Creative ElectronGET A DEMO

X-ray News

Fireside Chat with the Xperts: Stump the Chumps IV

There’s just no stumping these two:  Drs. Glen Thomas and Bill Cardoso were back for another Fireside Chat with the Xperts, once again fielding questions from our audience.  This episode addressed the difference between XRF (X-ray fluorescence) and transmission X-ray inspection.  The “chumps” demonstrated once again that there are no simple answers when it comes to the science behind X-ray.

In addressing the question, the discussion thoroughly explains XRF, how it works and its common uses.  Not only do they cover the differences between XRF and transmission X-ray inspection, but how the two can compliment one another, for example when evaluating counterfeits.  And seemingly inevitably, a discussion of backscatter X-ray sneaks in. Register for upcoming Fireside Chats with the Xperts and view our archives here.

 

Transcript:

David Kruidhof:

So, it’s 10:00. It’s time for another fireside chat with the experts. We’ve been doing another Stump the Chumps this week. I have Dr. Bill Cardoso here and Dr. Glen Thomas with me. So, I have a couple of questions. We’re going to do our best to get through more than two this week, right guys?

Dr. Glen Thomas:

Absolutely.

Dr. Bill Cardoso:

Or one. We can do one as well.

Dr. Glen Thomas:

We’re not get-

David Kruidhof:

Or shrink it down to one. Well, this one… Yeah, anyways, we’ll try to get through at least two. So first question of the day, what is the difference between XRF and X-ray inspection?

Dr. Glen Thomas:

That could be an extremely long answer.

Dr. Bill Cardoso:

We’ll have to have two episodes on that one, Glen.

David Kruidhof:

Or it could be a one sentence answer, right?

Dr. Glen Thomas:

A one sentence, one bounces and one penetrates, right? XRF bounces off the sample. Essentially XRF will look at material composition, elemental composition of a component or of a sample. Whereas X-ray is a penetrating X-ray and it will actually traverse through the sample to produce an X-ray image, either on film or a detector. Quantitative is material composition, essentially is what you’re looking for with XRF.

Dr. Glen Thomas:

XRF generally is a low energy type of X-ray, it uses X-ray tubes and photodiodes for detectors. But yeah, it’s a very low energy and in a lot of cases, you’ll use a light isotope for a source. The reason for that is the isotope is pretty consistent in its output of X-ray or photon energy. That’s my… Yeah.

Dr. Bill Cardoso:

Yeah. So XRF is X-ray florescence, right? So it’s this fluorescence mechanism that makes the methodology so powerful and Glen, there is the same fluorescence mechanism that makes the fluorescent lights work, right?

Dr. Glen Thomas:

Absolutely.

Dr. Bill Cardoso:

It’s this property that because of fluorescent light, the chemistry of the elements they have inside the lights, that once you apply electricity between an anode and a cathode, you’re going to have light because of how the electrons move in the shells of the atom. When they come back, they emit a photon and depending on the material or the chemical that you have inside the light bulb, you’re going to have color, right?

Dr. Bill Cardoso:

What makes XRF a very interesting methodology and we played with it. I know you’ve done that as well, Glen, with some success, mostly failures, but XRF it’s somewhat similar to X-ray inspection that we talk about in transmission X-ray inspection. That’s what we call transmission, right, because the X-rays that get out of the source, they go through the material like Glen said and they cast a shadow of X-ray photons into the sensor. Then that shadow is what we call the image.

Dr. Bill Cardoso:

That’s why good old days they called the shadowgram. The X-ray image was called a shadowgram, but the X-ray fluorescence takes advantage of a very interesting property, right, that materials have. That if you hit them with, in this case, X-rays, the electrons just like the fluorescent, like the atoms of this material, right, whatever the material is, you’re going to knock them down. Once they recoil and they come back to their shells, they will emit an X-ray photon. That’s why it feels like the X-ray bounces on the material. In an X-ray, transmission X-ray inspection or imaging that you do, this is your sample, this piece of paper is your sample.

Dr. Bill Cardoso:

You have the X-ray source here, the sensor on the other side, the X-rays go through, and then you collect the image on the other side. XRF works through florescence. You have the X-ray source here, and you’ve got to put it at an angle, because X-rays are going to hit the sample and they’re going to come out on the same side of the sample, off your sample. So your sensors going to be here, on the top of the sensor as well for the sample. Collect that information and what you collect is not an image, right? That’s why there’s some confusion sometimes between a backscatter X-ray and XRF. XRF you’re going to be collecting photons, actually photons bouncing back from the sample and you don’t read an image, you read a spectrum, right? Once you read the spectrum, you find that different elements have different fingerprints.

Dr. Bill Cardoso:

That fingerprint can be read as a spectrogram, right, the spectrograph of the specific sample. So if you look at the spectral response to X-rays for gold, for silver, for platinum, they have very different fingerprints, right? If you take an XRF, you put it in a golden sample, you’re going to see a beautiful spectrogram of gold. If you do with platinum, you see the beautiful spectrum of platinum. There is a wide range of software that looks for specific peaks on that spectrogram to find spectrum, to find and identify which sample you’re looking at, right? So you’re going to see several peaks. Gold has a few peaks, silver has a couple more, platinum has a few. So there’s each one and each of those peaks happen in specific energies, right?

Dr. Bill Cardoso:

By reading those energies, you know exactly what element you are sampling, you were looking at. So that’s very powerful to, for example, in the 40s and 50s was very common to use lead-based paint, right? Lead-based paint, as you probably know, is extremely dangerous, right? Especially because lead has a sweeter taste. So kids would love to just eat a flake from the paint and get lead poisoning. I mean, lead is one element that you don’t really remove from your system, right? Unlike iron, where you can do blood draws, it can remove the amount of iron in your blood. Lead just stays in your body, because it loves to be stuck to bones. So you do have a maximum amount of lead that you can consume over your lifetime. So the XRF, the X-ray fluorescence techniques became very popular when people testing for lead paint, right?

Dr. Bill Cardoso:

So you go into your wall, a lot of this, this XRF systems, they come and ship a gun, right? So you pull the trigger. The trigger either opens the shutter for a radioactive element. It could be Cobalt-60, Cobalt-57. It can be a little piece of Caesium depending on what kind of equipment you’re using. So you open the shutter and then the X-rays, or some of those kids, they had gamma rays shine on the sample. You get the bounce back and you get the reading to figure out if the paint is lead-based or not. The more modern XRF systems nowadays are using active X-ray source or electronic based resources, similar to the ones we use with the target and cathode and an anode to excite and create X-rays.

Dr. Bill Cardoso:

So another very popular, useful XRF toys. Again, looking for lead and lead has a very easy spectrum to read, so you can tell right away if you have something lead-based or not. Things get a little more complicated if you start combining elements. If you have compounds, if you have mixed elements in one sample, and there are different algorithms out there. They do, it’s basically deconvolution. So imagine if you have two or three spectra on top of each other, right, in a bunch of peaks and you try to figure out, okay, that’s gold plus silver plus platinum. So we end up with some very, fairly complex spectra to be able to deconvolute to you find all the elements are there. But commercial XRF systems are capable of doing that and doing that fairly well. There are other XRF units that can go with a wide arrange of elements. Those are usually that benchtop ones that you see, where you have to grab the sample, put in a little plate and then close the door and then the system does the analysis.

Dr. Glen Thomas:

 

Dr. Bill Cardoso:

And so that’s the short answer.

Dr. Glen Thomas:

I got a question for you. Can we put an XRF source into an X-ray system? It seems like a perfect solution.

Dr. Bill Cardoso:

Yeah, you can actually, and we’ve done it before. It’s the same source, right? It’s the same source. For X-rays, we need more power, because you have to generate more X-rays to penetrate through. The XRF, You don’t need this much power. The challenge becomes focusing, right, because if you look at the X-ray beam that gets the sample and bounces back, is tiny. So when you are X-raying, a sample for imaging purposes, usually look in a larger area, right? So you have basically two things going different directions, one XRF, one’s focus, X-ray wants a larger area so you can create an image. If you have a field of view half a millimeter by half a millimeter on X-ray imaging it’s not going to do much good, right? It’s too tiny. The other use that XRF has when conflicts with X-ray imaging, is that XRF, likes sensors really close to the sample, because it’s one over r squared, right? That’s the attenuation of X-rays or photons in air.

Dr. Bill Cardoso:

In r, this is between the source and in the sensor, which means that to reduce radiation by four times, all you got to do is you move away twice from the source, right, because you have the r squared component in the denominator. So what happens is, the bottom line is that you have to put that sensor really close to the sample. When you’re imaging, you end up reading the sensor as well in front of the sample, so that’s another a problem. So you put it all together… Oh, and then the other thing for XRF, you kind of like to have a generator or an X-ray source that has a very, very known peak or end, right.

Dr. Bill Cardoso:

So you understand what is the spectrum, because when we say that our source is 80 kV, 80 kV is the maximum X-ray photon that comes out of the source. There is a whole range of other X-ray energies that the source is meeting, right. It’s a whole spectrum. So you want to have a very known spectrum that you are transmitting, so you know exactly what you’re leaving back. An X-ray Source that we use they’re variable for imaging and because we want them to varying because of the wide range of samples that you might be looking at. Put it all together, theoretically, yeah, you can combine both, but you end up having to compromise some of this design features that you end up not optimizing either, right?

Dr. Glen Thomas:

Right.

Dr. Bill Cardoso:

 

Dr. Glen Thomas:

[inaudible 00:13:54] some of that, especially since XRF is a reflective sort of X-ray. Physics tells us that photons lose about 70% of their energy once they bounce.

Dr. Bill Cardoso:

Exactly. Yeah.

Dr. Glen Thomas:

Just really complicates that, getting the detector close to the sample, right.

Dr. Bill Cardoso:

Yeah.

Dr. Glen Thomas:

And focusing, it doesn’t sound like a huge problem, but most XRF systems for general use benchtops have a turret system built in that will collimate that beam down to further… Be some more selective in the sampling, right?

Dr. Bill Cardoso:

Yeah.

Dr. Glen Thomas:

So we’re looking at a micro component or a surface mount component of high density. How do you aim that with a stage that’s not microns of resolution? So that was another issue that we ran into and then keep in mind that these complications that Bill and I are talking about are complications that we ran into after we said, “Yeah, that sounds like a great idea.”

Dr. Bill Cardoso:

Hold my beer. Let’s do it.

Dr. Glen Thomas:

Let’s do it. How card can that be, right?

Dr. Bill Cardoso:

When you talk about focusing, people sometimes conjure images of lenses focusing on X-rays or electrostatic plates and things like that. X-rays are, they are photons and as photons they don’t really have a electric charge. It’s hard, you can’t really focus them, right. So what you end up having to do, like Glen said, to collimating them. Collimation is nothing but you get a chunk of really heavy material like lead or tungsten and you put a pinhole through it, right?

Dr. Bill Cardoso:

So you basically showed all the X-rays hitting that collimator, except the ones that can escape and get out from the X-ray source. So you basically wasting most of the X-ray photons you are generating by hitting them on a collimator and you just use the ones that escape right through the pinhole. That’s how we focus X-ray sources, Right. Which has nothing to do by the way, with what happens at the target, right. When we reflect the electron beam on to the X-ray, onto the target, that whole process happens inside the tube. The collimation, what we’re talking about happens outside.

Dr. Glen Thomas:

Right, but for imaging, the same applies for the imaging. Collimation helps reduce scatter. X-ray detectors like to pick up a fairly straight beam of photons, a fairly straight beam would be that sweet spot in the center, right, that penumbra effect. So if we get a nice sweet spot in the center, we get a nice contrast image with sharp edges. When we start getting a lot of scatter off of a sample or off of the misalignment of an X-ray tube and the detector, then we start getting blurry edges and we have a real hard time getting good contrast.

Dr. Glen Thomas:

We do use collimation to eliminate scatter. Medical X-ray systems use a phenomenon called a Bucky. It’s really interesting concept. They take a grid, a calibrated grid and put it in front of the X-ray detector and the photons travel straight through and don’t see the grid. What happens is any scattered photons are actually deflected and obscured to improve the image quality. Bucky’s are really cool concepts. Again, it’s using physics and using maths to clean up that image. As a human body you’re about 80% water, so water’s a huge-

Dr. Bill Cardoso:

Yeah, it’s a pain.

Dr. Glen Thomas:

… Thing for X-ray and scatter. Yeah, the whole concept of putting an XRF source in there is quite difficult.

Dr. Bill Cardoso:

Yeah. When the backscatter, the scattering side, even inside cabinets, can be a pain, right, because just like the XRF that we’re talking about you have… Every time the X-ray hits the material, something’s going to reflect, right? They’re going to fluoresce. In an X-ray cabinet, we have not only lead, we have steel, we have copper, right? And we have a myriad of elements with the motion system. We have aluminum, we have a lot of stuff in there. Every time X-ray reflects was about half of its energy. Of course you have, depending on the energy levels that are working. If you have components scattering, but since we are low energy, components doesn’t really matter.

Dr. Bill Cardoso:

So you have some of these lower pass filters working, like Glen was saying, they’re really good at getting rid of this lower energy backscatter photons, right, because once they scattered, they lose half of their energy. So if the 80 kV and they come out with 640 kV, those filters grab the lower energy stuff. When the high energy goes through directly, and it’s not impacted by the X-ray. So you have those and that’s why a lot of times when you’re doing X-ray imaging, you’re going to put a filter or different types of, it can be a thin layer of lead, or it can be a layer of copper to mitigate some of these scattering side cabinet. But it can be a real problem. Can be a real problem.

Dr. Glen Thomas:

Right. Medical X-ray systems, whether they’re dental or medical for other body parts, they use filters in front of the beam. The FDA mandates a minimum amount of aluminum, a high grade aluminum in front of the X-ray source. So for the FDA and for the certification, it’s called a half value layer. And it’s essentially, you take a, say a 100 kV source and you fire it up, you get a number of X R per hour. And then you stick a minimum of 2.2 millimeters of aluminum in front of the beam. And you should be able to cut that output in half. And that’s how the FDA mandates that medical X-ray systems eliminate a lot of that scatter. So in that concept that you would use in a XRF system as well.

Dr. Bill Cardoso:

Exactly, because if you look at the spectrum of an X-ray source, it’s a wideband spectrum, right? If you look at the… If you imagine an analogy to audio, but if you think of energy, you have energy starting your variable energies all the way to 80 kV. You then have the comfortable shoulder, but you have all those energies, right, have X-ray photons, only 80 kV, if it’s an 80 kV source. You have every other energy being populated as well. What those filters do, they are low-pass filters, right? So, when a job is a high… So ideally, the ideal X-ray source has only one energy. If it’s 130 kV source, you have only photons at 130 kV. So all of this filtering, all those things we are doing, is to try to take a wideband signal and shrink it to a narrow band, right, around the power that you’re looking to image, right.

Dr. Bill Cardoso:

Why does the FDA care about it, right? Why do they care? Well, because you don’t want to be blasted by all those energies, they’re not even used to build an image, right? They’re just getting stuck in your body, they’re not going through, right, because like Glenn said, our bodies are 70% of water. Water is great at stopping radiation and in scattering everything, right? So all of those low energy photons that you’re being blasted with are not being used to make an image. So the FDA says, “You know what? Make sure that every single X-ray photon hitting your body is going to be used to generate an image,” and thus you need to use those filters, right.

Dr. Glen Thomas:

Right, exactly.

Dr. Bill Cardoso:

It’s crazy how sometimes actually people thought about this stuff, right? Like, “Huh, this actually makes sense”. It doesn’t happen very often, but once in a while I actually make sense.

David Kruidhof:

Oh, I think so we have for one question.

Dr. Bill Cardoso:

Oh, we have the Counterfeit Expo next week, right, David?

David Kruidhof:

Yeah.

Dr. Bill Cardoso:

So XRF is also used for counterfeit detection, right? Mostly for leaded and lead-free components. So if you buy a component and it’s a new spec as leaded part and you use your XRF and you figure out that it’s lead-free, pins are lead free, all the solder is lead-free, then you know that you have discrepancy there that you have to look at, right. So XRF is one of the tools in toolbox to help you find counterfeit components, right. X-ray imaging for, there’s a bunch of different things you can use X-ray imaging for, counterfeit detection. But for the most part, you look at internal construction of each component and figured out if the are what they should be. Sometimes there’s something in there. An XRF is to look for the composition, right. So you have to understand, and you can even do some of the plastic as well. If you know what the plastics made of.

David Kruidhof:

Nice. Yeah. So like I said, we’re going to get through more than two questions today. So I got to ask some yes or no questions. Oh, yeah, so we’ve got about two minutes left, but Bill, you mentioned backscatter X-ray as well. I know that’s used for inspection, obviously different than XRF and transmission X-ray. Do you have a one minute further explanation of backscatter for our attendees?

Dr. Bill Cardoso:

Yeah. I think the X-ray backscatter X-rays that TSA at the airports used to use, they don’t use it anymore, now it’s all my microwave, the X-ray, because of health concerns and we’re not going to get into the politics of it right now, but they were banned from the airport here in US. But that is reflection. So you basically blast the sample with X-rays. What you do is usually it’s got a very narrow beam, so you collimate and you have a spinning X-ray source, if you will, that goes through the sample and you look at the backscatter energy of each one of those points and you should collect a bunch of those points. You’ll build an image. But again, it’s very, very powerful system for Homeland Security, for cargo inspection and for looking for concealed guns or bombs on the people’s body.

David Kruidhof:

Yeah. I think that those handheld devices are very common for, you said, border check, or just looking for drugs inside of bumpers of a car or something like that, right?

Dr. Bill Cardoso:

No, they don’t have a handheld backscatter X-ray.

David Kruidhof:

Oh, it’s not backscatter?

Dr. Bill Cardoso:

No.

David Kruidhof:

Okay. I guess that’s something else that I don’t know.

Dr. Glen Thomas:

Some of those backscatter X-ray systems are huge and especially car and vehicle based. They’re amazing. For an X-ray geek, they’re just amazing, right?

Dr. Bill Cardoso:

Yeah. When we were looking for a name for the X-ray van in the early 2000s, New York had an X-ray van, which was actually a backscatter system. You can park near a box truck, for example, and figure out what was in the cargo next to the inspection system. But it’s a truck, it’s a van. It’s not a smaller system.

David Kruidhof:

Okay. I’ll have to go do my homework on that one then.

Dr. Bill Cardoso:

Can we talk for next week or-

David Kruidhof:

There you go.

Dr. Bill Cardoso:

… Next time.

David Kruidhof:

Next time. All right. Well, it is 10:30. So thank you all for joining us. As Bill alluded to, we’re going to start doing these every other week. So we won’t have one next week, but we will have one on the following Wednesday, which is August 12th. So look forward to-

Dr. Bill Cardoso:

No, you were right. The have regular… They have the backscattered… Do they have handheld backscatter? I’m trying to remember, because I’ve seen the through ones. Oh, we’ll talk next time or we’re going to start a whole new hour of conversation here.

David Kruidhof:

They are handheld for inspecting that way. Maybe it’s not backscatter though, but yeah, I guess that I’ll look into it.

Dr. Bill Cardoso:

Yeah. I’m trying to remember exactly what is technology use?

David Kruidhof:

Okay.

Dr. Glen Thomas:

It moves pretty quickly. Technology and X-ray.

David Kruidhof:

All right.

Dr. Bill Cardoso:

All right, till next time.

David Kruidhof:

So for next time.

Dr. Bill Cardoso:

Bye.

David Kruidhof:

Thanks Glen. Thanks Bill

Dr. Bill Cardoso:

You too, bye-bye.

Dr. Glen Thomas:

Take care.