On 16th July, 1945 at 5:29 AM in Jornada del Muerto desert near Alamogordo, New Mexico, the first successful test for nuclear weapons took place. Robert Oppenheimer and his team was working on this as a part of the Manhattan Project for the last three years. What happened that day forever changed the course of World history.
The successful test allowed United States military to drop nuclear bomb over Hiroshima on August 6, 1945 and over Nagasaki on August 9, 1945 that completely destroyed the two cities killing hundreds of thousands of people in the process. The move effectively ended the World War 2. Today I am to going to tell you how Oppenheimer and his team made the world’s first atomic bomb.
Discovery of nuclear fission and earlier scientific development
The invention of nuclear bomb was not an instant development as you may think. The project got help from the decades of research and development undertaken by physicists all around the world.
It all started with the discovery of radioactivity by Henri Becquerel, Marie Curie, and Ernest Rutherford in the late 19th century. Their work laid the foundation for studying atomic nuclei and the radiation.
In 1905, young Albert Einstein introduced the theory of special relativity while working as a Clerk in Switzerland. His theory of mass and energy equivalence, proved that a small amount of mass can produce huge amount of energy in specific conditions.
In 1911, Ernest Rutherford performed his groundbreaking experiment that provided the conclusion, that most of the atom’s mass is concentrated in a tiny,positively charged nucleus at the center of the atom and it is surrounded by electrons.
In 1913, Danish physicist Niels Bohr introduced the Bohr’s model. His theory helped in understanding the structure of atoms, stability and various energy levels of electrons.
At first no one thought that atoms can produce massive amount of energy. Because at that time, it was almost impossible to break them. Rutherford said that “Anyone who expects a source of power from the transformation of these atoms is talking moonshine”.
Even Einstein said “There is not the slightest indication that nuclear energy will ever be obtainable – it would mean that the atom would have to be shattered at will.”
In early 1930s, various scientists started experimenting on nuclear reactions. In 1932, British physicists Ernest Walton and John Cockroft broke the lithium nuclei with the help of proton through particle acceleration. Their work demonstrated the conversion of matter into energy and it will later help in the discovery of nuclear fission.
But the energy produced through their particle accelerator was very low because the positively charged protons were repelled by the positive charges of the nuclei. That same year, another British physicists James Chadwick discovered the existence of a neutron in his Cambridge laboratory.
Neutron is neutral (uncharged), so it will not have the problem proton was having during the bombardment. In 1933, Hungarian physicists Leo Szilard introduced the idea of nuclear chain reaction. He realized that if a neutron could cause the fission of an atomic nucleus, it could release additional neutrons, which, in turn, could cause the fission of more nuclei, creating a sustaining chain reaction.
In 1938, German physicists Otto Hahn and Fritz Strassmann used Szilard’s idea to conduct an experiment that will change the world forever. They saw that when Uranium is bombarded with neutrons, it got split into smaller elements.
After the incident, Hann sent the findings to his former colleague Lise Meitner, a physicist who fled Nazi Germany and was working in Stockholm, Sweden. Meitner with the help of her nephew Otto Frisch, provided the theoretical explanation for the discovery and coined the term ‘Nuclear Fission‘. They published their discovery in January 1939.
On 29th January 1939, Luis Alvarez, an experimental physicist and a colleague of Robert Oppenheimer, encountered the findings while reading The San Francisco Chronicle during his haircut. He quickly got up in the middle of his haircut and ran towards Oppenheimer’s office to show him.
After reading the article, Oppenheimer refused to believe it and through a calculation he tried to prove that nuclear fission is never possible. Alvarez, an experimental physicist himself, repeated the experiment and found out the that the article is actually true.
Alvarez showed his experiment to Oppenheimer and after some time, he not only agreed, he also figured out that the initial bombardment will cause a nuclear chain reaction that will emit a massive amount of energy. That energy can be used to create an atomic bomb.
World War 2 Begins
On 1st September,1939, Nazi Germany under the leadership of Chancellor Adolf Hitler, invaded Poland despite warnings from Britain and France. Soviet Union, at that time an ally of Germany, also invaded Poland from the east. Within weeks they occupied the whole country and then divided between them.
Right after the invasion, Britain and France issued an ultimatum asking for complete withdrawal of troops from Poland. Hitler refused and on September 3rd,1939, Britain and France declared war on Germany, marking the beginning of World War 2.
After declaring war on Germany, there was a phone war for some time. The Allies literally did nothing for quite a while. But in April 1940, Hitler invaded Denmark and Norway. In may, Hitler started a full invasion of France and quickly occupied the whole country defeating both French and British army.
That same year, Hitler also attempted to invade Britain but failed. Next year, in an unexpected turn of events, Hitler betrayed Stalin and invaded the Soviet Union, an ideological enemy of fascism, in June 1941.
But the biggest turning point of the war was the Japanese attack on Pearl Harbor. On December 7th, 1941, Japanese Imperial Navy launched a surprise attack on United States Naval base in Pearl Harbor. The well co-ordinated attack destroyed several American battle ships and other naval assets.
The attack also killed almost 2400 American soldiers and injured more than a thousand people. The incident changed American public view about the war and filled them with rage. The next day on December 8th, 1941, US formally declared war on Japan, thus entering the World War 2.
Uranium Committee and early nuclear research
On 2nd August, 1939, around a month before Hitler invaded Poland, Albert Einstein, who fled Nazi Germany and Hungarian physicist Leo Szilard wrote a letter to US President Franklin D. Roosevelt, requesting him to launch a research project on nuclear physics and warned that if Germany builds a nuclear bomb first, it will be a catastrophic for the free world.
In response to the letter, President Roosevelt formed the Advisory Committee on Uranium in October 1939. Roosevelt appointed engineer Lyman Briggs to lead the committee. Lyman conducted the first committee meeting on 21st October, 1939. Prominent scientists like Enrico Fermi, Leo Szilard, Edward Teller, Ernest Orlando Lawrence was part of that committee.
The committee evaluated the potential military applications of nuclear energy. The committee recognized the significance of uranium sources, especially for the isotope U-235 and they also found out that they can use the newly discovered Plutonium in University of California (1940) for creating a nuclear chain reaction and thus a bomb.
In mid 1940, Roosevelt upgraded the committee to National Research Defence Committee (NRDC). US also started collaborating with its ally Britain to conduct and share research. Britain established the MAUD committee to do research in response to the memorandum of scientist Otto Frisch and Rudolf Peierls in 1940.
Frisch and Peierls recently figured out the critical mass of Uranium, which is essential to start the nuclear chain reaction. In mid 1941, President Roosevelt created the Office of Scientific Research and Development and the previously formed NRDC became the S-1 Unit of the organisation.
On October 9th,1941, President Roosevelt approved the atomic programme and scientists around the country started conducting research on separating Uranium 235 (needed for nuclear chain reaction) from the more abundant Uranium 238 (which doesn’t undergo chain reaction). Natural uranium contains about 0.7% of U-235 and 99.3% of U-238.
At that time, various scientists were working on 5 different seperation technique – electromagnetic separation, gaseous diffusion, thermal diffusion, gas centrifuges and heavy water process. On 23 May 1942, the committee decided to pursue all of the techniques to figure out the separation.
Ultimately they used both gas diffusion and electromagnetic seperation for Uranium enrichment. Prominent scientists like Eger Murphree, Ernest Orlando Lawrence, Philip Abelson, Jesse Wakefield Beams, Harold Urey and Arthur Compton played a huge part in separation process.
The committee secured around $54 million from US government with the approval of President Roosevelt to conduct research and development on Uranium sources and seperation.
They also found out that Plutonium will be an excellent choice for making a bomb because it can also be created from Uranium-238 and it needs less critical mass (10KG) compared to that of Uranium-235 (52KG) for a sustained nuclear chain reaction.
In mid 1942, Oppenheimer, who was working in University of California, got involved in the research of neutron diffusion and hydrodynamics. His research was instrumental in calculations of required critical mass for explosion.
Oppenheimer and his colleague Enrico Fermi completed their research and came up with the theoretical basis for a fission bomb. In June and July of 1942, scientists from University of California and University of Chicago reviewed the calculations and agreed that fission bomb is now possible. There was also a possibility that the nuclear chain reaction will not stop and ultimately ignite the atmosphere and destroy the entire world. But later it was found that the possibility is next to zero.
The Manhattan Project
The code name for this secret operation was given ‘The Manhattan Project’, becoz of the project’s headquarter in Manhattan Engineer District. Later in December, President Roosevelt approved funding of around $500 million to get things going.
On December 2nd,1942, the first breakthrough of the Manhattan Project happened. That day, a group of scientists under the command of Enrico Fermi, successfully produced a self-sustaining nuclear chain reaction through the help of reactor Chicago Pile-1 (CP-1), which was made of graphite blocks and uranium fuel.
The experiment secretly took place under the Stagg football field of University of Chicago. This experiment confirmed that they can actually make a nuclear bomb that will explode and it also laid the groundwork of today’s nuclear power plant and related research.
Research and Engineering Sites
To conduct research and development for the atomic bomb, there were several sites chosen and each of the site played their individual part in making the bomb. Oakland, Tennessee, was chosen for Uranium and Plutonium enrichment.
On 29 September 1942, US government authorized the Corps of Engineers to acquire 56,000 acres of land selected by Groves for $3.5 million. The purchase affected more than 1000 families, they were forced to leave the place by government order.
The Oakland site became the area where several factories were manufactured for Uranium enrichment. Plants like S-50, K-25 and Y-12 played essential part and employed thousands of people. Graphite X-10 reactor was also based there.
The most important site of the project was the research laboratory at Los Alamos, New Mexico, under the directory of Oppenheimer. Groves wanted a secure and private place for the research and Oppenheimer suggested the remote hilly area where he had happy moments while growing up.
Almost $500,000 spent on acquiring the land and initially Groves thought $300,000 will be enough for construction project but within a year the entire cost of the Project Y surpassed over $7 million. The cost included the building of laboratories and even building an entire town to house the scientists and their family.
In Hanford, Washington, Groves spent $5 million to acquire 430,000 acres of land in an isolated area nearby Columbia river. This area became the site of Hanford Engineer Works, where in collaboration with Dupont, the B reactor was created for Plutonium production.
In Chicago, there were plans to build large factories for Plutonium production but later it was transferred to Oak Ridge. Instead it became the site of various related to nuclear reactors including the Chicago Pile-1, the first artificial nuclear reactor. Research also continued in Harvard University and MIT.
In Canada, the project established Heavy Water reactors in British Columbia and Ontario. Dupont also worked on heavy water sites in West Virginia and Alabama. Members of Air Force, who will drop the bomb, trained at Wendover Airfield in Utah.
After various research, the scientists decided to work on two designs – the gun type bomb named ‘Little Boy‘ and implosion type bomb ‘Fat Man‘. Uranium-235 was used in Little Boy and Plutonium-239 was used in Fat Man.
The Gun type design included a sub-critical mass or little bit less than the critical mass of Uranium-235 and a gun barrel or the breech. Some part of U-235 will be attached to the barrel and another part will be on the other end of the structure.
If we use a explosion to fire the barrel, the U-235 attached to it will hit the other in the opposite end, resulting in a mass that will be higher than the critical mass. This situation will start a chain reaction and create a massive explosion.
But the gun type bomb was not suitable for Plutonium. The team already had less Uranium-235 and the gun type design was not very effective. Plutonium was a more practical choice because it’s critical mass is 10kg so we need less of it.
If Plutonium is used in a gun type bomb, plutonium-239 would absorb a neutron and become plutonium-240. It will result in a early chain reaction and thus pre-detonation before reaching the critical mass. Because of it, the yield of bomb will be drastically reduced.
So Oppenheimer decided to go with another type of design that was proposed, an Implosion type bomb. It included an ellipsoid-shaped core of plutonium-239 in the middle and it was surrounded by conventional explosive materials.
The idea was, when we create an explosion surrounding the Plutonium core, it will compress it and increase the density, resulting in reaching the critical mass and thus starting a chain reaction that will create a huge nuclear explosion.
Oppenheimer also decided to put a neutron reflector in the middle of the core and surrounding explosives. It will help in containing and redirecting the escaping neutrons back into the core, increasing the efficiency of the chain reaction.
They also increased the success rate of the bomb by putting a neutron source/initiator named ‘Urchin’ in the middle of the Plutonium core to begin the nuclear chain reaction.
It was made of beryllium and polonium, seperated by a layer of nickel and gold. When the explosion happens and compression occurs, the alpha particles of polonium will force beryllium to release neutrons thus starting the chain reaction.
The Trinity Test
There were some doubts about the success of Implosion type Plutonium bomb, so many recommended to perform a fizzle test to check the yield is enough. Oppenheimer later suggested to do a complete nuclear bomb test.
Planing for the test began in March 1944. The site that was selected for the Trinity test was at the Jornada del Muerto desert of Alamogordo Bombing and Gunnery Range, which is now part of the White Sands Missile Range in New Mexico.
Oppenheimer and his team established a base camp codenamed ‘Camp Y‘ for the project. For the test, they made an implosion type Plutonium bomb named the ‘Gadget’. To detonate the bomb, it was kept hanging from a 30 metre steel tower because it will be helpful to identify what will happen when it is dropped from a plane.
At 5:29 AM on 16th July, 1945, they remotely detonated the nuclear bomb. It generated an energy equivalent to 20 kilotons of TNT and a mushroom cloud of almost 12 KM height. The shock of the bomb was felt from 160 KM away and the destruction was much powerful than Oppenheimer comprehended.
The test verified the theoretical calculations and the overall feasibility of the nuclear bomb. Test happened a day before the Potsdam conference, where new US President Harry S. Truman met UK’s Winston Churchill and Soviet Union’s Joseph Stalin to discuss the future after the war.
It gave US a powerful position to not only end the war but also influence post war policy of countries around the World. Reducing Soviet Union’s aggression in the east was also a major motivating factor.
Bombing of Hiroshima and Nagasaki
The Potsdam conference in Germany, issued the Potsdam declaration which essentially stated that if Japan doesn’t unconditionally surrender then they will suffer unimaginable consequences.
During the conference, Truman also informed Stalin about the new bomb but Stalin already knew about it from the spies. Japan didn’t comply with the declaration and kept on fighting. US decided to end the war quickly by using the bomb.
After successful Trinity test, a committee was established to identify appropriate target to drop the bomb and it was led by physicist Arthur Compton. Cities like Kyoto and Yokohama was considered but later Kyoto was removed because of its cultural significance.
On 6th August,1945, a modified Boeing B-29 jet nicknamed ‘Enola Gay’ piloted by Paul Warfield Tibbets Jr., dropped the Gun type Uranium-235 bomb ‘Little Boy’ over Hiroshima, a major port city and a military base of the Japanese Empire.
The bomb detonated at 530 metre altitude and released an energy equivalent to 13 kilotons of TNT. It instantly killed 70,000 people and vaporized more than 70% of the buildings. Within a month, another 70,000 will die because of radio activity related issues.
But Japan refused to surrender. US tried to end things diplomatically after the bombing but Japan didn’t negotiate and kept on fighting. In Japanese culture, surrender is unacceptable and instead they will give their life proudly defending their nation.
So 3 days later on 9th August, another modified B-29 jet nicknamed ‘Bockscar’ piloted by Charles W. Sweeney, dropped the implosion type Plutonium bomb ‘Fat Man’ over Nagasaki, also a major port and industrial city of the Japanese Empire. Initially, the target was Kokura but Sweeney couldn’t follow the visual instructions given because of clouds.
After the second bombing that killed almost 50,000 people, Japan started reducing its military activity and started negotiating with the US. They formally surrendered on 2nd September, 1945 aboard Navy ship USS Missouri in Tokyo Bay. It marked the official ending of the second World War.
Aftermath and Legacy
Although initially supported the use of atomic bomb, the bombing of Hiroshima and Nagasaki and the scale of destruction and death left Oppenheimer traumatized. Around a week after the last bombing, Oppenheimer went to Washington D.C with a letter asking for arms control.
Oppenheimer reportedly cried in a meeting with President Truman saying he has blood in his hand. He represents the voice of majority of scientists in the post world war era. Oppenheimer spent the rest of his life calling out military actions and promoting arms control.
Later in his life, in an interview, Oppenheimer recalls what he thought after the Trinity test, he said “We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent.”
He added “I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, ‘Now I am become Death, the destroyer of worlds.’ I suppose we all thought that, one way or another.” Oppenheimer died at the age of 62 due to throats cancer caused by his smoking habit.
Historians still debate the necessity of using the atomic bomb. Many argue that it was necessary to end the war quickly and save thousands of lives because a complete invasion of Japan will be very costly.
The bomb was also a presentation of strength infront of the aggresive Soviet Union. Critic says Japan was already in the brink of surrender and there were no excuse to use the atomic bomb. Nevertheless, it changed the course of history for ever.
After the war, Soviet Union figured out how to make an atomic bomb. On 29th August,1949, they successfully detonated a nuclear bomb making them the second country to have such kind of weapon. This incident led US to invest in making a hydrogen Bomb.
On 1st November,1952, US successfully detonated the ‘Ivy Mike‘ hydrogen bomb. It created an energy equivalent to 10.4 megatons of TNT, almost 400 times more powerful than the bomb used in the Trinity test. This was the beginning of an arms race between the two super powers that will continue for another 4 decades.
In October 1962, during the height of Cold War, US and Soviet Union were almost close to start a nuclear war but good diplomacy prevented the armageddon. Throughout the years, Soviet Union and US signed several treaties like Non Proliferation Treaty for arms control.
As of today, there are nine countries who possess nuclear weapons: US, Russia, China, India, UK, France, Israel, North Korea and Pakistan.