IM Interview : Discovery Tech : Discovery Channel

X-rays from Scotch Tape! Who Knew?

Tracy Staedter chats with Juan Escobar, a tribologist who is studying why Scotch tape radiates X-rays.

Juan Escobar

Likes watching tape peel.

Vision for X-ray

The simple technique could be used to develop a portable, inexpensive X-ray machine that works without electricity.

Links Tracy Likes

  Ripped Scotch Tape Emits X-Rays

  How X-rays works

  Take the pet X-ray quiz!

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12:02 PM escobarjuanvalentin: Hi Tracy

imtracynotstacy: Hi there! ready?

escobarjuanvalentin: I'm all yours

imtracynotstacy: Great! So let me start out by asking where you're chatting from.

12:03 PM escobarjuanvalentin: from UCLA

Dept of Physics and Astronomy

imtracynotstacy: in an office or lab? escobarjuanvalentin: lab

imtracynotstacy: could you give us a visual? What do you see around you?

12:05 PM escobarjuanvalentin: well... there is a levitated table with a vacuum chamber

lots of cabinets with instruments

lots of journal papers on stacks

waiting to be read or re-read

12:06 PM imtracynotstacy: what's your area of research?

escobarjuanvalentin: I'd say tribology

experimental imtracynotstacy: what is tribology?

escobarjuanvalentin: it is the science of interacting surfaces

of rubbing, charge transfer etc...imtracynotstacy: ahhhh.....so you study things like why balloon stick to walls when you rub them on your hair? ( not to get us off topic before we even get started!)

escobarjuanvalentin: yes, thats correct

12:09 PM why things stick together imtracynotstacy: Ok, so let's get on topic. I'm chatting with you today because of your work with the scotch tapes that releases x rays...........there's a lot to unravel here, so let's start with a very simple questions

What is your role on the research team?

escobarjuanvalentin: A co-worker and I did the experiments

12:11 PM (carlos camara)

and along with my advisor, Seth Putterman, we wrote the article togather

imtracynotstacy: are you a professor?

escobarjuanvalentin: No, I am a PhD candidate (grad student)

12:13 PM imtracynotstacy: So what I understand is that when you unpeel scotch in a vacuum, it unleashes X rays. I mean, whoa. So many questions.....but first, have I got the gist of it right?

scotch tape escobarjuanvalentin: yes, that's right

of the kind you buy from your local store

imtracynotstacy: okay, can you remind me what a vacuum is? escobarjuanvalentin: sure, its an enclosed volume that has less pressure than the atmosphere

imtracynotstacy: And why on earth did you (or your teammates) come up with the idea of unpeeling scotch tape in a vaccum?

12:17 PM escobarjuanvalentin: Here in the lab, we had been working on triboluminescence

(the emission of light upon mechanical treatment) imtracynotstacy: ok

escobarjuanvalentin: a former post-doc had found than when mercury slides in glass, it emits lights that come in picosecond bursts

12:19 PM this was found to be due to charge transfer

this lead us to dig into the literature for other phenomena

that also emitted light upon contact we found that as early as 1930, a Russian by the name Obreimoff had found evidence that mica could emit x-rays when split in vacuum From the same Russian school, they did other sets of experiments in 1953 and in 1989 showing that also adhesives would emit x-rays when peeled in vacuum we had to see it for ourselves

And it turns out they were right We found that peeling tape emits no only some x-rays, but a lot of them

so many, that it is possible to take an x-ray image of a human finger

12:24 PM with the x-rays emitted from the tape being peeled at 10cm/s for a 10 second exposure

imtracynotstacy: Can you remind me what X-rays are?

escobarjuanvalentin: its electromagnetic radiation

just like light

12:25 PM except that the energies are at least 1000 larger than a visible photon

In other words, it is high energy light

imtracynotstacy: okso the X rays are not emitted under normal atmospheric pressure?

I mean from peeling he scotch tape?

escobarjuanvalentin: Not from scotch tape, at least according to the test we made. You need a vacuum chamber for that

12:27 PM (there could be other brands or types that do, but I think it is unlikely)

imtracynotstacy: okay.....so peeling the tape off in a vacuum is releasing high energy light, i.e. X-rays. Why? escobarjuanvalentin: It has to do with charge separation.

12:29 PM when tape is peeled, the sticky side and the dry side are left with oppopsite charges

(you can see this at your office) usually, a lot of those charges quickly meet the other side (electrons are emitted) helped by air molecules

imtracynotstacy: wait, how do I see the opposite charges at my office?

12:31 PM escobarjuanvalentin: do you have scotch tape there?

peel a portion of it

imtracynotstacy: one sec.....let me get some.

escobarjuanvalentin: bring your hand close to it (slowly) you'll see your hand attracts it did you try?

12:34 PM imtracynotstacy: trying now, but when I peel back the tape it doesn't stay peeled off, it goes back down to the surface. escobarjuanvalentin: right! thats because of the electrostatic attraction beteen the two surfaces

imtracynotstacy: yeah, it seems to snap back to the surfce almost

escobarjuanvalentin: if you do it slowly enough, you'll be able to attract it with your hand

12:36 PM imtracynotstacy: I can see the attraction forces, cuz even though it's not attracted to my hand, if I peel it back far enough, it bends back and sticks to itself

escobarjuanvalentin: right well, when there are no molecules of air around, the surface densities (of charge) are much higher

this allows the electrons to gain a lot more potential energy as you separate the two sides

then

12:38 PM imtracynotstacy: electrons gain energy.....but isn't light photons? sorry my physics are not great

escobarjuanvalentin: yes, I was getting to that

electrons gain more energy such that when they collide against the other side of the tape they slow down abruptly

and when that happens, x-rays are emitted

in a process that is called

"bremmstralung" radiation

12:41 PM imtracynotstacy: so electrons gain energy, collide with molecules in the tape, slow abruptly and then release radiation. right? It reminds of being in a car that is going fast it crashes into a wall, but the person in side keeps moving forward

so it's like the electron stops but it's energy keeps going forward and that energy is the X-ray?

12:43 PM escobarjuanvalentin: No, in general when a charged particle is decelerated, it emits radiation

imtracynotstacy: oh

escobarjuanvalentin: when it slows down a lot, the energy of the radiation is high In general, commercial x-ray generator works in the same way

imtracynotstacy: really?

escobarjuanvalentin: the difference is that the energy that is provided to the electrons does not come from contact electrification

12:45 PM imtracynotstacy: where does it come from?

escobarjuanvalentin: sometimes just from a capacitor (connected to the power line)

others from the high fields of ferroelectric crystals but it always involves accelerating electrons and then slamming them against something

imtracynotstacy: ok.....so is it a big surprise to see so much radiation getting released from scotch tape?

escobarjuanvalentin: To me, it was a big surprise

yes

12:47 PM imtracynotstacy: How does the radiation from the tape compare to a commercial machine?

escobarjuanvalentin: the energy per photon is about 15keV

in a commercial one, it can be much higher plus the flux is relatively smaller too

but it is nonetheless still enough to take an x-ray picture using, for example, a dental film imtracynotstacy: And what are the potential applications for this technique with the tape?

12:50 PM escobarjuanvalentin: it shows how very large charge densities can be obtained from contact electrification, so that maybe something similar can be harnessed into a reliable x-ray source that is capable of operating just by mechanical means, without plugging into the wall

12:52 PM imtracynotstacy: why make such a low tech version?

escobarjuanvalentin: what do you mean? of an x-ray source?

imtracynotstacy: like why make an X-ray machine that is capable of being operated by mechanical means?

if that's what you're saying.....

12:54 PM escobarjuanvalentin: Potentially it could be turned into a portable unexpensive machine but it is hard to know if it could compete with current technologies

But is opens up the possibility of other directions, other approaches maybe somone will find the right way of applying this principle into something useful for our daily lives

12:57 PM imtracynotstacy: So what's your next step? Are you going to test more adhesives? Have you moved on to something else? escobarjuanvalentin: Yes, we want to try other adhesives with different substrates

there are some important scientific questions that we would like to answer like, why are the charge densities so high to begin with, and how could you make them even larger Another relevant question for a possible application is to find an adhesive that also leads to x-rays but that does not evaporate so much upon peeling (when you peel the tape you notice it smells funny)

(well, not funny, it just smells)

that means its evaporating, and that increases the vacuum

sorry, that kills the vacuum

we'd like to supress that Also, that other tribological systems can lead to x-ray when done in vacuum

1:04 PM imtracynotstacy: Very interesting.

Well, I think that wraps this up!

Thanks so much for taking the time to chat.

1:05 PM escobarjuanvalentin: thank you Tracy

imtracynotstacy: great. have a good day and I'll send you the link when it's live

1:07 PM escobarjuanvalentin: sounds good

nice meeting you

take care

CONTENT

X-rays from Scotch Tape! Who Knew?

Juan Escobar

Vision for X-ray

Links Tracy Likes

Fast Facts About Juan

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