An extended periodic table theorizes about chemical elements beyond those currently known and proven. The element with the highest atomic number known is oganesson (Z = 118), which completes the seventh period (row) in the periodic table. All elements in the eighth period and beyond thus remain purely hypothetical.

Elements beyond 118 would be placed in additional periods when discovered, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements. Any additional periods are expected to contain more elements than the seventh period, as they are calculated to have an additional so-called g-block, containing at least 18 elements with partially filled g-orbitals in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969.[1][2] The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Despite many searches, no elements in this region have been synthesized or discovered in nature.[3]

According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals, but spin–orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number. Seaborg’s version of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects. Models that take relativistic effects into account predict that the pattern will be broken. Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to Z = 172, and found that several were displaced from the Madelung rule.[4] As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table.

Elements in this region are likely to be highly unstable with respect to radioactive decay and undergo alpha decay or spontaneous fission with extremely short half-lives, though element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. Other islands of stability beyond the known elements may also be possible, including one theorised around element 164, though the extent of stabilizing effects from closed nuclear shells is uncertain. It is not clear how many elements beyond the expected island of stability are physically possible, whether period 8 is complete, or if there is a period 9. The International Union of Pure and Applied Chemistry (IUPAC) defines an element to exist if its lifetime is longer than 10−14 seconds (0.01 picoseconds, or 10 femtoseconds), which is the time it takes for the nucleus to form an electron cloud.[5]

As early as 1940, it was noted that a simplistic interpretation of the relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α ≈ 137.036 (the reciprocal of the fine-structure constant), suggesting that neutral atoms cannot exist beyond element 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point.[6] On the other hand, a more rigorous analysis calculates the analogous limit to be Z ≈ 168–172 where the 1s subshell dives into the Dirac sea, and that it is instead not neutral atoms that cannot exist beyond this point, but bare nuclei, thus posing no obstacle to the further extension of the periodic system. Atoms beyond this critical atomic number are called supercritical atoms.

Elements beyond the actinides were first proposed to exist as early as 1895, when Danish chemist Hans Peter Jørgen Julius Thomsen predicted that thorium and uranium formed part of a 32-element period which would end at a chemically inactive element with atomic weight 292 (not far from the 294 for the only known isotope of oganesson). In 1913, Swedish physicist Johannes Rydberg similarly predicted that the next noble gas after radon would have atomic number 118, and purely formally derived even heavier congeners of radon at Z = 168, 218, 290, 362, and 460, exactly where the Aufbau principle would predict them to be. In 1922, Niels Bohr predicted the electronic structure of this next noble gas at Z = 118, and suggested that the reason why elements beyond uranium were not seen in nature was because they were too unstable. The German physicist and engineer Richard Swinne published a review paper in 1926 containing predictions on the transuranic elements (he may have coined the term) in which he anticipated modern predictions of an island of stability: he first hypothesised in 1914 that half-lives should not decrease strictly with atomic number, but suggested instead that there might be some longer-lived elements at Z = 98–102 and Z = 108–110, and speculated that such elements might exist in the Earth’s core, in iron meteorites, or in the ice caps of Greenland where they had been locked up from their supposed cosmic origin.[7] By 1955, these elements were called superheavy elements.[8]

The first predictions on properties of undiscovered superheavy elements were made in 1957, when the concept of nuclear shells was first explored and an island of stability was theorized to exist around element 126.[9] In 1967, more rigorous calculations were performed, and the island of stability was theorized to be centered at the then-undiscovered flerovium (element 114); this and other subsequent studies motivated many researchers to search for superheavy elements in nature or attempt to synthesize them at accelerators.[8] Many searches for superheavy elements were conducted in the 1970s, all with negative results. As of April 2022, synthesis has been attempted for every element up to and including unbiseptium (Z = 127), except unbitrium (Z = 123),[10][11][12] with the heaviest successfully synthesized element being oganesson in 2002 and the most recent discovery being that of tennessine in 2010.[10]

As some superheavy elements were predicted to lie beyond the seven-period periodic table, an additional eighth period containing these elements was first proposed by Glenn T. Seaborg in 1969. This model continued the pattern in established elements and introduced a new g-block and superactinide series beginning at element 121, raising the number of elements in period 8 compared to known periods.[1][2][8] These early calculations failed to consider relativistic effects that break down periodic trends and render simple extrapolation impossible, however. In 1971, Fricke calculated the periodic table up to Z = 172, and discovered that some elements indeed had different properties that break the established pattern,[4] and a 2010 calculation by Pekka Pyykkö also noted that several elements might behave differently than expected.[13] It is unknown how far the periodic table might extend beyond the known 118 elements, as heavier elements are predicted to be increasingly unstable. Glenn T. Seaborg suggested that practically speaking, the end of the periodic table might come as early as around Z = 120 due to nuclear instability.[14]

Predicted structures of an extended periodic table

[edit]

There is currently no consensus on the placement of elements beyond atomic number 120 in the periodic table.

All hypothetical elements are given an International Union of Pure and Applied Chemistry (IUPAC) systematic element name, for use until the element has been discovered, confirmed, and an official name is approved. These names are typically not used in the literature, and the elements are instead referred to by their atomic numbers; hence, element 164 is usually not called "unhexquadium" or "Uhq" (the systematic name and symbol), but rather "element 164" with symbol "164", "(164)", or "E164".[15]

At element 118, the orbitals 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d and 7p are assumed to be filled, with the remaining orbitals unfilled. A simple extrapolation from the Aufbau principle would predict the eighth row to fill orbitals in the order 8s, 5g, 6f, 7d, 8p; but after element 120, the proximity of the electron shells makes placement in a simple table problematic.

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Extended periodic table

1 1 H 2 He 2 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 3 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 4 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 5 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 6 55 Cs 56 Ba 57 La 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 7 87 Fr 88 Ra 89 Ac 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 102 No 103 Lr 104 Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 110 Ds 111 Rg 112 Cn 113 Nh 114 Fl 115 Mc 116 Lv 117 Ts 118 Og 8 119 Uue 120 Ubn 121 Ubu 122 Ubb 123 Ubt 124 Ubq 125 Ubp 126 Ubh 127 Ubs 128 Ubo 129 Ube 130 Utn 131 Utu 132 Utb 133 Utt 134 Utq 135 Utp 136 Uth 137 Uts 138 Uto 139 Ute 140 Uqn 141 Uqu 142 Uqb 143 Uqt 144 Uqq 145 Uqp 146 Uqh 147 Uqs 148 Uqo 149 Uqe 150 Upn 151 Upu 152 Upb 153 Upt 154 Upq 155 Upp 156 Uph 157 Ups 158 Upo 159 Upe 160 Uhn 161 Uhu 162 Uhb 163 Uht 164 Uhq 165 Uhp 166 Uhh 167 Uhs 168 Uho

Not all models show the higher elements following the pattern established by lighter elements. Burkhard Fricke et al., who carried out calculations up to element 184 in an article published in 1971, also found some elements to be displaced from the Madelung energy-ordering rule as a result of overlapping orbitals; this is caused by the increasing role of relativistic effects in heavy elements (They describe chemical properties up to element 184, but only draw a table to element 172.)[4][16]

H																			He
Li	Be													B	C	N	O	F	Ne
Na	Mg													Al	Si	P	S	Cl	Ar
K	Ca	Sc			Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y			Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La		Ce–Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac		Th–Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og
119	120	121	122–141	142–155	156	157	158	159	160	161	162	163	164
165	166													167	168	169	170	171	172

Fricke et al.’s format is more focused on formal electron configurations than likely chemical behaviour. They place elements 156–164 in groups 4–12 because formally their configurations should be 7d2 through 7d10. However, they differ from the previous d-elements in that the 8s shell is not available for chemical bonding: instead, the 9s shell is. Thus element 164 with 7d109s0 is noted by Fricke et al. to be analogous to palladium with 4d105s0, and they consider elements 157–172 to have chemical analogies to groups 3–18 (though they are ambivalent on whether elements 165 and 166 are more like group 1 and 2 elements or more like group 11 and 12 elements, respectively). Thus, elements 157–164 are placed in their table in a group that the authors do not think is chemically most analogous.[17]

Vadim Nefedov [ru], Malvina Trzhaskovskaya, and Victor Yarzhemskii carried out calculations up to 164 (results published in 2006). They considered elements 158 through 164 to be homologues of groups 4 through 10, and not 6 through 12, noting similarities of electron configurations to the period 5 transition metals (e.g. element 159 7d49s1 vs Nb 4d45s1, element 160 7d59s1 vs Mo 4d55s1, element 162 7d79s1 vs Ru 4d75s1, element 163 7d89s1 vs Rh 4d85s1, element 164 7d109s0 vs Pd 4d105s0). They thus agree with Fricke et al. on the chemically most analogous groups, but differ from them in that Nefedov et al. actually place elements in the chemically most analogous groups. Rg and Cn are given an asterisk to reflect differing configurations from Au and Hg (in the original publication they are drawn as being displaced in the third dimension). In fact Cn probably has an analogous configuration to Hg, and the difference in configuration between Pt and Ds is not marked.[18]

Cs	Ba	La–Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac–Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg*	Cn*	Nh	Fl	Mc	Lv	Ts	Og
119	120	121–157	158	159	160	161	162	163	164

Pekka Pyykkö used computer modeling to calculate the positions of elements up to Z = 172 and their possible chemical properties in an article published in 2011. He reproduced the orbital order of Fricke et al., and proposed a refinement of their table by formally assigning slots to elements 121–164 based on ionic configurations.[13]

In order to bookkeep the electrons, Pyykkö places some elements out of order: thus 139 and 140 are placed in groups 13 and 14 to reflect that the 8p1/2 shell needs to fill, and he distinguishes separate 5g, 8p1/2, and 6f series.[13] Fricke et al. and Nefedov et al. do not attempt to break up these series.[17][18]

Computational chemist Andrey Kulsha has suggested two forms of the extended periodic table up to 172 that build on and refine Nefedov et al.’s versions up to 164 with reference to Pyykkö’s calculations.[19] Based on their likely chemical properties, elements 157–172 are placed by both forms as eighth-period congeners of yttrium through xenon in the fifth period;[19] this extends Nefedov et al.’s placement of 157–164 under yttrium through palladium,[18] and agrees with the chemical analogies given by Fricke et al.[17]

Kulsha suggested two ways to deal with elements 121–156, that lack precise analogues among earlier elements. In his first form (2011, after Pyykkö’s paper was published),[19] elements 121–138 and 139–156 are placed as two separate rows (together called "ultransition elements"), related by the addition of a 5g18 subshell into the core, as according to Pyykkö’s calculations of oxidation states,[13] they should, respectively, mimic lanthanides and actinides.[19][20] In his second suggestion (2016), elements 121–142 form a g-block (as they have 5g activity), while elements 143–156 form an f-block placed under actinium through nobelium.[21]

Kulsha’s first suggested form Kulsha’s second suggested form

Thus, period 8 emerges with 54 elements, and the next noble element after 118 is 172.[22]

In 2023, Smits, Düllmann, Indelicato, Nazarewicz, and Schwerdtfeger made another attempt to place elements from 119 to 170 in the periodic table based on their electron configurations. The configurations of a few elements (121–124 and 168) did not allow them to be placed unambiguously. Element 145 appears twice, some places have double occupancy, and others are empty.[23]

Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og 119 120 125 126 127 128 129 130 131 132 133/134 135 136 137 138 139 140 141 142/143 144 145 145 146 147 148/149 150 151 152 153 154 155 156 157 158/159 160 161 162 163 164 167 165 166 169 170

Searches for undiscovered elements

[edit]

Attempts have been made to synthesize the period 8 elements up to unbiseptium, except unbitrium. All such attempts have been unsuccessful. An attempt to synthesize ununennium, the first period 8 element, is ongoing as of 2025.

The synthesis of element 119 (ununennium) was first attempted in 1985 by bombarding a target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at Berkeley, California:

254 99Es + 48 20Ca → 302119* → no atoms

No atoms were identified, leading to a limiting cross section of 300 nb.[24] Later calculations suggest that the cross section of the 3n reaction (which would result in 299119 and three neutrons as products) would actually be six hundred thousand times lower than this upper bound, at 0.5 pb.[25]

From April to September 2012, an attempt to synthesize the isotopes 295119 and 296119 was made by bombarding a target of berkelium-249 with titanium-50 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany.[26][27] Based on the theoretically predicted cross section, it was expected that an ununennium atom would be synthesized within five months of the beginning of the experiment.[28] Moreover, as berkelium-249 decays to californium-249 (the next element) with a short half-life of 327 days, this allowed elements 119 and 120 to be searched for simultaneously.[29]

249 97Bk + 50 22Ti → 299119* → no atoms

The experiment was originally planned to continue to November 2012,[30] but was stopped early to make use of the 249Bk target to confirm the synthesis of tennessine (thus changing the projectiles to 48Ca).[31] This reaction of 249Bk + 50Ti was predicted to be the most favorable practical reaction for formation of element 119,[27] as it is rather asymmetrical,[28] though also somewhat cold.[31] (254Es + 48Ca would be superior, but preparing milligram quantities of 254Es for a target is difficult.)[28] Nevertheless, the necessary change from the "silver bullet" 48Ca to 50Ti divides the expected yield of element 119 by about twenty, as the yield is strongly dependent on the asymmetry of the fusion reaction.[28]

Due to the predicted short half-lives, the GSI team used new "fast" electronics capable of registering decay events within microseconds.[27] No atoms of element 119 were identified, implying a limiting cross section of 70 fb.[31] The predicted actual cross section is around 40 fb, which is at the limits of current technology.[28]

The team at RIKEN in Wakō, Japan began bombarding curium-248 targets with a vanadium-51 beam in January 2018[32] to search for element 119. Curium was chosen as a target, rather than heavier berkelium or californium, as these heavier targets are difficult to prepare.[33] The 248Cm targets were provided by Oak Ridge National Laboratory. RIKEN developed a high-intensity vanadium beam.[34] The experiment began at a cyclotron while RIKEN upgraded its linear accelerators; the upgrade was completed in 2020.[35] Bombardment may be continued with both machines until the first event is observed; the experiment is currently running intermittently for at least 100 days a year.[36][33] The RIKEN team’s efforts are being financed by the Emperor of Japan.[37] The team at the JINR plans to attempt synthesis of element 119 in the future, probably via the 243Am + 54Cr reaction, but a precise timeframe has not been publicly released.[38][39]

Following their success in obtaining oganesson by the reaction between 249Cf and 48Ca in 2006, the team at the Joint Institute for Nuclear Research (JINR) in Dubna started similar experiments in March–April 2007, in hope of creating element 120 (unbinilium) from nuclei of 58Fe and 244Pu.[40][41] Isotopes of unbinilium are predicted to have alpha decay half-lives of the order of microseconds.[42][43] Initial analysis revealed that no atoms of element 120 were produced, providing a limit of 400 fb for the cross section at the energy studied.[44]

244 94Pu + 58 26Fe → 302120* → no atoms

The Russian team planned to upgrade their facilities before attempting the reaction again.[44]

In April 2007, the team at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, attempted to create element 120 using uranium-238 and nickel-64:[45]

238 92U + 64 28Ni → 302120* → no atoms

No atoms were detected, providing a limit of 1.6 pb for the cross section at the energy provided. The GSI repeated the experiment with higher sensitivity in three separate runs in April–May 2007, January–March 2008, and September–October 2008, all with negative results, reaching a cross section limit of 90 fb.[45]

In June–July 2010, and again in 2011, after upgrading their equipment to allow the use of more radioactive targets, scientists at the GSI attempted the more asymmetrical fusion reaction:[46]

248 96Cm + 54 24Cr → 302120 → no atoms

It was expected that the change in reaction would quintuple the probability of synthesizing element 120,[47] as the yield of such reactions is strongly dependent on their asymmetry.[28] Three correlated signals were observed that matched the predicted alpha decay energies of 299120 and its daughter 295Og, as well as the experimentally known decay energy of its granddaughter 291Lv. However, the lifetimes of these possible decays were much longer than expected, and the results could not be confirmed.[48][49][46]

In August–October 2011, a different team at the GSI using the TASCA facility tried a new, even more asymmetrical reaction:[50][31]

249 98Cf + 50 22Ti → 299120* → no atoms

This was also tried unsuccessfully the next year during the aforementioned attempt to make element 119 in the 249Bk+50Ti reaction, as 249Bk decays to 249Cf. Because of its asymmetry,[51] the reaction between 249Cf and 50Ti was predicted to be the most favorable practical reaction for synthesizing unbinilium, although it is also somewhat cold. No unbinilium atoms were identified, implying a limiting cross-section of 200 fb.[31] Jens Volker Kratz predicted the actual maximum cross-section for producing element 120 by any of these reactions to be around 0.1 fb;[52] in comparison, the world record for the smallest cross section of a successful reaction was 30 fb for the reaction 209Bi(70Zn,n)278Nh,[28] and Kratz predicted a maximum cross-section of 20 fb for producing the neighbouring element 119.[52] If these predictions are accurate, then synthesizing element 119 would be at the limits of current technology, and synthesizing element 120 would require new methods.[52]

In May 2021, the JINR announced plans to investigate the 249Cf+50Ti reaction in their new facility. However, the 249Cf target would have had to be made by the Oak Ridge National Laboratory in the United States,[53] and after the Russian invasion of Ukraine began in February 2022, collaboration between the JINR and other institutes completely ceased due to sanctions.[54] Consequently, the JINR now plans to try the 248Cm+54Cr reaction instead. A preparatory experiment for the use of 54Cr projectiles was conducted in late 2023, successfully synthesising 288Lv in the 238U+54Cr reaction,[55] and the hope is for experiments to synthesise element 120 to begin by 2025.[56]

Starting from 2022,[34] plans have also been made to use 88-inch cyclotron in the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, California, United States to attempt to make new elements using 50Ti projectiles.[57][58] First, the 244Pu+50Ti reaction was tested, successfully creating two atoms of 290Lv in 2024. Since this was successful, an attempt to make element 120 in the 249Cf+50Ti reaction began in 2025.[59][60][61][62] The Lawrence Livermore National Laboratory (LLNL), which previously collaborated with the JINR, is collaborating with the LBNL on this project.[63]

The synthesis of element 121 (unbiunium) was first attempted in 1977 by bombarding a target of uranium-238 with copper-65 ions at the Gesellschaft für Schwerionenforschung in Darmstadt, Germany:

238 92U + 65 29Cu → 303121* → no atoms

No atoms were identified.[11]

The first attempts to synthesize element 122 (unbibium) were performed in 1972 by Flerov et al. at the Joint Institute for Nuclear Research (JINR), using the heavy-ion induced hot fusion reactions:[10]

238 92U + 66,68 30Zn → 304, 306122* → no atoms

These experiments were motivated by early predictions on the existence of an island of stability at N = 184 and Z > 120. No atoms were detected and a yield limit of 5 nb (5,000 pb) was measured. Current results (see flerovium) have shown that the sensitivity of these experiments were too low by at least 3 orders of magnitude.[12]

In 2000, the Gesellschaft für Schwerionenforschung (GSI) Helmholtz Center for Heavy Ion Research performed a very similar experiment with much higher sensitivity:[10]

238 92U + 70 30Zn → 308122* → no atoms

These results indicate that the synthesis of such heavier elements remains a significant challenge and further improvements of beam intensity and experimental efficiency is required. The sensitivity should be increased to 1 fb in the future for better quality results.

Another unsuccessful attempt to synthesize element 122 was carried out in 1978 at the GSI Helmholtz Center, where a natural erbium target was bombarded with xenon-136 ions:[10]

nat 68Er + 136 54Xe → 298, 300, 302, 303, 304, 306122* → no atoms

In particular, the reaction between 170Er and 136Xe was expected to yield alpha-emitters with half-lives of microseconds that would decay down to isotopes of flerovium with half-lives perhaps increasing up to several hours, as flerovium is predicted to lie near the center of the island of stability. After twelve hours of irradiation, nothing was found in this reaction. Following a similar unsuccessful attempt to synthesize element 121 from 238U and 65Cu, it was concluded that half-lives of superheavy nuclei must be less than one microsecond or the cross sections are very small.[64] More recent research into synthesis of superheavy elements suggests that both conclusions are true.[28][65] The two attempts in the 1970s to synthesize element 122 were both propelled by the research investigating whether superheavy elements could potentially be naturally occurring.[10]

Several experiments studying the fission characteristics of various superheavy compound nuclei such as 306122* were performed between 2000 and 2004 at the Flerov Laboratory of Nuclear Reactions. Two nuclear reactions were used, namely 248Cm + 58Fe and 242Pu + 64Ni.[10] The results reveal how superheavy nuclei fission predominantly by expelling closed shell nuclei such as 132Sn (Z = 50, N = 82). It was also found that the yield for the fusion-fission pathway was similar between 48Ca and 58Fe projectiles, suggesting a possible future use of 58Fe projectiles in superheavy element formation.[66]

Unbiquadium (E124)

[edit]

Scientists at GANIL (Grand Accélérateur National d’Ions Lourds) attempted to measure the direct and delayed fission of compound nuclei of elements with Z = 114, 120, and 124 in order to probe shell effects in this region and to pinpoint the next spherical proton shell. This is because having complete nuclear shells (or, equivalently, having a magic number of protons or neutrons) would confer more stability on the nuclei of such superheavy elements, thus moving closer to the island of stability. In 2006, with full results published in 2008, the team provided results from a reaction involving the bombardment of a natural germanium target with uranium ions:

238 92U + nat 32Ge → 308, 310, 311, 312, 314124* → fission

The team reported that they had been able to identify compound nuclei fissioning with half-lives > 10−18 s. This result suggests a strong stabilizing effect at Z = 124 and points to the next proton shell at Z > 120, not at Z = 114 as previously thought. A compound nucleus is a loose combination of nucleons that have not arranged themselves into nuclear shells yet. It has no internal structure and is held together only by the collision forces between the target and projectile nuclei. It is estimated that it requires around 10−14 s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes a nuclide, and this number is used by IUPAC as the minimum half-life a claimed isotope must have to potentially be recognised as being discovered. Thus, the GANIL experiments do not count as a discovery of element 124.[10]

The fission of the compound nucleus 312124 was also studied in 2006 at the tandem ALPI heavy-ion accelerator at the Laboratori Nazionali di Legnaro (Legnaro National Laboratories) in Italy:[67]

232 90Th + 80 34Se → 312124* → fission

Similarly to previous experiments conducted at the JINR (Joint Institute for Nuclear Research), fission fragments clustered around doubly magic nuclei such as 132Sn (Z = 50, N = 82), revealing a tendency for superheavy nuclei to expel such doubly magic nuclei in fission.[66] The average number of neutrons per fission from the 312124 compound nucleus (relative to lighter systems) was also found to increase, confirming that the trend of heavier nuclei emitting more neutrons during fission continues into the superheavy mass region.[67]

Unbipentium (E125)

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