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Untrihexium
136Uth
-

Uth

Uoh
untripentiumuntrihexiumuntriseptium
Appearance
unknown
General properties
Name, symbol, number untrihexium, Uth, 136
Pronunciation /ntrˈhɛksiəm/
Element category superactinides
Group, period, block N/A, 8, g
Mass number not applicable[1]
Electron configuration [og] 5g106f48s28p2
(predicted)[2]
2, 8, 18, 32, 42, 22, 8, 4
(predicted)[2]
136
Physical properties
unknown
Atomic properties
unknown
Most stable isotopes
Main article: Isotopes of untrihexium
iso NA half-life DM DE (MeV) DP
362Uth
(predicted)[1]
syn ms or lower fission
vter

Untrihexium, Uth, is the temporary name for element 136. Isotopes are predicted in the bands 446Uth to 387Uth and 371Uth to 355Uth. There may be isotopes in the band from the neutron dripline to 447Uth, but it is not possible to predict which ones are possible. Reported half-lives are all less than 1 hr, and most are under 1 sec. Forty-one isotopes in the bands 447Uth to 432Uth and 423Uth to 393Uth are predicted to form. All Uth isotopes, predicted or guessed, will last less than 1000 sec after the event which led to their formation.

NUCLEAR PROPERTIES[]

INFORMATION SOURCES[]

While studies addressing specific issues have been carried out to very high N(1). and to moderate Z(2), (Z,N) or (Z,A) maps predicting half-lives and decay modes are almost completely limited to the region below Z = 130 and N = 220. There appears to be only one such map which extends beyond that region and is accessible(3).

(Z,N) maps for half-life and decay mode in Ref. 3 extend as high as Z = 175 and N = 333. Half-lives are reported as bands 3 orders of magnitude wide (0.001 - 1 sec, for example), and should be considered accurate only to within +/- orders of magnitude (presumably from band center. (A nuclide reported to be in the 0.001 - 1 sec band should be considered to have a possible half-life between 10-4.5 sec and 101.5 sec.) Decay modes are limited alpha emission, beta emission, proton emission, and fission; and to the principal one for each nuclide. There are areas where two modes (or more) may be important, meaning that small uncertainties is model parameters could have produced different results. It is also possible that cluster decay may become important above the neutron shell closures at N = 228 and 308.

Ref. 3 does have two significant weakness in the way data are presented. Nuclides which are beta-stable are identified by black squares, overwriting decay mode and half-life information. In addition, nuclides having half-lives less than 10-09 sec are not reported, which obscures the distinction between nuclides having half-lives in the 10-09 and 10-14 sec band and nuclear drops whose half-life is under 10-14 sec.

Above Z around 126, predictions in Ref. 3 may not reach the neutron dripline. This can be an important limitation because the only processes which can form nuclei at more than atoms / star quantity generate very neutron-rich nuclei. It is possible to to make a crude, but conservative (high N) guess for the dripline's location by averaging predicted values for even-N nuclei.{See "The Final Element" (this wiki).} It is also possible to guess at regions of the (Z,N) or (Z,A) plane in which a fission barrier high enough to permit nuclides exists by using a first-order, liquid drop model. {See "Nuclear Guesswork" (this wiki).} Specific numbers are reported for these guesses, not with the expectation that they are accurate, but because they are consistent from element to element. They allow construction of a map which at least hints at where in the (Z,A) plane nuclides may be found.

GUESSED PROPERTIES[]

A simple liquid-drop picture indicates that 485Uth to 447Uth are unlikely to decay by neutron emission and are stable enough against fission to allow beta decay. Between 469Uth and 447Uth, Ref. 3 probably makes no predictions, but extrapolation from higher Z indicates that it would predict mainly short-lived, fission-decaying nuclides. Nuclear properties above 446Uth are highly uncertain, but it is possible that some relatively long-lived, beta-decaying isotopes of Uth are possible. It is possible to state that half-lives longer than 1 sec are implausible between the neutron dripline (nominally 485Uth) and 447Uth.

PREDICTED PROPERTIES[]

Isotopes in the band 446Uth - 433Uth are predicted to decay by beta emission. Since predicted half-lives are in the 10-06 - 0.001 sec range and beta decay partial half-lives far from stability have a minimum near 0.001 sec(4), that is about where half-lives should lie.

Isotopes in the band 432Uth - 427Uth are predicted to decay by fission. It appears to be possible for structure to destabilize a nuclide(5), so the data reported appear to be realistic, Half-lives predicted are in the 10-06 - 0.001 sec range at the upper end of this band and in the 0.001 - 1 sec range at the lower. Beta emission is probably an important secondary decay mode.

Isotopes in the band 426Uth - 401Uth are predicted to decay by beta emission. Half-lives are predicted to lie between 0.001 and 1 sec. Partial half-lives for beta decay should increase as N declines and the number of beta decays required to reach beta stability declines.

Between 400Uth and 394Uth, isotopes are predicted for which odd-N nuclides decay by beta emission with 0.001 - 1 sec half-lives and even-N nuclides decay by fission with shorter half-lives.

Between 393Uth and 387Uth, reported decay modes and half-lives become somewhat chatotic. Three nuclides are reported, all of which are reported to have half-lives in the 10-06 - 0.001 sec range. Beta emission and fission are reported dominant decay modes. It is not clear how reliable data returned by Ref 3 are in this band.

There is a gap from 386Uth to 372Uth 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.

Between 371Uth and 361Uth most drops are predicted to last long enough to be nuclides, but half-lives are microsecond-scale or shorter, except for a few isotopes which may reach millisecond-scale near N = 228. Fission is predicted to dominate throughout this band.

Two fission-decaying nuclides, 357Uth and 355Uth are predicted. Both their half-lives are predicted to be less than 0.001 sec.

N = 258 CLOSURE

The model used to predict decay properties of Uth isotopes has a relatively weak neutron shell closure at N = 258. Some neutron-dripline studies have indicated a strong closure at N = 258. If that closure is strong, some isotopes in the 396Uth to 386Uth band may decay by beta emission rather than fission as predicted. They will probably be short-lived, but act as precursors to long-lived nuclides. By contrast, one or more isotopes in the band 385Uth to 370Uth may be long lived, with half-lives exceeding 1000 sec, because they are daughters of long-lived, alpha-decaying species. Interpolating between 472Uhq and 293Cn gives a reasonable value for maximum half-life of any nuclides stabilized by a strong N = 258 closure of 0.5 yr. Either alpha decay or beta decay may occur in this band, but fission can be expected to be suppressed.

These are not predictions of decay properties for nuclides in the vicinity of N = 258. This entire exercise is qualitative guesswork. No numbers, but a tantalizing hint of what might be.

OCCURRENCE[]

FORMATION[]

Where nuclear drops between the neutron dripline (nominally 485Uth) and 447Uth can be nuclides, they may form. Heavier isotopes may form directly from disintegrating neutron star material, and the remainder may form via beta decay chains from lower-Z nuclides. Since some of these chains may be terminated by short-lived, fission-decaying nuclides, it is not possible to say which isotopes of Uth in this range can form.

Nearly all nuclear drops in the bands 446Uth to 390Uth and 371Uth to 361Uth, as well as 387Uth, 357Uth, and 355Uth are predicted to be nuclides. All are too far from the neutron dripline to form directly. It is possible to simulate the formation of nuclides via decay chains using data from Ref. 3 and assuming an initial distribution close to the neutron dripline. Details of the model are provided in "Nuclear Decay Chains at High A" in this wiki. Per that model, 41 predicted isotopes; 446Uth to 432Uth, 423Uth to 400Uth, 398Uth, and 393Uth; can form.

Neutron capture may be able to produce nuclides up to A around 360 before fission attrition stops further growth. It is implausible that neutron capture can form any Uth isotope.

PERSISTENCE[]

417Uth and heavier isotopes will vanish within 1000 sec after a neutron star merger which led to their formation, or lie at higher Z than beta-decay chains which end in nuclides which fission with a half-life not much greater than 1 sec.

416Uth through 401Uth are predicted to be short-lived, beta-decaying species or to be unable to form because they lie at higher Z than beta-decay chains which end in nuclides that fission with a half-life not much greater than 1 sec,

At 400Uth and below, all beta-decay chains end in short-lived, fissioning nuclides. No other isotopes of Uth persist for a significant time.

Calculations done under maximum half-life assumptions and with all nuclides initially populated still point to all isotopes of Uth vanishing within 105.5 (3.16E05) sec.

N = 258 SHELL CLOSURE

Some studies of the neutron dripline indicate a strong shell closure at N = 258, instead of the relatively weak one occurring in the predictive models, If so, and if peak half-lives in the region do approach 0.5 yr; it is possible that one or more Uth isotopes may persist for up to 60 yrs, probably as a daughter of a long-lived ancestor.

ATOMIC PROPERTIES[]

Electron structure of Uth has been predicted by several sources (see "Extended Periodic Table" in Wikipedia). Up to Z = 137, an atom's nucleus may be regarded as pointlike for the purpose of calculating electron configurations, which means predicted electron structure and behavior can be read more confidently. Its consensus electron configuration has been predicted(6) to be [Og] 5g10 6f4 8s2 8p21/2.

REFERENCES[]

1. for example, "Nuclear Energy Density Functionals: What Do We Really Know?"; Aurel Bulgac, Michael McNeil Forbes, and Shi Jin; Researchgate publication 279633220 or arXiv: 1506.09195v1 [nucl-th] 30 Jun 2015.

2. for example "Fission Mechanism of Exotic Nuclei"; Research Group for Heavy Element Nuclear Science; http://asrc.jaea.go.jp/soshiki/gr/HENS-gr/np/research/pageFission_e.html.; 17 Sept 17.

3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.

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. "Magic Numbers of Ultraheavy Nuclei"; Vitali Denisov; Physics of Atomic Nuclei; researchgate.net/publications/225734594; July 2005.

6. "Extended Periodic Table", Wikipedia.

7. 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

(07-02-20)

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