Lead

Lead (Pb) is the name for element 82. It is in Group 14 and Period 6. The element has been known since ancient times. The Romans called it "plumbum" and used it for pipes, which explains both where its symbol and the English words "plumber" and "plumbing" come from.

Thallium through polonium form a band in which elements transition from being mainly of chemical interest to being mainly of nuclear interest. Lead is abundant (no element with Z > 56 is more abundant), easily worked, and has been studied for thousands of years. It is also the stable endpoint of all three active actinide decay chains, as well as being a "reflector" which turns actinide decay chains back toward polonium. 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 lead's beta decays, actinide chains oscillate back and forth until they arrive at lead or bismuth (chain almost extinct).

NUCLEAR PROPERTIES

At least 99 isotopes of Pb have been predicted, of which 41 have been observed between ²¹⁸Pb and ¹⁷⁸Pb (plus 51 isomers). From the neutron dripline down to ²⁰⁹Pb, all isotopes (and their isomers) decay by beta emission. Down to ²¹¹Pb, decay is solely by beta emission and half-lives range from millisecond-scale at the dripline to 15 sec at ²¹⁸Pb to 10.64 hr at ²¹²Pb.

²¹⁰Pb has a (rather long) half-life of 22.2 yrs; and is a descendant of 238U, making it more abundant than any decay chain nuclide with A < 226. It has a thin [ BR_a(²¹⁰Pb) = 1.9E-08. ] alpha decay branch, leading to ²⁰⁶Hg. This is the only involvement of mercury in an actinide decay chain. 210Pb has a partial half life against alpha decay on the order of 1.2E09 yrs, which is the low Z end of the N = 128 effect, except for changes in x ratios in b+xn decays and possible stabilization against neutron decay at very low Z.

²⁰⁸Pb has 82 protons and 126 neutrons, which makes it very stable. [ It is doubly magic. ] Theoretically, it decays by alpha emission, with an available decay energy (Q_a) of 0.5 MeV. That gives it a half-life (t12) of 8.2E28 yrs, the longest half-life against alpha decay By comparison, the longest lived radioactive nuclide, ¹⁹⁰Pt, has Q_a(¹⁹⁰Pt) = 3.25 MeV. It can also, in principle, fission - but that happens maybe once per universe. ²⁰⁸Pb is both effectively and observationally stable.

²⁰⁷Pb, ²⁰⁶Pb, and ²⁰⁴Pb are also predicted to release energy upon alpha decay: Q_a(²⁰⁷Pb) = 0.39 MeV, Q_a(²⁰⁶Pb) = 1.14 MeV, and Q_a(²⁰⁴Pb) = 1.97 MeV. Their half-lives will exceed 10²⁰ yrs. In principle, they can also release energy by fission, but that's less likely. These isotopes are effectively and observationally stable.

²⁰⁵Pb decays by electron capture and has a half-life of 1.73E07 years, comparable to that of ²⁴⁷Cm. It is the second-longest-living nuclide which undergoes beta decay (in this case, positive beta decay), after 92Nb.

Positive beta decay has been observed between ²⁰³Pb and ¹⁸¹Pb. Between ²⁰³Pb and ¹⁹²Pb, it is either the only decay mode, or has a weak (BR < 0.001) alpha decay branch (which occurs at ^197m1Pb ¹⁹⁶Pb ¹⁹⁴Pb, and ¹⁹²Pb); and half-lives decline from 52 hrs to 3.5 min. There is an exception to both criteria in the band - ²⁰⁴Pb. It has a 0.01 branch ratio for alpha decay, but also has a 52500 year half-life. Its beta-decay half-life is long enough to allow competition by alpha decay. Between ¹⁹¹Pb and ¹⁸¹Pb, both decay modes are active and half-lives decline to the seconds range. Lighter isotopes are observed or predicted to decay by alpha emission.

Lead is over twice as abundant in the solar system as any other Period 6 transition metal⁽¹⁾. This is a result of two nuclear effects. Lead has four effectively stable isotopes, ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb. All of these can be produced by slow neutron capture in highly-evolved stars of all masses. All but ²⁰⁴Pb are also produced by rapid neutron capture followed by beta decay (r process), which only occurs in supernovae and neutron star mergers (²⁰⁴Pb is blocked by ²⁰⁴Hg). As might be expected, ²⁰⁴Pb is rare [0.014 isotopic mole fraction (imf)], but the abundance of the other isotopes isn't just due to an r-process contribution. ²⁰⁸Pb (0.524 imf) ends the ²³²Th decay chain, ²⁰⁷Pb (0.221 imf) ends the ²³⁵U chain, and ²⁰⁶Pb (0.241 imf) terminates the ²³⁸U chain. Also contributing to the abundance of ²⁰⁸Pb is the fact that it has closed neutron and proton shells (doubly-magic) That means it has a small cross-section for capturing another neutron and becoming (via ²⁰⁹Pb) ²⁰⁹Bi. S-process neutron capture ends at ²⁰⁸Pb.

In addition to the stable ones, five isotopes of Pb are part of actinide decay chains. Concentration of each can be computed by multiplying overall branch ratio from chain head to the isotope in question by the ratio of isotope half-life to chain head half-life to give concentration relative to chain head concentration. That can, if useful, be multiplied by the total quantity of chain head isotope to give quantity of each isotope in absolute terms. This gives [²¹¹Pb]/[²³⁵U] = 9.75E-14, [²¹⁴Pb]/[²³⁸U] = 1.14E-14, and [²¹²Pb]/[²³²U] = 8.64E-14 or n(²¹¹Pb) = 314 mol/planet, n(²¹⁴Pb) = 5200 mol/planet, and n(²¹²Pb) = 36700 mol/planet. ²⁰⁹Pb forms either by b+n decay at ²¹⁰Tl from ²³⁸U or by all paths from ²³⁷Np, resulting in [²⁰⁹Pb]/[²³⁸U] = 1.6E-21 via the ²¹⁰Tl route and [²⁰⁹Pb]/[²³⁸U] = 3.3E-37 via the ²³⁷Np route. The former dominates, implying that n(²⁰⁹Pb) = 0.00072 mol/planet.

The last isotope in this group, ²¹⁰Pb, has a [²¹⁰Pb]/[²³⁸U] = 4.97E-09 (about 5 parts/billion). This is enough to make recently-refined lead measurably radioactive. Lead is the material normally used to provide radiation shielding, but its own radiation can become problematic for very sensitive measurements. As a result, physicists have used "shipwreck lead" - ballast recovered from wrecks of ancient ships - for radiation shielding where needed. This has led to controversy with archeologists.

AT0MIC PROPERTIES

Lead is a Group 14 element. Like tin above it, Pb is metallic, although its electrical and thermal conductivities are low. Unlike lighter members of Group 14, it is relatively difficult to produce Pb⁴⁺. This is a result of high nuclear charge, which causes s electron orbitals to shrink and become more tightly bound than they would otherwise be.

Lead is abundant, readily reduced from widespread ores, low-melting, and easy to work. It is legendary for the low solubility of its salts - a phenomenon of practical interest. In many environments, lead forms a passivating layer that protects it from corrosion. Lead has been known and commercially important since ancient times for that reason. Lead's use for those purposes is declining, but its importance as a means of storing electric power is increasing. Use of solar and wind power for generation means storing excess power against times when those power sources are unavailable. The most mature technology for large battery banks uses lead-acid chemistry, just like the batteries in gasoline-powered cars. Storing a lot of electricity means building even larger banks, and the safe way to do that is with a proven technology.

REFERENCES:

(1) "Abundances of the Elements (Data Page)" in Wikipedia; "Ahrens" column. References to original sources found in that article.

(2) "Ancient Roman Metal Used for Physics Experiments Ignites Science Feud"; Clara Moscowitz; Scientific American; 12-18-2013.

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

(02-27-22)