Polonium (Po)

Every element identified before 1898 was found by chemistry or by light — a reaction that behaved oddly, a precipitate that would not fit, a spectral line in the wrong place. Polonium was found by an electrometer.

Pierre Curie's quartz piezoelectric electrometer measured how strongly a sample ionised the air above it. Marie Curie used it to work through pitchblende systematically, splitting each fraction and following whichever part carried more activity than its uranium content justified. The trail led to a fraction that followed bismuth through the separations, and in July 1898 the Curies announced a new element there. The card credits Pierre; the method, the measurements and the naming were Marie's.

She called it polonium. Poland at that point had been partitioned between Russia, Prussia and Austria for over a century and did not appear on any map of Europe. Putting the name into the title of a paper in Comptes Rendus was a deliberate political act, and as far as the periodic table goes it remains a singular one: no other element is named for a country that did not exist at the time.

A cube, which sounds ordinary and is not

Metals crystallise in a small number of efficient packing arrangements — face-centred cubic, body-centred cubic, hexagonal close-packed — because those fill space well and minimise energy. The simple cubic lattice, one atom at each corner of a cube and nothing in the middle, wastes nearly half the available volume and is essentially never seen.

Polonium adopts it anyway. Its α phase is the only known case of an element taking a simple cubic structure at ordinary temperature and pressure, and the explanation involves relativistic effects on the 6p electrons that make the bonding unusually directional. It is the sort of fact that survives in textbooks precisely because there is no second example to compare it with.

That same 6p configuration puts polonium in group 16 under tellurium, and the card above calls it a metalloid. Its electrical behaviour is straightforwardly metallic, and plenty of sources classify it as a metal. This is one of the periodic table's genuinely unsettled boundary cases rather than a settled fact reported inconsistently.

One hundred and forty watts per gram

Polonium-210's half-life of 138 days is short enough to make it fiercely active and long enough to make it storable, and its alpha decay releases 5.3 MeV with almost no accompanying gamma radiation. The combination gives a specific thermal power of about 140 watts per gram. A capsule of it warms itself to several hundred degrees with no input of any kind.

That property gave polonium its main historical job. The Soviet Lunokhod rovers carried polonium-210 heaters to keep their electronics alive through the fourteen-Earth-day lunar night — not generating electricity, simply refusing to freeze. The same isotope was the neutron source in the initiators of the first fission weapons, mixed with beryllium so that alpha particles striking beryllium nuclei would release neutrons at the required instant.

The one use that is still routine is quieter. Alpha particles ionise air very efficiently over a short path, so a sealed polonium source mounted in a bar or brush neutralises static charge on moving webs of paper, film and plastic. Printing presses and film-coating lines have used them for decades, and they are the reason a few hundred grams of polonium are made each year at all.

Almost none of it is natural

Polonium occurs in uranium ore as a fleeting member of the uranium-238 decay chain, at roughly 0.1 milligrams per tonne. Recovering the Curies' first samples meant processing pitchblende residues by the tonne for quantities that were never weighed.

Every practically useful gram is made instead by irradiating bismuth-209 in a reactor: bismuth-210 forms and beta-decays to polonium-210. Global output has run at something like a hundred grams a year, and for most of the past half-century almost all of it came from Russian facilities and was exported for antistatic devices. Two longer-lived isotopes exist — polonium-209 at 124 years and polonium-208 at 2.9 years — but both require an accelerator and neither has ever been cheap enough to displace polonium-210.

Polonium in tobacco

Tobacco leaves accumulate polonium-210, and they do it in two ways. Lead-210 present in the atmosphere from radon decay settles on the leaf surface and is trapped by the sticky glandular hairs, and phosphate fertilisers derived from apatite carry radium and its descendants into the soil. The polonium survives combustion and reaches the small airways in smoke particles, where it deposits at bronchial branch points — the same locations where smoking-related tumours preferentially arise.

Internal research documents released through tobacco litigation show that the industry investigated polonium in its product from the 1960s onward and understood the implications. How much of smoking's lung cancer burden polonium accounts for is disputed, and the honest summary is that it is a real contributor within a mixture containing many carcinogens, not the hidden single cause it is sometimes presented as.

London, 2006

Alexander Litvinenko, a former officer of the Russian security services living in Britain, fell ill in London on 1 November 2006 and died on 23 November. Polonium-210 was identified as the cause only in the final hours of his life.

The delay is a direct consequence of the physics. Alpha particles are stopped by a sheet of paper, by the dead outer layer of skin, and by the window of a standard survey instrument — so a person carrying a lethal quantity of an alpha emitter internally reads as clean on the equipment hospitals and emergency services actually own. Polonium-210 emits a gamma ray in roughly one decay in a hundred thousand, and it was that faint signal, looked for on a hunch with a spectrometer, that finally identified it. A British public inquiry reported in 2016 that Litvinenko had been deliberately poisoned with polonium-210 and named those it held responsible.

The episode is also why polonium's contamination behaviour is well documented in the open literature: the isotope's trail through hotels, restaurants and aircraft was mapped in detail during the investigation, and the exercise demonstrated how readily a soluble alpha emitter spreads on surfaces.

The cost to the family that found it

Irène Joliot-Curie, the Curies' elder daughter, was working with a sealed polonium capsule in 1946 when it ruptured. She died of leukaemia in 1956. The connection has never been proven and she had accumulated substantial exposure over a working lifetime from many sources, but the incident is part of the standard account of her illness — and it is a reminder that polonium's danger has nothing to do with penetrating radiation and everything to do with getting inside the body, where the short range of an alpha particle stops being protective and becomes the entire problem.