20% enrichment

Why is 20% enrichment, claimed by Pres. Ahmedinejad of Iran, in a speech
commemorating the 31st anniversary of the Iranian revolution, so
significant? While 20% enriched U-235 is the level used for medical
irradiation, it is not sufficient for weapons use, although it is the
step before enrichment to 90% that is used for nuclear weapons.

Natural abundance of U-235 is 1% mixed with the non-radioactive isotope U-
238 at 99%. To enrich the U-235 content from 1% to 20% requires a 20-
fold enrichment, so this is the most difficult step, to go from 20% to
90% requires only a 4.5 fold enrichment, so is easier. That means that
however long it has taken the Iranians to get to 20%, it will take a
fraction of that time for them to get to 90%. That is the cause for
concern! In addition to that, Iran has tested missiles that could deliver
a nuclear warhead if or when they develop it.

Isotopic enrichment is achieved by chemically transforming the uranium
ores into the gaseous substance uranium hexafluouride (UF6) which is then
processed through long centrifuges to allow the heavier isotope U-238 to
collect at the bottom and the lighter isotope U-235 to collect towards
the top. Since the separation is only partial the process must be
repeated many thousands of time. That is why the announcement a few
weeks ago that Iran had completed the operation of a further 300
centrifuges was worrying and was a prelude to the current announcement of
20% enrichment.

From now on we must assume thet the decision has been made by the
bellicose Iranian regime to achieve weapon's grade U-235, which means
that they are scarcely a year or so away from this achievement. However,
to take the actual step is a political decision, but we must assume that
this is what the Iranian regime is in the process of doing. So far the
response of the Obama administration is pathetic, they have done nothing
but talk. Obama has shown no leadership and has not spoken out firmly in
favor of the anti-regime forces in Iran, nor given them any support. He
is too concerned about the image of the US as interfering in the affairs
of other states, even if they are declared enemies. Will he now, before
it is almost too late wake up to the deadly threat that is looming over
all of us.