Unseptnilium

Unseptnilium, Usn, is the temporary name for element 170. Isotopes are predicted between ⁴⁸²Usn and ⁴⁶¹Usn (excluding probable artifacts), none of which have half-lives exceeding 0.001 sec. None of these predicted isotopes can form. Isotopes in the band ⁵⁸⁰Usn to ⁵⁶¹Usn are likely, most of which may form. All Usn isotopes will be gone less than 1000 sec. after the event which led to their formation.

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 ⁵⁰²Usn to ⁴³⁹Usn.

⁵⁰²Usn and ⁴⁹⁹Usn appear to be artifacts. N = 318 has been predicted⁽²⁾ to be a neutron closure, but N = 229 or 232 is far above that closure.

⁴⁹⁸Usn to ⁴⁸³Usn is a gap, which might mean half-lives below 10^-09 sec or might mean the model is going ragged at its edges.

The main band lies between ⁴⁸²Usn and ⁴⁶¹Usn. Format used to display these is: isotope(s); half-life in seconds; dominant decay mode; comments.

⁴⁸²Usn - ⁴⁸⁰Usn; 10^-09 - 10^-06; alpha; These are not unrealistic, particularly if N = 318 is also neutron-magic like N = 308.

⁴⁷⁹Usn - ⁴⁶⁸Usn; 10^-06 - 0.001; alpha.

⁴⁶⁷Usn - ⁴⁶⁵Usn; 10^-09 - 10^-06; alpha.

⁴⁶⁴Usn; < 10^-09; decay mode probably fission

⁴⁶³Usn - ⁴⁶¹Usn; 10^-09 - 10^-06; fission.

This pattern is to be expected, given a neutron shell closure at N = 308.

Isotopes decaying by alpha emission and having half-lives between 10^-09 and 10^-06 sec are also predicted in the band from ⁴⁴⁰Usn to ⁴³⁹Usn. Despite their short half-lives, the isotopes in this band are probably artifacts connected to those reported for Usu and Usb.

GUESSED PROPERTIES

Drops in the bands ⁵⁸⁰Usn to ⁵⁶¹Usn and ⁴⁷⁹Usn to ⁴⁷⁴Usn are unlikely to decay by neutron emission and are stable against fission. Nuclides in these bands are likely. Drops in the bands ⁶¹⁶Usn to ⁵⁸¹Usn, ⁵⁶⁰Usn to ⁴⁸⁰Usn, and ⁴⁷³Usn to ⁴³⁶Usn are unlikely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in these bands are unlikely.

COMPARISON

In the region where predictions and guesses overlap, the estimating technique lists only ⁴⁷⁹Usn to ⁴⁷⁴Usn as "likely". Ref. 1 predicts a much wider band of existing Usn isotopes.

OCCURRENCE

FORMATION

⁵⁸⁰Usn to ⁵⁶¹Usn 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.). Isotopes in this band may form directly or via beta decay chains from lower Z nuclides. Attrition from decay chains due to fission or beta+neutron(s) emission can be expected.

Many nuclear drops in the band ⁵⁰²Usn to ⁴³⁹Usn are predicted to be nuclides. They are all too far from the neutron dripline to form directly, and cannot form from lower Z nuclides because beta decay chains terminate at Z < 170.

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

PERSISTENCE

All Usn isotopes are expected to decay away to nothing within 1000 sec after the neutron star merger which led to their formation.

ATOMIC PROPERTIES

Electron structure of Usn has been predicted by several sources (see "Extended Periodic Table" in Wikipedia). However, these predictions should be used with caution. Orbital theory may break down at Z = 170. While only the innermost electrons would be qualitatively different, other orbitals are likely to be affected sufficiently to change the ground state occupation. Usn is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Usn to have different electronic structures. (That means it is no longer an element in the chemical sense.)

If these effects are small, Usn will be a p-block metal of the 8th period. Its electron configuration has been predicted⁽³⁾ to be [Og] 5g¹⁸ 6f¹⁴ 7d¹⁰ 8s² 8p²_1/2 8p²_3/2 9s² 9p²_1/2.

REFERENCES

1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4^th 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. "Extended Periodic Table", Wikipedia.

4. 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

(06-08-20)