 Cobalt @-@ 57 ( Co @-@ 57 or 57Co ) is a cobalt radioisotope most often used in medical tests , as a radiolabel for vitamin B12 uptake , and for the Schilling test . Cobalt @-@ 57 is used as a source in Mössbauer spectroscopy and is one of several possible sources in X @-@ ray fluorescence devices . 
