BBC: The Manhattan Project

 On August the sixth 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 Wordl War. But it came at a terrible human cost, which some have called a crime against humanity. 

The invention of teh atomic bomb, which resulted from the cooperation between the US millitary 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 Two, scientists had known about the potential energy inside uranium, the heavist 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?

a) hydrogen  b) carbon   or c) oxygen 

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

OK, Rob, we'll find out the answer dlater 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 wiht BBC Radio 4 programme, In Our Time:

In 1938, the discovery was made that if you use uranium, the atoms of uranium, which are the heaviest that occur naturally in the periodic table, they're very fragile... and the discovery was that if you just almost touched them with a single neutron, that's a nuclear particle, the uranium was like a drop of water, it would just break apart, split in two... and the action of splitting the uranium has become known as fission. 

Atoms of uranium are very fragile- easily broken or damaged. In 1938, it was discovered that when nuclear particles called neutrons were fired at uranium atoms, they would split, or break in two. 

The process of splittidng uranium, or fission, did two things. First, it released huge amounts of energy, a billion times more than would be released in a normal chemical reaction. 

Secondly, the act of splitting atoms released two more neutrons. These new neutrons were freed to hit more uranium, creating four neutrons, which in turn were freed and created eight, then sixteen and so on, making what's known as a chemical chain reaction. 

In everyday English, a chain reaction is a series of events where each event becomes the cause of the next. 

The politics behind the development of the atomic bomb was no less complex than the science. In the same year that Hitler invaded Poland, two Jewish scientsits exiled from Nazi Germany- Rudolf Pelerls, and Otto Frish- first realized uranium's power as a weapon of war. Listen as Professor Frank Close takes up the story for BBC Radio 4 programme, In Our Time:

Having had the idea and the shock of the discovery, you immediately then Think, 'maybe scientists in Geramany has already had the same idea and come to the same conclusions- could Hitler already by building such a weapon?' And in their memorandom which they wrote and reached the British government they said it's conceivable that Germany is in fact developing this weapon, and the only defence against it is to have on yourself. 

After their discovery, Peieris and Frish were worried that the Nazis had already found out how to weaponize uranium. It was conceivable, or believable, that Germany was building an atomic bomb. 

The shared this terrifying thought in their famous memorandum- a short written report on a specific topic. As soon as US President Franklin Roosevelt read it, he started the Manhattan Project, and the race to build on atomic bomb began. 

In a strange twist of history, it turned out that Hitler hadn't been building atomic bombs at all. And Hiroshima, the Japanese city distroyed in 1945, was rebuilt and stands as a symbol of peace today. 

Let's end on a lighter note, Sam, with your question. 

Yes, I asked which is the lightest element in the periodic table. It's A, hydrogen, the lightest of all gases which come at the very start of the periodic table, having the atomic number1.

Ah, if only I'd remembered what our chemistry teacher taught us about the periodic table- a chart grouping all the chemical elements according to their atomic number.