Did Oppenheimer invent the atomic bomb?. I was listening to the radio the other day to
an interview with Cillian Murphy, the actor who plays Robert Oppenheimer in the new film
of the same name and the interviewer started by saying, “what’s it like to play the
man who invented the atomic bomb?” The thought that sprung to my mind was, hang on, Oppenheimer
didn’t invent the bomb, he was highly instrumental in bringing it from a theory to an actual
working device but he wasn’t the sole inventor as it’s often thought.
So If Oppenheimer didn’t invent the Atomic bomb who did?
Robert Oppenheimer is often quoted as inventing the atomic bomb but that is not only incorrect
but overlooks other key figures and events of nuclear development that go back several
decades before the Trinity test in the desert of New Mexico on July 9th, 1945.
The first use of the phrase “atomic bomb” was in HG Wells’s 1913 Novel “The World
set free”. Wells was aware of the work of Frederick Soddy, Kasimir Fajans and Ernest
Rutherford into radioactive elements. It was known that radium decayed away gradually over
thousands of years and while the rate of energy release was small the total amount of energy
released was huge. Wells thought that a new type of bomb based
on carolinium which was at the time incorrectly thought to be a component of Thorium would
be used. Instead of exploding in one big bang, these
atomic bombs would induce a blazing continual explosion with a half life of 17 days so that
is "never entirely exhausted” and battlefields, where the bombs had been used, would radiate
matter and become “centres of inconvenient rays”, a rather a prophetic view of a future
nuclear battlefield and the radiation left behind.
This reference might not be scientifically correct but Leó Szilárd, one of the key
figures in the development of the bomb and who conceived the idea of the neutron chain
reaction which is key to a nuclear explosion, read Wells’s book in 1932 before he came
up with the idea in 1933 and filed for patents for it in 1934, coincidence, maybe, maybe
not. The journey to the atomic bomb was one done
in many small steps by many theorists and scientists long before Oppenheimer directed
the scientific side of the Manhattan Project. Many think that Einstein was part of it, after
all, it was his 1905 equation, E=MC2 that showed the tremendous amount of energy that
could be released from converting matter into energy by nuclear means but at the time no
one knew how this could be done. Einstein’s main role was in 1939 to write
a letter to President Roosevelt to consider setting up what would become the Manhattan
Project after he discovered that two German scientists had split the uranium atom in 1938,
and he thought Hitler might also developing a nuclear weapon. At that time, it was thought
that a viable bomb would need a sphere of uranium weighing between 12 and 40 tons which
would only be deliverable by boat, though this would be enough to destroy an entire
port and maybe some of the surrounding area, which Einstein pointed out in his letter to
Roosevelt. From early 20th century up until the 1930s
more and more discoveries were made about atoms and the energy they released when they
broke down during the natural decay process but the research into how this could be sped
up is what led directly to the atomic bomb. A key discovery was that of the neutron by
James Chadwick at the Cavendish Laboratory at the University of Cambridge in February
1932 and in April 1932 John Cockcroft and Ernest Walton split lithium atoms with accelerated
protons, the first time an atom had been split. A neutron is a subatomic particle that has
a neutral, not a positive or a negative charge and is essential to the production of nuclear
power and nuclear weapons. When a Uranium atom is split it gives off
2 or 3 neutrons, as well as a great deal of energy in the form of heat and gamma rays
and leaves behind two new nuclei of barium-144 and krypton-89.
If one of these neutrons strikes another Uranium atom, that will split that and give off 2
or 3 more neutrons plus the energy. Each time more neutrons are created than the atoms which
are split, this cascade effect allows a nuclear chain reaction to occur and grow exponentially.
The difference between a nuclear reactor and a bomb is that in the reactor, this chain
reaction is controlled by neutron-absorbing materials such as silver and boron, in a bomb
the reaction is amplified by neutron reflectors around the uranium core to make it run out
of control and create a nuclear explosion. Shortly after the neutron was discovered,
Leó Szilárd came up with the chain reaction theory which we just described in 1933 and
scientists in Europe worked on ways to split heavy atoms like uranium with a team lead
by Enrico Fermi in Italy and Otto Hahn and Fritz Strassmann in Berlin. The Berlin lab
split the Uranium atom in 1938 and this is what pushed Einstein to write to Roosevelt.
In 1939 in Paris, a group of scientists including Frédéric Joliot-Curie, Hans von Halban,
Lew Kowarski, and Francis Perrin noted that more neutrons were given off than atoms split
suggesting that a self-contained chain reaction could be possible and that the amount of energy
given off with each split was greater than anything seen before at 200 million electron
volts. However, this only occurred in the most common
form of Uranium, U-238 which made up 99.3% of all Uranium found on earth, when it was
hit with fast energy neutrons. Although U-238 was fissile meaning that it
would split, much of the reactions with slow neutrons would go on to create plutonium 239
which is very rare in nature but easily made in a reactor core and is even more fissile
than Uranium 235, something that Oppenheimer would use to his advantage later.
Because of the lower reaction rate it was calculated that large sphere of U-238 in the
range of between 12 and 40 tons would be needed to make a bomb.
However, Physicist Neils Bohr theorized that the much rarer Uranium 235 which made up only
0.7% of all the uranium found and is much more fissile when it reacted with the slow
thermal neutrons and more likely to create a nuclear explosion.
Meanwhile, in Britain serious consideration was being given to the viability of an atomic
bomb and various groups worked on the issue. George Thomson, at Imperial College London,
and Mark Oliphant at Birmingham University were one of the teams.
Oilphant gave the job of calculating the critical mass to two German refugee scientists, Rudolf
Peierls and Otto Frisch. This was because they couldn’t work on his radar project
as they were classed as enemy aliens and could not get security clearance.
When Peierls calculated the mass required for a U-235 reaction as Neils Bohr had theorized,
he found that a sphere weighing just a few kilograms would be enough to create a chain
reaction that would yield an equivalent explosion to that of thousands of tons of TNT.
The resulting Frisch–Peierls memorandum was the first technical explanation of how
a practical nuclear weapon could work. Suddenly this changed everything, by using
Uranium-235 the bomb could be much smaller and lighter and that meant that it could be
delivered by plane to almost anywhere. Now the race was on for the British to refine
as much weapons grade uranium 235 as possibe and Project Tube Alloys was created to do
this. The MAUD Committee led by Niels Bohr was also setup with joint help from the Canadians
to determine if an atomic bomb was feasible. Refining the amount of uranium-235 required
would need to be done on an industrial scale because of its rarity and making the bomb
would take up a huge amount of resources, R & D and the best minds avalable, most of
which were devoted to the war effort. After the fall of France in 1940 and takeover
of most of Europe by the Nazis, the threat of invasion and the nuclear secrets possibly
falling into the hands of the Germans was uppermost on the mind of Churchill and so
Britain took the decision to ask the U.S. for help.
The man chosen to do this was Henry Tizard, a British scientist and chairman of the Aeronautical
Research Committee, which had ran the development of radar before the war.
The so-called Tizard mission to the US would offer Britain’s most closely guarded secrets
including microwave radar, proximity fuse, the jet engine, designs for rockets, superchargers,
gyroscopic gunsights, submarine detection devices, self-sealing fuel tanks, plastic
explosives and of course the Frisch–Peierls memorandum describing the feasibility of an
atomic bomb and the work they had done so far.
All this in return for help in manufacturing these items on mass well away from any threat
of invasion. Some likened it to giving away the family silver in the hope of a greater
return but Britain was in a tight spot at the time.
Tizard went to America in 1941 and met Vannevar Bush who headed the U.S. Office of Scientific
Research and Development (OSRD) through which almost all wartime military R&D was carried
out. Tizard told Bush about the Tube Alloys project and the conclusion of the MAUD committee
that an atomic bomb was feasible but would require far more resources than the British
could supply alone. Bush met with Roosevelt and Vice President
Henry Wallace on October 9th, 1941 and explained to them about the British atomic bomb project,
the Maud Committee findings and the German nuclear energy project and the threat however
unknown it posed. Now Roosevelt had the proof that Einstein’s
letter had initiated back in 1939 that an atomic bomb could be built but now it could
be small enough to be delivered by bomber like any other bomb. Roosevelt not only approved
the program, he expedited it to top priority. In March 1942, Bush sent a report to Roosevelt
outlining work by Robert Oppenheimer on the nuclear cross section of uranium-235. Oppenheimer's
calculations backed up Frisch & Peierls findings that the critical mass of a sphere of Uranium-235
was in the range of 2.5 to 5 kilograms, with a destructive power of around 2,000 tons of
TNT. Moreover, it appeared that the newly discovered plutonium might be even more fissile
and powerful. General Leslie Groves was appointed director
of what would be called the Manhattan Project. He had the experience to run very large military
projects and all the logistics involved including building the Pentagon, which up until 2023
was the worlds largest office building by floor area at 620,000 sqm.
When Groves met Oppenheimer, he was a highly respected University of California, Berkeley
physicist who had made significant contributions to theoretical physics, including achievements
in quantum mechanics and nuclear physics. Groves wanted to discuss the creation of a
secret lab where the Atomic bomb would be designed and built.
Groves said that he chose Oppenheimer because he demonstrated an "overweening ambition"
to drive the project forward which he didn’t see in other scientists. Oppenheimer also
was well versed in not only physics but chemistry, metallurgy, ordnance, and engineering, something
that made him an ideal interface between the scientists and the military and governing
bodies. A couple of things did concern Groves about
Oppenheimer. Although Oppenheimer was a great scientist he was not a Nobel prize winner
like many of those who would be working under him and Groves thought this might cause resentment.
He also lacked experience in running large projects and his left-leaning views and his
association with the American Communist Party was something of concern at the time and would
come back to haunt him after the war but Groves was sure he had picked the right man for the
Job and history showed that he did. Oppenheimer may not have invented the bomb
and was a nobel prize winner but in almost every other sense he was the father of the
bomb and what he did was more than most nobel prize winner
He brought together and cultivated the brightest minds that the allies had available to them.
He was there every step of the way, at every major decision leading from the front as they
took what was a theoretical model that the British had shared with them in the Tizard
mission to the worlds first and very real nuclear weapon.
Like the moon landings two and half decades later, everything had to be built from scratch,
nothing like this had ever been attempted before.
One of the main ideas he drove was the development of a second type of bomb which used Plutonium
239 instead of Uranium 235 because it was more fissile and released 1.7 times more energy.
It could made from the much more common uranium 238 in a reactor much more quickly than refining
Uranium 235, so much more could be made in the limited time available. This went on to
be used in the second bomb, the “Fat Man” plutonium core bomb dropped on Nagasaki.
From the huge effort required in sourcing and refining of both enough Uranium 235 and
plutonium, to the precise triggering of the implosion sequence to within millionths of
a second, and the development of new fast and slow explosive to work together. And all
this hoping that the reaction would be strong enough to last before the bomb blew itself
apart. The challenges to overcome were legion but Oppenheimer got everyone to work together
even when the obstacles seemed overwhelming. Whatever your views on whether nuclear weapons
should or shouldn’t exist today, you have got to hand it to Oppenheimer and the rest
of the Manhattan project team, even if its just for the huge amount of work and brain
power that was expended. However, as Oppenheimer discovered, once created
there was no way to put the genie back in the bottle and mankind had become the first
creature on planet Earth that had created the means to bring about its own destruction.
78 years on from the Trinity test and we’re all still here but how long we can keep from
using the ultimate deterrent in an ever more fractious world, well that’s another story.
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