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This article is about an undiscovered element. Once it is discovered, this article will be edited with more information.

Untriquadium, Utq, is the temporary name for element 134. It is expected to be a transient element, one without long-lived isotopes or long-lived precoursers. Utq may form during neutron star mergers.

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

Up to Z = 140, Ref. 1 predicts no nuclides with N > 314. For Z > 140, it predicts heavier, fission-decaying isotopes, some of which have lifetimes exceeding 0.001 sec. While it is possible that this absence indicates extremely short half-lives for all heavy isotopes of elements with low atomic number, there are two objections to this interpretation. The first is that all such nuclides are very neutron-rich. At least some of them should have half-lives >10^-09 sec. The second is that no isotopes are reported for either even-Z or odd-Z, unlike what is reported for Z > 140. A more likely interpretation of the pattern reported is that nuclides with N > 314 were not modeled. That interpretation will be used here, and Ref. 1 will be used only up to the limiting N reported for each element. Heavier isotopes will be guessed at using a liquid-drop model.

Ref 1 predicts isotopes ranging from Utq 444 to Utq 383, Utq 369 to Utq 355, and Utq 317 to Utq 317.

Format used to display properties of specific isotopes of Utq is: isotope(s); half-life in seconds; dominant decay mode; comments.

Utq 444 - Utq 430; 10^-06 - 1; beta. This region of the half-life map is masked, but beta decay partial half-lives far from stability have a minimum near 0.001 sec(2).

Utq 429 - Utq 425; 10^-06 - 1; fission. Half-lives are masked in this band. 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 the data reported appear to be realistic, given that half-lives are in the vicinity of 0.001 sec and that beta emission is an important secondary decay mode.

Utq 424 - Utq 405; 10^-06 - 1; beta. Half-lives are masked in this band, but can be expected to be near 0.001 sec.

Utq 404 - Utq 397; 0.001 - 1; mixed. Beta emission dominates, except for Utq 402 and Utq 398 for which fission is dominant. Both modes probably occur in all isotopes in this band.

Utq 396 - Utq 393; mixed; mixed. Beta-decaying isotopes with 0.001 - 1 sec half-lives are predicted for odd-N species. Fissioning isotopes with shorter half-lives are predicted for even-N nuclides.

Utq 392 - Utq 390; mixed; mixed. In this band, the odd-N isotope Utp 391 is predicted to fission quickly, while the odd-N isotopes decay by beta emission with 0.001 - 1 sec half-lives. This pattern is somewhat unexpected.

Utq 3989 - Utq 387; <10^-09; fission.

Utq 386 - Utq 384: 0.001 - 1; beta.

Utq 383; 10^-09 - 10^-06; fission.

There is a gap from Utq 382 Utq 370 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.

Near the predicted N = 228 shell closure, Ref. 1 includes (pp 11 & 12) a more detailed look at expected partial half-lives against both alpha decay and fission. (Alpha decay predictions are hard to read, though.) Properties of Utq isotopes are reported to be

Utq 369 - Utq 366; <10^-06; fission. The isotope Utq 367 is predicted to be beta-stable, which obscures its other data. The properties reported are estimated from adjacent nuclides.

Utq 365 - Utq 363; 10^-06 - 0.001; fission. Onlu Utq 363 can be read directly. The others are beta-stable so their properties must be estimated.

Utq 362; 0.001 - 1; alpha. This appears to be correct, although alpha halflives from p 11 are difficult to read.

Utq 361; 10^-06 - 0.001; fission.

Utq 360 - Utq 356; <10^-06; fission.

Utq 355; 10^-06 - 0.001; fission. This long half-life is difficult to understand, and may be an artifact.

Such stabilization as a shell closure at N = 228 provides falls off quickly for N < 228, which is opposite of what is predicted at N = 184 and 308.

A few isotopes are predicted to exist near the N = 184 closure.

Utq 317 - Utq 313; 10^-06; fission.

Only odd-N isotopes have jhalf-lives exceeding 10^-09 sec

GUESSED PROPERTIES

Drops in the band Utq 477 to Utq 445 are unlikely to decay by neutron emission and are stable against fission. Nuclides in this band are likely. The estimating technique used does not permit estimation of fission half-lives, so it is uncertain whether the band of highly unstable nuclides predicted to lie above N = 318 continues to Utq. The band reported near N = 295 does continue, so it is likely that the heavier one does too. Below Utq 445, the availability of predictions makes guessing unnecessary.

FORMATION

Since a disintegrating neutron star can supply neutron-rich pieces of nuclear matter of the correct size (see "Neutron Star", this wiki), Utq isotopes can form where inhibition of fission allows beta decay from the neutron dripline.

Isotopes in the band Utp 481 to Utp 446 are estimated to form by a series of beta decays from the neutron dripline. This conclusion will not be valid above Utq 452 if a band of short-lived, fission-decaying nuclides (or even nuclear drops) does occur above N = 318.

Beta decay from the neutron dripline is also predicted to form nuclei within the region described in Ref. 1. Although only one decay mode is reported for each nuclide, branching decay can be expected unless the partial half-life against one mode of decay is much shorter than any of the others. In practice, that means beta decay series will extend either to nuclides which are stable against beta decay, nuclides lighter than beta-stable nuclides (which can decay by positron emission), or whose spontaneous fission partial half-lives are under 1 us.

Under this assumption, isotopes in the bands Utq 445 to Utq 391 can form. It is improbable that isotopes in the band Utq 392 to Utp 363 can form because beta decay chains are terminated at lower Z. It is also improbable that isotopes in the band Utq 362 to Utq 355, or Utq 317 to Utq 313 can form, since they are on the proton-rich side of beta stability.

ATOMIC PROPERTIES

Utq is expected to be an 8th period active metal (superactinide). Its consensus electron configuration has been predicted to be [Og] 5g8 6f4 8s2 8p21/2.

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. "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".

3.  “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.

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

(07-04-20)

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