X-Ray Phosphor Screens for Radiography
X-ray phosphor screens for radiography turn an invisible X-ray shadow into visible light. The X-rays coming out of the subject carry the whole image, but most detectors cannot make much of them until that radiation has been converted into light they are built to read. The screen does the converting, so a CCD or CMOS sensor, the same kind of chip that sits in a digital camera, can record the picture. Analytical Components makes these screens to order in St Leonards-on-Sea, East Sussex, coating every one in a Class 10,000 (ISO 7) cleanroom under an ISO 9001:2015 certified quality system.
Send us a drawing and an energy range and we will come back with a coating recommendation. Call +44 (0) 1424 850004 or use our contact form.
How a radiographic image is formed
Radiography works by shadow. X-rays pass through the subject, and dense material absorbs more of them than light material does. What comes out the other side is a pattern of strong and weak radiation that maps the structure inside. That pattern is the image, but it is written in radiation, and it has to be turned into something a camera can see.
That is the screen’s job. A phosphor screen is a thin, even layer of phosphor coated onto a base, usually glass or metal, and the base is what we call the substrate. When an X-ray photon hits the coating, the phosphor absorbs its energy and gives it straight back out as visible light, brightest where the most radiation arrives. Nothing further down the chain can recover detail the screen has already lost, which is why its evenness and its light output set a ceiling on what the rest of the system can do.
What radiography asks of a screen that other techniques do not
Radiography usually images a whole object in a single exposure, whether that is a chest, a horse’s fetlock, a turbine casting or a suitcase. That has two consequences for the screen.
The first is field size. A small sensor screen only has to be even across a few square centimetres. A radiographic screen may have to hold the same coating thickness and the same light output right across a much bigger area. Uneven coating shows up as a bright or dark region in the raw image, and while detector calibration is designed to correct for exactly that, the more the screen leaves for calibration to fix, the less headroom you have everywhere else.
The second is the sheer spread of energies involved. Radiography runs from the relatively low energies used for extremity and dental work up to the very high energies needed to get through thick metal sections. No single phosphor covers all of that well, which is why we ask about the energy range of your system before recommending anything.
Matching the phosphor to your radiographic energy range
The established phosphor for X-ray work is gadolinium oxysulfide, written Gd₂O₂S and also called Gadox, GOS or P43. It converts a high proportion of the radiation it absorbs into light, its behaviour is well documented, and the light it gives off sits at the wavelengths silicon detectors read best. Gadox is doped with a trace of a second element called an activator, and that element decides what colour the screen glows and how quickly it stops. We supply all three:
- Gadox: Tb for hard X-rays. Its emission peaks at 545nm, in the green part of the spectrum, and spreads across 382 to 622nm, which maps well onto standard silicon detectors. It is the usual choice for lower frame rate radiography, where resolution and light output matter more than speed, and it coats evenly and cost-effectively.
- Gadox: Pr for ultra-high speed imaging and backscatter detection, where the detector reads X-rays bounced back off the subject rather than passed through it. It stops glowing faster, which is what stops one frame smearing into the next.
- Gadox: Eu for extremely high energy X-rays, where getting through the subject at all is the governing requirement.
We are also very experienced with P22G, P46 and P47, and we are happy to discuss other phosphor types. You might need a different emission wavelength, or a different decay time, which is the term for how quickly a screen stops glowing once the radiation stops. If you want the background theory first, our guide to what X-ray scintillators are covers it without the jargon.
Resolution against brightness
Two more things shape how a screen behaves, and each one is a trade-off you cannot design your way out of.
Start with particle size. We can supply phosphor with a particle size anywhere from 1.5µm to 25µm. Smaller particles scatter less light sideways, so the image comes out sharper. That is what you want for fine detail. Larger particles give more light out for the same radiation in, which matters when brightness or keeping the dose down comes first.
Then there is coating thickness, which we can take from a few microns up to a few hundred. A thicker layer stops more X-rays and gives a brighter image, but light made deep in the coating spreads sideways before it escapes, so the picture goes softer. There is no universally right answer. It depends on what your detector can read and what the radiograph has to show, and it is a conversation worth having at the design stage rather than after the first prototype. Our guide to choosing the right phosphor screen for your application works through the same decisions in more detail.
Undercoats, overlays and protective finishes
The phosphor layer is rarely the whole screen. The layers around it do real work of their own.
An ITO undercoat, indium tin oxide, goes onto substrates that do not conduct electricity, such as float glass and fibre optic plates. It conducts while staying optically transparent, so you get an electrical connection between the screen and the instrument without a meaningful light penalty.
An aluminium overlay sits on top of the phosphor. It makes the screen conductive, and it catches light that would otherwise escape out of the front face and turns it back down through the phosphor towards the detector. It also keeps ambient light from reaching the phosphor from outside, so less of what your sensor reads is stray signal.
A potassium silicate coating, the process usually called waterglass, is there for screens that have to survive handling. Phosphor coatings are damaged by the lightest touch, and a screen a service engineer can reach is a screen that will eventually be touched. If that is your situation, it is worth specifying at the start rather than discovering it in the field.
Substrates for radiographic equipment
The substrate is normally decided by how the screen mounts and what it feeds. We coat Gadox onto:
- Float glass and other glass types
- Fibre Optic Plates (FOP), usually specified where the phosphor layer has to couple directly to a sensor
- Stainless steel, copper and aluminium
- Silicon
- Mylar, where the design needs to flex
- Direct coatings onto the cathode of vacuum tubes
If none of those quite fits your form factor, tell us anyway. We have added coating methods steadily over the years, and a substrate that looks awkward on paper is often workable in practice.
Where our X-ray screens end up
Screens we have already supplied are working in:
- industrial radiography of large objects
- X-ray cabinets for postal screening
- Dual energy computed tomography
- Ultra-high speed imaging and backscatter detectors, using Gadox: Pr
- Electron beam detection in scanning and transmission electron microscopes
Sector by sector, we have separate pages on screens for medical imaging, hospitals, security screening, industrial inspection and imaging cameras. Full technical detail for every option is on our phosphor screen scintillators page, and the whole range is on our products page.
What working with us looks like
We are a small team, so when you ring up with a question about why a batch came out the way it did, you get someone who understands the coating process rather than a sales filter. We take on volume production runs and single bespoke pieces, and a good deal of our work starts as a prototype.
Site visits are welcome, and we would encourage one before you commit to a production run. We work under NDAs where a project needs it, and there is more on how we work on our about us page.
To be clear about scope, we make the component, not the finished instrument. We supply the manufacturers and integrators who build radiographic equipment, rather than selling individual screens to the people who operate it.
Frequently Asked Questions
Which Gadox variant suits high-speed radiography?
Gadox: Pr. It stops glowing faster than the other variants, which is what allows ultra-high speed imaging and backscatter detection without one frame smearing into the next. For standard, lower frame rate radiography, Gadox: Tb gives better resolution and light output, and Gadox: Eu is for the very high energies used to get through thick sections.
Does a thicker phosphor coating always give a better radiograph?
No, and this is the trade-off most worth understanding before you specify. A thicker layer stops more X-rays and gives a brighter image, but light made deep in the coating spreads sideways before it escapes, so the picture goes softer. We coat from a few microns to a few hundred, and we would want to see your detector specification before suggesting a number.
Can you coat screens for large-format radiography?
Send us the dimensions and we will confirm what is achievable. Screens are made to your drawing rather than to a standard catalogue size, so the honest answer depends on the format and the substrate rather than on a fixed maximum we could quote here.
Do you supply replacement screens for existing radiography machines?
No. We make phosphor screens as components to be built into equipment at the point of manufacture. If you operate a radiographic system and need a replacement part, your equipment supplier is the right first call, because they hold the specification for that device.
Next steps
If you are specifying X-ray phosphor screens for radiography, the most useful things to send us are the energy range, the substrate and the dimensions, plus whatever you know about the detector sitting behind the screen. We will come back with a coating recommendation and a quote. If you are early enough that the specification is still moving, that is a better time to talk to us, not a worse one. Fill in our contact form, email info@analyticalcomponents.uk, or call +44 (0) 1424 850004 and speak to someone who understands the coating process.
X-ray phosphor screens are vital for enhancing image quality across various applications. In medical imaging, dental imaging, and veterinary imaging, they provide clear, detailed visuals for accurate diagnostics. These screens are also essential for security screening, ensuring reliable detection. In industrial inspection, they help maintain product integrity and safety. Additionally, X-ray phosphor screens improve performance in imaging cameras, supporting high-quality imaging in diverse settings.