Nihonium

Nihonium (Nh) is the name of element 113. Wikipedia has an article which provides a lot of information about the element.  This article will focus on things Wikipedia does not stress: heavy isotopes and formation.

The longest lived Nh isotopes are predicted to lie in the band from ²⁹⁷Nh to ²⁹¹Nh. Peak half-life is predicted to be over 1/3 year.

Heavy isotopes, A > 310, are likely to form during neutron star mergers, but will vanish within 1000 sec of the event which led to their formation. The isotope ²⁹⁵Nh may also form, both in neutron star mergers and supernovae. If it does form, it will persist for over 300 years.

NUCLEAR PROPERTIES

INFORMATION SOURCES

This article uses two main resources chosen because of their independence from one another. A third source provides quantitative data over a limited range.

At least one document maps half-life and decay mode for elements below Z = 175 from the neutron dripline down to isotopes which are too neutron-poor to survive any appreciable length of time⁽¹⁾. Maps on pp 15 & 18 address the entire (Z,N) region covered, but report only the dominant decay mode and report half-lives only to within a band three orders of magnitude wide (0.001 - 1 sec, for example). More detailed estimates of these properties can be extracted from maps on pp 11 & 12, but only for a limited range of Z and N. Half-life data are reported by colors, which makes numerical estimates laborious to produce. This document is connected to Japan's KTUY model.

An independent map of half-lives and decay modes exists⁽²⁾. This one is limited to A = 339, as well as to Z = 132. It does not show short-lived isotopes well, and gives half-lives only within rather broad and awkward bands. It does show multiple decay modes for single nuclides. It originates from models used by the Russian agency JINR, so is completely independent of Ref. 1.

Japan Atomic Energy Agency (JAEA) maintains an on-line chart of nuclides which includes decay properties of many predicted nuclides⁽³⁾ - unlike charts published by Korea Atomic Energy Research Institute (KAERI) or the (U.S.) National Nuclear Data Center (NNDC). This chart gives separate numerical values for partial half-lives against fission, beta emission (both b^- and b⁺), and alpha emission. These appear to be systematically too long, but are probably reliable to within an order of magnitude in most cases.

PREDICTED PROPERTIES

Even-N isotopes from the neutron dripline down to ³⁵⁶Nh are predicted to have half-lives in the 0.001 - 1 sec range. [Half-lives aren't reported directly, but the properties of beta decay indicate that half-lives close to 0.001 sec are likely⁽⁴⁾]. In a few cases, fission is predicted to be the dominant decay mode, but may be a significant secondary mode for other isotopes. Odd-N drops in this band decay by neutron emission.

Isotopes in the band ³⁵⁵Nh to ³¹⁹Nh are predicted to decay by beta emission, with half-lives in the 0.001 - 1 sec range. Some light isotopes in this band may have fission as a secondary decay mode.

Ref. 1 predicts that fission will become the principal decay mode in the ³¹⁸Nh to ³¹³Nh band, but half lives are predicted remain long. Most are predicted to lie in the 0.001 - 1 sec range, but two are predicted to have half-lives exceeding 1 sec. Ref. 2 indicates much shorter half-lives in this band.

Ref. 1 predicts that ³¹²Nh will decay by fission with a half-life in the range 10^-6 - 0.001 sec range. Ref. 2 predicts a shorter half-life.

Ref 1 predicts a gap from ³¹¹Nh to ³⁰⁴Nh, All isotopes in this band have half-lives under 10^-6 sec, and most may not even survive the 10^-14 sec needed to qualify as nuclides. Ref. 2 predicts all will have half-lives under 10^-6, which is as short a time as that document reports. Fission is the predicted decay mode in both cases.

The band ³⁰³Nh to ³⁰⁰Nh is a transition region which contains significant differences between the predictions of Ref. 1 & 3, and those of Ref. 2. The former predict a rapid rise in half-life to the 1 - 1000 sec range as A declines, and a transition to alpha emission as the dominant mode of decay at ³⁰¹Nh indicating increased stability with respect to fission near N = 184. Ref. 2 predicts that fission will dominate throughout the band, and that half-lives will be shorter.

Below ³⁰⁰Nh, there have been many studies of decay properties. There does seem to be consensus that fission will not be a significant decay mode, that half-lives will peak just below ²⁹⁸Nh, and that long half-lives will be possible near N = 184. Ref. 3 predicts that ²⁹⁷Nh will decay exclusively by alpha emission with a half-life of 1.1 years; that ²⁹⁵Nh will also decay by alpha emission alone, with a half-life around 110 days; and that ²⁹¹Nh will have a half-life around 4 1/4 days and decay by a mix of alpha emission and positron emission. It predicts other Nh isotopes will have considerably shorter half-lives and with beta decay (b- or b+). Ref. 3 correlates well with Ref 2 regarding decay modes. Further comparison of predicted decay properties or evaluation of likely actual properties is out of scope for this article.

Observed half-lives are found in the band ²⁸⁷Nh to ²⁸²Nh, with outliers at ²⁹⁰Nh and ²⁷⁸Nh⁽⁵⁾.

²⁹⁰Nh has an observed half-life on the order of 2 sec, and decays by alpha emission. This is 1% of the half-life predicted in Ref. 3, which also predicts (b+ / EC) decay. ²⁸⁷Nh is also observed to decay by alpha emission with a 5.5 sec half-life. Ref. 3 predicts (b+ / EC) decay and a half-life 10 times longer. Taken together, these data hint that Ref. 3's predictions for alpha decay partial half-lives are too long.

At the other end of the band, ²⁷⁸Nh is observed to alpha decay with a 0.0014 sec half-life. Adjacent isotopes both above and below it are predicted in Ref. 3 to decay by fission with substantially shorter half-lives.

The lightest isotope reported by any of Refs. 1 through 3 is ²⁷¹Nh. There may be a few lighter nuclides with half-lives in the 10^-14 - 10^-9 sec range, but half-lives will quickly decline below the minimum needed for a nuclear drop to qualify as a nuclide.

OCCURRENCE

FORMATION

Nihonium isotopes from the neutron dripline to ³¹⁷Nh, plus ³¹⁵Nh, can form. Most are mainly beta-emitters; but some, particularly at low A, decay principally by fission. All are short-lived. Beta-decay chains that would lead to ³¹⁶Nh and to the band ³¹⁴Nh to ²⁹⁴Nh are truncated by fission at Z < 113. This band includes predicted long-lived Nh isotopes. Beta decay chains leading to ²⁹³Nh and lighter isotopes are cut off at Z < 113 by alpha-decaying species. Material ejected from a disintegrating neutron star is expected to lead to production of all Nh isotopes which can form.

The heavy band extends from the neutron dripline to ³¹¹Nh, All isotopes in this band can form. Heavier isotopes in that band can form directly as a neutron star disintegrates; largely from dripline nuclides, but also as fission daughters of very large nuclear drops. Lighter isotopes require a chain of beta decays to form, but there are no lower-Z nuclides in this range of A which fission so rapidly that a beta-decay branch cannot occur. The lightest isotopes are themselves short-lived, fission decaying species. It is unlikely that neutron capture can reach this range of A.

Neutron capture may be able to produce nuclides up to A around 380 before fission attrition stops further growth. Neutron capture is expected to contribute to production of almost all Nh isotopes.

As the article Superheavy Island is Deserted shows, chains with A between 300 and 296 end at Z < 112. The article does indicate that it may be possible for ²⁹⁵Nh to form, although in minute quantities. Whether it can form is dependent on whether ²⁹⁵Cn has a b- decay branch. Ref. 3 indicates a beta decay branch, and its location relative to beta-stable Cn isotopes and beta-decaying isotopes of lower Z indicate that a (b-) branch is likely. Below ²⁹⁵Nh, beta decay chains terminate at Z = 112 or below.

PERSISTENCE

All heavy (A > 310) isotopes have short half-lives and are the result of beta decay of short-lived nuclides. They are expected to disappear completely less than 1000 sec after a neutron star merger of similar event which led to their formation.

Using the values in Ref. 3, it appears that ²⁹⁵Nh may persist for up to 330 years after an event which led to its formation.

ATOMIC PROPERTIES

Wikipedia's article "Nihonium" addresses the element's atomic properties and chemistry in some detail. Although its formation is uncertain, and the amounts which can form outside the laboratory are tiny, it does appear to be possible that Nh chemistry can exist without the presence of chemists.

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. “Systematic Study of Decay Properties of Heaviest Elements.”; Y. M. Palenzuela, L. F. Ruiza, A. Karpov, and W. Greiner; Bulletin of the Russian Academy of Sciences, Physics.  Vol . 76, No.11, pp 1165 – 1177; 2012

3. "Chart of the Nuclides, 2014", Japan Atomic Energy Agency; website available using "chart of nuclides" and "JAEA" as internet search terms.

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. "Nihonium", Wikipedia article.

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

(10-10-20)