium | rowspan=2|²⁵²Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 149 | rowspan=2|252.09505(20)# | rowspan=2| | α (~98%) | ²⁴⁸Md | rowspan=2|7−# |- | SF (~2%) | (various) |-id=Lawrencium-253 | rowspan=2|²⁵³Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 150 | rowspan=2|253.09503(18) | rowspan=2|632(46)&nbsp;ms | α (99%) | ²⁴⁹Md | rowspan=2|(7/2−) |- | SF (1.0%) | (various) |-id=Lawrencium-253m | rowspan=2 style="text-indent:1em" | ^253mLr | rowspan=2 colspan="3" style="text-indent:2em" | 30(100)#&nbsp;keV | rowspan=2| | α (88%) | ²⁴⁹Md | rowspan=2|(1/2−) |- | SF (12%) | (various) |-id=Lawrencium-254 | rowspan=3|²⁵⁴Lr | rowspan=3 style="text-align:right" | 103 | rowspan=3 style="text-align:right" | 151 | rowspan=3|254.09624(10) | rowspan=3| | α (71.7%) | ²⁵⁰Md | rowspan=3|4+# |- | β⁺ (28.3%) | ²⁵⁴No |- | SF (<0.1%) | (various) |-id=Lawrencium-254m | style="text-indent:1em" | ^254mLr | colspan="3" style="text-indent:2em" | 110(6)&nbsp;keV | | α | ²⁵⁰Md | 1+# |-id=Lawrencium-255 | rowspan=2|²⁵⁵Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 152 | rowspan=2|255.096562(19) | rowspan=2| | α (85%) | ²⁵¹Md | rowspan=2|1/2− |- | β⁺ (15%) | ²⁵⁵No |-id=Lawrencium-255m1 | rowspan=2 style="text-indent:1em" | ^255m1Lr | rowspan=2 colspan="3" style="text-indent:2em" | 32(2)&nbsp;keV | rowspan=2| | IT (~60%) | ²⁵⁵Lr | rowspan=2|(7/2−) |- | α (~40%) | ²⁵¹Md |-id=Lawrencium-255m2 | style="text-indent:1em" | ^255m2Lr | colspan="3" style="text-indent:2em" | 796(12)&nbsp;keV | <1&nbsp;μs | IT | ^255m1Lr | (15/2+) |-id=Lawrencium-255m3 | style="text-indent:1em" | ^255m3Lr | colspan="3" style="text-indent:2em" | 1465(12)&nbsp;keV | | IT | ^255m2Lr | (25/2+) |-id=Lawrencium-256 | rowspan=3|²⁵⁶Lr | rowspan=3 style="text-align:right" | 103 | rowspan=3 style="text-align:right" | 153 | rowspan=3|256.09849(9) | rowspan=3| | α (85%) | ²⁵²Md | rowspan=3|(0−,3−)# |- | β⁺ (15%) | ²⁵⁶No |- | SF (<0.03%) | (various) |-id=Lawrencium-257 | ²⁵⁷Lr | style="text-align:right" | 103 | style="text-align:right" | 154 | 257.09948(5)# | | α | ²⁵³Md | 7/2−# |-id=Lawrencium-257m | rowspan=2 style="text-indent:1em" | ^257mLr | rowspan=2 colspan="3" style="text-indent:2em" | 100(50)#&nbsp;keV | rowspan=2|<br>[] | α? | ²⁵³Md | rowspan=2|(1/2−) |- | IT? | ²⁵⁷Lr |-id=Lawrencium-258 | rowspan=2|²⁵⁸Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 155 | rowspan=2|258.10175(11)# | rowspan=2| | α (97.4%) | ²⁵⁴Md | rowspan=2| |- | β⁺ (2.6%) | ²⁵⁸No |-id=Lawrencium-259 | rowspan=2|²⁵⁹Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 156 | rowspan=2|259.10290(8)# | rowspan=2| | α (78%) | ²⁵⁵Md | rowspan=2|1/2−# |- | SF (22%) | (various) |-id=Lawrencium-260 | rowspan=2|²⁶⁰Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 157 | rowspan=2|260.10550(13)# | rowspan=2| | α (80%) | ²⁵⁶Md | rowspan=2| |- | β⁺ (20%) | ²⁶⁰No |-id=Lawrencium-261 | ²⁶¹Lr | style="text-align:right" | 103 | style="text-align:right" | 158 | 261.10688(22)# | | SF | (various) | 1/2−# |-id=Lawrencium-262 | rowspan=2|²⁶²Lr | rowspan=2 style="text-align:right" | 103 | rowspan=2 style="text-align:right" | 159 | rowspan=2|262.10962(22)# | rowspan=2|~ | β⁺ | ²⁶²No | rowspan=2| |- | SF | (various) |-id=Lawrencium-264 | ²⁶⁴Lr | style="text-align:right" | 103 | style="text-align:right" | 161 | 264.11420(47)# | | SF | (various) | |-id=Lawrencium-266 | ²⁶⁶Lr | style="text-align:right" | 103 | style="text-align:right" | 163 | 266.11987(58)# | <br>[] | SF | (various) | |-

Nucleosynthesis

Cold fusion

²⁰⁵Tl(⁵⁰Ti,xn)^{255−x}Lr (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. In 2022, two states (²⁵³Lr and ^253mLr) were found.

²⁰³Tl(⁵⁰Ti,xn)^{253−x}Lr (x=2)

This reaction was studied in a series of experiments in 1976 by Yuri Oganessian and his team at the FLNR. In 2022, two states (²⁵¹Lr and ^251mLr) were found.

²⁰⁸Pb(⁴⁸Ti,pxn)^{255−x}Lr (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−x}Lr

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−x}Lr (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−x}Lr (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&nbsp;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−x}Lr (x=4)

This reaction was studied in 1970 by the team at the FLNR. They were able to detect an 8.38&nbsp;MeV alpha activity with a half-life of 20 s. This was assigned to ²⁵⁵Lr.

²⁴⁸Cm(¹⁵N,xn)^{263−x}Lr (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−x}Lr (x=3,4)

This reaction was studied in 1988 at the LBNL in order to examine the possibility of producing ²⁶²Lr and ²⁶¹Lr without using the exotic ²⁵⁴Es target, and successfully accomplished this. After chemical purification of the Lr from the reaction, they were able to measure fission from ²⁶¹Lr with an improved half-life of 44 minutes. The production cross-section was 700 pb; from this a 14% electron capture branch of ^261mRf was calculated if this isotope had been produced via the 5n channel rather than the p4n channel. This is an upper limit, as it was determined that the p4n channel does occur. A lower bombarding energy (93&nbsp;MeV instead of 97&nbsp;MeV) was then used to measure the production of ²⁶²Lr in the p3n channel; as it was calculated that any electron capture of ²⁶²Rf should be negligible, the 4n channel was discounted. The isotope was successfully detected and a 240 pb cross-section measured. This detection of the p3n channel supported the p4n assignment for the lighter isotope. For neither was there any attempt to differentiate the SF and EC+SF decay modes.

²⁴⁶Cm(¹⁴N,xn)^{260−x}Lr (x=3?)

This reaction was studied briefly in 1958 at the LBNL using an enriched ²⁴⁴Cm target (5% ²⁴⁶Cm). They observed a ~9&nbsp;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−x}Lr

This reaction was studied briefly in 1958 at the LBNL using an enriched ²⁴⁴Cm target (5% ²⁴⁶Cm). They observed a ~9&nbsp;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−x}Lr (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&nbsp;MeV and an improved half-life of 2.7 minutes. The calculated cross-section was 8.7&nbsp;nb.

²⁵²Cf(¹¹B,xn)^{263−x}Lr (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&nbsp;MeV, with half-lives of about 8 and 15 seconds, respectively. The 8.6&nbsp;MeV activity was tentatively assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁸Lr, resulting from the 5n exit channel. The 8.4&nbsp;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&nbsp;MeV was subsequently associated with nobelium.

²⁵²Cf(¹⁰B,xn)^{262−x}Lr (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&nbsp;MeV, with half-lives of about 8 and 15 seconds, respectively. The 8.6&nbsp;MeV activity was tentatively assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁸Lr. The 8.4&nbsp;MeV activity was also assigned to ²⁵⁷Lr. Later results suggest a reassignment to ²⁵⁶Lr. The 8.2&nbsp;MeV was subsequently associated with nobelium.

²⁵⁰Cf(¹⁴N,αxn)^{260−x}Lr (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&nbsp;MeV. This was assigned to ²⁵⁷Lr.

²⁴⁹Cf(¹¹B,xn)^{260−x}Lr (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−x}Lr (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−x}Lr (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:

Isotopes

Fourteen isotopes of lawrencium plus seven isomers 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 an isomeric level in ²⁵³Lr from the decay of the corresponding isomer in ²⁵⁷Db. The ground state was assigned spin and parity of 7/2−, decaying by emission of an 8794&nbsp;keV alpha particle with a half-life of 0.57&nbsp;s. The isomeric level was assigned spin and parity of 1/2−, decaying by emission of an 8722&nbsp;keV alpha particle with a half-life of 1.49&nbsp;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

• Isotope masses from:
• Half-life, spin, and isomer data selected from the following sources.