Explosions: How We Shook the World Page #6

---

intrigued by was why it made this particular indentation

from the indentation on the explosives

and understanding the way in which this happens

led to a completely new way of using explosives.

When a lump of explosive detonates,

the shock wave radiates out from every part of its surface.

So you've got your dent in the explosive here

and you've got your target there,

as the shock wave comes out,

instead of the bit at the back ending up with a weaker effect,

it ends up actually stronger,

because the shock wave is coming out in all directions, like this.

When it reaches the centre of the indentation, they tend to meet,

like jets of water in the middle of that dent

and this effect here magnifies the shock wave that you've got leaving

there, sending it into the plate and this is actually the area

of maximum pressure here.

And once this was understood, shock waves could be directed to

focus the power of the explosion exactly where it was wanted.

People started making cavities in their explosive to increase

the power of the shock wave,

but then, with the pressures of war, came a new step forward.

When you line that cavity

with a hard material, almost invariably metal,

then you enter the domain of what's known as the shaped charge.

Right.

Conventional shaped charges

are filled with high explosive in a factory.

Right.

This is something that I designed for filling by the user.

It means that it can travel on aeroplanes and so on without...

- DIY shaped charges.

- Exactly that.

Now, in this case

we're going to go back to probably the first type of liner -

this is called the liner - that was used in a shaped charge.

- That's just a cone of copper, isn't it?

- It is indeed.

Having that copper on there, I guess it's the sort of

the equivalent of using a bullet or a cannonball.

It's the same, if you go - kcrrr! - and fire an empty cartridge,

then you get a loud bang and an explosion,

but nothing that's going to do any significant harm.

Whereas if you put a bullet in the end of it, if you see what I mean,

and fire it, then it pushes out something of a significant mass,

and that can do some damage.

Yes. The great advantage is that this metal travels enormously faster

than any cannonball.

I'll show you what I mean.

If you put plastic explosive in here and then you push this copper cone

into the explosive, when I initiate at this end,

a detonation wave travels from here to there.

- Right.

- The first thing it hits is the apex of the cone

and that apex of the cone is driven forward.

The whole cone is collapsed.

In fact, it collapses in such a way that it turns inside out.

Right, because the end bits hit first and that starts moving.

Wow, that's an astonishing thing to get your head round.

It is a bit of a shock at first.

What happens is that the inner part of the copper, not the whole

mass of it, by any means, the inner part of the copper

forms into a sort of wire, which is called the jet.

And that's not molten, it's still solid copper.

Yes, but coming not in that direction, coming in that direction.

And that almost piles in like a nail through the steel,

driving its way in.

Yes. It pushes the target material out of the way

and it pushes it aside as the tip of the jet

hits the steel and flows back along the outside of the rod.

Then there's a new increment of metal.

This is constantly being replaced and when it's all used up it stops,

won't go any deeper.

Are we in a position that we can try this and I can see?

Absolutely. This box, I'm pleased to tell you, is full of explosive.

- Good.

- What I'll do is take some out.

This is standard British plastic explosive.

It's similar to the American C4,

but it is actually much easier to use for filling charges.

You can just ram it in and then put the cone in.

We're going to test it with what looks like

an impossibly solid block of steel.

There is a critical distance at which the jet

will be at its most penetrating before it breaks up,

so the charge has legs to hold it the right height from our target.

Right, see you in about two minutes.

- Yes, and don't panic.

- I won't.

Firing.

Four, three, two, one...

- Wow!

- Let's go and see what we've done, shall we?

It seems astonishing, because that was just a massive thump,

that something extremely accurate will have occurred from that.

Well, let's see.

Ooh...

Well, it's gone in at least that deep

because I can push that in, but then

the proof of the pudding will be turning it over

and see if we have achieved anything the other end. Yep!

Oh, yes!

That's gone through over a foot of steel.

The thing that I find even more surprising is you know full well

if you've got a copper nail like that,

no matter how hard you hit it...

You will hardly dent the steel.

Exactly! Yet you get a good amount of plastic explosive with

a nice shape behind it and you can drive it the whole way through.

These cone-shaped charges allowed people to get much more

focused power from their explosives

and during the coming World Wars,

revolutionised the power of handheld weapons such as the bazooka.

Nowadays they're used in all sorts of military and civil applications

such as opening up oil wells, and Sidney designs them

especially for bomb disposal,

but other shapes have been developed as well, for different tasks.

This long L-shaped liner can turn the shock wave into a blade,

as the sides are slammed together.

Instead of the cone's penetrating jet, this cutting blade is axe-like,

designed for demolition jobs.

Four, three, two, one...

It seemed as if the power of explosives had reached a maximum.

The chemical compositions were carefully designed

and the power of the shock wave could now be channelled,

but there was still explosive potential beyond imagination

to be realised.

By the end of the 19th century, chemists were discovering

new elements all the time, and some of them appeared to give off energy.

They called this rather bizarre property radioactivity.

It was a New Zealand physicist, Ernest Rutherford, who was one of

the first to understand the potential of radioactivity.

Already understanding that it was caused by the atoms of the elements breaking down,

he wrote this in 1904 -

"If it should ever be found possible to control at will

"the rate of disintegration of the radio elements,

"an enormous amount of energy could be obtained

"from a small amount of matter."

It was a prophetic statement,

although he later said, "Anyone who expects a useful

"power source from the transformation of these atoms

"is talking moonshine."

Even a genius doesn't get it right every time.

The investigation of radioactivity and the nucleus of atoms continued

as researchers sought to understand the minute structure of the world

around us, but some people were already seeing the potential

for extracting the power released when nuclei are broken apart

and in the winter of 1938, with war already brewing

Rate this script:0.0 / 0 votes