 A polonium-beryllium modulated neutron initiator, known as an "urchin" because its shape resembled a sea urchin, was developed to start the chain reaction at precisely the right moment.This work with the chemistry and metallurgy of radioactive polonium was directed by Charles Allen Thomas of the Monsanto Company and became known as the Dayton Project.Testing required up to 500 curies per month of polonium, which Monsanto was able to deliver.