A turning point in history
The atomic bomb is one of the most powerful and destructive inventions ever made. Its development during World War II, and its use against two Japanese cities in 1945, changed warfare, international politics and science forever. Studying it helps us understand the responsibility that comes with scientific discovery.
The science
In the 1930s, scientists discovered that the nuclei of certain heavy atoms, like uranium, could split when struck by a neutron. This is nuclear fission. It releases a huge amount of energy, as predicted by Einstein’s equation E = mc², along with more neutrons. Those neutrons can split other nuclei, causing a chain reaction.
| Year | Discovery |
|---|---|
| 1938 | Otto Hahn and Fritz Strassmann observe uranium splitting |
| 1939 | Lise Meitner and Otto Frisch explain it and name it fission |
| 1939 | Albert Einstein signs a letter warning U.S. President Roosevelt that Germany might build such a weapon |
| 1942 | Enrico Fermi’s team creates the first controlled chain reaction in a reactor in Chicago |
The same science that powers nuclear energy plants can also be used to make weapons. In a power plant, the chain reaction is carefully controlled. In a weapon, it is uncontrolled and releases its energy almost instantly.
The Manhattan Project
Fearing that Nazi Germany would build an atomic weapon first, the United States launched the secret Manhattan Project in 1942, with help from Britain and Canada.
| Fact | Detail |
|---|---|
| Leaders | General Leslie Groves; physicist J. Robert Oppenheimer directed the Los Alamos laboratory |
| Size | About 130 000 people at sites across the U.S. |
| Cost | About US$2 billion at the time |
| Canada’s role | Uranium from the Eldorado mine at Port Radium on Great Bear Lake (NWT) was processed in Port Hope, Ontario; a research lab in Montreal and the Chalk River site in Ontario worked on nuclear reactors |
| First test | "Trinity," July 16, 1945, in the New Mexico desert |
The Dene people of Délı̨nę, whose men carried uranium ore from Port Radium without being told of its dangers, later raised concerns about health effects in their community. In 1998, they travelled to Japan to express their sorrow to survivors of the bombings.
Hiroshima and Nagasaki
Germany surrendered in May 1945, but war with Japan continued.
- On August 6, 1945, the United States dropped an atomic bomb on Hiroshima.
- On August 9, a second bomb was dropped on Nagasaki.
- Japan announced its surrender on August 15, ending World War II.
| Hiroshima | Nagasaki | |
|---|---|---|
| Estimated deaths by the end of 1945 | About 140 000 | About 74 000 |
Many people died instantly from the blast and heat. Others died later from burns, injuries and radiation sickness. Survivors, called hibakusha in Japanese, faced higher rates of cancer and other illnesses for decades.
Historians still debate whether using the bombs was necessary to end the war. Some argue it prevented an invasion that would have cost even more lives; others argue Japan was close to surrendering, or that a demonstration could have been used instead.
The nuclear age
| Year | Event |
|---|---|
| 1949 | The Soviet Union tests its first atomic bomb; the Cold War arms race begins |
| 1952 | The far more powerful hydrogen bomb is tested |
| 1962 | Cuban Missile Crisis brings the world close to nuclear war |
| 1963 | Partial Test Ban Treaty ends atmospheric testing by the U.S., USSR and UK |
| 1968 | Nuclear Non-Proliferation Treaty (NPT) |
| 1980s | At its peak, the world had about 70 000 nuclear weapons |
| 2017 | Treaty on the Prohibition of Nuclear Weapons adopted at the UN |
| Today | About 12 000 nuclear weapons remain, held by nine countries |
Nuclear disarmament
Many people and countries have worked toward nuclear disarmament.
- Canada chose not to build its own nuclear weapons, although it had the knowledge and materials.
- The Pugwash Conferences, first held in Pugwash, Nova Scotia, in 1957, brought scientists together to reduce the danger of nuclear war. They won the 1995 Nobel Peace Prize.
- Hiroshima survivor Setsuko Thurlow, who later lived in Toronto, accepted the 2017 Nobel Peace Prize on behalf of the International Campaign to Abolish Nuclear Weapons.
Peaceful uses of nuclear science
The science behind fission also has peaceful uses:
- Nuclear power: Canada’s CANDU reactors generate about 15% of Canada’s electricity, and over half of Ontario’s.
- Medicine: radioactive isotopes for diagnosing and treating cancer; Canada was a pioneer in cobalt-60 cancer therapy.
- Science: dating fossils and studying the universe.
Ethics in science
The atomic bomb raised deep questions:
- Are scientists responsible for how their discoveries are used?
- Should some research be limited?
- How can the world prevent catastrophic weapons from being used?
After the Trinity test, Oppenheimer recalled a line from Hindu scripture: "Now I am become Death, the destroyer of worlds."
Common mistakes
- Thinking nuclear power plants can explode like bombs. They are designed very differently and cannot.
- Thinking only the U.S. was involved in the Manhattan Project. Britain and Canada contributed.
Try it yourself
- Make a timeline from the discovery of fission (1938) to today’s nuclear treaties.
- Read about a hibakusha survivor’s story. What message did they want to share?
- Hold a respectful class discussion: should scientists consider how their work might be used?
Quick recap
- Nuclear fission splits heavy atoms, releasing huge energy in a chain reaction.
- The Manhattan Project built the first atomic bombs with help from Britain and Canada.
- Atomic bombs destroyed Hiroshima and Nagasaki in August 1945.
- The Cold War arms race followed; treaties and activists have worked to reduce nuclear weapons.
- Nuclear science also has peaceful uses in energy and medicine.