Scotch tape is crazy stuff

by Stephanie Chasteen on December 11, 2008

scotchYeah, yeah, I know, this is old news, but I finally got around to reading the articles about the fact that Scotch tape emits x-rays. I’ve known for a while that when you stick scotch tape to something and then peel it off, the scotch tape gets charged (negatively for those who care). This is a great way to make a cheap electroscope for your classroom (or just anytime you want to find out the charge on something). Just stick Scotch tape to a table, peel it off, and then hold it near some Charged Object. If the tape is repelled, then the Charged Object is negatively charged (since like charges repel). Try it, it’s cool.

So, anyway, when you peel the tape off the table, it gets negatively charged by ripping electrons off the table. This is, in effect, a current — electrons are flowing from the table to the tape. If you peel tape off a table in a dark room you’ll see light. From what I gather, as the electrons slow down when they hit the tape, they give off radiation (this would be Bremsstrahlung or “Braking” radiation). When you do this in a dark room, you’re seeing that radiation as visible light.

The new research shows that if you do it in a vacuum, instead of these visible photons (which are just a form of electromagnetic radiation with a relatively low energy), you get x-rays (electromagnetic radiation with high energy). The x-rays were strong enough to take a picture of one of the researchers’ finger.

The NY Times article on this says:

All of the experiments were conducted with Scotch tape, manufactured by 3M. The details of what is occurring on the molecular scale are not known, the scientists said, in part because the Scotch adhesive remains a trade secret.

Other brands of clear adhesive tapes also gave off X-rays, but with a different spectrum of energies. Duct tape did not produce any X-rays, Dr. Putterman said. Masking tape has not been tested.

{ 3 comments }

timur December 11, 2008 at 2:54 am

If it was because of the braking electrons, wouldn’t the light be visible right when you stick the tape to the table? I am guessing the reason for light emission is some kind of discharge like in lightning.

sciencegeekgirl December 11, 2008 at 1:26 pm

Hi Timur,

When you first stick the tape to the table, the electrons haven’t moved at all. When you rip the tape from the table, it pulls electrons from the table onto the tape. That movement of electrons from table to tape is created by the act of pulling the tape away from the table, not sticking it there in the first place.

I believe lightening is somewhat different. In lightening, there is a strong electric field between the cloud and the ground. That field is strong enough to overcome the electrical breakdown of air and the air ionizes. What that means is that the electrons get ripped off the molecules in the air by that strong field. Those electrons can flow through the air — it’s become a plasma, which can conduct electricity. The strong electric current flowing through that air-plasma from the cloud to the ground makes the air glow.

I’m not sure what role the “braking” radiation plays in lightening — something to look into!

sciencegeekgirl December 11, 2008 at 6:55 pm

So, my resident lightening expert (Paul Doherty) says —

“While Bremstrahlung is typically applied to electrons that stop in matter thus decelerating and emitting radiation, it actually applies to any radiation by an electron that is free before interacting with another charge and free after the interaction.

So in this broad sense it does apply to the electron collisions that occur in lightning.”

I’m not quite sure what that means, phenomenologically, but it sounds like it has some effect, but perhaps it’s mostly a matter of semantics.

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