Among traces that inspectors detected last year are some refined to 90 percent of the rare 235 isotope, the diplomats said.

Nitrogen-15 is a rare stable isotope of nitrogen.

Look at all these metals, and the rare isotopes readily available on surface scrapings!

High concentrations of uranium's rare 235 isotope can fuel warheads.

Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons.

They could usually salvage enough gold and rare isotopes to fund the building of a new ship and still have cash left over.

It's a most unusual compound, composed of several rare isotopes.

The scientific challenge, on which untold billions have been spent, is to separate the extremely rare isotope from the common one.

The lab's scientists investigate the properties of rare isotopes and nuclear reactions.

The reactor also produces rare isotopes for use in medicine and industry.