Isotopes of nobelium

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Isotopes of nobelium  (102No)
Main isotopes [1] Decay
abun­dance half-life (t1/2) mode pro­duct
253No synth 1.6 min α 55% 249Fm
β+ 45% 253Md
254Nosynth51 sα90% 250Fm
β+10% 254Md
255Nosynth3.5 minα61% 251Fm
β+39% 255Md
257Nosynth25 sα99% 253Fm
β+1% 257Md
259Nosynth58 minα75% 255Fm
ε 25% 259Md
SF <10%–

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.

Contents

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] [n 6]
Excitation energy [n 6]
248No102146248.08662(24)#<2 μs0+
249No [2] [3] 102147249.0878(3)#38.3(28) ms α 245Fm5/2+
SF (<0.23%)(various)
250No [4] 102148250.08756(22)#4.0(4) μsSF(various)0+
α (rare)246Fm
250m1No~1250 keV23(4) μs IT 250No(6+)
SF (<3.5%)(various)
250m2No0.7+1.4
−0.3 μs		IT250m1No
251No [5] 102149251.088945(4) [6] 0.80(1) sα (91%) [5] 247Fm(7/2+)
β+ (9%)251Md
SF (0.14%)(various)
251m1No105(3) keV [7] 1.02(3) sα247mFm(1/2+)
β+?251Md
251m2No>1700 keV~2 μsIT251No
252No [8] 102150252.088967(10)2.42(6) sα (70.1%)248Fm0+
SF (29.1%)(various)
β+ (0.8%)252Md
252m1No1254 keV100(3) msIT252No(8−)
252m2No921(118) μsIT252No
253No [1] 102151253.090564(7)1.57(2) minα (55%)249Fm(9/2−)
β+ (45%)253Md
SF (rare)(various)
253m1No167.5(5) keV30.3(1.6) μsIT253No(5/2+)
253m2No1196(107) keV706(24) μsIT253No19/2+#
253m3No1256(113) keV552(15) μsIT253No25/2+#
254No [1] 102152254.090956(11)51.2(4) sα (90%)250Fm0+
β+ (10%)254Md
SF (0.17%)(various)
254m1No1296.4(1.1) keV264.9(1.4) msIT (98.0%)254No(8−)
SF (2.0%)(various)
α (<1%)250Fm
254m2No3217(300)# keV184(3) μsIT254m1No16+#
SF (<1.2%)(various)
255No [9] 102153255.093191(16)3.52(18) min [1] α (61.4%)251Fm1/2+
β+ (38.6%)255Md
255m1No240–300 keV109(9) μsIT255No(11/2−)
255m2No1400–1600 keV77(6) μsIT255m1No(19/2,21/2,23/2)
255m3No≥1500 keV1.2+0.6
−0.4 μs		IT255m1No(≥19/2)
256No [10] 102154256.094283(8)2.91(5) sα (99.47%)252Fm0+
SF (0.53%)(various)
EC (rare)256Md
256mNo [11] 7.8+8.3
−2.6 μs		IT256No(5−,7−)
257No [12] 102155257.096888(7)24.5(5) sα253Fm(3/2+)
β+ (rare)257Md
258No [1] 102156258.09821(11)#1.23(12) msSF(various)0+
α (rare)254Fm
259No102157259.10103(11)#58(5) minα (75%)255Fm9/2+
EC (25%)259Md
SF (<10%) [13] )(various)
260No102158260.10264(22)#106(8) msSF(various)0+
262No [n 7] 102160262.10746(39)#~5 msSF(various)0+
This table header & footer:
  1. ↑ mNo – 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
    IT: Isomeric transition
    SF: Spontaneous fission
  5. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  6. 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. ↑ Not directly synthesized, occurs as decay product of 262Lr

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. [15] 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. [2]

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−xNo

This 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−xNo

The 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−xNo

This 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−xNo

This 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 to253,252,251102. 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−xNo

This 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 contaminant250mFm, 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 ResidueObserved No isotope
262Lr262No
269Hs, 265Sg, 261Rf257No
267Hs, 263Sg, 259Rf255No
254Lr254No
261Sg, 257Rf253No
264Hs, 260Sg, 256Rf252No
255Rf251No

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
IsotopeYear discoveredDiscovery reaction
249No2020204Pb(48Ca,3n)
250Nom2001204Pb(48Ca,2n)
250Nog2006204Pb(48Ca,2n)
251No1967244Cm(12C,5n)
252Nog1959244Cm(12C,4n)
252Nom~2002206Pb(48Ca,2n)
253Nog1967242Pu(16O,5n),239Pu(18O,4n)
253Nom1971249Cf(12C,4n)
254Nog1966243Am(15N,4n)
254Nom11967?246Cm(13C,5n),246Cm(12C,4n)
254Nom2~2003208Pb(48Ca,2n)
255No1967246Cm(13C,4n),248Cm(12C,5n)
256No1967248Cm(12C,4n),248Cm(13C,5n)
257No1961?, 1967248Cm(13C,4n)
258No1967248Cm(13C,3n)
259No1973248Cm(18O,α3n)
260No1985254Es + 22Ne,18O,13C – transfer
262No1988254Es + 22Ne – transfer (EC of 262Lr)

Nuclear isomerism

254No

The 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.

253No

In 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.

252No

In 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.

250No

In 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.

ProjectileTargetCN1n2n3n4n
48Ca208Pb256No254No: 2050 nb ; 22.3 MeV
48Ca207Pb255No253No: 1310 nb ; 22.4 MeV
48Ca206Pb254No253No: 58 nb ; 23.6 MeV252No: 515 nb ; 23.3 MeV251No: 30 nb ; 30.7 MeV250No: 260 pb ; 43.9 MeV
48Ca204Pb252No250No: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.

ProjectileTargetCN3n4n5n6n
26Mg232Th258No254No:1.6 nb253No:9 nb252No:8 nb
22Ne238U260No256No:40 nb255No:200 nb254No:15 nb
22Ne236U258No254No:7 nb253No:25 nb252No: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. [2]

Related Research Articles

Meitnerium is a synthetic chemical element; it has symbol Mt and atomic number 109. It is named after Lise Meitner and is an extremely radioactive synthetic element. The most stable known isotope, meitnerium-278, has a half-life of 4.5 seconds, although the unconfirmed meitnerium-282 may have a longer half-life of 67 seconds. The GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, first created this element in 1982.

Nobelium is a synthetic chemical element; it has symbol No and atomic number 102. It is named after Alfred Nobel, the inventor of dynamite and benefactor of science. A radioactive metal, it is the tenth transuranium element, the second transfermium, and is the penultimate member of the actinide series. Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of twelve nobelium isotopes are known to exist; the most stable is 259No with a half-life of 58 minutes, but the shorter-lived 255No is most commonly used in chemistry because it can be produced on a larger scale.

Rutherfordium is a synthetic chemical element; it has symbol Rf and atomic number 104. It is named after physicist Ernest Rutherford. As a synthetic element, it is not found in nature and can only be made in a particle accelerator. It is radioactive; the most stable known isotope, 267Rf, has a half-life of about 48 minutes.

Roentgenium is a synthetic chemical element; it has symbol Rg and atomic number 111. It is extremely radioactive and can only be created in a laboratory. The most stable known isotope, roentgenium-282, has a half-life of 130 seconds, although the unconfirmed roentgenium-286 may have a longer half-life of about 10.7 minutes. Roentgenium was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the physicist Wilhelm Röntgen, who discovered X-rays. Only a few roentgenium atoms have ever been synthesized, and they have no practical application.

Livermorium is a synthetic chemical element; it has symbol Lv and atomic number 116. It is an extremely radioactive element that has only been created in a laboratory setting and has not been observed in nature. The element is named after the Lawrence Livermore National Laboratory in the United States, which collaborated with the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, to discover livermorium during experiments conducted between 2000 and 2006. The name of the laboratory refers to the city of Livermore, California, where it is located, which in turn was named after the rancher and landowner Robert Livermore. The name was adopted by IUPAC on May 30, 2012. Six isotopes of livermorium are known, with mass numbers of 288–293 inclusive; the longest-lived among them is livermorium-293 with a half-life of about 80 milliseconds. A seventh possible isotope with mass number 294 has been reported but not yet confirmed.

Copernicium is a synthetic chemical element; it has symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 30 seconds. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It was named after the astronomer Nicolaus Copernicus on his 537th anniversary.

Flerovium is a synthetic chemical element; it has symbol Fl and atomic number 114. It is an extremely radioactive, superheavy element, named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered in 1999. The lab's name, in turn, honours Russian physicist Georgy Flyorov. IUPAC adopted the name on 30 May 2012. The name and symbol had previously been proposed for element 102 (nobelium), but was not accepted by IUPAC at that time.

Nihonium is a synthetic chemical element; it has the symbol Nh and atomic number 113. It is extremely radioactive: its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the periodic table, nihonium is a transactinide element in the p-block. It is a member of period 7 and group 13.

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, and seven isomers. The longest-lived known isotope is 266Lr with a half-life of 11 hours.

Rutherfordium (104Rf) is a synthetic element and thus has no stable isotopes. A standard atomic weight cannot be given. The first isotope to be synthesized was either 259Rf in 1966 or 257Rf in 1969. There are 16 known radioisotopes from 253Rf to 270Rf and several isomers. The longest-lived isotope is 267Rf with a half-life of 48 minutes, and the longest-lived isomer is 263mRf with a half-life of 8 seconds.

Dubnium (105Db) is a synthetic element, thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 261Db in 1968. Thirteen radioisotopes are known, ranging from 255Db to 270Db, along with one isomer (257mDb); two more isomers have been reported but are unconfirmed. The longest-lived known isotope is 268Db with a half-life of 16 hours.

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 thirteen known radioisotopes from 258Sg to 271Sg and five known isomers. The longest-lived isotopes are 267Sg with a half-life of 9.8 minutes and 269Sg with a half-life of 5 minutes. Due to a low number of measurements, and the consequent overlapping measurement uncertainties at the confidence level corresponding to one standard deviation, a definite assignment of the most stable isotope cannot be made.

Bohrium (107Bh) is an artificial element. Like all artificial elements, it has no stable isotopes, and a standard atomic weight cannot be given. The first isotope to be synthesized was 262Bh in 1981. There are 11 known isotopes ranging from 260Bh to 274Bh, and 1 isomer, 262mBh. The longest-lived isotope is 270Bh with a half-life of 2.4 minutes, although the unconfirmed 278Bh may have an even longer half-life of about 690 seconds.

Hassium (108Hs) 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 265Hs in 1984. There are 13 known isotopes from 263Hs to 277Hs and up to six isomers. The most stable known isotope is 271Hs, with a half-life of about 46 seconds, though this assignment is not definite due to uncertainty arising from a low number of measurements. The isotopes 269Hs and 270Hs respectively have half-lives of about 12 seconds and 7.6 seconds. It is also possible that the isomer 277mHs is more stable than these, with a reported half-life 130±100 seconds, but only one event of decay of this isotope has been registered as of 2016.

Darmstadtium (110Ds) 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 269Ds in 1994. There are 11 known radioisotopes from 267Ds to 281Ds and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 14 seconds. However, the unconfirmed 282Ds might have an even longer half-life of 67 seconds.

Copernicium (112Cn) 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 277Cn in 1996. There are seven known radioisotopes ; the longest-lived isotope is 285Cn with a half-life of 30 seconds.

Flerovium (114Fl) 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 289Fl in 1999. Flerovium has six known isotopes, along with the unconfirmed 290Fl, and possibly two nuclear isomers. The longest-lived isotope is 289Fl with a half-life of 1.9 seconds, but 290Fl may have a longer half-life of 19 seconds.

Moscovium (115Mc) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no known stable isotopes. The first isotope to be synthesized was 288Mc in 2004. There are five known radioisotopes from 286Mc to 290Mc. The longest-lived isotope is 290Mc with a half-life of 0.65 seconds.

Livermorium (116Lv) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 293Lv in 2000. There are six known radioisotopes, with mass numbers 288–293, as well as a few suggestive indications of a possible heavier isotope 294Lv. The longest-lived known isotope is 293Lv with a half-life of 53 ms.

Unbiunium, also known as eka-actinium or element 121, is a hypothetical chemical element; it has symbol Ubu and atomic number 121. Unbiunium and Ubu are the temporary systematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be the first of the superactinides, and the third element in the eighth period. It has attracted attention because of some predictions that it may be in the island of stability. It is also likely to be the first of a new g-block of elements.

References

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  10. ↑ Hoffman, D. C.; Lee, D. M.; Gregorich, K. E.; et al. (1 February 1990). "Spontaneous fission properties of 2.9-s 256No". Physical Review C. 41 (2): 631–639. Bibcode:1990PhRvC..41..631H. doi:10.1103/PhysRevC.41.631. PMID   9966395.
  11. ↑ Kessaci, K.; Gall, B. J. P.; Dorvaux, O.; et al. (11 October 2021). "Evidence of high-K isomerism in 256
    102    No
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  12. ↑ Asai, M.; Tsukada, K.; Sakama, M.; et al. (2 September 2005). "Experimental Identification of Spin-Parities and Single-Particle Configurations in 257No and Its α-Decay Daughter 253Fm". Physical Review Letters. 95 (10): 102502. Bibcode:2005PhRvL..95j2502A. doi:10.1103/PhysRevLett.95.102502. PMID   16196924.
  13. ↑ "Table of Isotopes decay data".
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