## Angels, Demons and antimatter

18.05.2009 21:17

On Saturday I went to see Angels & demons. It was entertaining to watch, although it was apparent at times that whoever wrote the script was more at home in medieval myths than physics. I guess I got used to weird things characters tend to say in Hollywood movies whenever the topic of conversation shifts to science.

One thing that did made me curious is a scene towards the end when they had to get rid of an anti-matter explosive device in the middle of Rome with 5 minutes to spare. So a guy jumps into a helicopter and flies straight up. When the time is up, the helicopter is high enough that the explosion only causes a spectacular fireworks display and shatters some frescoes.

At the first thought, that seemed like a really bad idea to me. They say that the explosion had an equivalent yield of 5 kT of TNT, which is comparable to a small nuclear bomb. This kind of devices do the greatest damage when they're exploded at some height above the target, so is it really feasible to save a city in the way shown in the movie?

First question is how high can you get in an average helicopter in 5 minutes? After sampling some random technical specs on Wikipedia it appears that the rate of climb of a helicopter varies from 6 m/s in civilian to 13 m/s in military craft. In the movie they use a police or a medical helicopter. It's also empty, so take an average, say 8 m/s, to get a nice rounded figure of 500 m/min.

Second question: How dangerous is a 5 kT explosion at 2500 m if you're standing right below it (like the crowds does in the movie)?

Unfortunately the Strangelove Slide Rule doesn't provide this kind of calculation. I did some more searching and found a couple of old DOS programs from the US Defense Nuclear Agency that answer exactly this kind of questions (they're complete with warnings to reset the computer after entering classified data - I guess they haven't yet come to shredding hard disks at that stage).

The result shows that 5 kT explosion will cause a shock-wave with 10 kPa of maximum pressure on the ground zero directly below. That's a little under 1.5 PSI, which is, according to the previously mentioned slide rule, not so bad for any by-standers. Such a shock will shatter windows, but won't knock down houses or even damage most people's hearing.

Surprisingly, that's exactly what you see in the movie. So this may be one case where they actually got it right.

Posted by | Categories: Ideas

I loved the pretty fireworks :3. Anyway it's interesting that, for one time, they not only centered on the reaction that would cause a blast like that, but also on the realistic simulation of it.

Posted by Frank

The part of the science I wondered about concerns two things. It seems with an antimatter explosion, the conversion of normal matter to energy (equal to the amount of antimatter) would be nearly complete -- wouldn't that douse the area around the explosion with a massive blast of gamma rays (and probably other forms of nuclear radiation) ? Also, perhaps I'm wrong, but I'm thinking the explosion at that height would probably also generate an electromagnetic pulse that would destroy every device with electronics in central Italy at the least.

Cheers

BW

Posted by BW

I guess the amount of radiation emitted would also be roughly similar to a nuclear explosion. Air is actually pretty opaque to gamma rays and the initial pulse of radiation given of by an explosion is usually not dangerous, unless you're so close that you have other things to worry about.

The sliderule gives around 0.1 REM, which is not that bad.

You're probably right about the electromagnetic pulse, but I have no data to check that.

Posted by Tomaž

I am concerned with ironic opposite of an antimatter bomb; I worry that think film may fill the public with false worries and fears about further antimatter research, just at a time when gigantic breakthroughs involving the importance of antimatter.

The exciting ongoing debate over the new model can be viewed or joined at hypography dot com, go to the "aternative theories" board index and then look for threads containing the word "Dominium"

I believe this explosion is all wrong. At 2500m this would be optimum height for a 5kt explosion. It would reek havoc on Rome and Vatican City. Not to mention the EMP damage to every electrical device around. This movie also gives the wrong impression about anti-matter.

Posted by Barry

Barry, so you say my calculations are wrong? Can you show how you got your estimate of the damage?

Posted by Tomaž