Bismuth

Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a pentavalent post-transition metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when freshly produced, but is often seen in air with a pink tinge owing to surface oxidation. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals.

Bismuth metal has been known since ancient times, although until the 18th century it was often confused with lead and tin, which share some physical properties. The etymology is uncertain, but possibly comes from Arabic bismuth, meaning having the properties of antimony or German words weisse masse or wismuth ("white mass"), translated in the mid-sixteenth century to New Latin bisemutum.

Thallium through polonium form a band in which elements transition from being mainly of chemical interest to being mainly of nuclear interest. Bismuth is rare in both earth's crust and the solar system. It's solar abundance is 0.77 that of gold and 0.05 that of lead. It is easily reduced, being a Group 15 metal, easily worked, and has been studied for three centuries. It is also the stable endpoint of a nearly-extinct actinide decay chain, as well as moving actinide decay chains toward both polonium and thallium. These chains arrive in this band at the end of long series of alpha decays. They arrive neutron-rich. Between polonium's alpha decays and thallium's beta decays, actinide chains oscillate back and forth until they arrive at lead or bismuth.

²⁰⁹Bi is effectively stable, but was discovered to decay by alpha emission in 2003. However, with a half life more than a billion times the estimated age of the universe, its radioactivity is of purely theoretical interest, having no effect on the element's physics or chemistry. (See Stable Elements.)

Nuclear properties

Bismuth's most striking nuclear property is its stability against alpha decay above N = 126. From Po on out, there is a trough of alpha instability that bottoms out at sub-microsecond half-lives. ²¹¹Bi does have the shortest half-life against alpha decay of any Bi isotope with N > 126 - 2.14 minutes, or, if you prefer, 128,000,000 microseconds (usec).

As a stripe across the nuclear landscape, Bi behaves like a small element below ²⁰⁹Bi and like an actinide above it. At least 85 isotopes have been predicted, of which 37 have been observed. 52 isomers are also reported, an average of more than one per isotope. From the neutron dripline near ²⁶⁷Bi (N=184) down to ²¹⁵Bi, only beta decay has been observed or predicted. Half-lives peak at 7.6 min in ²¹⁵Bi. Between ²¹⁴Bi and ²¹⁰Bi, alpha emission is an active mode of decay, although it is dominant only in ²¹¹Bi and ^212m1Bi and is weak in both ²¹⁴Bi and ²¹⁰Bi. The isomer ^210mBi doesn't count in that context. It is a high-spin isomer whose beta-decay mode is so strongly blocked by angular momentum conservation issues that it decays solely by alpha emission with a 3E06 yr half-life. ²¹⁰Bi in its ground state has a half-life of 5.01 days and decays almost entirely by beta emission [BR(a) = 1.3E-06].

²⁰⁹Bi is effectively stable. It is reported to decay by alpha emission with a half-life of 2.01E19 years, which is equivalent to saying that a sample of ²⁰⁹Bi which formed when a first-generation star went supernova has lost 0.5 parts per billion of its original mass due to radioactive decay.

Positive-beta decay decay sets in at ²⁰⁸Bi, and is the only active decay mode down to ²⁰⁴Bi. Half-lived decline from ²⁰⁸Bi's 36800 yr, through ²⁰⁷Bi's 32.9 yr, to ²⁰⁴Bi's 11.22 hrs. Isomer half-lives, on the other hand, rise from ^208mBi to ^204m1Bi (0.013 sec). Weak alpha-decay branches occur at ²⁰³Bi, ²⁰²Bi, ^201m1Bi, ²⁰¹Bi, and ^199m1Bi, but other isotopes and isomers show only positive beta decay down to ¹⁹⁸Bi. Between ¹⁹⁷Bi and ¹⁹⁴Bi, alpha decay is rare, with one exception ^197m1Bi has a dominant (BR = 0.55) alpha decay branch. ^195m1Bi, which has BR(a) = 0.33, is second. Between ¹⁹³Bi and ¹⁸⁶Bi, both alpha and positron emission decay modes are active, with alpha becoming stronger as A declines. Proton emission is predicted to dominate in the lightest Bi isotopes. Fission does not play a role.

45 of bismuth's 52 isomers are associated with the proton-rich isotopes below ²⁰⁹Bi. Of the 45 isotopes lighter than ²⁰⁹Bi, only ²⁰⁵Bi has no observed isomers. They are about evenly divided, 21 to 24, between isomers whose half-lives compared to the associated ground state half life is 0.001 or greater [ t12(^A*Z)/t12(^AZ) >= 0.001. ] and isomers for which the ratio is smaller. Seven isomers in this band have longer half-lives than their associated ground-state nuclide. Independent decay is the rule, with only 7 isomers undergoing isomeric transition (IT) to their ground states. In all cases, branch ratios may differ between ground and isomeric states, but both ground and isomeric states decay by the same modes. Absolute half-lives in isomers of these lighter isotopes include 24 with ms to sec half-lives, 8 with us to ms half-lives, and 13 with ns to us half-lives. The very short-lived isomers are clustered in the ²¹⁰Bi to ¹⁹⁷Bi band. The significance of this clustering isn't clear.

Isomers are fewer (7) in the band above 209Bi. They remain common, being associated with six isotopes, and generally decay independently - only two IT branches are reported. Decay modes are, with the exception of ^210mBi, qualitatively the same.

Most Bi forms via beta decay chains originating in nuclides near the neutron dripline which were produced either by a rapid series of neutron captures (r process) in a supernova or while a neutron star's crust is disintegrating at the beginning of a merger. A neutron star merger (kilonova) may also bring up high-A nuclides which beta decay to Bi. Isotopes from the dripline down to ²⁰⁹Bi can form in this way. No lighter isotopes can do so. A second process, a series of neutron captures which occur at a slow rate, mixed with beta decays which occur more quickly than neutron captures (s-process). This process can only produce ²⁰⁹Bi and heavier. That process occurs in most highly evolved stars (red giants). At an even slower rate, it occurs in celestial bodies of all sizes down at least to planets. A third process can produce lighter isotopes. At over roughly 10 GK, black-body photon energy starts to become high enough to cause nuclei to eject particles, usually neutrons from neutron-rich nuclides and alphas from more proton-rich ones. (Gamma capture promoting a nucleus to a fission isomer isn't an issue at Bi.) Neutrons emitted by the heavier Bi isotopes can produce isotopes below ²⁰⁹Bi, although in small quantities and quantities which fall quickly as A declines.

^210mBi appears to have a neutron capture cross section comparable to that of its ground state, which implies it forms in about equal abundance as its ground state and within an order of magnitude of initial concentration of uranium^(1),(2). However, beta decay energy (ground state to ground state) of ²¹⁰Pb is 63.5 +/- 0.5 [63.5(5)] keV⁽³⁾. IT transition energy for ^210mBi is 271.31(11) keV, which means beta decay of ²¹⁰Pb cannot form ^210mBi. It does not form in large amounts during a neutron star merger or supernova. Some may form via photon capture/neutron ejection [g(²¹¹Bi,^210mBi)n] reactions using ²¹¹Bi as feedstock. The latter does form in quantity during a supernova or neutron star merger and its half-life of 2.14 min is far longer than the 1 - 10 sec required to turn a star into a neutron star and an expanding cloud of debris or to turn a neutron star into either part of a black hole or part of a massive, rapidly spinning neutron star and an expanding cloud of debris. But, because it lies at the end of a beta-decay chain, ²¹¹Bi will form after the extreme temperatures which exist for a second or two have ceased to be a factor. During the brief time a supernova or kilonova event is occurring, matter forming via the r process (and initially high-A material) lies close to the dripline. In this region, beta decay chains interlace into a network because most beta decays lead to daughters which have unbound neutrons which they quickly eject. At the same time, this kind of (b+n) decay is operating on the next-heavier beta decay chain. To a first order approximation g(^AZ,^A-1Z)n and g(^A+1Z,^AZ)n reactions are in balance, which means each chain can be regarded as independent. ²¹¹Bi will become abundant during a supernova or kilonova; but, by the time it forms, its environment will be cool enough to prevent g(²¹¹Bi,^210mBi)n from producing ^210mBi in more than minute amounts.

A supernova or neutron star merger will produce large quantities of all the isotopes above ²⁰⁸Bi. This first abundance will soon disappear, although traces of ²⁰⁸Bi could survive long enough to be injected into a cloud core about to collapse into a stars-and-planets system. What traces of ^210mBi which do form won't become extinct for millions of years - well past the time needed for a planet's formation.

When the first wave of primordial Bi isotopes becomes extinct, six radioactive isotopes remain: ²¹⁵Bi and ²¹¹Bi are descendants of ²³⁵U, ²¹⁴Bi and ²¹⁰Bi are descendants of ²³⁸U, ²¹³Bi (and ²⁰⁹Bi) descend from ²³⁷Np (itself resulting from ²³⁵U and ²³⁸U), and ²¹²Bi descends from ²³²Th. Of these, ²¹⁰Bi is the most abundant, with [²¹⁰Bi]/[²³⁸U] = 3.1E-12, some 500 times more abundant than ²¹⁴Bi. Concentration of the others is most conveniently expressed in terms of earths: [²¹⁴Bi] = 3900 mol/planet, [²¹²Bi] = 2000 mol/planet, [²¹¹Bi] = 19 mol/planet, and [²¹⁵Bi] = 5.7E-05 mol/planet. Formation of [213Bi] is lost in background charged-particle-reaction background noise.

²⁰⁹Bi is the endpoint of a chain which would be extinct except for two things. First, the spontaneous fission of ²³⁸U, which causes ²³⁵U to capture neutrons. About 0.2 of the time, the fusion produces a nucleus of ²³⁶U (the rest of the time it causes fission). ²³⁶U also captures neutrons to make ²³⁷U, which beta-decays to ²³⁷Np, which decays to ²⁰⁹Bi. Second, in about 0.00009 of its decays, ²¹⁰Tl beta decays to an excited state (isomer) of lead, ^210*Pb, which contains an unbound neutron, causing it to decay to ²⁰⁹Pb in less than 10^-14 sec. ²⁰⁹Pb decays to ²⁰⁹Bi. Even though it is rare, the second mechanism produces more ²⁰⁹Bi because of the very slow rate at which ²³⁷Np forms.

Atomic properties

Bismuth is a p block element in Group 15. It is more metallic than its lighter homologs N, P, As, and Sb. It is capable of taking any oxidation state from 1- to 5+, but is most commonly found in the 3+ state. Its chemistry appears to be unsurprising.

The element is quite rare, but bismuth minerals are known and native (chemically uncombined) bismuth have been found.

References

1. "Evaluation of the 210m Bi/ 210g Bi Branching Ratio of the 209 Bi( n, ?? ) 210 Bi Cross Section in the Neutron Energy Range from 200 keV to 3.0 MeV"; Akira Icihara & Keiichi Shibata; Journal of Nuclear Science and Technology 40(11):980-982, November 2003.
2. "Determination of the ²⁰⁹Bi(n,g)²¹⁰Bi and ²⁰⁹Bi(n,g)^210m,gBi reaction cross sections in a cold neutron beam"; A.Borella, T.Belgya, S.Kopecky, F.Gunsing, M.Moxon, M.Rejmund, P.Schillebeeckx, & L.Szentmiklósi; Nuclear Physics A Volume 850, Issue 1, 15 January 2011, Pages 1-21; https://doi.org/10.1016/j.nuclphysa.2010.11.006
3. NuDat 3.0 Database; National Nuclear Data Center (NNDC); www.nndc.bnl.gov/nudat3/

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

(02-25-22)