Havar® Foil (Light Tight)

Light-tight Havar® foil is produced at a thickness sufficient to block visible light completely while remaining thin enough to transmit particle beams, ionising radiation, or charged particles with minimal energy loss. This simultaneous optical opacity and radiation transparency is the defining requirement for cyclotron target entrance windows, particle detector windows, and alpha spectrometry windows — where the foil must seal the assembly against ambient light contamination while allowing the beam or radiation of interest to pass through with as little attenuation as possible.

Havar® (UNS R30004) is a precipitation-hardenable cobalt-chromium-nickel alloy with additions of tungsten, molybdenum, and manganese. Its unique value in beam window applications comes from the combination of properties that no single alternative material replicates: high tensile strength to withstand differential pressure across the window, radiation stability so performance does not degrade under sustained proton irradiation, extremely low outgassing compatible with ultra-high vacuum beam optics, and non-magnetic behaviour that avoids interference with beam transport systems. It is also the only thin foil material with a well-characterised nuclear activation cross-section dataset, making it usable simultaneously as a window and a beam monitor foil.

Havar® derives its high strength primarily through cold reduction. A minimum of 80% cold work must be applied before age hardening to develop peak tensile and fatigue properties — more intensive processing than Elgiloy® or Phynox® require. The foil is supplied cold-rolled, meaning it arrives at peak or near-peak strength and is ready either for immediate use or for age hardening as a final step. All cutting, profiling, and joining must be completed before any age hardening treatment is applied.

The scientific basis for Havar®'s use in cyclotron targets has been established through decades of published research. Cross-section measurements for proton-induced reactions on Havar® foils have confirmed that the nuclear activation products generated within the window itself are manageable and do not compromise target purity or personnel dose rates at typical production beam currents. Published thermal modelling has confirmed that Havar®'s combination of tensile strength and thermal conductivity is sufficient to prevent foil rupture under sustained high-current irradiation when adequate coolant flow is maintained on the downstream face. No other commercially available thin foil material offers this combination of validated radiation stability, mechanical performance, and beam monitor functionality.

Havar® foil is the established entrance window material for a broad range of PET and therapeutic isotope targets, including ¹⁸F (fluorodeoxyglucose production), ⁶⁴Cu and ⁶⁸Ga (PET imaging), ⁸⁹Zr (antibody labelling), and ²¹¹At (targeted alpha therapy). Its well-characterised stopping power and nuclear activation behaviour across the proton energy range relevant to medical cyclotrons (roughly 10–30 MeV) make it the reference material against which alternative window candidates are benchmarked.

Yes. Havar® has an extremely low outgassing rate, qualifying it for use in synchrotron beamlines, hermetic vacuum barriers, alpha spectrometry windows, time-of-flight mass spectrometry windows, and plasma physics chamber windows — all environments where outgassing from the window material would contaminate the vacuum or degrade analytical performance. Electron beam and laser welding are the preferred joining methods for vacuum-side assemblies because they offer precise heat input control and a minimal heat-affected zone, which is critical for maintaining the dimensional stability and mechanical integrity of foil at light-tight gauges.

Yes. Chemical milling and electrochemical machining (ECM) are applicable for complex or delicate geometries where mechanical contact must be avoided. These non-contact processes are particularly relevant for producing thin membranes, microstructured foils, or components with intricate internal features that cannot be achieved mechanically. Because they introduce no residual stress or edge work-hardening, they are well suited to Havar® at the thin gauges involved in light-tight applications.

Laser cutting is the preferred method for profiling light-tight foil into circular windows or custom shapes. It produces clean, burr-free edges with tight dimensional tolerances and a minimal heat-affected zone — important for maintaining mechanical properties at the gauge thicknesses used in beam windows. Both CO₂ and fibre laser systems are applicable depending on the thickness and geometry involved. For cold-rolled material before age hardening, precision blanking with hardened carbide tooling is also effective where geometry allows.

In cyclotron target service, beam heating raises the foil temperature significantly during irradiation. Havar® retains a substantial proportion of its room-temperature strength well above 400 °C — considerably better elevated-temperature performance than Elgiloy® or Phynox®, which are limited to around 315 °C. Its oxidation resistance in air extends to approximately 800 °C, due to the tungsten-stabilised chromia surface layer. For cryogenic applications such as detector windows in low-temperature physics experiments, Havar® is equally reliable, with dimensional stability confirmed down to cryogenic temperatures.

Havar®'s non-magnetic behaviour is intrinsic to its cobalt-chromium matrix and is retained throughout cold rolling and age hardening. This matters wherever the window is close to beam transport magnets, detector coils, or other magnetically sensitive components — ferromagnetic window materials would distort field homogeneity and affect beam optics or detector performance. It is also a requirement for MRI-compatible enclosures and sealed radiation source assemblies used in clinical environments.

Havar® offers significantly higher tensile strength than titanium or aluminium at comparable thicknesses. This allows a thinner window that reduces beam energy loss while maintaining the structural integrity needed to withstand pressurised target assemblies. Published comparisons confirm superior window lifetime for Havar® under the combined thermal stress and fatigue cycling of beam-on/beam-off operation in high-current cyclotron targets. Titanium and aluminium are lower atomic number and lower density, which means less stopping power per unit thickness, but neither offers the strength-to-thickness ratio that allows Havar® to operate reliably at the gauges needed for a light-tight window under high beam current conditions.

Yes. Custom thicknesses, cut dimensions, and laser-profiled circular or shaped windows can be produced to your drawing with no minimum order quantity. Request a quote with your diameter, thickness, and required condition and we will confirm availability and lead time.

Choose light-tight foil when the application specification requires complete optical opacity alongside particle beam or radiation transparency — cyclotron target entrance windows, particle detector windows, alpha spectrometry windows, and plasma physics chamber windows are the typical use cases. Standard Havar® foil covers a broader thickness range and is appropriate where light exclusion is not a requirement: pressure diaphragms, hermetic barriers, gap spacers, and spring stock.