  Krypton-85 is an anthropogenic beta-decaying isotope which produces low
energy backgrounds in dark matter and neutrino experiments, especially those
based upon liquid xenon. Several technologies have been developed to reduce the
Kr concentration in such experiments. We propose to augment those separation
technologies by first adding to the xenon an 85Kr-free sample of krypton in an
amount much larger than the natural krypton that is already present. After the
purification system reduces the total Kr concentration to the same level, the
final 85Kr concentration will have been reduced even further by the dilution
factor. A test cell for measurement of the activity of various Kr samples has
been assembled, and the activity of 25-year-old Krypton has been measured. The
measured activity agrees well with the expected activity accounting for the
85Kr abundance of the earth atmosphere in 1990 and the half-life of the
isotope. Additional tests with a Kr sample produced in the year 1944 (before
the atomic era) have been done in order to demonstrate the sensitivity of the
test cell.
