Pole-position goniometer

Bikewer · 24th May 2012, 11:51 AM

While checking out the physics department last night, I saw a piece of equipment sitting in the hall. All precision-machined bits and gears and clamps... Wondered what it was.

The label said...Pole-position goniometer. Fascinating. Didn't tell me a thing.

So...Google. There were four or five citations I attempted to read through. It was worse that Star Trek techno-speak. I now know it has something to do with X-ray examination of crystals, but beyond that nothing.
Any physicists in the house?

Madalch · 24th May 2012, 12:33 PM

I seem to recall that it's a thing for holding a crystal in an X-ray beam at a particular angle (which can be changed), so that the diffraction of X-rays from the crystal can be measured. You mount the crystal on the goniometer, send a beam of X-rays at it, rotate the crystal through all possible angles, and measure the intensity of the X-rays bouncing off as a function of the angle.

This may sound like a particularly useless thing to do, but it enables you to determine the distances and angles between the various atoms that make up the crystal, allowing you to basically build a perfect model of the molecules of the crystal (not just seeing the structure, but measuring all the bond lengths and angles as well).

So you get molecular pictures like these:

Madalch · 24th May 2012, 12:43 PM

The one on the right is from my thesis work.

mijopaalmc · 24th May 2012, 01:53 PM

Sounds like a sex toy.

Bikewer · 24th May 2012, 03:25 PM

Thanks for the lucid explanation. I do agree that "goniometer" sounds like a Japanese sex toy.

Ziggurat · 24th May 2012, 03:47 PM

Originally Posted by Bikewer

Thanks for the lucid explanation. I do agree that "goniometer" sounds like a Japanese sex toy.

If it wasn't before, it will be now! I've got some money to go make....

quarky · 24th May 2012, 03:54 PM

Originally Posted by Madalch

The one on the right is from my thesis work.

Nice molecule. What is it?

Nice explanation too.

Pulvinar · 24th May 2012, 04:48 PM

Offhand I'd guess it's an alkynyl-bridged heterobinuclear complex of rhodium and iridium.

(Ok, I cheated...)

Alareth · 24th May 2012, 07:05 PM

Now I have the theme song stuck in my head.

YouTube Video This video is not hosted by the JREF. The JREF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.

I AGREE

quarky · 24th May 2012, 08:22 PM

That was evil.

Why did I have to watch the whole thing?

Madalch · 24th May 2012, 09:23 PM

Originally Posted by Pulvinar

Offhand I'd guess it's an alkynyl-bridged heterobinuclear complex of rhodium and iridium.

That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate.

Finn McR · 24th May 2012, 10:01 PM

So, "I seem to recall..." means, "I have this totally covered, having done x-ray crystallography work for my thesis." Clever dog. Why not whip out the diffraction equation and some quantum mechanics while you are at it?

The goniometer idea is both simple and complex. Incoming particles (typically photons) interact with a sample (bounce off of it). It is usually easier to think in terms of waves and wavelengths. When the angle at which they bounce off means that an integer number of the waves reinforce, you get a nice signal. X-rays have a good wavelength range to probe many materials, as the atomic spacings are the right size to give good diffraction patterns (spread the incoming x-ray photons into readable spectra).

Pulvinar · 24th May 2012, 11:12 PM

Originally Posted by Madalch

That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate.

Ah, better with a little mustard oil...

I should have read the abstract closer.

Madalch · 25th May 2012, 01:21 AM

Originally Posted by Finn McR

So, "I seem to recall..." means, "I have this totally covered, having done x-ray crystallography work for my thesis." Clever dog. Why not whip out the diffraction equation and some quantum mechanics while you are at it?

Not really- I made the compound and grew the crystal, and then begged Bob the crystallographer to run it for me. He eventually said, "Sure- just let me put it on the goniometer head", to which I replied, "The gonny-what?"

My memory of how crystallography works is minimal- I don't remember the diffraction eq'n, and I barely remembered making that particular compound until I saw the ORTEP.

anor277 · 25th May 2012, 02:30 AM

Ah, those were the days (+20 year ago). Just to add that even in those days, X-ray crystallography was the cheapest and preferred method for determination of molecular structure. (Of course, you had to grow a sizeable crystal - approx. 0.5 x 0.5 x 0.5 mm - and this was sometimes problematic.)

With the old instruments, the time it took to index a particular crystal was 4-8 hours (this is the preliminary in solving the structure, you get unique space group parameters) and maybe another 24-48 hours to collect a data-set.

Modern CCD X-ray diffraction instruments can index structures in something like 10 minutes, and collect a data set in as little as an hour. The software has also become proportionately powerful. Even a duffer can solve an X-ray crystal structure with a little guidance. As a bonus, the crystal size you can use for experiments is something you can barely see sometimes (0.1 x 0.1 x 0.1 mm for example) - when you see a X-ray diffraction specialist these days the common response is that the crystals are too big and have to be cut. In the old days the crystals were always too small.

Dave Rogers · 25th May 2012, 02:38 AM

I'm familiar with the appearance, function and use of goniometers, having done an undergraduate physics course many, many years ago that included an XRD experiment on the practical course. (I don't get involved in anything that subtle these days as all the crystals I work with are cubic with known axes.) The bit I don't recognise is the "Pole Position" part. Is this just such a flashy and brilliant goniometer that it has a natural head start over all other goniometers? (Sorry.) Or does it just describe the way the goniometer mounts the sample in the X-ray beam? And has anyone else noticed how much fun it is to say "goniometer"?

Dave

sphenisc · 25th May 2012, 03:28 AM

It shouldn't be confused with the goninometer, a delicate device used to measure Glaswegian expressions of desire for an action to desist.

arthwollipot · 25th May 2012, 03:33 AM

Originally Posted by Madalch

That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate.

That's what she said.

Cuddles · 25th May 2012, 06:10 AM

Originally Posted by anor277

As a bonus, the crystal size you can use for experiments is something you can barely see sometimes (0.1 x 0.1 x 0.1 mm for example)

That big? We can deal with samples down to 5um, although admittedly most of the beamlines are usually closer to 20um. I suppose technically the individual samples in powder diffraction are even smaller, but that's kind of cheating.

Madalch · 25th May 2012, 10:26 AM

Originally Posted by anor277

Ah, those were the days (+20 year ago). Just to add that even in those days, X-ray crystallography was the cheapest and preferred method for determination of molecular structure. (Of course, you had to grow a sizeable crystal - approx. 0.5 x 0.5 x 0.5 mm - and this was sometimes problematic.)

My crystallographic day was just over ten years ago. Right near the end of my thesis work, we got a new CCD detector, which meant that all the crystals that I was throwing away because they were too small for diffraction were now suddenly just right. I think I got three structures out of five just in the last few months of work.

Ziggurat · 25th May 2012, 10:51 AM

Originally Posted by Cuddles

That big? We can deal with samples down to 5um, although admittedly most of the beamlines are usually closer to 20um. I suppose technically the individual samples in powder diffraction are even smaller, but that's kind of cheating.

Yeah, that's definitely cheating. If you're illuminating more than one grain at a time with your beam, then your sample is more than one grain.

On the other end of the spectrum, with neutron scattering they brag about how big they can get their crystals. As in, multiple cubic centimeters with some materials.

Madalch · 25th May 2012, 10:57 AM

Originally Posted by Ziggurat

On the other end of the spectrum, with neutron scattering they brag about how big they can get their crystals. As in, multiple cubic centimeters with some materials.

Hey- everyone appreciates a nice, big crystal.

(Not mine, sadly.)

Alareth · 25th May 2012, 11:11 AM

Originally Posted by quarky

That was evil.

Why did I have to watch the whole thing?

You misspoke sir, that was one of the best themes of the 80's. We're talking Kenny Loggins "Danger Zone" levels of awesome.

quarky · 25th May 2012, 11:17 AM

Originally Posted by Madalch

That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate.

That's my 'pick-up' line.

Soapy Sam · 25th May 2012, 04:07 PM

Originally Posted by sphenisc

It shouldn't be confused with the goninometer, a delicate device used to measure Glaswegian expressions of desire for an action to desist.

Kindly do not repeat this.

Evilgiraffe · 25th May 2012, 04:10 PM

Originally Posted by Bikewer

While checking out the physics department last night, I saw a piece of equipment sitting in the hall. All precision-machined bits and gears and clamps... Wondered what it was.

The label said...Pole-position goniometer. Fascinating. Didn't tell me a thing.

So...Google. There were four or five citations I attempted to read through. It was worse that Star Trek techno-speak. I now know it has something to do with X-ray examination of crystals, but beyond that nothing.
Any physicists in the house?

It's possibly a slight mis-speaking. Should probably be a pole-figure goniometer. As others have said, a goniometer is a device for centering and orienting a crystal in an x-ray beam for crystallographic analysis.

If your sample is a perfect single crystal, the reflections from individual crystal planes will always occur at the same angle with a given intensity. However, if you have an imperfect crystal, the planes will have a spread of orientations and intensities. By following the angular dependence of a peak intensity, you can determine the distribution of crystal plane orientations. This is done by constructing a pole figure.

If you have a sample that is composed of many small crystallites, as in powder crystallography, the average intensity of reflections from all of the crystallites converge to the 1-dimensional projection of the 3-dimensional data set you would get from a single crystal. However, if for some reason you have a preferred orientation in your sample, if your crystallites are platey or needle-like they will tend to align, and some reflections will be over-represented in your data set. A pole figure can be used to determine and quantify this "texture" in your sample.

24th May 2012, 11:51 AM	#1
Bikewer Philosopher Join Date: Sep 2003 Location: St. Louis, Mo. Posts: 9,536	Pole-position goniometer While checking out the physics department last night, I saw a piece of equipment sitting in the hall. All precision-machined bits and gears and clamps... Wondered what it was. The label said...Pole-position goniometer. Fascinating. Didn't tell me a thing. So...Google. There were four or five citations I attempted to read through. It was worse that Star Trek techno-speak. I now know it has something to do with X-ray examination of crystals, but beyond that nothing. Any physicists in the house?

24th May 2012, 12:33 PM	#2
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	I seem to recall that it's a thing for holding a crystal in an X-ray beam at a particular angle (which can be changed), so that the diffraction of X-rays from the crystal can be measured. You mount the crystal on the goniometer, send a beam of X-rays at it, rotate the crystal through all possible angles, and measure the intensity of the X-rays bouncing off as a function of the angle. This may sound like a particularly useless thing to do, but it enables you to determine the distances and angles between the various atoms that make up the crystal, allowing you to basically build a perfect model of the molecules of the crystal (not just seeing the structure, but measuring all the bond lengths and angles as well). So you get molecular pictures like these:
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker Last edited by Madalch; 24th May 2012 at 12:38 PM.

24th May 2012, 12:43 PM	#3
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	The one on the right is from my thesis work.
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker

24th May 2012, 01:53 PM	#4
mijopaalmc Illuminator Join Date: Mar 2007 Posts: 4,638	Sounds like a sex toy.
mijopaalmc Illuminator Join Date: Mar 2007 Posts: 4,638

24th May 2012, 03:47 PM	#6
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,220	Originally Posted by Bikewer Thanks for the lucid explanation. I do agree that "goniometer" sounds like a Japanese sex toy. If it wasn't before, it will be now! I've got some money to go make....
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

24th May 2012, 03:25 PM	#5
Bikewer Philosopher Join Date: Sep 2003 Location: St. Louis, Mo. Posts: 9,536	Thanks for the lucid explanation. I do agree that "goniometer" sounds like a Japanese sex toy.

24th May 2012, 03:54 PM	#7
quarky Banned Join Date: Oct 2007 Posts: 20,454	Originally Posted by Madalch The one on the right is from my thesis work. Nice molecule. What is it? Nice explanation too.
quarky Banned Join Date: Oct 2007 Posts: 20,454

24th May 2012, 04:48 PM	#8
Pulvinar Muse Join Date: Aug 2009 Posts: 820	Offhand I'd guess it's an alkynyl-bridged heterobinuclear complex of rhodium and iridium. (Ok, I cheated...)
Pulvinar Muse Join Date: Aug 2009 Posts: 820

24th May 2012, 08:22 PM	#10
quarky Banned Join Date: Oct 2007 Posts: 20,454	That was evil. Why did I have to watch the whole thing?
quarky Banned Join Date: Oct 2007 Posts: 20,454

24th May 2012, 09:23 PM	#11
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	Originally Posted by Pulvinar Offhand I'd guess it's an alkynyl-bridged heterobinuclear complex of rhodium and iridium. That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate.
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker

24th May 2012, 10:01 PM	#12
Finn McR Guest Join Date: Mar 2009 Location: East Coast USA Posts: 285	So, "I seem to recall..." means, "I have this totally covered, having done x-ray crystallography work for my thesis." Clever dog. Why not whip out the diffraction equation and some quantum mechanics while you are at it? The goniometer idea is both simple and complex. Incoming particles (typically photons) interact with a sample (bounce off of it). It is usually easier to think in terms of waves and wavelengths. When the angle at which they bounce off means that an integer number of the waves reinforce, you get a nice signal. X-rays have a good wavelength range to probe many materials, as the atomic spacings are the right size to give good diffraction patterns (spread the incoming x-ray photons into readable spectra).

24th May 2012, 11:12 PM	#13
Pulvinar Muse Join Date: Aug 2009 Posts: 820	Originally Posted by Madalch That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate. Ah, better with a little mustard oil... I should have read the abstract closer.
Pulvinar Muse Join Date: Aug 2009 Posts: 820

25th May 2012, 01:21 AM	#14
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	Originally Posted by Finn McR So, "I seem to recall..." means, "I have this totally covered, having done x-ray crystallography work for my thesis." Clever dog. Why not whip out the diffraction equation and some quantum mechanics while you are at it? Not really- I made the compound and grew the crystal, and then begged Bob the crystallographer to run it for me. He eventually said, "Sure- just let me put it on the goniometer head", to which I replied, "The gonny-what?" My memory of how crystallography works is minimal- I don't remember the diffraction eq'n, and I barely remembered making that particular compound until I saw the ORTEP.
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker

25th May 2012, 02:30 AM	#15
anor277 Critical Thinker Join Date: Apr 2004 Posts: 313	Ah, those were the days (+20 year ago). Just to add that even in those days, X-ray crystallography was the cheapest and preferred method for determination of molecular structure. (Of course, you had to grow a sizeable crystal - approx. 0.5 x 0.5 x 0.5 mm - and this was sometimes problematic.) With the old instruments, the time it took to index a particular crystal was 4-8 hours (this is the preliminary in solving the structure, you get unique space group parameters) and maybe another 24-48 hours to collect a data-set. Modern CCD X-ray diffraction instruments can index structures in something like 10 minutes, and collect a data set in as little as an hour. The software has also become proportionately powerful. Even a duffer can solve an X-ray crystal structure with a little guidance. As a bonus, the crystal size you can use for experiments is something you can barely see sometimes (0.1 x 0.1 x 0.1 mm for example) - when you see a X-ray diffraction specialist these days the common response is that the crystals are too big and have to be cut. In the old days the crystals were always too small.
anor277 Critical Thinker Join Date: Apr 2004 Posts: 313

25th May 2012, 02:38 AM	#16
Dave Rogers Bandaged ice that stampedes inexpensively through a scribbled morning waving necessary ankles Join Date: Jan 2007 Location: In a world lit only by fire. Posts: 17,894	I'm familiar with the appearance, function and use of goniometers, having done an undergraduate physics course many, many years ago that included an XRD experiment on the practical course. (I don't get involved in anything that subtle these days as all the crystals I work with are cubic with known axes.) The bit I don't recognise is the "Pole Position" part. Is this just such a flashy and brilliant goniometer that it has a natural head start over all other goniometers? (Sorry.) Or does it just describe the way the goniometer mounts the sample in the X-ray beam? And has anyone else noticed how much fun it is to say "goniometer"? Dave
	__________________ "We will punish the murderer together. Our punishment will be more generosity, more tolerance and more democracy." - Fabian Stang, Mayor of Oslo SSKCAS, covert member

25th May 2012, 03:28 AM	#17
sphenisc Illuminator Join Date: Jul 2004 Posts: 3,750	It shouldn't be confused with the goninometer, a delicate device used to measure Glaswegian expressions of desire for an action to desist.
sphenisc Illuminator Join Date: Jul 2004 Posts: 3,750

25th May 2012, 03:33 AM	#18
arthwollipot Observer of Phenomena Join Date: Feb 2005 Location: The other side of your screen Posts: 43,038	Originally Posted by Madalch That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate. That's what she said.
	__________________ Jadey (in RvB game thread): I just want to take a moment to commend Arth on his role as Parasitic Alien Tumor. I think he really connected with the character and there were times when I forgot that he was just acting. That's the kind of talent that you can't teach.

25th May 2012, 06:10 AM	#19
Cuddles Decoy Moderator Join Date: Jul 2006 Location: A magical land full of pink fluffy sheeps and bunnies Posts: 16,597	Originally Posted by anor277 As a bonus, the crystal size you can use for experiments is something you can barely see sometimes (0.1 x 0.1 x 0.1 mm for example) That big? We can deal with samples down to 5um, although admittedly most of the beamlines are usually closer to 20um. I suppose technically the individual samples in powder diffraction are even smaller, but that's kind of cheating.
	__________________ I am not a little teapot.

25th May 2012, 10:26 AM	#20
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	Originally Posted by anor277 Ah, those were the days (+20 year ago). Just to add that even in those days, X-ray crystallography was the cheapest and preferred method for determination of molecular structure. (Of course, you had to grow a sizeable crystal - approx. 0.5 x 0.5 x 0.5 mm - and this was sometimes problematic.) My crystallographic day was just over ten years ago. Right near the end of my thesis work, we got a new CCD detector, which meant that all the crystals that I was throwing away because they were too small for diffraction were now suddenly just right. I think I got three structures out of five just in the last few months of work.
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker

25th May 2012, 10:51 AM	#21
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 26,220	Originally Posted by Cuddles That big? We can deal with samples down to 5um, although admittedly most of the beamlines are usually closer to 20um. I suppose technically the individual samples in powder diffraction are even smaller, but that's kind of cheating. Yeah, that's definitely cheating. If you're illuminating more than one grain at a time with your beam, then your sample is more than one grain. On the other end of the spectrum, with neutron scattering they brag about how big they can get their crystals. As in, multiple cubic centimeters with some materials.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

25th May 2012, 10:57 AM	#22
Madalch The Jester Join Date: Nov 2006 Location: The wet coast. Posts: 8,706	Originally Posted by Ziggurat On the other end of the spectrum, with neutron scattering they brag about how big they can get their crystals. As in, multiple cubic centimeters with some materials. Hey- everyone appreciates a nice, big crystal. (Not mine, sadly.)
	__________________ As the size of an explosion increases, the number of social situations it is incapable of resolving approaches zero. -Vaarsuvius It's a rum state of affairs when you feel like punching a jar of mayonnaise in the face. -Charlie Brooker

25th May 2012, 11:11 AM	#23
Alareth Expert Expertologist Join Date: Aug 2006 Location: Florida Posts: 6,683	Originally Posted by quarky That was evil. Why did I have to watch the whole thing? You misspoke sir, that was one of the best themes of the 80's. We're talking Kenny Loggins "Danger Zone" levels of awesome.
	__________________ Pixelated Reality \| Alareth Does Art! Light travels faster than sound, which is why some people appear bright, until you hear them speak

25th May 2012, 11:17 AM	#24
quarky Banned Join Date: Oct 2007 Posts: 20,454	Originally Posted by Madalch That's a good guess, but it's incorrect. I made it by reacting an alkynyl-bridged heterobinuclear complex of rhodium and iridium with butyl isothiocyanate; the alkynyl group leaves the bridging position, and is replaced by the sulfur of the isothiocyanate. That's my 'pick-up' line.
quarky Banned Join Date: Oct 2007 Posts: 20,454

25th May 2012, 04:07 PM	#25
Soapy Sam NLH Join Date: Oct 2002 Posts: 25,885	Originally Posted by sphenisc It shouldn't be confused with the goninometer, a delicate device used to measure Glaswegian expressions of desire for an action to desist. Kindly do not repeat this.
Soapy Sam NLH Join Date: Oct 2002 Posts: 25,885

25th May 2012, 04:10 PM	#26
Evilgiraffe Scatterer of X-rays Join Date: Aug 2007 Location: Oxfordshire Posts: 742	Originally Posted by Bikewer While checking out the physics department last night, I saw a piece of equipment sitting in the hall. All precision-machined bits and gears and clamps... Wondered what it was. The label said...Pole-position goniometer. Fascinating. Didn't tell me a thing. So...Google. There were four or five citations I attempted to read through. It was worse that Star Trek techno-speak. I now know it has something to do with X-ray examination of crystals, but beyond that nothing. Any physicists in the house? It's possibly a slight mis-speaking. Should probably be a pole-figure goniometer. As others have said, a goniometer is a device for centering and orienting a crystal in an x-ray beam for crystallographic analysis. If your sample is a perfect single crystal, the reflections from individual crystal planes will always occur at the same angle with a given intensity. However, if you have an imperfect crystal, the planes will have a spread of orientations and intensities. By following the angular dependence of a peak intensity, you can determine the distribution of crystal plane orientations. This is done by constructing a pole figure. If you have a sample that is composed of many small crystallites, as in powder crystallography, the average intensity of reflections from all of the crystallites converge to the 1-dimensional projection of the 3-dimensional data set you would get from a single crystal. However, if for some reason you have a preferred orientation in your sample, if your crystallites are platey or needle-like they will tend to align, and some reflections will be over-represented in your data set. A pole figure can be used to determine and quantify this "texture" in your sample.