Experimental Physics for Complete Morons

This is why I keep coming back to scienceblogs... to learn useful things

And that is why you iz da profezor!

You really should invest in some homeopathic lead bricks...much lighter.

It is counterintuitive. That is, if your intuition is based not on personal experience but on TV and movies. Have you ever seen people stealing gold bullion? Looks pretty easy. And rolling boulders off cliffs? Piece of cake.

When I was an undergrad, one of my fellow students was hired to work in a HEP lab. He was given the task of moving a few hundred lead bricks from one building to another, a backbreaking task that took the better part of a week.

He stacked the bricks in a pile next to a wall, and after it was done, an older lab tech came by and told him "No, I wanted them over there" and pointed to the other side of the room. So he had to move the whole pile AGAIN.

Separate from that incident... I remember a talk by a guy who was working on a double beta decay neutrino experiment; he explained that they used lead from Roman shipwrecks because it had a very low Pb-210 background (half life is 22 years, so the stuff sitting on the bottom of the ocean for a few thousand years had mostly decayed). http://www.newscientist.com/article/mg13117772.600-particle-physicists-…

I looked and looked, and found this little gem I saw once on Keith Olbermann's Oddball:
http://www.youtube.com/watch?v=XFRh2SU6eik
This overloaded donkey cart is a short and similar demonstration of the laws of physics

Lead bricks are really heavy.

But a pound of them weighs far less than a pound of feathers.

Ha...reminds me of the time I had to move. After loading what I thought was a manageable number of books into a box, I picked it up and the box bottom fell out.

Wood is heavy. Paper is mushed wood. Ergo, books are heavy.

Yeah, but uranium bricks are heavier. Although I would never foresee any university professor having a large supply of uranium bricks, I would imagine he or she would probably force his or her graduate students to move them around from one location to another for amusement.

If I recall correctly, Mike Moe once had an experiment fall over on him late at night in the lab and had to wait until the next morning to be rescued. I think it was a bunch of pieces of sheet steel. Coincidentally with Adam above, he was working on a double beta decay experiment at the time I knew him, but I don't think it was the double beta lab where the accident occured.

Lab work should generally be done with at least one other person within shouting distance. Electricity will put you in the hospital, along with chemicals and gravity.

Lead bricks are really heavy.

But not "heavier than a lead minister" -- an amusing and occasionally useful phrase I first heard in rural New Hampshire.

In terms of radiation protection per unit of mass, is lead really such a great solution? Given its density, I don't doubt it's gangbusters per unit of volume, but mass is a bit different.

Johan-

The interactions of photons and charged particles depends not just on the density of material, but the atomic number (Z) as well. For one reason, the average binding energy of the electrons increases with Z, so photoelectric emissions lead to larger energy losses. Materials with higher Z are more efficient at stopping photons and charged particles per unit mass.

Neutrons, on the other hand, are more easily stopped by light elements, which is why water or plastic (both have lots of H atoms) is used for neutron shielding. The reason light elements are better here is that neutrons slow down by colliding with nuclei. A neutron colliding with a single stationary proton (the H nucleus) will transfer a significant amount of its momentum to the proton and lose speed. A neutron colliding with a heavy nucleus is like bouncing a ping pong ball off of a bowling ball -- the neutron (ping pong ball) will head off in a new direction, but without losing much speed.

It is not uncommon for some experiments to have both layers of lead and layers of plastic.

Here is where you can learn from the old masters. When Fermi was creating his first atomic pile, the uranium was sealed in tin cans.

They hired the football team to come and pile up the cans.

Some years ago, a UWashington prof told me the following story:

The UW Physics dep't, after years of delays, finally got a new freight elevator installed in the physics building. Soon after, a professor had a shipment of lead bricks delivered to the loading dock, and told two grad students to bring them upstairs to his lab. So they loaded them into the elevator, all at once, not noticing that the elevator floor seemed to be getting a little low relative to the loading dock.

They pushed the "up" button, the doors closed, the elevator made a funny groaning sound, and the doors opened again. Oops.

So they unloaded the elevator, and pushed the "up" button. Another funny noise, no motion.

The elevator repairman comes out the next week, and is well and truly croggled. It's the first time he's ever seen an elevator shaft with the guide rails *bent*