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8/13/2019 Pyroelectric Crystal Research(Www.unc.Edu-~Jlkesler)

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Pyroelectric CrystalResearch with Dr. Stephen

ShafrothJessica Kesler

Spring 2005Physics 102


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Pyro.. What?

A pyroelectric crystal is an asymmetric

crystal that becomes electrically charged

on heating and cooling

In this experiment we used LiNbO3


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Thats great.. So what?

These crystals can actually shoot off

electrons

These can knock out electrons from

other elements and give off specific x-rays,

so that you can see what elements are

present in a substance


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Shooting electrons.. That sounds

violent!

All you do is heat up the crystal using a

specific current and then turn off the

current to let the crystal cool back off to

room temperature

We used 1.2 mA

In case you were wondering, a common

pyroelectric crystal is amber


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The Setup

Incoming current

To heat the crystal

resistor

crystal


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Initial Temperature

- +

- +

- +

- +

- +

- +

- +- +

- +

- +

The crystal has no net charge.


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Heating

+

- +- +

+

- +

-

- +-

- +

- +

The crystal is still neutral but has less surface charge. The gas

around it has not changed.

This side is

attached to the

resistor, soelectrons do not

shoot off and

affect the results.


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Highest Temperature

- +

- +

- +

- +

- +

- +

Back to neutral, with less surface charge.


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Cooling

-

- +

-

- +

- +

+

- +

+

- +

- +

Electrons shoot off the crystal.


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Interesting.

So now that these electrons are shooting

off in a vacuum, what substance are we

going to find the elements of?


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LEAVES!


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Cool..

You can tell the differences in leaves by

changes in light elemental uptake

(different peaks are different sizes)

Underside and topside

Time of year

Tip and other parts?


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Leaf Setup

detector


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Specifications For This Lab

1.2 mA current

Heat to about 110 degrees Celsius

25 mTorr vacuum


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Inside the lab


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More Inside the Lab


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What Collected Data


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The X-Rays Looked Like This


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What was my part?

I wrote a LabVIEW program that displayed

the temperature versus time and the

ratemeter voltage versus time


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Front Panel


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More of the Front Panel


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The Rest of the Front Panel


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Diagram


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The Last of the Diagram


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Cooling Front Panel


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Another Cooling Front Panel


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Heating Front Panel


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The Rest of the Heating Front

Panel


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Problems with LabVIEW

Does not show temperature or rate as you

go along in time, so have to guess when to

turn the current off

Always takes much longer than calculated

time (could be computer)

Freezes/ crashes frequently


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Problems with the Project While I

Was There

Bad pump, leaks

Bad DAQ board

Spectrometer and Mac ComputerCrashing

Leaf falling

Energy labels mixed upRatemeter stopped working


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By the End..

LabVIEW was working

Ratemeter was working

No leaks, good vacuum Energy still mixed up

Working leaf

New holder netting to keep leaf from falling into pump

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