A method of controlling or containing radioactive contamination by providing a neutron absorbing material to a radioactive contamination site. Preferably the neutron absorbing material is present as a powder, granule, slurry or suspension, allowing the neutron absorbing material to blanket cover the radioactive contamination site. Suitable neutron absorbing materials include lanthanide elements having a cross section of 100 Barns or greater, as well as hafnium, zirconium, tantalum, silver, indium, and hydrogen.