Roentgenium

Roentgenium (Rg) is the name of element 111. 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 Rg isotopes are predicted to form in both supernovae and neutron star mergers. ²⁹³Rg may persist for as much as 5000 yrs after an event which formed it, and ²⁹¹Rg may persist for roughly 300 yrs, It is uncertain whether ²⁸⁹Rg can form; but, if it does, it can be expected to persist for about 2 yrs. It is also possible that ²⁹²Rg can form; if it does, it may persist for 3 days. All other isotopes will persist for less than 1 day. Numerous isotopes heavier than ³⁰⁵Rg can be expected to form, but disappear within 1000 sec.

One atomic property not addressed in Wikipedia is Rg's expected low electrical conductivity, which is anomalous for its Group.

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 ³⁵⁴Rg 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 ³⁵³Rg to ³¹¹Rg 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 ³¹⁰Rg to ³⁰⁷Rg band. Predicted half-lives in this band remain long, some exceeding 1 sec. Ref. 2 also predicts fission, but predicts much shorter half-lives.

Both sources predict decay by fission and short half-lives in the ³⁰⁶Rg to ³⁰¹Rg band.

Ref. 1 and Ref. 2 differ in the ³⁰⁰Rg to ²⁹⁸Rg band, The former predicts half-lives rising to more than 1 sec and transition from fission to beta emission as the dominant decay mode at ²⁹⁸Rg. Ref. 2 predicts only fission and much shorter half-lives.

Below ²⁹⁸Rg, 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 shortly below ²⁹⁶Rg, and that long half-lives will be possible near N = 184. ²⁹¹Rg, which Ref. 3 predicts will have a 2.1 yr half-life and decay solely by alpha emission is the longest lived Rg isotope. (That reference also predicts partial half-lives against alpha decay of more than 1 yr for all isotopes from ²⁹⁰Rg to ²⁸⁵Rg.). The second longest lasting isotope is predicted to be ²⁸⁹Rg with a half-life of 4.6 days and about 25% alpha decay branch. This is a pattern to be expected with odd-Z elements. All other isotopes should have half-lives under 3 hrs. Fission is predicted to become a significant decay mode at or below ²⁸⁶Rg and the predominant mode at or below ²⁷⁷Rg. Further comparison of predicted decay properties or evaluation of likely actual properties is out of scope for this article.

The unconfirmed isotope ²⁸⁶Rg has been reported to decay by alpha emission with a half-life of 11 min. Ref. 3 predicts a half-life of 13 min, but predicts that it will decay almost exclusively by fission. The light isotopes ²⁷⁴Rg and ²⁷²Rg are observed to have half-lives of a few milliseconds and to decay by alpha emission. Adjacent odd-N isotopes both above and below show that fission is expected to be the predominant decay mode and that half-lives are probably about 0.1 msec in this band.

The lightest isotope reported in the vicinity of N = 184 by any of Refs. 1 through 3 is ²⁶⁴Rg. 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 no isotopes with half-lives exceeding 10^-09 sec in the vicinity of the N = 126 neutron shell closure.

OCCURRENCE

FORMATION

Rg isotopes from the neutron dripline to ³⁰⁵Rg can form. Heavier isotopes in this band can form directly as a neutron star disintegrates; 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 ³⁰⁵Rg, it is necessary to examine the possibility of fission attrition cutting off beta-decay chains below Z = 111. 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. Set 1 indicates that ³⁰⁴Rg, ³⁰³Rg, ³⁰¹Rg, ²⁹⁵Rg, and ²⁹⁴Rg can form, but only in small quantities, while Set 2 indicate that none of them can form. Their existence is possible, but uncertain.

Both data sets predict that attrition by fission will not prevent the formation of ²⁹³Rg and lighter isotopes. However, Ref. 3 predicts that ²⁹²Ds, and ²⁹⁰Ds through ²⁸⁶Ds do not decay by beta emission, thus cutting off formation of Rg isotopes with those values of A. Note that this pattern is typical of large even-Z elements. Ref. 2 indicates that ²⁹²Ds and ²⁸⁹Ds will decay by beta emission, which is also typical of the same pattern, but shifted to lower Z. It is, therefore, likely that ²⁹¹Ds can form; and that formation of ²⁹²Rg and ²⁸⁹Rg is possible, but uncertain. Both sources agree that ²⁸⁸Rg and lighter isotopes cannot form due to the presence of lower-Z nuclides which interrupt beta-decay chains at Z < 111.

Material ejected from a disintegrating neutron star can be expected to cover the entire A range of Rg isotopes which can form. 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 supernovae as well as neutron star mergers can be expected to contribute to Rg production.

PERSISTENCE

By a considerable margin, ²⁹³Rg is predicted to persist for the longest time, not disappearing completely until roughly 5000 years after the supernova, neutron star merger, or other event that caused it to form. Of the others, ²⁹¹Rg may be expected to persist for around 300 yrs and ²⁸⁹Rg for 2 yrs (if it can form at all). If ²⁹²Rg 292 can form, it may be expected to persist for 3 days. All other isotopes of Rg persist for less than 1 day, and most will persist less than 1000 sec.

ATOMIC PROPERTIES

Wikipedia's article "Roentgenium" 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 Rg chemistry can exist without the presence of chemists.

One significant detail is not addressed in Wikipedia's article. Predicted electron configuration for Rg includes 2 7s electrons. Other Group 11 elements have a lone n s electron, which accounts for their very high electrical conductivity. Rg is likely to be significantly less conductive than the other Group 11 elements.

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. "Roentgenium", 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

(10-13-20)