Isotopes of nobelium explained

Nobelium (₁₀₂No) 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 (and correctly identified) was ²⁵⁴No in 1966. There are fourteen known radioisotopes, which are ²⁴⁸No to ²⁶⁰No and ²⁶²No, and many isomers. The longest-lived isotope is ²⁵⁹No with a half-life of 58 minutes. The longest-lived isomer is ^251m1No with a half-life of 1.02 seconds.

List of isotopes

|-| ²⁴⁸No| style="text-align:right" | 102| style="text-align:right" | 146| 248.08662(24)#| <2 μs||| 0+|-| rowspan=2|²⁴⁹No^{[1] [2]} | rowspan=2 style="text-align:right" | 102| rowspan=2 style="text-align:right" | 147| rowspan=2|249.0878(3)#| rowspan=2|38.3(28) ms| α | ²⁴⁵Fm| rowspan=2|5/2+|-| SF (<0.23%)| (various)|-|-| rowspan=2|²⁵⁰No^[3] | rowspan=2 style="text-align:right" | 102| rowspan=2 style="text-align:right" | 148| rowspan=2|250.08756(22)#| rowspan=2|4.0(4) μs| SF| (various)| rowspan=2|0+|-| α (rare)| ²⁴⁶Fm|-| rowspan=2 style="text-indent:1em" | ^250m1No| rowspan=2 colspan="3" style="text-indent:2em" |~1250 keV| rowspan=2|23(4) μs| IT| ²⁵⁰No| rowspan=2|(6+)|-| SF (<3.5%)| (various)|-| style="text-indent:1em" | ^250m2No| colspan="3" style="text-indent:2em" | | | IT| ^250m1No| |-| rowspan=3|²⁵¹No^[4] | rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 149| rowspan=3|251.088945(4)^[5] | rowspan=3|0.80(1) s| α (91%)^[4] | ²⁴⁷Fm| rowspan=3|(7/2+)|-| β⁺ (9%)| ²⁵¹Md|-| SF (0.14%)| (various)|-| rowspan=2 style="text-indent:1em" | ^251m1No| rowspan=2 colspan="3" style="text-indent:2em" | 105(3) keV^[6] | rowspan=2|1.02(3) s| α| ^247mFm| rowspan=2|(1/2+)|-| β⁺?| ²⁵¹Md|-| style="text-indent:1em" | ^251m2No| colspan="3" style="text-indent:2em" | >1700 keV| ~2 μs| IT| ²⁵¹No| |-| rowspan=3|²⁵²No^[7] | rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 150| rowspan=3|252.088967(10)| rowspan=3|2.42(6) s| α (70.1%)| ²⁴⁸Fm| rowspan=3|0+|-| SF (29.1%)| (various)|-| β⁺ (0.8%)| ²⁵²Md|-| style="text-indent:1em" | ^252m1No| colspan="3" style="text-indent:2em" | 1254 keV| 100(3) ms| IT| ²⁵²No| (8−)|-| style="text-indent:1em" | ^252m2No| colspan="3" style="text-indent:2em" || 921(118) μs| IT| ²⁵²No| |-| rowspan=3|²⁵³No| rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 151| rowspan=3|253.090564(7)| rowspan=3|1.57(2) min| α (55%)| ²⁴⁹Fm| rowspan=3|(9/2−)|-| β⁺ (45%)| ²⁵³Md|-| SF (rare)| (various)|-| style="text-indent:1em" | ^253m1No| colspan="3" style="text-indent:2em" | 167.5(5) keV| 30.3(1.6) μs| IT| ²⁵³No| (5/2+)|-| style="text-indent:1em" | ^253m2No| colspan="3" style="text-indent:2em" | 1196(107) keV| 706(24) μs| IT| ²⁵³No| 19/2+#|-| style="text-indent:1em" | ^253m3No| colspan="3" style="text-indent:2em" | 1256(113) keV| 552(15) μs| IT| ²⁵³No| 25/2+#|-| rowspan=3|²⁵⁴No| rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 152| rowspan=3|254.090956(11)| rowspan=3|51.2(4) s| α (90%)| ²⁵⁰Fm| rowspan=3|0+|-| β⁺ (10%)| ²⁵⁴Md|-| SF (0.17%)| (various)|-| rowspan=3 style="text-indent:1em" | ^254m1No| rowspan=3 colspan="3" style="text-indent:2em" | 1296.4(1.1) keV| rowspan=3|264.9(1.4) ms| IT (98.0%)| ²⁵⁴No| rowspan=3|(8−)|-| SF (2.0%)| (various)|-| α (<1%)| ²⁵⁰Fm|-| rowspan=2 style="text-indent:1em" | ^254m2No| rowspan=2 colspan="3" style="text-indent:2em" | 3217(300)# keV| rowspan=2|184(3) μs| IT| ^254m1No| rowspan=2|16+#|-| SF (<1.2%)| (various)|-| rowspan=2|²⁵⁵No^[8] | rowspan=2 style="text-align:right" | 102| rowspan=2 style="text-align:right" | 153| rowspan=2|255.093191(16)| rowspan=2|3.52(18) min| α (61.4%)| ²⁵¹Fm| rowspan=2|1/2+|-| β⁺ (38.6%)| ²⁵⁵Md|-| style="text-indent:1em" | ^255m1No| colspan="3" style="text-indent:2em" | 240–300 keV| 109(9) μs| IT| ²⁵⁵No| (11/2−)|-| style="text-indent:1em" | ^255m2No| colspan="3" style="text-indent:2em" | 1400–1600 keV| 77(6) μs| IT| ^255m1No| (19/2,21/2,23/2)|-| style="text-indent:1em" | ^255m3No| colspan="3" style="text-indent:2em" | ≥1500 keV| | IT| ^255m1No| (≥19/2)|-| rowspan=3|²⁵⁶No^[9] | rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 154| rowspan=3|256.094283(8)| rowspan=3|2.91(5) s| α (99.47%)| ²⁵²Fm| rowspan=3|0+|-| SF (0.53%)| (various)|-| EC (rare)| ²⁵⁶Md|-| style="text-indent:1em" | ^256mNo^[10] | colspan="3" style="text-indent:2em" || | IT| ²⁵⁶No| (5−,7−)|-| rowspan=2|²⁵⁷No^[11] | rowspan=2 style="text-align:right" | 102| rowspan=2 style="text-align:right" | 155| rowspan=2|257.096888(7)| rowspan=2|24.5(5) s| α| ²⁵³Fm| rowspan=2|(3/2+)|-| β⁺ (rare)| ²⁵⁷Md|-| rowspan=2|²⁵⁸No| rowspan=2 style="text-align:right" | 102| rowspan=2 style="text-align:right" | 156| rowspan=2|258.09821(11)#| rowspan=2|1.23(12) ms| SF| (various)| rowspan=2|0+|-| α (rare)| ²⁵⁴Fm|-| rowspan=3|²⁵⁹No| rowspan=3 style="text-align:right" | 102| rowspan=3 style="text-align:right" | 157| rowspan=3|259.10103(11)#| rowspan=3|58(5) min| α (75%)| ²⁵⁵Fm| rowspan=3|9/2+|-| EC (25%)| ²⁵⁹Md|-| SF (<10%)^[12])| (various)|-| ²⁶⁰No| style="text-align:right" | 102| style="text-align:right" | 158| 260.10264(22)#| 106(8) ms| SF| (various)| 0+|-| ²⁶²No^[13] | style="text-align:right" | 102| style="text-align:right" | 160| 262.10746(39)#| ~5 ms| SF| (various)| 0+

Nucleosynthesis

Cold fusion

²⁰⁸Pb(⁴⁸Ca,xn)^256−xNo (x=1,2,3,4)This cold fusion reaction was first studied in 1979 at Flerov Laboratory of Nuclear Reactions (FLNR). Further work in 1988 at GSI measured EC and SF branchings in ²⁵⁴No. In 1989, the FLNR used the reaction to measure SF decay characteristics for the two isomers of ²⁵⁴No. The measurement of the 2n excitation function was reported in 2001 by Yuri Oganessian at the FLNR.

Patin et al. at the LBNL reported in 2002 the synthesis of ^255–251No in the 1-4n exit channels and measured further decay data for these isotopes.

The reaction has recently been used at Jyväskylän Yliopisto Fysiikan Laitos (JYFL) using the RITU set-up to study K-isomerism in ²⁵⁴No. The scientists were able to measure two K-isomers with half-lives of 275 ms and 198 s, respectively. They were assigned to 8⁻ and 16⁺ K-isomeric levels.

The reaction was used in 2004–5 at the FLNR to study the spectroscopy of ^255–253No. The team were able to confirm an isomeric level in ²⁵³No with a half-life of 43.5 s.

²⁰⁸Pb(⁴⁴Ca,xn)^252−xNo (x=2)This reaction was studied in 2003 at the FLNR in a study of the spectroscopy of ²⁵⁰No.

²⁰⁷Pb(⁴⁸Ca,xn)^255−xNo (x=2)The measurement of the 2n excitation function for this reaction was reported in 2001 by Yuri Oganessian and co-workers at the FLNR. The reaction was used in 2004–5 to study the spectroscopy of ²⁵³No.

²⁰⁶Pb(⁴⁸Ca,xn)^254−xNo (x=1,2,3,4)The measurement of the 1-4n excitation functions for this reaction were reported in 2001 by Yuri Oganessian and co-workers at the FLNR.The 2n channel was further studied by the GSI to provide a spectroscopic determination of K-isomerism in ²⁵²No. A K-isomer with spin and parity 8⁻ was detected with a half-life of 110 ms.

²⁰⁴Pb(⁴⁸Ca,xn)^252−xNo (x=2,3)The measurement of the 2n excitation function for this reaction was reported in 2001 by Yuri Oganessian at the FLNR. They reported a new isotope ²⁵⁰No with a half-life of 36 μs. The reaction was used in 2003 to study the spectroscopy of ²⁵⁰No.They were able to observe two spontaneous fission activities with half-lives of 5.6 μs and 54 μs and assigned to ²⁵⁰No and ²⁴⁹No, respectively.The latter activity was later assigned to a K-isomer in ²⁵⁰No.^[14] The reaction was reported in 2006 by Peterson et al. at the Argonne National Laboratory (ANL) in a study of SF in ²⁵⁰No. They detected two activities with half-lives of 3.7  μs and 43  μs and both assigned to ²⁵⁰No, the latter associated with a K-isomer. In 2020, a team at FLNR repeated this reaction and found a new 9.1-MeV alpha particle activity correlated to ²⁴⁵Fm and ²⁴¹Cf, which they assigned to the new isotope ²⁴⁹No.

Hot fusion

²³²Th(²⁶Mg,xn)^258−xNo (x=4,5,6)The cross sections for the 4-6n exit channels have been measured for this reaction at the FLNR.

²³⁸U(²²Ne,xn)^260−xNo (x=4,5,6)This reaction was first studied in 1964 at FLNR. The team were able to detect decays from ²⁵²Fm and ²⁵⁰Fm. The ²⁵²Fm activity was associated with an ~8 s half-life and assigned to ²⁵⁶102 from the 4n channel, with a yield of 45 nb. They were also able to detect a 10 s spontaneous fission activity also tentatively assigned to ²⁵⁶102.Further work in 1966 on the reaction examined the detection of ²⁵⁰Fm decay using chemical separation and a parent activity with a half-life of ~50 s was reported and correctly assigned to ²⁵⁴102. They also detected a 10 s spontaneous fission activity tentatively assigned to ²⁵⁶102.The reaction was used in 1969 to study some initial chemistry of nobelium at the FLNR. They determined eka-ytterbium properties, consistent with nobelium as the heavier homologue. In 1970, they were able to study the SF properties of ²⁵⁶No.In 2002, Patin et al. reported the synthesis of ²⁵⁶No from the 4n channel but were unable to detect ²⁵⁷No.

The cross section values for the 4-6n channels have also been studied at the FLNR.

²³⁸U(²⁰Ne,xn)^258−xNoThis reaction was studied in 1964 at FLNR. No spontaneous fission activities were observed.

²³⁶U(²²Ne,xn)^258−xNo (x=4,5,6)The cross sections for the 4-6n exit channels have been measured for this reaction at the FLNR.

²³⁵U(²²Ne,xn)^257−xNo (x=5)This reaction was studied in 1970 at the FLNR. It was used to study the SF decay properties of ²⁵²No.

²³³U(²²Ne,xn)^255−xNoThe synthesis of neutron deficient nobelium isotopes was studied in 1975 at the FLNR. In their experiments they observed a 250 s SF activity, which they tentatively assigned to ²⁵⁰No in the 5n exit channel. Later results have not been able to confirm this activity and it is currently unidentified.

²⁴²Pu(¹⁸O,xn)^260−xNo (x=4?)This reaction was studied in 1966 at the FLNR. The team identified an 8.2 s SF activity tentatively assigned to ²⁵⁶102.

²⁴¹Pu(¹⁶O,xn)^257−xNoThis reaction was first studied in 1958 at the FLNR. The team measured ~8.8 MeV alpha particles with a half-life of 30 s and assigned to ^253,252,251102. A repeat in 1960 produced 8.9 MeV alpha particles with a half-life of 2–40 s and assigned to ²⁵³102 from the 4n channel. Confidence in these results was later diminished.

²³⁹Pu(¹⁸O,xn)^257−xNo (x=5)This reaction was studied in 1970 at the FLNR in an effort to study the SF decay properties of ²⁵²No.

²³⁹Pu(¹⁶O,xn)^255−xNoThis reaction was first studied in 1958 at the FLNR. The team were able to measure ~8.8 MeV alpha particles with a half-life of 30 s and assigned to^253,252,251102. A repeat in 1960 was unsuccessful and it was concluded the first results were probably associated with background effects.

²⁴³Am(¹⁵N,xn)^258−xNo (x=4)This reaction was studied in 1966 at the FLNR. The team were able to detect ²⁵⁰Fm using chemical techniques and determined an associated half-life significantly higher than the reported 3 s by Berkeley for the supposed parent ²⁵⁴No. Further work later the same year measured 8.1 MeV alpha particles with a half-life of 30–40 s.

²⁴³Am(¹⁴N,xn)^257−xNoThis reaction was studied in 1966 at the FLNR. They were unable to detect the 8.1 MeV alpha particles detected when using a N-15 beam.

²⁴¹Am(¹⁵N,xn)^256−xNo (x=4)The decay properties of ²⁵²No were examined in 1977 at Oak Ridge. The team calculated a half-life of 2.3 s and measured a 27% SF branching.

²⁴⁸Cm(¹⁸O,αxn)^262−xNo (x=3)The synthesis of the new isotope ²⁵⁹No was reported in 1973 from the LBNL using this reaction.

²⁴⁸Cm(¹³C,xn)^261−xNo (x=3?,4,5)This reaction was first studied in 1967 at the LBNL. The new isotopes ²⁵⁸No,²⁵⁷No and ²⁵⁶No were detected in the 3-5n channels. The reaction was repeated in 1970 to provide further decay data for ²⁵⁷No.

²⁴⁸Cm(¹²C,xn)^260−xNo (4,5?)This reaction was studied in 1967 at the LBNL in their seminal study of nobelium isotopes. The reaction was used in 1990 at the LBNL to study the SF of²⁵⁶No.

²⁴⁶Cm(¹³C,xn)^259−xNo (4?,5?)This reaction was studied in 1967 at the LBNL in their seminal study of nobelium isotopes.

²⁴⁶Cm(¹²C,xn)^258−xNo (4,5)This reaction was studied in 1958 by scientists at the LBNL using a 5% ²⁴⁶Cm curium target. They were able to measure 7.43 MeV decays from²⁵⁰Fm, associated with a 3 s ²⁵⁴No parent activity, resulting from the 4n channel. The 3 s activity was later reassigned to ²⁵²No, resulting from reaction with the predominant ²⁴⁴Cm component in the target. It could however not be proved that it was not due to the contaminant^250mFm, unknown at the time.Later work in 1959 produced 8.3 MeV alpha particles with a half-life of 3 s and a 30% SF branch. This was initially assigned to ²⁵⁴No and later reassigned to ²⁵²No, resulting from reaction with the ²⁴⁴Cm component in the target.The reaction was restudied in 1967 and activities assigned to ²⁵⁴No and ²⁵³No were detected.

²⁴⁴Cm(¹³C,xn)^257−xNo (x=4)This reaction was first studied in 1957 at the Nobel Institute in Stockholm. The scientists detected 8.5 MeV alpha particles with a half-life of 10 minutes. The activity was assigned to ²⁵¹No or ²⁵³No. The results were later dismissed as background.The reaction was repeated by scientists at the LBNL in 1958 but they were unable to confirm the 8.5 MeV alpha particles. The reaction was further studied in 1967 at the LBNL and an activity assigned to ²⁵³No was measured.

²⁴⁴Cm(¹²C,xn)^256−xNo (x=4,5)This reaction was studied in 1958 by scientists at the LBNL using a 95% ²⁴⁴Cm curium target. They were able to measure 7.43 MeV decays from²⁵⁰Fm, associated with a 3 s ²⁵⁴No parent activity, resulting from the reaction (²⁴⁶Cm,4n). The 3 s activity was later reassigned to²⁵²No, resulting from reaction (²⁴⁴Cm,4n). It could however not be proved that it was not due to the contaminant ^250mFm, unknown at the time.Later work in 1959 produced 8.3 MeV alpha particles with a half-life of 3 s and a 30% SF branch. This was initially assigned to ²⁵⁴No and later reassigned to ²⁵²No, resulting from reaction with the ²⁴⁴Cm component in the target.The reaction was restudied in 1967 at the LBNL and a new activity assigned to ²⁵¹No was measured.

²⁵²Cf(¹²C,αxn)^260−xNo (x=3?)This reaction was studied at the LBNL in 1961 as part of their search for element 104. They detected 8.2 MeV alpha particles with a half-life of 15 s. This activity was assigned to a Z=102 isotope. Later work suggests an assignment to ²⁵⁷No, resulting most likely from the α3n channel with the ²⁵²Cf component of the californium target.

²⁵²Cf(¹¹B,pxn)^262−xNo (x=5?)This reaction was studied at the LBNL in 1961 as part of their search for element 103. They detected 8.2 MeV alpha particles with a half-life of 15 s. This activity was assigned to a Z=102 isotope. Later work suggests an assignment to ²⁵⁷No, resulting most likely from the p5n channel with the ²⁵²Cf component of the californium target.

²⁴⁹Cf(¹²C,αxn)^257−xNo (x=2)This reaction was first studied in 1970 at the LBNL in a study of ²⁵⁵No. It was studied in 1971 at the Oak Ridge Laboratory. They were able to measure coincident Z=100 K X-rays from ²⁵⁵No, confirming the discovery of the element.

As decay products

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

Evaporation Residue	Observed No isotope
^262Lr	^262No
^269Hs, ^265Sg, ^261Rf	^257No
^267Hs, ^263Sg, ^259Rf	^255No
^254Lr	^254No
^261Sg, ^257Rf	^253No
^264Hs, ^260Sg, ^256Rf	^252No
^255Rf	^251No

Isotopes

Twelve radioisotopes of nobelium have been characterized, with the most stable being ²⁵⁹No with a half-life of 58 minutes. Longer half-lives are expected for the as-yet-unknown ²⁶¹No and ²⁶³No. An isomeric level has been found in ²⁵³No and K-isomers have been found in ²⁵⁰No, ²⁵²No and ²⁵⁴No to date.

Chronology of isotope discovery

Isotope	Year discovered	Discovery reaction
^249No	2020	^204Pb(^48Ca,3n)
^250No^m	2001	^204Pb(^48Ca,2n)
^250No^g	2006	^204Pb(^48Ca,2n)
^251No	1967	^244Cm(^12C,5n)
^252No^g	1959	^244Cm(^12C,4n)
^252No^m	~2002	^206Pb(^48Ca,2n)
^253No^g	1967	^242Pu(^16O,5n),^239Pu(^18O,4n)
^253No^m	1971	^249Cf(^12C,4n)
^254Nog	1966	^243Am(^15N,4n)
^254Nom1	1967?	^246Cm(^13C,5n),^246Cm(^12C,4n)
^254Nom2	~2003	^208Pb(^48Ca,2n)
^255No	1967	^246Cm(^13C,4n),^248Cm(^12C,5n)
^256No	1967	^248Cm(^12C,4n),^248Cm(^13C,5n)
^257No	1961?, 1967	^248Cm(^13C,4n)
^258No	1967	^248Cm(^13C,3n)
^259No	1973	^248Cm(^18O,α3n)
^260No	1985	^254Es + ^22Ne,^18O,^13C – transfer
^262No	1988	^254Es + ^22Ne – transfer (EC of ^262Lr)

Nuclear isomerism

²⁵⁴NoThe study of K-isomerism was recently studied by physicists at the University of Jyväskylä physics laboratory (JYFL). They were able to confirm a previously reported K-isomer and detected a second K-isomer. They assigned spins and parities of 8⁻ and 16⁺ to the two K-isomers.

²⁵³NoIn 1971, Bemis et al. was able to determine an isomeric level decaying with a half-life of 31 s from the decay of ²⁵⁷Rf. This was confirmed in 2003 at the GSI by also studying the decay of ²⁵⁷Rf. Further support in the same year from the FLNR appeared with a slightly higher half-life of 43.5 s, decaying by M2 gamma emission to the ground state.

²⁵²NoIn a recent study by the GSI into K-isomerism in even-even isotopes, a K-isomer with a half-life of 110 ms was detected for ²⁵²No. A spin and parity of 8⁻ was assigned to the isomer.

²⁵⁰NoIn 2003, scientists at the FLNR reported that they had been able to synthesise ²⁴⁹No, which decayed by SF with a half-life of 54 μs. Further work in 2006 by scientists at the ANL showed that the activity was actually due to a K-isomer in ²⁵⁰No. The ground state isomer was also detected with a very short half-life of 3.7 μs.

Chemical yields of isotopes

Cold fusion

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

Projectile	Target	CN	1n	2n	3n	4n
^48Ca	^208Pb	^256No		^254No: 2050 nb ; 22.3 MeV
^48Ca	^207Pb	^255No		^253No: 1310 nb ; 22.4 MeV
^48Ca	^206Pb	^254No	^253No: 58 nb ; 23.6 MeV	^252No: 515 nb ; 23.3 MeV	^251No: 30 nb ; 30.7 MeV	^250No: 260 pb ; 43.9 MeV
^48Ca	^204Pb	^252No		^250No:13.2 nb ; 23.2 MeV

Hot fusion

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

Projectile	Target	CN	3n	4n	5n	6n
^26Mg	^232Th	^258No		^254No:1.6 nb	^253No:9 nb	^252No:8 nb
^22Ne	^238U	^260No		^256No:40 nb	^255No:200 nb	^254No:15 nb
^22Ne	^236U	^258No		^254No:7 nb	^253No:25 nb	^252No:15 nb

Retracted isotopes

In 2003, scientists at the FLNR claimed to have discovered ²⁴⁹No, which would have been the lightest known isotope of nobelium. However, subsequent work showed that the 54 μs fission activity instead originated from an excited state of ²⁵⁰No.^[15] The discovery of this isotope was later reported in 2020; its decay properties differed from the 2003 claims.

References

1. Joint Institute for Nuclear Research, 2020 . 23 June 2021 . 117–118 . 26 June 2021.
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12. Web site: Table of Isotopes decay data.
13. Not directly synthesized, occurs as decay product of ²⁶²Lr
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• Isotope masses from:
  • M. Wang . G. Audi . A. H. Wapstra . F. G. Kondev . M. MacCormick . X. Xu. 2012 . The AME2012 atomic mass evaluation (II). Tables, graphs and references. . Chinese Physics C . 36 . 12 . 1603–2014 . 10.1088/1674-1137/36/12/003. 2012ChPhC..36....3M . 11858/00-001M-0000-0010-23E8-5 . 250839471 . etal.
    • Half-life, spin, and isomer data selected from the following sources.