[spycosis]

These clean-up workers were allowed a dose of 25 rem before being replaced. This is the equivalent of about 2,500 chest X-rays. However, a large part of the dose they received was not just gamma radiation, they would undoubtably have absorbed alpha emitters into their bodies which would not show up on the dosimeter badges and is incredibly dangerous inside the body (Litvinenko died primarily from alpha radiation poisoning), and also a huge portion of the dose would have been neutron radiation which turns atoms in the body into radioactive isotopes.

Sodium for example becomes a radioactive isotope (Na 24) which then emits gamma rays and beta radiation deep inside the body as it decays over a period of weeks into a stable form of magnesium. The lead shielding they wore offered no protection at all from the neutron radiation as this passes through heavy elements with ease.