Kollimators

Kollimators are devices that restrict the direction of a beam of particles or radiation. By blocking off-axis rays, they transform a diffuse source into a beam with a defined angular acceptance, enabling more accurate imaging, measurement, and alignment. Collimation improves spatial resolution and reduces background, but it reduces signal intensity because many rays are absorbed in the process.

Types and mechanisms: In optical systems, kollimators use tubes, apertures, or lens assemblies to produce or select near-parallel rays for beam characterization or instrument alignment. In x-ray and gamma-ray instrumentation, common designs include parallel-hole, pinhole, and slit collimators. Neutron and other particle colliders use similar geometries with materials chosen for high attenuation. Each design trades off angular resolution, field of view, and photon or particle throughput.

Construction and materials: Kollimators are typically made from high-density metals such as lead, tungsten, or tantalum. The bore diameter, channel length, and pattern determine the angular acceptance and spatial resolution. Longer, narrower channels yield finer resolution but lower throughput. For different energy ranges, material choice and shielding are tailored to balance penetration, stray radiation, and heat load.

Applications and limitations: In medical imaging, parallel-hole collimators are used in gamma cameras and SPECT to map radiotracer distributions, while pinhole or high-resolution collimators suit small-region imaging. In astronomy and nuclear physics, kollimators define detector fields of view and suppress background. Limitations include added weight and bulk, substantial photon loss, and sensitivity to scattering and misalignment. They are selected to match the energy range and resolution requirements of the system.