# Isotopes of lawrencium

Lawrencium ($_{103}$Lr) 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 $^{258}$Lr in 1961. There are fourteen known isotopes from $^{251}$Lr to $^{266}$Lr, except $^{263}$Lr and $^{265}$Lr, and seven isomers. The longest-lived known isotope is $^{266}$Lr with a half-life of 11 hours.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity |
| Spin and parity |||
| $^{251}$Lr | 103 | 148 | 251.09418(32)# | 24.4+7.0 −4.5 ms | α | $^{247}$Md | 7/2− |
| $^{251}$Lr | 103 | 148 | 251.09418(32)# | 24.4+7.0 −4.5 ms | SF | (various) | 7/2− |
| $^{251m}$Lr | 117(27) keV | 117(27) keV | 117(27) keV | 42+42 −14 ms | α | $^{247}$Md | 1/2− |
| $^{252}$Lr | 103 | 149 | 252.09526(26)# | 369(75) ms [0.36+0.11 −0.07 s] | α (~98%) | $^{248}$Md | |
| $^{252}$Lr | 103 | 149 | 252.09526(26)# | 369(75) ms [0.36+0.11 −0.07 s] | SF (~2%) | (various) | |
| $^{252}$Lr | 103 | 149 | 252.09526(26)# | 369(75) ms [0.36+0.11 −0.07 s] | β$^+$? | $^{252}$No | |
| $^{253}$Lr | 103 | 150 | 253.09509(22)# | 632(46) ms | α (>97%) | $^{249}$Md | (7/2−) |
| $^{253}$Lr | 103 | 150 | 253.09509(22)# | 632(46) ms | SF (1.0%) | (various) | (7/2−) |
| $^{253}$Lr | 103 | 150 | 253.09509(22)# | 632(46) ms | β$^+$ (<2%) | $^{253}$No | (7/2−) |
| $^{253m}$Lr | 30(100)# keV | 30(100)# keV | 30(100)# keV | 1.32(14) s | α (>86%) | $^{249}$Md | (1/2−) |
| $^{253m}$Lr | 30(100)# keV | 30(100)# keV | 30(100)# keV | 1.32(14) s | SF (12%) | (various) | (1/2−) |
| $^{253m}$Lr | 30(100)# keV | 30(100)# keV | 30(100)# keV | 1.32(14) s | β$^+$ (<2%) | $^{253}$No | (1/2−) |
| $^{254}$Lr | 103 | 151 | 254.096240(100) | 11.9(9) s | α (71.7%) | $^{250}$Md | (4+) |
| $^{254}$Lr | 103 | 151 | 254.096240(100) | 11.9(9) s | β$^+$ (28.3%) | $^{254}$No | (4+) |
| $^{254}$Lr | 103 | 151 | 254.096240(100) | 11.9(9) s | SF (<0.1%) | (various) | (4+) |
| $^{254m}$Lr | 110(6) keV | 110(6) keV | 110(6) keV | 20.3(4.2) s | α | $^{250}$Md | (1−) |
| $^{254m}$Lr | 110(6) keV | 110(6) keV | 110(6) keV | 20.3(4.2) s | β$^+$ | $^{254}$No | (1−) |
| $^{254m}$Lr | 110(6) keV | 110(6) keV | 110(6) keV | 20.3(4.2) s | IT? | $^{254}$Lr | (1−) |
| $^{255}$Lr | 103 | 152 | 255.096562(19) | 31.1(1.1) s | α (85%) | $^{251}$Md | 1/2− |
| $^{255}$Lr | 103 | 152 | 255.096562(19) | 31.1(1.1) s | β$^+$ (15%) | $^{255}$No | 1/2− |
| $^{255}$Lr | 103 | 152 | 255.096562(19) | 31.1(1.1) s | SF (rare) | (various) | 1/2− |
| $^{255m1}$Lr | 32(2) keV | 32(2) keV | 32(2) keV | 2.54(5) s | IT (~60%) | $^{255}$Lr | (7/2−) |
| $^{255m1}$Lr | 32(2) keV | 32(2) keV | 32(2) keV | 2.54(5) s | α (~40%) | $^{251}$Md | (7/2−) |
| $^{255m2}$Lr | 796(12) keV | 796(12) keV | 796(12) keV | <1 μs | IT | $^{255m1}$Lr | (15/2+) |
| $^{255m3}$Lr | 1465(12) keV | 1465(12) keV | 1465(12) keV | 1.78(0.05) ms | IT | $^{255m2}$Lr | (25/2+) |
| $^{256}$Lr | 103 | 153 | 256.09849(9) | 27.9(1.0) s | α (85%) | $^{252}$Md | (0−,3−)# |
| $^{256}$Lr | 103 | 153 | 256.09849(9) | 27.9(1.0) s | β$^+$ (15%) | $^{256}$No | (0−,3−)# |
| $^{256}$Lr | 103 | 153 | 256.09849(9) | 27.9(1.0) s | SF (<0.03%) | (various) | (0−,3−)# |
| $^{257}$Lr | 103 | 154 | 257.09942(5)# | 1.24+0.85 −0.36 s | α | $^{253}$Md | (9/2+,7/2−) |
| $^{257}$Lr | 103 | 154 | 257.09942(5)# | 1.24+0.85 −0.36 s | β$^+$ (rare) | $^{257}$No | (9/2+,7/2−) |
| $^{257}$Lr | 103 | 154 | 257.09942(5)# | 1.24+0.85 −0.36 s | SF (rare) | (various) | (9/2+,7/2−) |
| $^{257m}$Lr | 100(50)# keV | 100(50)# keV | 100(50)# keV | 200+160 −60 ms | α | $^{253}$Md | (1/2−) |
| $^{257m}$Lr | 100(50)# keV | 100(50)# keV | 100(50)# keV | 200+160 −60 ms | IT | $^{257}$Lr | (1/2−) |
| $^{258}$Lr | 103 | 155 | 258.10176(11)# | 3.54+0.46 −0.36 s | α (97.4%) | $^{254}$Md | |
| $^{258}$Lr | 103 | 155 | 258.10176(11)# | 3.54+0.46 −0.36 s | β$^+$ (2.6%) | $^{258}$No | |
| $^{259}$Lr | 103 | 156 | 259.10290(8)# | 6.2(3) s | α (78%) | $^{255}$Md | 1/2−# |
| $^{259}$Lr | 103 | 156 | 259.10290(8)# | 6.2(3) s | SF (22%) | (various) | 1/2−# |
| $^{259}$Lr | 103 | 156 | 259.10290(8)# | 6.2(3) s | β$^+$ (rare) | $^{259}$No | 1/2−# |
| $^{260}$Lr | 103 | 157 | 260.10551(13)# | 3.0(5) min | α (80%) | $^{256}$Md | |
| $^{260}$Lr | 103 | 157 | 260.10551(13)# | 3.0(5) min | β$^+$ (20%) | $^{260}$No | |
| $^{260}$Lr | 103 | 157 | 260.10551(13)# | 3.0(5) min | SF (rare) | (various) | |
| $^{261}$Lr | 103 | 158 | 261.10688(22)# | 39(12) min | SF | (various) | 1/2−# |
| $^{261}$Lr | 103 | 158 | 261.10688(22)# | 39(12) min | α (<10%) | $^{257}$Md | 1/2−# |
| $^{262}$Lr | 103 | 159 | 262.10961(22)# | ~4 h | β$^+$ | $^{262}$No | |
| $^{262}$Lr | 103 | 159 | 262.10961(22)# | ~4 h | SF (<10%) | (various) | |
| $^{262}$Lr | 103 | 159 | 262.10961(22)# | ~4 h | α (<7.5%) | $^{258}$Md | |
| $^{264}$Lr | 103 | 161 | 264.11420(47)# | 4.8+2.2 −1.3 h | SF | (various) | |
| $^{266}$Lr | 103 | 163 | 266.11983(56)# | 22(14) h [11+21 −5 h] | SF | (various) | |
| This table header & footer: view ||||||||
* ↑ $^m$Lr – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* ↑ Modes of decay: SF:Spontaneous fission
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ The experiment in which alpha decay of two $^{251}$Lr states was reported did not take into account spontaneous fission branches.
* ↑ Not directly synthesized, occurs as a decay product of $^{256}$Db
* ↑ Not directly synthesized, occurs as a decay product of $^{288}$Mc
* ↑ Not directly synthesized, occurs as a decay product of $^{294}$Ts

## Nucleosynthesis
### Cold fusion
#### $^{205}$Tl($^{50}$Ti,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 $^{253}$Lr in the 2n exit channel. In 2022, two states ($^{253}$Lr and $^{253m}$Lr) were found.

#### $^{203}$Tl($^{50}$Ti,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 ($^{251}$Lr and $^{251m}$Lr) were found.

#### $^{208}$Pb($^{48}$Ti,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 $^{246}$Cf, a descendant of $^{254}$Lr.

#### $^{208}$Pb($^{45}$Sc,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.

#### $^{209}$Bi($^{48}$Ca,xn)$^{257−x}$Lr (x=2)

This reaction has been used to study the spectroscopic properties of $^{255}$Lr. 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 $^{255}$Lr. The work provided evidence for an isomeric level in $^{255}$Lr.

### Hot fusion
#### $^{243}$Am($^{18}$O,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 to$^{256}$Lr or $^{257}$Lr. Later work suggests an assignment to $^{256}$Lr. 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 $^{256}$Lr or $^{257}$Lr and later to solely $^{256}$Lr.

#### $^{243}$Am($^{16}$O,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 MeV alpha activity with a half-life of 20s. This was assigned to$^{255}$Lr.

#### $^{248}$Cm($^{15}$N,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$^{260}$Lr,$^{259}$Lr and $^{258}$Lr from the 3-5n exit channels.

#### $^{248}$Cm($^{18}$O,pxn)$^{265−x}$Lr (x=3,4)

This reaction was studied in 1988 at the LBNL in order to assess the possibility of producing $^{262}$Lr and $^{261}$Lr without using the exotic $^{254}$Es target. It was also used to attempt to measure an electron capture (EC) branch in $^{261m}$Rf from the 5n exit channel. After extraction of the Lr(III) component, they were able to measure the spontaneous fission of $^{261}$Lr 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 $^{262}$Lr 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 $^{261}$Lr was most likely produced by a p3n channel and an upper limit of 14% for the electron capture branch of $^{261m}$Rf was therefore suggested.

#### $^{246}$Cm($^{14}$N,xn)$^{260−x}$Lr (x=3?)

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

#### $^{244}$Cm($^{14}$N,xn)$^{258−x}$Lr

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

#### $^{249}$Bk($^{18}$O,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 $^{260}$Lr. The reaction was further studied in 1988 to study the aqueous chemistry of lawrencium. A total of 23 alpha decays were measured for $^{260}$Lr, 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.

#### $^{252}$Cf($^{11}$B,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% $^{252}$Cf). 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 $^{257}$Lr. Later results suggest a reassignment to $^{258}$Lr, resulting from the 5n exit channel. The 8.4 MeV activity was also assigned to $^{257}$Lr. Later results suggest a reassignment to $^{256}$Lr. This is most likely from the 33% $^{250}$Cf component in the target rather than from the 7n channel. The 8.2 MeV was subsequently associated with nobelium.

#### $^{252}$Cf($^{10}$B,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% $^{252}$Cf). 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 $^{257}$Lr. Later results suggest a reassignment to $^{258}$Lr. The 8.4 MeV activity was also assigned to $^{257}$Lr. Later results suggest a reassignment to $^{256}$Lr. The 8.2 MeV was subsequently associated with nobelium.

#### $^{250}$Cf($^{14}$N,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 MeV. This was assigned to$^{257}$Lr.

#### $^{249}$Cf($^{11}$B,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 Lr$^{3+}$ activity. The reaction was repeated in 1976 at Oak Ridge and 26s $^{256}$Lr was confirmed by measurement of coincident X-rays.

#### $^{249}$Cf($^{12}$C,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 $^{258}$Lr from the p2n channel.

#### $^{249}$Cf($^{15}$N,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 $^{258}$Lr and $^{257}$Lr from the α2n and α3n and channels. The reaction was repeated in 1976 at Oak Ridge and the synthesis of $^{258}$Lr was confirmed.

#### $^{254}$Es + $^{22}$Ne – transfer

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

### 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 |
| $^{294}$Ts, $^{290}$Mc, $^{286}$Nh, $^{282}$Rg, $^{278}$Mt, $^{274}$Bh, $^{270}$Db | $^{266}$Lr |
| $^{288}$Mc, $^{284}$Nh, $^{280}$Rg, $^{276}$Mt, $^{272}$Bh, $^{268}$Db | $^{264}$Lr |
| $^{267}$Bh, $^{263}$Db | $^{259}$Lr |
| $^{278}$Nh, $^{274}$Rg, $^{270}$Mt, $^{266}$Bh, $^{262}$Db | $^{258}$Lr |
| $^{261}$Db | $^{257}$Lr |
| $^{272}$Rg, $^{268}$Mt, $^{264}$Bh, $^{260}$Db | $^{256}$Lr |
| $^{259}$Db | $^{255}$Lr |
| $^{266}$Mt, $^{262}$Bh, $^{258}$Db | $^{254}$Lr |
| $^{261}$Bh, $^{257}$Db$^{g,m}$ | $^{253}$Lr$^{g,m}$ |
| $^{260}$Bh, $^{256}$Db | $^{252}$Lr |
| $^{255}$Db | $^{251}$Lr |

## Isotopes

Summary of all lawrencium isotopes known :
| Isotope | Year discovered | discovery reaction |
| $^{251}$Lr$^g$ | 2005 | $^{209}$Bi($^{48}$Ti,2n) |
| $^{251}$Lr$^m$ | 2022 | $^{203}$Tl($^{50}$Ti,2n) |
| $^{252}$Lr | 2001 | $^{209}$Bi($^{50}$Ti,3n) |
| $^{253}$Lr$^g$ | 1985 | $^{209}$Bi($^{50}$Ti,2n) |
| $^{253}$Lr$^m$ | 2001 | $^{209}$Bi($^{50}$Ti,2n) |
| $^{254}$Lr$^g$ | 1985 | $^{209}$Bi($^{50}$Ti,n) |
| $^{254}$Lr$^m$ | 2019 | |
| $^{255}$Lr$^g$ | 1970 | $^{243}$Am($^{16}$O,4n) |
| $^{255}$Lr$^{m1}$ | 2006 | |
| $^{255}$Lr$^{m2}$ | 2009 | |
| $^{255}$Lr$^{m3}$ | 2008 | |
| $^{256}$Lr | 1961? 1965? 1968? 1971 | $^{252}$Cf($^{10}$B,6n) |
| $^{257}$Lr$^g$ | 1958? 1971 | $^{249}$Cf($^{15}$N,α3n) |
| $^{257}$Lr$^m$ | 2018 | |
| $^{258}$Lr | 1961? 1971 | $^{249}$Cf($^{15}$N,α2n) |
| $^{259}$Lr | 1971 | $^{248}$Cm($^{15}$N,4n) |
| $^{260}$Lr | 1971 | $^{248}$Cm($^{15}$N,3n) |
| $^{261}$Lr | 1987 | $^{254}$Es + $^{22}$Ne |
| $^{262}$Lr | 1987 | $^{254}$Es + $^{22}$Ne |
| $^{264}$Lr | 2020 | $^{243}$Am($^{48}$Ca,6α3n) |
| $^{266}$Lr | 2014 | $^{249}$Bk($^{48}$Ca,7α3n) |
Fourteen isotopes of lawrencium plus seven isomers have been synthesized with $^{266}$Lr being the longest-lived and the heaviest, with a half-life of 11 hours. $^{251}$Lr is the lightest isotope of lawrencium to be produced to date.

### Lawrencium-253 isomers

A study of the decay properties of $^{257}$Db (see dubnium) in 2001 by Hessberger et al. at the GSI provided some data for the decay of $^{253}$Lr. Analysis of the data indicated the population of an isomeric level in $^{253}$Lr from the decay of the corresponding isomer in $^{257}$Db. 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 $^{255}$Lr formed in the reaction $^{209}$Bi($^{48}$Ca,2n)$^{255}$Lr has provided evidence for an isomeric level.