Brad DeLong's Semi-Daily Journal (2004)

Kr-85: 36 Protons, 49 Neutrons

Chad Orzel is going to spend the summer looking for Krypton atoms--and not just any Krypton atoms: those with 49 neutrons. He expects to find one every several hours.

Uncertain Principles: Our proposal is basically to adapt the ATTA method, which has been used to count rare isotopes of Kr in pure samples of Kr, to look for Kr atoms in a sample of Ne or Xe. At the level of purity they're looking for, this would amount to trapping one Kr atom every few hours, which is tedious, but doable. That measurement can give you the fractional abundance of Kr atoms in the gas that they're liquifying for their detectors, which can be combined with the known abundance of Kr-85 to get the background level for their detector.

So, by detecting an atom or two every few hours, with a small-scale and relatively cheap apparatus, I can provide information that will be used to determine how many of the few thousand counts a year that show up in multi-million dollar astrophysical detectors are just noise. It's amazing how Science works...

If you happen to find any, I'm sure he would like to know...