The Nuclear AgeThe Earth exploded into the nuclear age on 16 July 1945. On that day, the U

The Nuclear Age

The Earth exploded into the nuclear age on 16 July 1945. On that day, the US tested a completely new type of weapon in the New Mexico desert. Crafted from a tennis-ball-sized plutonium sphere (钚球), the bomb produced an explosion equivalent to 20,000 tons of TNT.

Sixty years on, tens of thousands of tonnes of plutonium and enriched uranium (浓缩铀) have been produced. The global nuclear arsenal (兵工厂) stands at about 27,000 bombs. Nine countries very proba-bly possess nuclear weapons,while 40 others have access to the materials and technology to make them.

But nuclear technology has also been used for peaceful means. The first nuclear reactor to provide electricity to a national grid opened in England in 1956. Now, 442 reactors in 32 nations produce 16% of the world's electricity.

Nuclear power has been championed as a source of cheap energy. But this was weakened at the end of the 20th century by reactor accidents, the problems of radioactive waste disposal, competition from more-efficient electricity sources and unavoidable links to nuclear weapons proliferation (核武器扩散). Nonetheless, growing evidence for global warming had led some to argue that nuclear power is the only way to generate power without emitting greenhouse gases.

Dropping the bomb

The Hiroshima (广岛) bomb was made of enriched uranium, compressed by detonating explosives to achieve a supercritical mass (超临界质量). The Nagasaki(长崎) bomb was made of plutonium.

Following 1945, the US developed massively destructive hydrogen bombs. Some are equivalent to many millions of tons of TNT, and yield vast amounts of energy through nuclear fusion. Nuclear weapons technology has been adapted for many military uses, such as intercontinental missiles, huge fission (裂变) weapons, mini-nukes (微型核弹), gamma ray weapons, nuclear landmines (地雷), and nuclear defence missiles.

By bombing Japan, the US started a worldwide arms race, and the Cold War with the Soviet Union. The Soviets developed and tested their own bomb in 1949. The United Kingdom achieved the feat in 1952, followed by France in 1960, China in 1964 and most recently India and Pakistan in 1998.

Israel is widely thought to possess nuclear weapons and North Korea declared in 2005 that it did too, though neither has conducted tests. Iraq and Libya (利比亚) have attempted to develop them in the past, and Iran has been accused of having a secret nuclear weapons programme.

Stopping the Spread

While up to nine nations have nuclear weapons, 187 others have promised not to manufacture them. Twenty countries such as Switzerland, Brazil, Argentina, Canada and South Africa once had programmes; but as signatories to the 1968 Treaty on the Non Proliferation of Nuclear Weapons (NPT), later abandoned them.

The NPT aimed to limit the spread of atomic weapons and bound the five original nuclear weapons states to sharing nuclear technology and materials for peaceful means mainly through US and Russian disarmament, the treaty has achieved the decommissioning (退役) of 38,000 warheads (弹头) since 1986.

However, the treaty is under strain in 2005. Nuclear-armed states stand accused of failing to reduce their arsenals (兵工厂), and of considering new weapons, like mini-nukes. Iran reached an agreement with Europe to halt uranium enrichment activities, but may renege (食言)on that deal.

The 1996 Comprehensive Nuclear Test Ban Treaty is an attempt to limit test detonations and slow nuclear armament, but the US senate refused to approve of it in 1999.

Controlling the remains of the Soviet Union's vast and poorly protected nuclear arsenal is another great challenge.

The International Atomic Energy Agency is struggling to keep track of smuggling and the black market in nuclear materials and technology, and fears of te

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