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Hello, this is 6 Minute English from BBC Learning English, I'm Sam.

And hello, I'm Rob.

On August the 6th, 1945, the US Aircraft Enola Gay dropped an atomic bomb on the City of Hiroshima.

Instantly killing 70,000 people. When Japan refused to surrender, a second bomb was dropped

on Nagasaki three days later. Many believe the bombings quickened the end of the Second World War,

but it came as a terrible human cost, which some have called a crime against humanity.

The invention of the atomic bomb, which resulted from the cooperation between the US military

and some of the world's leading scientific minds, was known as the Manhattan Project.

In this programme, we'll take a look into the science and the politics of the Manhattan

Project, and as usual, we'll learn some new vocabulary as well.

Even before World War II, scientists had known about the potential energy inside Uranium,

the heaviest metal in the periodic table, a diagram which groups the chemical elements

into rows and columns, according to their atomic number and symbol.

The challenge for science was learning how to unleash this potential energy in a controlled way.

We'll hear more soon, but first I have a question for you Rob.

I mentioned that Uranium is the heaviest element in the periodic table,

but which is the lightest? Is it a hydrogen, be carbon or sea oxygen?

Well, oxygen is a gas, so it must be pretty light, so I'll say sea oxygen.

Okay, Rob will find out the answer later in the programme. First, let's find out a bit more

about the science of Uranium from Frank Close, an Oxford professor of theoretical physics

in conversation with BBC Radio 4 programme in our time.

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