How to do you prefer your Mexican....well done or extra crispy...???
Cobalt-60, 60Co, is a synthetic radioactive isotope of cobalt with a half-life of 5.2714 years. It is produced artificially by neutron activation of the isotope 59Co. 60Co decays by beta decay to the stable isotope nickel-60 (60Ni). The activated nickel nucleus emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is
27Co + n → 60
27Co → 60
28Ni + e− + ν
e + gamma rays.
"MeV" stands for Million electron Volts and is an indicator of the energy of each fission reaction.
yah...very technical, but the long and the short of that Cobalt 60 emits both Gamma rays and Beta Particles (loose electrons) as it decays, and is extremely dangerous when in close contact. One of the significant fallout hazards of many nuclear weapons bursts is Colbalt 60, and in fact wrapping a nuclear device in Cobalt 60 and letting it be atomized and widely disbursed is one of the early ways of enhancing the effects of nuclear weapons.
These guys were being fried the entire time they were close to this stuff, and what the safe distance is depends on just how much Cobalt 60 they were exposed to and for how long.