linguistic:paraphrasing
Isotope nucleosynthesis

Americium has been produced in small quantities in nuclear reactors for decades, and kilograms of its Am and Am isotopes have been accumulated by now. Nevertheless, since it was first offered for sale in 1962, its price, about US$1,500 per gram (US$43,000/oz) of Am, remains almost unchanged owing to the very complex separation procedure. The heavier isotope Am is produced in much smaller amounts; it is thus more difficult to separate, resulting in a higher cost of the order US$100,000–US$160,000 per gram (US$2,800,000–US$4,500,000/oz).

Americium is not synthesized directly from uranium – the most common reactor material – but from the plutonium isotope Pu. The latter needs to be produced first, according to the following nuclear process:

The capture of two neutrons by Pu (a so-called (n,γ) reaction), followed by a β-decay, results in Am:

The plutonium present in spent nuclear fuel contains about 12% of Pu. Because it beta-decays to Am, Pu can be extracted and may be used to generate further Am. However, this process is rather slow: half of the original amount of Pu decays to Am after about 15 years, and the Am amount reaches a maximum after 70 years.

The obtained Am can be used for generating heavier americium isotopes by further neutron capture inside a nuclear reactor. In a light water reactor (LWR), 79% of Am converts to Am and 10% to its nuclear isomer Am:

Americium-242 has a half-life of only 16 hours, which makes its further conversion to Am extremely inefficient. The latter isotope is produced instead in a process where Pu captures four neutrons under high neutron flux: