Hassium

Hassium, Hs, is the name of element 108. 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.

From the perspective of nuclear stability, studies of Hs seem to vary from source to source more widely than is true of nearby elements with both higher and lower Z. This seems to reflect weakening of stabilization by the Z = 114 proton shell closure and the weak beta-decay instability near N = 184.

The isotopes ²⁸¹Hs and heavier can all form (although fission will reduce the amount which forms in the vicinity of ²⁹⁵Hs). Most of these are short-lived, but ²⁹⁰Hs to ²⁸⁸Hs are predicted to have half-lives on the order of 0.3 yr and ²⁸⁷Hs is predicted to have a half-life on the order of 0.2 yr. The first two may persist for 50 yrs after an event which leads to their formation, and ²⁸⁷Hs may persist a bit longer than 30 yrs.

The half-life of ²⁹²Hs is particularly uncertain, but may be as great as 200 yrs. That implies it may persist for as much as 30000 yrs after an event which leads to its formation.

²⁹⁰Hs to ²⁸⁷Hs might, in principle, cool enough in kilonova remnants to interact chemically, but not in detectable amounts. If ²⁹²Hs has its maximum plausible half-life, it might appear in detectable amounts in both kilonova and supernova remnants.

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 ³⁰³Hs are predicted to decay primarily by beta emission, usually with half-lives in the 0.001 - 1 sec range. Isotopes at the light end of this band are likely to decay by a mixture of beta emission and fission.

Between ³⁰²Hs and ²⁹⁴Hs, 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 ³⁰⁰Hs and ²⁹⁸Hs to ²⁹⁶Hs, which are predicted to have half-lives under 0.001 sec. Ref. 2 predicts decay by fission throughout the band ³⁰⁴Hs to ²⁹⁴Hs. It predicts lower stability, with all isotopes in the band having half-lives below 0.001 sec; and isotopes in the band ³⁰²Hs to ²⁹⁸Hs, plus ²⁹⁶Hs, having half-lives under 10^-06 sec, That implies Ref. 2 predicts that beta emission is a minor decay branch throughout this band..

Ref. 1 predicts that beta decay will predominate in the isotopes ²⁹³Hs to ²⁹¹Hs plus ²⁸⁹Hs. It predicts a half-life for ²⁹²Hs on the order of 10^3.5 sec (1 hr), half-lives of ²⁹³Hs and ²⁹¹Hs under 1000 sec, and a half-life for ²⁸⁹Hs in the vicinity of 10^4.5 sec (10 hrs). Ref. 4 predicts a partial half-life against beta decay on the order of 200 sec, but partial half-lives against alpha decay around 10⁰⁶ sec (0.03 yr) for ²⁹¹Hs 291 and 10⁰⁷ sec (0.3 yr) for ²⁸⁹Hs. It reports a half-life for ²⁹²Hs on the order of 7E09 sec (200 yr), but that number may be a default value rather than an actual prediction. If that prediction is invalid, Ref. 4 predicts a partial half-life against alpha decay of more than 10⁷ yr. However, that reference ignores fission. If ²⁹²Hs does not beta-decay, it is possible that it will fission, with a half-life in the range of 10⁰⁶ to 10⁰⁸ sec (0.03 to 30 yr)^(5.),(6). The situation is confused, but ²⁹²Hs will probably have a half-life under 200 yr, and is likely to decay by all three modes: alpha emission, beta emission, and fission.

Ref. 1 predicts that ²⁹⁰Hs will decay by alpha emission with a half-life on the order of 10⁰⁶ sec (12 days). Ref. 2 predicts that it will decay by beta emission with a half-life of under a day. Ref. 4 also predicts decay by beta emission, but predicts the same questionable half-life as it did for ²⁹²Hs. In the absence of beta decay, it predicts decay by alpha emission with a half-life on the order of 10¹⁴ sec, As before, Refs 5 & 6 predict decay by fission with a half-life in the 10⁰⁶ - 10⁰⁷ sec. The weight of evidence points toward a half-life under 10⁰⁷ sec (0.3 yr) and decay by fission.

Ref. 1 predicts that ²⁸⁸Hs will decay by alpha emission with a half-life on the order of 10^4.5 sec (10 hrs). Ref. 2 predicts that it will decay by beta emission with a half-life of under a day. Ref. 4 also predicts decay by beta emission, but predicts the same questionable half-life as it did for ²⁹²Hs. In the absence of beta decay, it predicts decay by alpha emission with a half-life on the order of 8000 yr, As before, Refs 5 & 6 predict decay by fission with a half-life in the 10⁰⁶ - 10⁰⁷ sec. The weight of evidence points toward a half-life under 10⁰⁷ sec (0.3 yr) and decay by fission.

Ref. 1 predicts that ²⁸⁷Hs will decay by alpha emission with a half-life on the order of 10⁹ sec (30 yrs). Ref. 2 predicts that it will decay by beta emission with a half-life of under a day. Ref. 4 also predicts decay by beta emission with a half-life 6E06 sec (70 days). It appears likely that ²⁸⁷Hs will decay by beta emission with a half-life up to 70 days.

For ²⁸⁶Hs, Ref. 1 predicts alpha decay and a half-life on the order of 10000 sec. Ref. 2 and 3 predict decay predominantly by fission with a half-life of < 1 day and 4 days respectively.

For ²⁸⁵Hs, all references predict decay by beta emission. Ref. 3 predicts a half-life around 800 sec, which is consistent with the others.

In the band ²⁸⁴Hs to ²⁸⁰Hs, the predominant decay mode is predicted to be by fission. Ref. 3 predicts a half-life for ³⁸³Hs of around 110 days and half-lives for the others of < 1 day.

Refs. 1 & 3 predict that ²⁷⁹Hs will decay by alpha emission. Ref. 3 predicts a half-life on the order of 6000 sec (2 hr) which appears to be consistent with the other sources.

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 ²⁷⁷Hs⁽⁷⁾, which decays by fission. Ref. 7 reports an 0.011 sec half-life, which is consistent with Ref. 1, but Ref. 3 indicates 11.8 min. Refs 1 and 2 predict a half-life < 0.001 sec, so it appears that Ref. 3 left the "s" off of "ms".

Predicted half-lives and decay modes for the unobserved isotopes ²⁷⁶Hs to ²⁷⁴Hs, and ²⁷²Hs are not unreasonable if there is a deformed (nonspherical) neutron shell closure at N = 162.

Wikipedia addresses ²⁷⁰Hs and nonspherical shell closures in some detail.

The lightest isotope reported in the vicinity of N = 184 by any of Refs. 1 through 3 is ²⁵⁴Hs. 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 4 isotopes in the band ²³⁷Hs to ²³⁴Hs will have half-lives over 10^-09 sec range. ²³⁵Hs is predicted to decay by proton emission and have a half-life in the 10^-06 - 0.001 sec range. The others are predicted to have half-lives under 10^-06 sec. ²³⁴Hs is predicted to decay by alpha emission and both ²³⁷Hs and ²³⁶Hs by fission. These isotopes appear to be stabilized by the N = 126 neutron shell closure.

OCCURRENCE

FORMATION

Hs isotopes from the neutron dripline to ²⁸¹Hs can form. Heavier isotopes in this 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. Fission-decaying nuclides with Z < 108 with A in the vicinity of 295 can be expected to reduce the quantity of material which reaches Hs, but will not completely block the decay chains.

Ref. 4 predicts that ²⁸⁰Hs cannot form because ²⁸⁰Sg is beta-stable. Ref. 3 indicates that ²⁸⁰Sg decays so rapidly by fission that no beta decay is possible, whether or not the nuclide is beta-stable. Either way, it can't form.

Ref. 3 predicts that ²⁷⁹Hs cannot form because ²⁷⁹Bh decays too rapidly by fission for any significant amount of beta decay to occur.

The evidence seems to indicate ²⁷⁸Hs and lighter cannot form due to blocking at Sg.

Both high-A nuclides ejected when a neutron star disintegrates and high-A nuclides produced by rapid electron capture can produce all isotopes of Hs which can form. Several studies of rapid neutron capture (r process) indicate that neutron capture reactions can produce nuclides with A up to 380 before fission attrition cuts off further growth. Both supernovae and neutron star mergers contribute to the production of Hs.

PERSISTENCE

It appears possible that ²⁹²Hs may persist for as much as 30000 years after a supernova, neutron star merger, or other event which led to its formation. Other isotopes are expected to persist for shorter times. ²⁹⁰Hs, ²⁸⁹Hs, and ²⁸⁸Hs, may survive for roughly 50 yrs; ²⁸⁷Hs may survive longer than 30 yr. It is unlikely that other isotopes will persist for more than 1 year.

ATOMIC PROPERTIES

Wikipedia's article "Hassium" addresses the element's atomic properties and chemistry in some detail. It is not clear whether any Hs 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. "Decay Properties and Stability of Heaviest Elements"; A. V. Karpov, V. I. Zagrebaev, Martinez Palenzuela, L. Felipe Ruiz and Walter Greiner; International Journal of Modern Physics E, Vol. 21, No. 2 (2012). (p.9)

6. "Heaviest Nuclei From ⁴⁸Ca-induced Reactions", Yuri Oganessian; Journal of Physics G: Nuclear and Particle Physics,34(2007) R165–R242. (See p. R 170.)

7. "Isotopes of Hassium", 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

(10-19-20)