Untrioctium

Untrioctium
138Uto
- ↑ Uto ↓ Uoo Extended periodic table untriseptium ← untrioctium → untriennium
Appearance
unknown
General properties
Name, symbol, number	untrioctium, Uto, 138
Pronunciation	/uːntraɪˈɒktiəm/
Element category	superactinides
Group, period, block	N/A, 8, g
Mass number	not applicable
Electron configuration	[Uuo] 5g126f37d18s28p2 (predicted) 2, 8, 18, 32, 44, 21, 9, 4 (predicted)
Physical properties
unknown
Atomic properties
unknown
Most stable isotopes
Main article: Isotopes of untrioctium
iso NA half-life DM DE (MeV) DP 366Uto (predicted) syn
v • t • e • r

Untrioctium, Uto, is the temporary name for element 138. Isotopes are predicted in the bands ⁴⁵¹Uto to ³⁹⁵Uto, ³⁷¹Uto to ³⁶⁵Uto, and ³⁵⁹Uto. There may be isotopes in the band from the neutron dripline to ⁴⁵²Uto, but it is not possible to predict which ones are possible. Reported half-lives are all less than 1 hr, and most are under 1 sec. Forty isotopes in the bands ⁴⁵¹Uto to ⁴³⁴Uto and ⁴²³Uto to ⁴⁰²Uto are predicted to form. Four predicted isotopes, ⁴³⁸Uto and ⁴³⁶Uto through ⁴³⁴Uto, may persist for up to 2 days after the event which led to their formation. All other isotopes will last less than 1000 sec.

Uto may be proton-magic.

NUCLEAR PROPERTIES

INFORMATION SOURCES

While studies addressing specific issues have been carried out to very high N⁽¹⁾. and to moderate Z⁽²⁾, (Z,N) or (Z,A) maps predicting half-lives and decay modes are almost completely limited to the region below Z = 130 and N = 220. There appears to be only one such map which extends beyond that region and is accessible⁽³⁾.

(Z,N) maps for half-life and decay mode in Ref. 3 extend as high as Z = 175 and N = 333. Half-lives are reported as bands 3 orders of magnitude wide (0.001 - 1 sec, for example), and should be considered accurate only to within +/- orders of magnitude (presumably from band center. (A nuclide reported to be in the 0.001 - 1 sec band should be considered to have a possible half-life between 10^-4.5 sec and 10^1.5 sec.) Decay modes are limited alpha emission, beta emission, proton emission, and fission; and to the principal one for each nuclide. There are areas where two modes (or more) may be important, meaning that small uncertainties is model parameters could have produced different results. It is also possible that cluster decay may become important above the neutron shell closures at N = 228 and 308.

Ref. 3 does have two significant weakness in the way data are presented. Nuclides which are beta-stable are identified by black squares, overwriting decay mode and half-life information. In addition, nuclides having half-lives less than 10^-09 sec are not reported, which obscures the distinction between nuclides having half-lives in the 10^-09 and 10^-14 sec band and nuclear drops whose half-life is under 10^-14 sec.

Above Z around 126, predictions in Ref. 3 may not reach the neutron dripline. This can be an important limitation because the only processes which can form nuclei at more than atoms / star quantity generate very neutron-rich nuclei. It is possible to to make a crude, but conservative (high N) guess for the dripline's location by averaging predicted values for even-N nuclei.{See "The Final Element" (this wiki).} It is also possible to guess at regions of the (Z,N) or (Z,A) plane in which a fission barrier high enough to permit nuclides exists by using a first-order, liquid drop model. {See "Nuclear Guesswork" (this wiki).} Specific numbers are reported for these guesses, not with the expectation that they are accurate, but because they are consistent from element to element. They allow construction of a map which at least hints at where in the (Z,A) plane nuclides may be found.

GUESSED PROPERTIES

Properties at high A: A simple liquid-drop picture indicates that ⁴⁹²Uto to ⁴⁵²Uto are unlikely to decay by neutron emission and are stable enough against fission to allow beta decay. Between ⁴⁷¹Uto and ⁴⁵²Uto, Ref. 3 probably makes no predictions, but extrapolation from higher Z indicates that it would predict mainly short-lived, fission-decaying nuclides. Nuclear properties above ⁴⁵¹Uto are highly uncertain, but it is possible that some relatively long-lived, beta-decaying isotopes of Uto are possible. It is possible to state that half-lives longer than 1 sec are implausible between the neutron dripline (nominally ⁴⁹²Uto) and ⁴⁵²Uto.

Properties Near N = 258: Ref. 3 indicates a weak shell closure at N = 258. Some other models, constructed to study rapid neutron capture processes, indicate a strong closure at N = 258^{(citation needed)}. No predictions, however, exist for decay properties of nuclides near ³⁹⁶Uto. Based on similarities to closures at N = 184, 228, and 308/318, the effect of a strong shell closure at N = 258 would be to stabilize a band from ⁴⁰⁰Uto down to ³⁸⁸Uto against fission, allowing decay by beta or alpha emission and half-lives in excess of 0.001 sec. Estimating from ²⁹³Cn, ³⁵⁴Ubh, and ⁴⁷²Uhq, and from its predicted stability against beta decay, ³⁹⁶Uto itself is expected to decay by alpha emission and might, optimistically, have a half-life on the order of 1 year. Some other nuclides in the ⁴⁰⁰Uto - ³⁸⁸Uto band will probably have half-lives exceeding 1000 sec, whether they decay by alpha or beta emission.

PREDICTED PROPERTIES

Isotopes in the band ⁴⁵¹Uto - ⁴³⁹Uto are predicted to decay by beta emission. Predicted half-lives are in the 0.001 - 1 sec range. Actual half-lives are probably a few milliseconds and increase with declining N as the number of decays required to reach beta stability falls.

Isotopes in the band ⁴³⁸Uto - ⁴³⁰Uto are predicted to decay by fission. It appears to be possible for structure to destabilize a nuclide⁽⁴⁾, so the data reported appear to be realistic, At the upper end of this band, though, half-lives are unrealistically high, since partial half-lives against beta emission should be on the order of milliseconds this far from beta stability⁽⁵⁾. Half-lives decline as N falls, which is expected.

Isotopes in the band ⁴²⁹Uto - ⁴⁰³Uto are predicted to decay by beta emission. Half-lives are predicted to lie between 0.001 and 1 sec. Partial half-lives for beta decay should increase as N declines and the number of beta decays required to reach beta stability declines.

Between ⁴⁰²Uto and ³⁹⁸Uto, odd-N isotopes are predicted to decay by beta emission with 0.001 - 1 sec half-lives, and even-N isotopes are predicted to decay by fission with short - and declining - half-lives,

Isotopes in the band ³⁹⁷Uto to ³⁹⁵Uto have half-lives greater than expected, and decay via modes which are somewhat confusing. It is likely some predictions are artifacts.

There is a gap from ³⁹⁴Uto to ³⁷²Uto in which properties are not reported. These may be short lived nuclides or nuclear drops whose half-life is less than 10^-14 sec. It appears to be the expected destabilized region above N = 228.

Between ³⁷¹Uto and ³⁶⁵Uto drops are predicted to last long enough to be nuclides, but half-lives are microsecond-scale or shorter. Fission is predicted to dominate throughout this band.

Another gap is predicted between ³⁶⁴Uto and ³⁶⁰Uto. This may indicated very short lived nuclides or nuclear drops which don't last long enough to qualify as nuclides.

³⁵⁹Uto is predicted to decay by fission with a short half-life. This appears to be a nuclide which popped above the 10^-09 sec model threshold.

N = 258 CLOSURE

The model used to predict decay properties of Uto isotopes has a relatively weak neutron shell closure at N = 258. Some neutron-dripline studies have indicated a strong closure at N = 258. If that closure is strong, one or more isotopes in the band ³⁹⁶Uto to ³⁷⁷Uto may even have half-lives exceeding 1000 sec. Note that the group included doubly-magic ³⁹⁶Uto itself. Interpolating between ⁴⁷²Uhq and ²⁹³Cn gives a reasonable value for maximum half-life of any nuclides stabilized by a strong N = 258 closure of 0.5 yr. Either alpha decay or beta decay may occur in this band, but fission can be expected to be suppressed.

These are not predictions of decay properties for nuclides in the vicinity of N = 258. This entire exercise is qualitative guesswork. No numbers, but a tantalizing hint of what might be.

OCCURRENCE

FORMATION

Where nuclear drops between the neutron dripline (nominally ⁴⁹²Uto) and ⁴⁵²Uto can be nuclides, they may form. Heavier isotopes may form directly from disintegrating neutron star material, and the remainder may form via beta decay chains from lower-Z nuclides. Since some of these chains may be terminated by short-lived, fission-decaying nuclides, it is not possible to say which isotopes of Uto in this range can form.

Nearly all nuclear drops in the bands ⁴⁵¹Uto to ³⁹⁵Uto, ³⁷¹Uto to ³⁶⁵Uto, and ³⁵⁹Uto are predicted to be nuclides. All are too far from the neutron dripline to form directly. It is possible to simulate the formation of nuclides via decay chains using data from Ref. 3 and assuming an initial distribution close to the neutron dripline. Details of the model are provided in "Nuclear Decay Chains at High A" in this wiki. Per that model, 40 predicted isotopes; ⁴⁵¹Uto to ⁴³⁴Uto and ⁴²³Uto to ⁴⁰²Uto; can form.

Neutron capture may be able to produce nuclides up to A around 360 before fission attrition stops further growth. It is implausible that neutron capture can form any Uto isotope. A small amount of fission infall may contribute to nuclides up to A = 406 (nominal).

PERSISTENCE

⁴³⁹Uto and heavier isotopes, plus ⁴³⁷Uto will vanish within 1000 sec after a neutron star merger which led to their formation.

⁴³⁸Uto, ⁴³⁶Uto, and ⁴³⁵Uto are predicted to decay by fission, have half-lives in the 1 - 1000 sec range, and be located at the end of beta-decay chains. They can be expected to persist for a time less than 105000 sec.

⁴³⁴Uto lies at the end of a beta-decay chain, but has a half-life of less than 1 sec. It will disappear within 10^2.5 sec.

⁴³³Uto to ⁴¹⁸Uto are blocked from forming via beta decay from the dripline by fission at Z < 138.

⁴¹⁷Uto through ⁴¹⁵Uto, and ⁴¹³Uto through ⁴⁰³Uto are predicted to be short-lived, beta-decaying species,

⁴¹⁴Uto is predicted to decay by fission with a long half-life. This nuclide's decay properties are unlike those of the others in its vicinity. It is probably an artifact. ⁴¹⁴Uto probably decays by beta emission and has a half-life in the vicinity of 1 sec.

No other isotopes of Uto persist for a significant time.

Calculations done under maximum half-life assumptions and with all nuclides initially populated still point to all isotopes of Uto vanishing within 10^5.5 (3.16E05) sec.

N = 258 SHELL CLOSURE

Some studies of the neutron dripline indicate a strong shell closure at N = 258, instead of the relatively weak one occurring in the predictive models, If so, and if peak half-lives in the region do approach 0.5 yr, it is possible that one or more isotopes in the band ³⁹⁶Uto to ³⁷⁷Uto may persist for up to 60 yrs. If so, unlike all nuclides with A > 396, small quantities of nuclides in that band may be injected into a stellar system other than the one in which neutron star merger occurred.

ATOMIC PROPERTIES

Electron structure of Uto has been predicted by several sources (see "Extended Periodic Table" in Wikipedia). However, these predictions should be used with caution. Uto is large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Uto to have different electronic structures. (That means it is no longer an element in the chemical sense.)

If this effect is small, Uto will be an active (superactinide) metal of the 8th period. Its electron configuration has been predicted⁽⁶⁾ to be [Og] 5g¹² 6f³ 7d¹ 8s² 8p²_1/2. (Note the 6f-7d change.)

REFERENCES

1. for example, "Nuclear Energy Density Functionals: What Do We Really Know?"; Aurel Bulgac, Michael McNeil Forbes, and Shi Jin; Researchgate publication 279633220 or arXiv: 1506.09195v1 [nucl-th] 30 Jun 2015.

2. for example "Fission Mechanism of Exotic Nuclei"; Research Group for Heavy Element Nuclear Science; http://asrc.jaea.go.jp/soshiki/gr/HENS-gr/np/research/pageFission_e.html.; 17 Sept 17.

3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.

4. "Magic Numbers of Ultraheavy Nuclei"; Vitali Denisov; Physics of Atomic Nuclei; researchgate.net/publications/225734594; July 2005.

5. "Nuclear Properties for Astrophysical Applications"; P. Moller & J. R. Nix; Los Alamos National Laboratory website; search by "LANL, T2", then "Nuclear Properties for Astrophysical Applications".

6. "Extended Periodic Table", Wikipedia.

7. Other references are found in the wiki articles cited.

9-Period Periodic Table of Elements
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	169 Uhe	170 Usn	171 Usu	172 Usb
9	173 Ust	174 Usq
Alkali metal Alkaline earth metal Lanthanide Actinide Superactinide Transition metal Post-transition metal Metalloid Other nonmetal Halogen Noble gas predicted predicted predicted predicted predicted predicted predicted predicted predicted

(06-29-20)