A 'cow' is column used to store a radionuclide. The 'cow' can be 'milked' by flushing the column to obtain a desired decay product. In this case, the cow contains an ammonium salt of molybdenum-90. The daughter isotope, technetium-99m is continually produced. The isotope obtained from the technetium cow has a 6 hour half-life and is used in bone scans.
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