In response to:

Iran & the Bomb: The Endgame from the February 5, 2015 issue

To the Editors:

Readers who may want to know further details about the definition of the separative work units (SWUs) involved in the Iranian nuclear project, and referred to in my “Iran and the Bomb: The Endgame” [NYR, February 5], should consult the definition given by the World Nuclear Association on its website:

A complex unit which is a function of the amount of uranium processed and the degree to which it is enriched, i.e., the extent of increase in the concentration of the U-235 isotope relative to the remainder. The unit is strictly: Kilogram Separative Work Unit, and it measures the quantity of separative work (indicative of energy used in enrichment) when feed and product quantities are expressed in kilograms.

Christopher de Bellaigue