Unpentbium, Upb, is the temporary name for element 152. Isotopes are predicted between Upb 475 and Upb 421. Reported half-lives are all less than 1 hr, and most are under 1 sec. Eleven isotopes in the band Upb 456 to Upb 446 can form. Beyond the region for which predictions are available, isotopes in the band Upb 546 to Upb 541 are likely. It is possible that all of them can form. One predicted isotope, Upb 446, may persist for up to 2 days after the event which led to its formation. All others will last less than 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 Upb 475 to Upb 421. Format used to display isotope properties is: isotope(s); half-life in seconds; dominant decay mode; comments.

Upb 475 - Upb 473; <10^-06; fission. Upb 474 has a half-live under 10^-09 sec.

Upb 472; 10^-09 - 10^-06; beta. Decay mode is an anomaly. Beta decay is not that rapid.

Upb 471 - Upb 470; 10^-06 - 0.001; fission. Fission half-lives this long are plausible only if there is a shell closure at N = 318(2). They are too far above N = 308 for it to stabilize nuclides against fission. If N = 308 is the only closure, these nuclides should either decay quickly by fission or decay decay in a millisecond time frame by beta emission.

Upb 469; 0.001 - 1; fission. A fission half-life this long is plausible only if there is a shell closure at N = 318. It is too far above N = 308 for that closure to stabilize it against fission. If N = 308 is the only closure, this nuclide should either decay quickly by fission or decay in a millisecond time frame by beta emission.

Upb 468 - Upb 445; 0.001 - 1; beta.

Upb 444; 0.001 - 1; 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 isotopes between Upb 444 and Upb 437 which decay in the manner predicted are not implausible.

Upb 443; 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, so isotopes between Upb 444 and Upb 437 which decay in the manner predicted are not implausible. Beta decay is likely to be an important secondary decay mode.

Upb 442; 0.001 - 1; 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, so isotopes between Upb 444 and Upb 437 which decay in the manner predicted are not implausible.

Upb 441; 1 - 1000; fission.  Predicted mode and half-life are plausible, as stated for Upb 443 above.

Upb 440; 0.001 - 1; beta. Alpha emission and fission are likely to be important secondary decay modes for this nuclide.

Upb 439; 1 - 1000; alpha. Beta emission and fission are likely to be important secondary decay modes.

Upb 438 - Upb 437; 0.001 - 1; fission. Half-lives and decay modes are plausible as described above.

Upb 436 - Upb 431; 0.001 - 1; alpha. Even-N nuclides in this band are beta-stable, so their properties are estimated from adjacent nuclides. The estimate for Upb 432 is particularly uncertain.

Upb 430 - Upb 427; 0.001 - 1; alpha and fission. Even-N isotopes in this band decay by fission, odd-N isotopes decay by alpha emission. This is reasonable, given the very strong stabilization that an unpaired neutron has on fission. All isotopes in this band are beta-stable, so both mode and half-life are estimated from adjacent nuclides. Due to rapidly changing half-lives and decay modes for nuclides in this region, these estimates are particularly uncertain.

Upb 426 - Upb 423; 10^-06 - 0.001; fission. Except for Upb 423, all isotopes in this band are beta-stable. Decay modes and half-lives are estimated from the properties of adjacent nuclides.

Upb 422 - Upb 421; 10^-09 - 10^-06; fission. Properties of Upb 422 are estimated, since it is predicted to be beta-stable.

Below N = 308, this pattern is generally to be expected, given a neutron shell closure at N = 308. Above this point, predictions become more confusing. Presence of relatively long-lived, fission-decaying isotopes of Upb indicates a more sophisticated structure than implied by a simple liquid-drop picture.

GUESSED PROPERTIES

Drops in the band Upb 546 to Upb 541 are unlikely to decay by neutron emission and are stable against fission. Nuclides in this band are likely. Drops in the band Upb 540 to Upb 486 are unlikely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in this band are unlikely. Below Upb 486, predictions are available.

OCCURRENCE

FORMATION

Upb 546 to Upb 541 are likely to be nuclides. Depending on the neutron dripline's actual location, nuclei in this A range may form when material over 700 - 800 meters deep is ejected from a neutron star during a merger. (See "Neutron Star", this Wiki.). These can form directly as neutron star material breaks up or by beta-decay chains from lower-Z nuclides.

Nearly all nuclear drops in the band Upb 475 to Upb 421 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 Upb 457 or heavier isotopes are terminated at Z < 152 by nuclides which fission so quickly that no beta-decay branch is possible.

In order to determine whether Upb 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 in the band Upb 456 to Upb 446 can form.

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

PERSISTENCE

The isotopes Upb 554 to Upb 543 are outside the range in which half-life predictions exist. They are all very neutron-rich, which implies half-lives under 1 sec(1),(4) are likely. They can be expected to vanish within 1000 sec after the neutron star merger (or similar event) which led to their formation.

One predicted isotope, Upb 446, Upb, may persist for a relatively long time, but is expected to disappear within 2 days after the event which led to its formation. All other predicted isotopes will be gone within 1000 sec.

ATOMIC PROPERTIES

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

If this effect is small, Upb will be an active (superactinide) metal of the 8th period. Its electron configuration has been predicted(5) to be [Og] 5g18 6f9 7d3 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.  “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.

(06-20-20)

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