The Hulk and Gammasphere

BuzzSkyline writes "The Hulk may be animated, but the Gammasphere that turns Bruce Banner's hissy fits into raging rampages is real. It's based on a gamma ray detector used at the Berkeley and Argonne National Labs. The actual machine doesn't make monsters, but it helps in studies of nuclear monstrosities. The American Institute of Physics reports on Gammasphere and its role in the movie at Inside Science News Service."

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Re:fun with gamma rays

[reverseengineer]

Well, gamma rays are dangerous, of course, but how dangerous is a matter of scale and situation. There's an old puzzle that goes something like this: You are given three radioactive cookies, and told one is an alpha emitter, one is a beta emitter, and one is a gamma emitter. You are told which is which. You are also told that you must hold exactly one of the cookies in your hand, you must put exactly one in your pocket, and you must eat the third cookie.

It turns out that the "best" solution is to hold the alpha emitter in your hand, put the beta emitter in your pocket, and eat the gamma emitter. The thickness of your skin should be sufficient to stop an alpha particle, your clothing should be able to stop most beta particles. Why should you eat the dangerous gamma cookie? Gamma rays are so penetrating that it would take at least an inch of lead to stop them. The other two choices (hand or pocket) wouldn't offer any meaningful amount of protection, so it would be best to protect yourself from the alpha and beta rays, and just hope the gamma source doesn't kill you.

And it might well not- most of the gamma particles will pass right through you actually. Some of them probably will collide with particles in your body, of course, and may do some serious damage to your cells. Proteins and lipids can be damaged and denatured- radiation burns. If DNA is damaged, cells may die as new proteins are no longer able to be constructed. The possibility also exists for damaged DNA to have tumor suppressor genes damaged and "turned off" by the radiation, leading to cancers. Yes, gamma radiation can be very dangerous, but its penetrating ability that makes it so dangerous also limits its effects, since most gamma radiation will pass right through you. Look at an even more extreme example of penetrating radiation- neutrinos. At this very moment, billions of neutrinos emitted in fusion reactions in the sun are streaming through your body, and if one happens to strike an particle in your body, it can do damage just as surely as any other form of radiation. In fact, not too long ago there was a story on /. that involved a blue-sky theoretical plan to destroy nuclear warheads with neutrinos.

It all comes down to the idea of mean free path- the average distance a particle will travel before it contacts another particle. When I say that an inch of lead will stop gamma rays, that's just shorthand for saying that the vast majority of gamma ray photons, fired at the lead, will collide with particles in the lead- the mean free path of a gamma ray through lead, then, is less than one inch. In comparision, the mean free path of a neutrino through lead is over a light year. Odds are pretty good that you will live your entire life, bombarded by quadrillions of neutrinos, without a single one interacting with a particle in your body- they are penetrating to the extent of being basically harmless.

Mean free path is dependent in part on the density of the medium a particle passes through, as well as the characteristices of the particle in question. Alpha particles are essentially helium nuclei, 2 protons, 2 neutrons. The doubly positive charge and the large size of this particle (on a quantum scale, anyway) mean that almost any solid or liquid matter is dense enough to stop alpha particles almost immediately. Beta particles are just electrons ejected from the nucleus in beta decay (a neutron "becomes" a proton, an electron, and an antineutrino. The latter two are ejected, but the proton stays, raising the atomic number of the atom by 1), and so have a charge of -1 and have about 1/1800 of the mass of a neutron or proton. Still, they're easily absorbed by thick fabric or a sheet of foil. Gamma rays are photons, and so are massless, move at the speed of light, and have no electric charge. It takes a considerable amount of a dense substance (like lead) to absorb gammas.

The damaging effects of these