Sunday, May 25, 2008

Indy's Atomic Fridge Ride

By now I'm sure most of you have heard of the scene in the new Indiana Jones movie where the title character survives a nuclear explosion by hiding in a lead-lined refrigerator. I get the bad feeling that I'm going to be answering questions about this for the remainder of my career, so I figure I may as well get started. Here's the summary:
1. There is such a thing as a lead-lined refrigerator.
2. This was not a feature that ordinary household refrigerators had in the 1950s.
3. Even a refrigerator made entirely of lead would probably not save you receiving a lethal radiation dose within the radius of the blast depicted in the film.
4. When attempting to survive a nuclear blast, do NOT hide in a refrigerator.

The lead-lined refrigerators are made to store materials used in nuclear medicine. The shielding they offer is pretty limited, only .125" of lead. Also, they're made to fit under a lab bench, and I doubt that any normal adult could shoehorn themselves inside of it. For comparison, let's explore the kind of radiation protection offered by a hypothetical refrigerator made entirely of lead.

According to Cresson Kearny, 1 cm (.4") of lead reduces the intensity of gamma rays by 50%. Therefore, 2" of lead would reduce gamma ray intensity to 6.25% of the original intensity. Note that this does not include the effects of neutron, beta, and alpha radiation. Calculating this is a LOT more complicated. As the 1977 edition of The Effects of Nuclear Weapons explained:
Neutron shielding is a different, and more difficult, problem than shielding against gamma rays. As far as the latter are concerned, it is merely a matter of interposing a sufficient mass of radiation between the source of gamma radiations and the recipient. Heavy metals, such as iron and lead, make good gamma-ray shields because of their high density. These elements alone, however, are not quite as satisfactory for neutron shielding.

Using the graphs provided in The Effects of Nuclear Weapons, it appears that from a distance of 1000 yards, a 20 kT fission explosion would result in a dose of about 4,000 rads from gamma and 4,000-6,000 from neutrons. Therefore, the shielding offered by our hypothetical lead fridge would reduce exposure to its occupant to 260 rads, with a presumably greater dose from neutrons. More than half of individuals exposed to 500+ rems will die of acute radiation poisoning, with several months of convalescence minimum. In short, Indy would not be up for a trip in the near-term to battle Soviet agents in exotic South American locales. Never mind the massive injuries he would have sustained from being flung around inside a heavy metal box.


Ashutosh said...

I thought similarly when I watched it yesterday, but then I said to myself..."It's INDY"...

DV8 2XL said...

I'm thinking just the thermal effects of the radiation front would finish him off even before the blast wave hit. In other words the fridge would turn into an oven real quick.

Sovietologist said...

I dunno, maybe the paint on the fridge ablated and saved him.

(This post largely reflects my disappointment with the film, which didn't live up to my hopes.)

DV8 2XL said...

Although I doubt that this will happen as a consequence of this movie, we cannot forget that cinema has had a huge impact on the public's perception of all things nuclear.

The two most infamous examples were "On the Beach" and "The China Syndrome" both of which did much to generate irrational fear, and were taken as documentaries by much of the public.

The swing of public opinion is moving back to being more accepting of atomic energy, however there also seems to be a parallel acceptance of nuclear weapons in some quarters that I find disturbing. Causal references by France, Britain, and the US in the last year or so about the possibility of a unilateral nuclear strike against other countries demonstrates a disturbing trend. While in is unlikely that such a strike would unleash thermonuclear Armageddon, the decision to use a nuclear weapon should not be seen to be s cavalier one and bellicose rhetoric of this nature is unlikely to create a political environment conducive to preventing proliferation.

Larry Grimm said...

The attenuation of a gamma ray in lead depends on the ray's energy. It takes more lead to shield a higher energy ray than a lower energy ray. The half-value layer of lead for a 100 keV ray is a little more than 0.1 mm, whereas it takes about 9 mm of lead for a 1MeV ray.
Neutrons must be slowed down to be harmful. Lead is fairly transparent to high speed neutrons. Things with high hydrogen content slow neutrons down quickly. With all the water in our bodies, we make lovely neutron moderators.
I concur with dv82xl; Indy would have been a nicely done thanksgiving turkey from the thermal effects.

Larry Grimm said...

The absorbtion of a gamma ray in lead depends on its energy. The half-value (one half the rays will be absorbed) for a 100 keV gamma is a little more than 0.1 mm of lead. For a 1 MeV gamma, it takes about 9 mm of lead. I doubt Indy's refrigerator had 3" of lead.
Neutrons need to be slowed down to really do us damage. A thin sheet of lead, e.g. 1/4", is pretty transparent to high speed neutrons. Materials with lots of hydrogen (cadmium and a few others also work well) slow down neutrons. With all the water we have in our bodies, we make nice neutron moderators.
I agree with dv82xl that likely Indy would have made a nice thanksgiving turkey from the thermal effects but it depends on how far he was from the epicenter.

Ayelis said...

I think Indy was banking less on the fact that he could sit inside a refrigerator for the duration of the blast, but more that the 'fridge would serve as a sturdy vehicle for the initial shock wave to throw him free of the blast radius.

Or maybe he knew something that we don't; that the government (in the canon of the movie, at least) lines all its nuclear-blast-test-refrigerators with super-anti-radiation shielding and heat shielding, for those unfortunate souls who happen to get caught in the wrong place at the wrong time. ;)

Tezcatlipoca said...

Considering the universe that the Indiana Jones movies take place in, I think it's only logical that Indy was able to transubstantiate the refrigerator in to the body of Christ, which obviously would be able to withstand an atomic blast.
I mean, the Ark of the Covenant was a real thing.
But maybe they addressed that in the movie. I dunno, I haven't watched it. (: