Those working on the project were ultimately responsible for creating the polonium-based modulated neutron initiators that were used to begin the chain reactions in the atomic bombs.

The Dayton Project developed techniques for extracting polonium from the lead dioxide ore in which it occurs naturally, and from bismuth targets that had been bombarded by neutrons in a nuclear reactor.

Ultimately, polonium-based neutron initiators were used in both the gun-type Little Boy and the implosion-type Fat Man used in the atomic bombings of Hiroshima and Nagasaki respectively.

He was then invited to a meeting in Washington D.C., with Brigadier General Leslie R. Groves, Jr., the director of the wartime Manhattan Project responsible for building an atomic bomb.

[4] They offered him a post as a deputy to Robert Oppenheimer, the director of the Los Alamos Laboratory in New Mexico, but he did not wish to move his family or give up his responsibilities at Monsanto.

[4] At Los Alamos, physicist Robert Serber proposed that instead of relying on spontaneous fission, the chain reaction inside the atomic bomb should be triggered by a neutron initiator.

Thomas took charge of the development of techniques to industrially refine polonium for use with beryllium in the "urchin" internal neutron initiators.

[12] Unit II was the Monsanto Rocket Propellant works off Betty Lane near Ohio State Route 741.

Initially only the bottom two floors were occupied, providing 560 square meters (6,000 sq ft) of laboratory space.

[15][16][12] In May 1945, five additional temporary buildings were constructed on land leased from the Board of Education that housed offices, a cafeteria, locker rooms, a physics laboratory and a laundry.

[17] By 1944, space was running short, and Monsanto began negotiations to acquire the Runnymede Playhouse in the wealthy residential Dayton suburb of Oakwood.

After small-scale tests at Unit III revealed that the process was practical, some three tons of lead dioxide were sent to the B plant, and 2.50 curies (93 GBq) were recovered.

They were shipped to Dayton by rail in wooden boxes, which were stored in a tile-lined cavity in the floor at Unit IV.

[34] Even at Clinton, unprotected bismuth proved problematic when a brick broke apart and chips fell into containers of uranium slugs, and had to be hazardously separated by hand by project personnel.

The problem was that the aluminium contained impurities such as iron, manganese, copper, lead, tin, zinc, silicon, titanium, nickel, magnesium, chromium, vanadium, bismuth and gallium, and when irradiated, these could form radioactive isotopes.

Most were of little concern for the Dayton Project, as they had short half-lives, and would become harmless during the slugs' cooling off period in water at Hanford; but iron could form iron-59, which had a half-life of 45 days, and produced gamma radiation.

The main problem with the process was that it required glass-lined containers due to the aqua regia, and mechanisms for safe handling of the radioactive material.

[35] The first consignment of polonium left for Los Alamos on 15 March 1944 in a lead-lined suitcase carried by a military courier.

[19][36] Initiator testing at Los Alamos required more polonium than anticipated, and in December 1944, Oppenheimer was forced to ask Thomas if he could ship 20 curies (0.74 TBq) per month.

The radioactive residue on their hands was measured with a special Geiger counter designed for the purpose by physicist John J.

The employee at Unit IV with the highest levels of polonium in her urine had contaminated her hair, and often held bobby pins in her mouth.

[19] George Koval was drafted into the United States Army in 1943, and was inducted into the Manhattan Project's Special Engineer Detachment.

He was initially assigned to the Clinton Engineer Works, where his job as a health physics officer gave him access to much of the site.

In order to increase the efficiency of the explosion, the initiator had to emit a large number of neutrons in a few microseconds while the plutonium core was fully compressed.

These grooves converted the shock wave of the implosion into jets that shattered the spheres and caused the beryllium and polonium to mix and emit neutrons.

Few of the scientific and technical staff wanted to move to Tennessee, and there were concerns about the dangers of polonium contamination at a plutonium processing site.

[46] The design called for an underground complex that could withstand a direct hit from a 910-kilogram (2,000 lb) bomb, with protection against biological and chemical weapons, at a cost of $17,900,000.

[48] Responsibility for nuclear weapons production was transferred from the Manhattan Project to the Atomic Energy Commission in 1947, but work continued on the Mound Laboratories.

Altogether, 14 major buildings were constructed with a total floor space of 34,000 square meters (366,000 sq ft) at a cost of $25.5 million.

[49] Due to fear of attack or sabotage, the former Scioto Laboratory Complex in Marion, Ohio, was acquired by the Atomic Energy Commission in 1948.