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Unquadpentium, Uqp, is the temporary name for element 145. It is expected to be a transient element, one without long-lived isotopes or long-lived precoursers. Uqp 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

Ref. 1 predicts isotopes ranging from Uqp 473 to Uqp 410, plus isotopes ranging from Uqp 374 to Uqp 367. The gap between these bands may be short lived nuclides or nuclear drops whose half-life is less than 10^-14 sec. Format used to display isotope properties is: isotope(s); half-life in seconds; dominant decay mode; comments.

Uqp 473 - Uqp 462; <10^-06; fission. Two isotopes, Uqp 471 and Uqp 363 are reported to have half-lives in the 10^-06 - 0.001 sec range, but such long-lived, isolated, fissioning nuclides appear to be artifacts.

Uqp 461 - Uqp 446; 0.001 - 1; beta.

Uqp 445 - Uqp 444; 1 - 1000; fission. These nuclides are around 10 steps from beta stability, which means even a 1 sec partial half-life against beta decay is questionably long(2), particularly in light of the shorter half-lives predicted for lighter, beta-decaying Uqp isotopes. They may be artifacts.

Uqp 443 - Uqp 440; 0.001 - 1; beta.

Uqp 439 - Uqp 436; 0.001 - 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. Beta emission can be expected to be an important secondary decay mode.

Uqp 435 - Uqp 427; 0.001 - 1; beta.

Uqp 426 - Uqp 417; 0.001 - 1000; mixed. Even-N isotopes in this band are predicted to decay by alpha emission with half-lives over 1 sec, odd-N isotopes are predicted to decay by beta emission with half-lives under 1 sec. This is not unrealistic if all half-lives are close to 1 sec.

Uqp 416 - Uqp 414; 0.001 - 1; mixed. Odd-Z, odd-N nuclides tend to have long fission half-lives, so the predicted beta decay of Uqp 415 and fission decay of the others is plausible.

Uqp 413; 10^-06 - 0.001; fission.

Uqp 412; 10^-09 - 10^-06; fission.

Uqp 411; 0.001 - 1; fission. Half-life of this isotope is unexpectedly long.

Uqp 410; 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.

Near the predicted N = 228 shell closure, properties of Uqp isotopes are reported to be

Uqp 374 - Uqp 373; 10^-09 - 10^-06; fission.

Uqp 372 - Uqp 369; <10^-09; fission.

Uqp 368 - Uqp 367; 10^-09 - 10^-06; alpha.

This is the pattern to be expected near a shell closure.

GUESSED PROPERTIES

Drops in the bands Uqp 519 to Uqp 486, Uqp 455 to Uqp 444, and Uqp 373 to Uqp 372 are unlikely to decay by neutron emission and are stable against fission. Nuclides in these bands are likely. Other drops are unlikely to survive long enough to be nuclides.

COMPARISON

Ref. 1 predicts that beta decay will occur below Uqp 461 while the estimating technique used indicates rapid fission down to Uqp 456. Both approaches indicate very short half-lives for nuclear drops in the Uqp 478 to Uqp 462 and Uqp 409 to Uqp 375 bands.

FORMATION

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

Isotopes in the band Uqp 519 to Uqp 486 can form by a series of beta decays from the neutron dripline. Formation of isotopes in this band is likely. It is improbable that other isotopes in the band Uqp 485 - Uqp 479 can form.

Beta decay from the neutron dripline also forms nuclei in 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, Uqp 455 to Uqp 413 and Uqp 411 to Uqp 410 can form. It is improbable that other isotopes in the bands Uqp 478 to Uqp 410 or Uqp 374 to Uqp 367 can form.

ATOMIC PROPERTIES

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

If this effect is small, Uqp will be an active (superactinide) metal of the 8th period. Its electron configuration has been predicted(4) to be [Og] 5g18 6f3 7d2 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. "Extended Periodic Table", Wikipedia.

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

(06-29-20)

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