Meitnerium

Meitnerium, Mt, is the name of element 109. 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 Mt isotopes are expected in the band from ²⁹¹Mt to ²⁸³Mt. ²⁸⁵Mt is predicted to be the longest lived, with a half-life between 2 & 5 years. This isotope should last between 300 and 800 years after an event which causes it to form. Of the other isotopes, ²⁸⁷Mt is predicted to have a half-life on the order of 8 days, and ²⁸⁴Mt & ²⁸³Mt are predicted to have half-lives of 1 & 5 hr - however only ²⁸⁷Mt can form. It may persist for perhaps 50 days. There are also numerous isotopes heavier than ²⁸⁷Mt which can be expected to form, but disappear within a day.

Mt is expected to be present in extremely young supernova or kilonova (neutron star merger) remnants, although probably in quantities too small to detect. It is likely that the chemistry of Mt is entirely synthetic.

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.

The U.S.'s Los Alamos National Laboratory (LANL) contains tabulated partial half-life data for alpha and beta decay⁽⁴⁾. If it included fission, it would be a primary resource for this article, but it does not. Where fission is not an issue, though, it constitutes a third independent source of decay properties.

PREDICTED PROPERTIES

Isotopes from the neutron dripline down to ³⁰⁵Mt are predicted to decay by beta emission. Most are predicted to have half-lives in the 0.001 - 1 sec range, but some of the lighter ones are predicted to reach half-lives of a few seconds.

Between ³⁰⁴Mt and ²⁹⁶Mt, Ref. 1 predicts that fission will be the dominant mode for decay; but it also predicts half-lives over 0.001 sec in most cases, which is long enough that beta decay will probably be an important secondary decay mode. The exceptions are ³⁰⁰Mt to ²⁹⁸Mt. Ref. 2 predicts decay by fission throughout the band ³⁰⁷Mt to ²⁹⁶Mt. It predicts lower stability, with all isotopes except ³⁰⁷Mt having half-lives below 0.001 sec, and isotopes in the band ³⁰⁴Mt to ²⁹⁸Mt having half-lives under 10^-06 sec, That implies Ref. 2 predicts that beta decay does not occur to any significant degree between ³⁰⁶Mt and ²⁹⁶Mt.

Ref. 1 predicts that beta decay will predominate between ²⁹⁵Mt and ²⁹⁰Mt, with half-lives > 1 sec in all cases. At ²⁹²Mt and below, Ref. 3 agrees, predicting half-lives of minutes to hour. Ref. 4 predicts beta decay, but calls for half-lives ranging up to several years, Since such extremely long beta-decay half-lives are rare in smaller nuclides, its predictions are likely to be high.

In the band ²⁸⁹Mt to ²⁸⁶Mt, the four sources used give mixed results. Ref. 1 predicts that ²⁸⁹Mt and ²⁸⁷Mt will decay by alpha emission with half-lives on the order of 10⁰⁶ sec, and the others by beta emission with half-lives of a few seconds, Ref, 2 predicts all will decay by beta emission, with half-lives of under a day.. Ref. 3 predicts all will decay by beta emission; with the half-life of ²⁸⁷Mt being around 8 hrs (and having a weak alpha emission branch), and the others predicted to have half-lives under 1 hr. Finally, Ref 4 predicts that alpha decay will predominate in ²⁸⁹Mt and ²⁸⁶Mt. However, it predicts unrealistically long beta-decay half-lives. On the whole, the predictions of Ref. 3 appear to be the most realistic.

Refs. 1, 3, and 4 predict that ²⁸⁵Mt will decay predominantly by alpha emission. Ref. 3 predicts a half-life near 2 yrs, an alpha decay branch ratio of 0.8, and fission as the only other decay mode. Ref. 4 does not address fission, but it predicts a half-life near 5 yrs, with an alpha decay branch ratio of 0.97. It does predict that beta decay will be a possible mode, but the partial half-life it reports is the same as that given for many nuclides and appears to be a default value. Ref. 3's prediction of decay either by alpha emission or fission appears to be the most realistic.

Ref. 3 seems to be the best source below ²⁸⁵Mt. It predicts (b+ / EC) for isotopes ²⁸⁴Mt, ²⁸³Mt, ²⁸²Mt, and ²⁸⁰Mt; with half lives on the order of 1 hr, 5 hr, 1/2 hr, and 5 min respectively. It also predicts that fission decay dominates for ²⁸¹Mt and that its half-life is around 8 sec. It should be noted that this value is short compared to partial fission decay half-lives predicted for adjacent even-N isotopes.

Ref 3 predicts that ²⁷⁹Mt will decay predominantly by alpha emission with a half-life on the order of 50 sec.

Further comparison of predicted decay properties or evaluation of likely actual properties is out of scope for this article.

The heaviest isotope for which observation has been reported is the unconfirmed ²⁸²Mt⁽⁵⁾, which decays by alpha emission with a half-life on the order of 70 sec. This is a different mode and much shorter half-life than what Refs 1 and 3 predict. (The half-life band for Ref. 2 is too wide to be informative in this case.)

Predicted half-lives and decay modes for the unobserved isotopes ²⁷³Mt to ²⁷¹Mt, ²⁶⁹Mt, and ²⁶⁷Mt are not inconsistent with the decay properties of observed isotopes in the band ²⁷⁸Mt to ²⁶⁶Mt.

The lightest isotope reported in the vicinity of N = 184 by any of Refs. 1 through 3 is ²⁵⁹Mt. There may be a few lighter nuclides with half-lives in the 10^-14 - 10^-09 sec range in this region, but half-lives will quickly decline below the minimum needed for a nuclear drop to qualify as a nuclide.

Ref. 1 predicts that no isotopes with neutron counts near N = 126 can have half-lives over 10^-09 sec.

OCCURRENCE

FORMATION

Mt isotopes from the neutron dripline to ³⁰³Mt can form. Heavier isotopes in this band can form directly as a neutron star disintegrates; largely from dripline nuclides. Lighter isotopes require a chain of beta decays to form, but all lower-Z nuclides in such chains have long enough partial half-lives against fission that attrition will not be severe. The lightest isotopes are themselves short-lived, fission decaying species.

Below ²⁹⁹Mt, it is necessary to examine the possibility of fission attrition cutting off beta-decay chains below Z = 110. The article "Superheavy Island is Deserted" (this wiki) tabulates two sets of data for attenuation by fission and cutoff by nuclides which do not have a beta decay branch. Set 1 is based on Refs. 1 & 3, and Set 2 is based on Ref. 2. Both sets indicate heavy fission attrition between ²⁹⁸Mt and ²⁹⁴Mt; however, Set 1 predicts that only ²⁹⁶Mt will be completely cut off, Ref. 2 predicts that ²⁹⁸Mt, ²⁹⁶Mt, ²⁹⁵Mt, and ²⁹⁴Mt will be completely cut off.

Both data sets predict that isotopes in the band ²⁹³Mt to ²⁸⁷Mt can form.

References 3 and 4 predict that ²⁸⁶Hs & ²⁸⁴Hs have no beta-decay branches, which implies that ²⁸⁶Mt and ²⁸⁴Mt cannot form. Ref. 2 predicts that neither ²⁸⁶Hs or ²⁸⁴Hs have beta decay branches. It is unlikely that ²⁸⁶Mt or ²⁸⁴Mt can form.

References 2, 3, and 4 all indicate that a beta-decay chain can reach ²⁸⁵Mt. It appears likely that ²⁸⁵Mt can form.

For ²⁸³Mt and lighter isotopes, there appears to be general agreement that formation does not occur.

Material ejected from a disintegrating neutron star can produce all of the isotopes of Mt which can form at all. Several studies of rapid neutron capture (r process) indicate that neutron capture reactions can produce nuclides with A up to around 380 before fission attrition stops further growth. This means that supernovae can enhance production of essentially all Mt isotopes.

PERSISTENCE

Refs. 3 & 4 predict that ²⁸⁵Mt will persist for up to 300 or 800 years respectively after a supernova, neutron star merger, or other event which leads to their formation. The isotopes ²⁸⁷Mt, and ²⁸³Mt may persist for 50 and 30 days respectively. Isotopes heavier than ²⁸⁷Mt will last for less than a day, while isotopes lighter than ²⁸³Mt cannot form in the first place.

ATOMIC PROPERTIES

Wikipedia's article "Meitnerium" addresses the element's atomic properties and chemistry in some detail. It is not clear whether any Mt can survive, outside the laboratory, to reach an environment cool enough for chemical interactions to occur. Certainly, it is impossible that detectable amounts can survive.

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. "Isotopes of Meitnerium", 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

(10-17-20)