CZT: the wonder material behind faster scans and sharper detectors

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Cadmium zinc telluride (CZT) is one of those materials that sounds like a chemistry-class footnote — until you see what it enables. In the BBC’s reporting, CZT sits at the centre of a quiet shift in medical imaging and radiation detection: faster scans, lower doses, and more information captured per photon.

The catch is that CZT is hard to make at scale. That scarcity is becoming a real constraint as hospitals, airports, and research labs all want the same thing: detectors that can “see” high‑energy radiation more precisely than older technology.

The medical imaging upgrade hiding inside a scanner

The BBC story opens with a patient experience detail that’s easy to overlook but important: time.

At Royal Brompton Hospital in London, some lung scans used to require patients to lie still — arms above their head — for 45 minutes. After the hospital installed a new scanner last year, those exams dropped to 15 minutes.

That improvement comes from two things working together:

  1. Better image processing in the scanner
  2. A detector material that captures the signal more efficiently: cadmium zinc telluride (CZT)

Dr Kshama Wechalekar, head of nuclear medicine and PET at Royal Brompton, calls the new images “beautiful” and describes the scanner as “an amazing feat of engineering and physics.”

This is not just about comfort. Shorter scans reduce motion blur (people inevitably fidget), increase throughput, and make advanced imaging easier to use for more patients.

Why CZT changes what “a detector” can do

Many people think of medical imaging as “a big machine takes a picture.” But for nuclear medicine and PET-like workflows, the core job is actually detecting invisible radiation and turning it into a usable map.

In the BBC report, the Royal Brompton scanner detects gamma rays emitted by a radioactive substance injected into the patient’s body. The scanner’s sensitivity has a direct clinical implication: less radioactive tracer is needed.

Dr Wechalekar says the team can reduce doses by about 30%.

That dose reduction is a big deal for two reasons:

  • It lowers patient exposure while keeping diagnostic quality.
  • It can reduce pressure on tracer supply chains (radioactive tracers have short half‑lives and are logistically complex).

So what’s special about CZT?

CZT is a semiconductor that can detect individual photons from X‑rays and gamma rays with very high precision. The BBC describes it as analogous to the silicon image sensor in a phone camera — but tuned for much higher-energy radiation.

When a high‑energy photon strikes CZT, it mobilises an electron, creating an electrical signal. That signal can be translated into an image.

Crucially, CZT can do this in a single conversion step (as explained by Kromek’s chief executive), which helps preserve more information — including the energy and timing of what hit the detector.

The manufacturing bottleneck: “like a server farm” of furnaces

If CZT is so useful, why isn’t it everywhere already?

Because it is extremely difficult to manufacture well.

The CZT used in Royal Brompton’s scanner was made by Kromek, a British company and one of only a handful of organisations globally that can supply the material. The company’s founding chief executive, Arnab Basu, explains that it took a long time for CZT to become an industrial-scale process.

At Kromek’s facility in Sedgefield, the BBC reports there are 170 small furnaces in one room — which Basu says looks “like a server farm.”

The production process is slow and unforgiving:

  • a special powder is heated in furnaces
  • it becomes molten
  • it is solidified into a single-crystal structure
  • the overall process can take weeks

Basu describes the crystal alignment process as “atom by atom,” with crystals rearranging so they become aligned.

That single‑crystal quality is the point: detectors need material that behaves consistently and predictably. Defects, impurities, or misalignment can ruin performance.

Beyond hospitals: airports, telescopes, and radiation detection

The BBC report makes clear that CZT is not a one‑industry material. It’s a platform ingredient that keeps turning up wherever you need to detect high-energy photons accurately.

Airports and security scanning

Basu says CZT-based scanners are currently used for explosives detection at UK airports, and for scanning checked baggage in some US airports.

He also adds a timeline that matters: Kromek expects CZT to move into hand luggage scanning “over the next [few] years.”

That suggests the technology is moving from specialised applications into higher‑throughput front-line screening — exactly where scale and reliability matter most.

Space and astronomy: X-rays from extreme objects

The story also introduces Henric Krawczynski at Washington University in St Louis, who has used CZT detectors on space telescopes attached to high altitude balloons.

Those detectors can pick up X‑rays emitted by:

  • neutron stars
  • plasma around black holes

Krawczynski wants very thin pieces of CZT — around 0.8mm — because thinner detectors can reduce background radiation pickup, leading to a cleaner signal.

He says he would like to buy 17 new detectors, but it has been difficult to obtain CZT in the thin form he needs.

The BBC reports he was unable to source the material from Kromek, with Basu noting that demand is high and research projects often need very particular detector structures.

Krawczynski says he may instead use CZT from previous work or an alternative material, cadmium telluride, for the next mission.

He also notes that mission schedules are in flux; it was due to fly from Antarctica in December, but timing has been affected by the US government shutdown.

Scarcity, in other words, hits both the physics and the project planning.

A second “big science” pull: Diamond Light Source

CZT is also tied to infrastructure-scale science.

The BBC notes that a major upgrade to the Diamond Light Source research facility in Oxfordshire — costing half a billion pounds — will improve its capabilities with CZT-based detectors.

Diamond Light Source is a synchrotron: it accelerates electrons around a ring at close to the speed of light, and magnets cause the electrons to shed energy in the form of X‑rays. Those X‑rays are routed down beamlines to study materials.

Some experiments have probed impurities in aluminium as it melts — work that could help improve recycled aluminium by understanding impurities better.

The facility’s upgrade is due to complete in 2030, and will produce X‑rays that are significantly brighter. Existing sensors would struggle, which is why CZT detectors matter.

Matt Veale, group leader for detector development at the Science and Technology Facilities Council (a stakeholder in Diamond), puts it bluntly: there’s no point upgrading the facility if you can’t detect the light it produces.

The strategic lesson: CZT is becoming a chokepoint material

The interesting thing about CZT isn’t only that it’s “amazing.” It’s that its production profile resembles other strategic tech materials:

  • hard to manufacture
  • requires specialised equipment
  • slow, high-yield processes matter
  • demand is growing across unrelated sectors

When a material becomes a chokepoint, you tend to see the same downstream effects:

  • prioritisation of high-margin or high-volume customers
  • research groups adapting designs to whatever they can source
  • pressure for more suppliers and more capacity
  • competition between public-good applications (medicine, research) and commercial ones (security scanning)

The BBC story hints at that tension without turning it into a morality play. Kromek says it supports many research organisations, but also that it’s difficult to do “a hundred different things” when every detector design is bespoke.

That’s the real constraint: CZT isn’t just scarce — it’s custom

Bottom line

CZT is a rare combination of “boring” and transformative: a semiconductor crystal that quietly upgrades imaging and detection wherever it’s installed. The BBC’s reporting shows the upside in concrete terms — a £1m scanner at Royal Brompton cutting lung scan time from 45 minutes to 15 and enabling about 30% lower tracer doses — and the downside too: a global supply bottleneck that forces hard choices about who gets the most advanced detectors, and when.

Sources

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