The results of cross-section measurements for the reactions ²⁰⁹Bi(¹²C,X)Au, E=4.8 and 25.2 GeV and ²⁰⁹Bi(²⁰Ne,X)Au, E=8.0 GeV are reported. The observed yields of the gold isotopes show a similar dependence on mass number for each reaction, differing slightly in the position of the centroid of the distribution. As the projectile energy increases, the inferred excitation energy of the primary residues remains the same or decreases slightly. This observation is in agreement with the predictions of the intranuclear cascade model of relativistic heavy ion collisions.

NUCLEAR REACTIONS ²⁰⁹Bi(¹²C,X)Au, E=4.8,25.2 GeV; ²⁰⁹Bi(²⁰Ne,X)Au, E=8.0 GeV; measured Au isotopic distributions, relativistic heavy ions, target fragmentation, Ge(Li) spectroscopy.

Energy dependence of 209-Bi fragmentation in relativistic nuclear collisions, Aleklett, K., Morrissey D., Loveland W., McGaughey P., and Seaborg G. , Physical Review C, 3/1981, Volume 23, Issue 3, p.1044 - 1046, (1981)

Polonium metal structureIt is suggested that poisoning by polonium-210 may have caused the death of Alexander Litvinenko, said to be a former Russian spy, in November 2006. Following his death at the end of November 2006, traces of polonium were found at several places he had visited before becoming ill. Before his death it was thought that thallium, or even radiothallium, might have been the cause of his illness. At the time of writing it is not clear who killed him, but not surprisingly the Russians deny it. Polonium-210 decays through the emission of α-particles and these emissions are noramlly easy to stop, but they are very dangerous if the polonium is inside the body.

Polonium is radioactive and present only in extremely low abundances in the environment. It is quite metallic in nature despite its location beneath oxygen in the periodic table. It is made in very small quantities through a nuclear reaction of bismuth. Neutron irradiation of ²⁰⁹bismuth (atomic number 83) gives ²¹⁰polonium (atomic number 84).

²⁰⁹Bi + ¹n → ²¹⁰Po + e^-

Polonium-210, ²¹⁰Po, transmutes into the lead isotope ²⁰⁶Pb by the emission of an α-particle. The half life for this process is just over 138 days meaning that after 138 days one-half of the original ²¹⁰Po has disappeared and after 2 times 138 days ³/₄ has gone.

²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He

The short half life of polonium-210 and the heat generated with the above radioactive decay means that polonium metal generates considerable heat (141 W), meaning that the metal and its compounds self-heat. This is a useful property and polonium can be used as a small heat source (if expensive!). It can be used in space satellites for this purpose and is especially desirable as there are no moving parts. It was also used in the lunar rovers to keep internal parts warm during the frigid lunar nights.

Polonium metal is unique in that it is the only element whose structure (known as the α-form) is a simple cubic array of atoms in which each atom is surrounded by six other polonium atoms. On gentle warming to 36°C, this converts into a second form known as the β-form.

Polonium dioxidePolonium dissolves in acids to form pink hydrated Po(II), presumably as[Po(OH₂)₆]²⁺. This seems to oxidize to yellow Po(IV) species perhaps as a consequence of oxidizing agents produced through the α-particle induced decay of water. The polonium(II) oxide PoO is known but this oxidizes easily to the Po(IV) oxide PoO₂.

Polonium dichlorideThe Po(II) halides PoX₂ (X = Cl, Br, I) are known (the chloride and bromide are particularly well characterised) while all the Po(IV) halides PoX₄ (X = F, Cl, Br, I) are known.

There are few crystallographically characterised polonium compounds largely because not many researchers work with polonium and the difficulties associated with characterising such radioactive compounds. The 14-electron polonium(IV) anion [PoI₆]^2– is strictly octahedral meaning the lone pair is sterochemically inactive.

Venus Cloud Tops
The BBC reported a few weeks ago that parts of Venus may be lead plated. David Whitehouse reports that

"The highlands of Venus are covered by a heavy metal 'frost', say planetary scientists from Washington University.

Because it is hot enough to melt lead at the surface, metals vaporise and condense at cooler, higher elevations.

This may explain why radar observations made by orbiting spacecraft show that the highlands are highly reflective.

Detailed calculations, to be published in the journal Icarus, suggest that lead and bismuth are to blame for giving Venus its bright, metallic skin."