Unquadoctium, Uqo, is the temporary name for element 148. Isotopes are predicted at Uqo 475 and between Uqo 467 and Uqo 415. Reported half-lives are all less than 1 hr, and most are under 1 sec. Predicted isotopes in the band Uqo 456 to Uqo 447, and Uqo 423, may form. All isotopes except Uqo 423 will become extinct in less than 1000 sec after the event which led to their formation. Uqo 423 itself will vanish within 2 days.


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.


Ref. 1 predicts isotopes ranging from Uqo 475 to Uqo 415. Format used to display isotope properties is: isotope(s); half-life in seconds; dominant decay mode; comments.

Uqo 475 - Uqo 466; <10^-06; fission.

Uqo 465; 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.

Uqo 464 - Uqo 442; 0.001 - 1; beta.

Uqo 441 - Uqo 437; 10^-06 - 1000; fission. Odd-N isotopes are predicted to have half-lives in the range 1 - 1000 sec; even-N isotopes are predicted to have half-lives in the range 10^-06 - 0.001 sec. 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. However there is a gap of at least three orders of magnitude between odd-N and even-N isotopes, which implies that one or the other is erroneous.

Uqo 436 - Uqo 434; 0.001 - 1; mixed. Uqo 435 is reported to decay by fission, the others by beta emission. It is likely that all isotopes in this band decay by a mixture of both modes.

Uqo 433; 1 - 1000; fission. A half-life is close to 1 second continues the pattern for Uqo 436 - Uqo 434, so is likely.

Uqo 432 - Uqo 427; 0.001 - 1; mixed. Fission is predicted to dominate decay for Uqo 430, with beta emission dominating the others. All nuclides in this band are likely to decay by a mixture of both modes.

Uqo 426; 0.001 - 1; fission. Adjacent Uqo isotopes decay by different principal modes. This isotope may decay by a mixture of alpha emission as well as beta emission and fission.

Uqo 425 - Uqo; 0.001 - 1000; mixed. Alpha emission dominates for odd-N nuclides. All decay modes are likely, as are half-lives in the vicinity of 1 sec.

Uqo 422 - Uqo 420; 0.001 - 1; fission. Even-N isotopes in this band are beta-stable, so their properties are estimated from adjacent nuclides. Mixed alpha emission and fission is likely.

Uqo 419 - Uqo 417; 10^-06 - 0.001; fission.

Uqo 416; <10^-09 ; fission. Even-n / even-Z isotopes tend to have short fission half-lives.

Uqo 415; 10^-09 - 10^-06; fission. This nuclide is reported to be beta-stable, so has a half-life >10^-09 sec. Fission is the most likely decay mode.

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.


(does not apply for this element)



Nuclear drops Uqo 475 and nearly all the drops in the band Uqo 467 to Uqo 415 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 Uqo 457 or heavier isotopes are terminated at Z < 148 by nuclides which fission so quickly that no beta-decay branch is possible.

In order to determine whether Uqo 456 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, 11 isotopes; Uqo 456 to Uqo 447, and Uqo 423; can form.

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


The heavier predicted isotopes Uqo 456 to Uqo 447 will disappear within 1000 sec after the event which led to their formation. Uqo 423 will vanish within 2 days.


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

If this effect is small, Uqo will be an active (superactinide) metal of the 8th period. Its electron configuration has been predicted(4) to be [Og] 5g18 6f6 7d2 8s2 8p21/2.


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. "Extended Periodic Table", Wikipedia.

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


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