The atomic bomb project relied on the contributions of very many people. Many emigre scientists were involved in the project, and many American scientists were too. Even people with no direct link to the project made contributions; Einstein, for example, in the letter to President Roosevelt stressing the urgency of determining the possible applications of fission to the war effort. Of course, there are a few people whose contributions can be considered most significant; these were Oppenheimer, Lawrence, Fermi, Szilard, and Groves.
Oppenheimer is often called the Father of the A-Bomb. Oppenhemier was an American who studied for a time at Gottingen. Primarily a theorist, Oppenheimer's work on the A-bomb project had been attempting to determine how much U235 would be needed for a critical mass for a bomb; however, he was chosen to direct the secret lab Los Alamos. Oppenheimer turned out to be the perfect man for the job, he convinced scientists to come to the remote facility; he ran the facility in a hands-on fashion, staying involved with the scientists at Los Alamos.
Lawrence was an important player in the bomb project. Lawrence was an American with a new approach to science: big science and the crash program. Los Alamos ran on these principles: it was big science because of the large number of scientists on the project and the large budget allotted to it; it was a crash program because nobody knew for sure how to build a nuclear bomb, so they had to learn by doing. It is also thanks to Lawrence and his cyclotron that the project was able to acquire enough enriched uranium for a bomb.
Enrico Fermi was a self-taught Italian scientist who came to America to escape fascist Italy. Fermi had experimented with neutron bombardment of atoms. even though he had first thought he was creating transuranium elements, not fission, he was the first to create an atomic pile that would sustain a fission chain reaction. Fermi's atomic pile also created plutonium, a transuranium element, as a byproduct; plutonium was created in small amounts, but enough for the Los Alamos facility to make 2 plutonium bombs.
Szilard's role in the project was his stress of self-censorship. Szilard was concerned with keeping the knowledge of fission out of the hands of the Nazis, to keep them from developing a nuclear bomb. Fermi did censor himself as a result of this, keeping secret the usefulness of pure carbon as a moderator.
Groves too was important to the bomb project. Though he was a military leader and not a scientist, his decision on Oppenheimer to direct Los Alamos was an important one. Many people considered Oppenheimer to be a risk due to his involvement in communist activities, but the success of the project proved that Groves had made a wise choice.
Mendel's 1865 paper was not well received by the scientific community at the time. The paper contained Mendel's idea of genetics. There were several reasons that Mendel's paper was not well received. One is that Mendel lived and worked in a monastery, and consequently he had very little connection to the rest of the scientific community. Mendel's idea had no nurturing environment of a few scientists who could support him. Another reason is that Mendel published his paper to an obscure local journal which most scientists wouldn't have read. It is not so much that the scientific community didn't like his paper; they simply didn't know about it. Another reason is that Mendel used math in his paper, and biologists at the time detested math. A final reason for the poor reception of Mendel's paper is that he was overshadowed by Darwin and his theory of evolution.
T.H. Morgan was an American scientist who is best known for his work with the fruit fly Drosophilia. Morgan's work built upon previous study of the sex chromosomes, chromosomes which appear differently in the two sexes. Morgan discovered that sex-linked traits occur when a gene is found on only one of the X or Y chromosomes (two X's making a female, XY making a male). MOrgan was able to map the locations of some genes on the chromosomes, using their frequencies of crossing-over.
Arthur Eddington was a proponent of Einstein's theory of relativity. In particular, Eddington believed that relativity's equation E=mc2 could be applied to the problem of what fueled the sun.
19th Century science had found the elements to have whole number rations for weights, but by the 20th Century scientists knew the masses were slightly different from that. Helium had close to a 4:1 weight ratio with hydrogen, but not exactly.
Eddington believed that E=mc2 could solve this dilemma. Combining 4 hydrogens into one helium would release the slight mass differnece as energy. Though the energy from one such fusion of hydrogen atoms would be slight, the great number of hydrogen and helium in the Sun indicated that this would produce enough energy to account for the Sun's present output. Eddington was able to estimate the lifetime of the Sun, about 10 billion years, which agreed nicely with geologists' evaluation of the age of the Earth.
The plutonium bomb had a different design from the uranium bomb's bullet approach. The plutonium bomb would require a faster assembly of a critical mass than the bullet approach of the U-bomb could do.
The orginal concept of the plutonium bomb was an implosion of two hemispheres of plutonium to form a critical mass. There was a problem with this: the possiblility existed that the explosives would cause plutonium to leak out, because the shockwaves wouldn't match the shape of the plutonium.
The final design fixed this: implosion lenses of a different density would be placed around the plutonium, reshaping the shockwave to the shape of the plutonium. Also, the plutonium was decided to be a subcritical single mass; the implosion would compress it to a high enough density to make it critical.
The scientists were unsure of the mechanism of the bomb, though; they didn't know if it would be reliable in non-laboratory conditions.
There were 5 methods for producing bomb-grade fissionable material. Two worked, one worked inefficiently, and two didn't work.