Unquadennium

Unquadennium, Uqe, is the temporary name for element 149. Isotopes are predicted for ⁴⁷⁷Uqe to ⁴⁷⁵Uqe. and for ⁴⁷¹Uqe to ⁴¹⁶Uqe. Reported half-lives are all less than 1 hr, and most are under 1 sec. Thirteen isotopes in the band ⁴⁵⁶Uqe to ⁴³⁵Uqe can form. Beyond the region for which predictions are available, ⁵³⁵Uqe is likely, and may form. ⁴⁴⁰Uqe and ⁴³⁸Uqe are expected to persist slightly more than 2 days after the event which led to their formation, while ⁴³⁵Uqe is expected to persist for somewhat less than 2 days. All other Uqe isotopes are expected to vanish within 1000 sec.

NUCLEAR PROPERTIES

Between Z = 175 and Z near 130, one set of predictions for half-life and principal decay mode has been published⁽¹⁾. Ref. 1 is publicly available and can be found via a search by paper title. Anyone interested in this element should study pp 15 and 18, which allow a given element to be understood in the context of adjacent nuclides.

These data are limited to nuclides for which N <= 333. Half-lives are presented in bands covering 3 orders of magnitude (0.001 sec to 1 sec, for instance) and are accurate to within +/- 3 orders of magnitude, which seems rather crude until the enormous extrapolation from what is known is taken into account, Minimum half-life is set at 10^-09 sec, rather than 10^-14 sec; which introduces a little uncertainty, but not a great deal because fission half-lives tend to transition quickly from values well above 10^-09 sec to values well below 10^-14 sec; and, while alpha-decay half-lives change more slowly, alpha emission is rarely dominant except where fission is suppressed. Significantly, beta-decay half-lives do not decline far below 10^-03 sec, even for highly energetic decays, so there is little uncertainty about neutron-rich nuclides.

Ref. 1 does have one significant weakness. Nuclides which are beta-stable are identified by black squares, overwriting decay mode and half-life information. In many cases, these data can be estimated from adjacent nuclides.

No predictions exist for N > 333. The liquid-drop sketch developed in "The Final Element" (this wiki) for Z = 176 and above can be used to guess at where nuclides with Z < 175 and N > 333 may exist. Probability criteria for this purpose were set in "Nuclear Guesswork" (this wiki). Below Z = 171, it is necessary to look only at nuclear drops which are not expected to decay by neutron emission and require only normal amounts of structural correction energy in order to suppress spontaneous fission.

PREDICTED PROPERTIES

Ref. 1 predicts isotopes ranging from ⁴⁷⁷Uqe to ⁴¹⁶Uqe. Format used to display isotope properties is: isotope(s); half-life in seconds; dominant decay mode; comments.

⁴⁷⁷Uqe - ⁴⁶⁸Uqe; <10^-06; fission.

⁴⁶⁷Uqe - ⁴⁶⁶Uqe; 0.001 - 1; fission. A fission half-life this long is plausible only if there is a shell closure at N = 318⁽²⁾. It is too far above N = 308 for stabilization against fission. Beta decay seems more likely.

⁴⁶⁵Uqe - ⁴⁴²Uqe; 0.001 - 1; beta.

⁴⁴¹Uqe - ⁴³⁹Uqe; 1 - 1000; fission. Ref 1 predicts a band of fission-decaying nuclides with N between 285 and 295. It appears to be possible for structure to destabilize a nuclide⁽³⁾, so short partial half-lives against fission in this region are plausible.

⁴³⁸Uqe; 0.001 - 1; fission. Half-life is probably close to 1 second.

⁴³⁷Uqe; 1 - 1000; alpha. Fission is probably a competing decay mode.

⁴³⁶Uqe - ⁴³⁵Uqe; 1 - 1000; fission. Alpha emission is likely to be a competing decay mode.

⁴³⁴Uqe; 0.001 - 1; fission. Alpha emission is likely to be a competing decay mode.

⁴³³Uqe - ⁴³²Uqe; 1 - 1000; alpha.

⁴³¹Uqe; 1 - 1000; fission.

⁴³⁰Uqe - ⁴²⁶Uqe; 1 - 1000; alpha. Fission may not be a factor in these isotopes of Uqe.

⁴²⁵Uqe; 0.001 - 1; fission.

⁴²⁴Uqe - ⁴²³Uqe; 0.001 - 1; alpha.

⁴²²Uqe - ⁴²⁰Uqe; 0.001 - 1; fission. Alpha emission is likely to be a competing decay mode.

⁴¹⁹Uqe; 0.001 - 1; alpha. Fission is likely to be a competing decay mode.

⁴¹⁸Uqe; 10^-06 - 0.001; fission.

⁴¹⁷Uqe; 10^-06 - 0.001; fission. This nuclide is predicted to be beta-stable, so its half-life and decay mode are estimated.

⁴¹⁶Uqe; 10^-09 - 10^-06; fission.

This pattern is generally to be expected, given a neutron shell closure at N = 308. Presence of a fission-decaying band in the N = 285 - 295 range indicates requires nuclear structure.

GUESSED PROPERTIES

The nuclear drop ⁵³⁴Uqe is unlikely to decay by neutron emission and is stable against fission. It is likely to be a nuclide. Drops in the band ⁵³³Uqe to ⁴⁸³Uqe are unlikely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in this band are unlikely. Below ⁴⁸³Uqe, predictions are available.

OCCURRENCE

FORMATION

⁵³⁵Uqe is likely to be a nuclide. Depending on the neutron dripline's actual location, nuclei of this A value may form when material over 700 - 800 meters deep is ejected from a neutron star during a merger. (See "Neutron Star", this Wiki.). This nuclide can form directly as neutron star material breaks up or by a beta-decay chain from lower-Z nuclides. The isotope ⁵³⁵Uqe is outside the range in which half-life predictions exist. It is very neutron-rich, which implies a half-life under 1 sec^(1),(4) is likely.

Nuclear drops ⁴⁷⁷Uqe to ⁴⁷⁵Uqe and all the drops in the band ⁴⁷¹Uqe to ⁴¹⁶Uqe are predicted to be nuclides. They are all too far from the neutron dripline to form directly. All beta-decay chains which would lead to ⁴⁵⁷Uqe or heavier isotopes are terminated at Z < 149 by nuclides which fission so quickly that no beta-decay branch is possible.

In order to determine whether ⁴⁵⁶Uqe and lighter isotopes can form, it is necessary to model the evolution of initial material by radioactive decay. Details of the model are provided in "Nuclear Decay Chains at High A" in this wiki. Per that model, 13 isotopes; ⁴⁵⁶Uqe to ⁴⁴⁷Uqe, ⁴⁴⁰Uqe, ⁴³⁸Uqe, and ⁴³⁵Uqe; can form. The three lightest are predicted by the model which populated all nuclides at time zero, and due to infall from long-lived beta-alpha-fission decay chains.

It is implausible that neutron capture can form any Uqe isotope.

PERSISTENCE

⁴⁵⁷Uqe and heavier isotopes will decay to nothing within 1000 sec after a neutron star merger which led to their formation.

⁴⁵⁶Uqe through ⁴⁴⁷Uqe, are all part of long-lived decay chains, but have half-lives under 1 sec themselves and no precursors whose half-lives exceed 1 sec. All will vanish within 1000 sec.

⁴⁴⁶Uqe through ⁴¹⁸Uqe are blocked from forming via beta decay from the dripline by fission at Z < 149.

⁴⁴⁰Uqe has a predicted half-life in the 1 - 1000 sec range, and has four precursors with half-lives in the same range. It is the last step in a decay chain whose total time to extinction, under 125000 sec, has been computed.

⁴³⁵Uqe has a predicted half-life under 1 sec range, but has three precursors with half-lives in the 1 - 100 sec range. ⁴³⁵Uqe is the last step in a decay chain whose total time to extinction, under 120000 sec, has been computed .

No other isotopes of Uqe persist for a significant time.

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

ATOMIC PROPERTIES

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

If this effect is small, Uqe will be an active (superactinide) metal of the 8th period. Its electron configuration has been predicted⁽⁵⁾ to be [Og] 5g¹⁸ 6f⁶ 7d³ 8s² 8p²_1/2.

REFERENCES

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

2.  “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105.

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

4. "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".

5. "Extended Periodic Table", Wikipedia.

6. 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

(06-22-20)