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Collimator

A collimator is a device that narrows a beam of particles or waves. In optics, it transforms diverging rays of light or other electromagnetic radiation from a point source into a parallel beam, thereby minimizing beam spread and enabling precise alignment for various applications.^[1] This function is typically achieved using a convex lens or curved mirror positioned such that the light source is at its focal point, producing rays that emerge parallel to the optical axis.^[2] The term originates from the Latin collimare, meaning "to aim," reflecting its role in directing beams accurately.^[3] Invented in the 1820s by English physicist Henry Kater for use in telescopes, the collimator was initially designed as a "floating collimator" for astronomical observations, serving to replace the plumb-line or level for precise alignment, marking an early advancement in practical astronomy.^[4] Over time, its design evolved to include adjustable apertures and reticles at the focal plane, allowing for the projection of images at optical infinity or the creation of convergent/divergent beams by varying the source position.^[1] Collimators are classified into types such as refractive (using lenses), reflective (using mirrors), single-element, and achromatic designs to correct for chromatic aberrations, with materials like high-density plastics or metals for specialized uses in radiation shielding.^[2] They find essential applications in astronomy for aligning telescopes, in spectroscopy for precise light measurement in instruments like spectrometers, in medical fields such as radiology and cancer radiotherapy to focus X-rays and limit patient exposure, and in laser systems for beam shaping in cutting tools and fiber optics.^[5] In particle physics and nuclear engineering, collimators also manage particle beams to protect equipment and reduce radiation hazards.^[6] These devices remain fundamental to optical engineering, ensuring high-fidelity beam control across scientific, industrial, and medical domains.

Fundamentals

Definition and Purpose

A collimator is an optical or mechanical device that filters a stream of rays or particles, such as light, X-rays, or neutrons, to produce a beam with minimal divergence, resulting in parallel rays or a narrow cone of radiation.^[1]^[5] The term originates from the Latin "collimare," meaning "to aim" or "to make parallel," reflecting its function of aligning divergent emissions into a directed output.^[7] This process ensures that the beam maintains coherence over distance, which is essential for applications involving electromagnetic waves or charged particles. The primary purpose of a collimator is to align and narrow beams for enhanced precision in scientific measurement, imaging, and therapeutic procedures. In optical systems, it reduces beam spread to improve resolution, as seen in telescopes where collimators produce parallel light paths for accurate celestial observations.^[8] In radiation contexts, collimators shield detectors from stray radiation by restricting photon paths, thereby minimizing background noise and improving signal quality in nuclear imaging.^[9] For therapy, such as in X-ray treatments, they limit exposure to targeted areas, reducing unnecessary radiation to surrounding tissues.^[10]

Basic Operating Principles

A collimator operates by selecting a subset of rays or particles emitted from a divergent point source that travel approximately parallel to a defined optical axis, thereby minimizing the angular spread of the output beam. Rays or particles from such a source naturally diverge due to their emission geometry, spreading out in a conical pattern; the collimator achieves parallelism through spatial filtering or redirection, effectively narrowing the beam's divergence angle. This process relies on the fundamental physics of propagation, where only those trajectories aligned within a narrow acceptance angle pass through, while off-axis components are absorbed, scattered, or deflected away.^[3]^[11]^[12] A key concept in collimation is the divergence angle \theta, which quantifies the beam's spread and is approximated geometrically as \theta \approx \frac{d}{L}, where d is the aperture diameter and L is the distance from the source to the aperture; smaller \theta indicates better collimation. In an ideal collimator with infinite L, \theta \to 0, producing perfectly parallel rays, though practical limits arise from finite dimensions and physical interactions. This approximation holds for small angles in geometric optics and particle beams, where the aperture acts as a selector for near-parallel paths.^[3]^[13]^[14] Collimators employ various mechanisms to achieve this narrowing, categorized by their interaction with the beam. Geometric collimation uses apertures or slits to absorb or scatter off-axis components, relying purely on spatial selection without altering the beam's direction. Refractive mechanisms, such as lenses, bend light rays through material interfaces to align them parallel, commonly applied to visible or infrared wavelengths. Reflective types utilize curved mirrors to redirect divergent rays into a parallel bundle, advantageous for high-power beams to avoid thermal damage in transmissive elements. Absorptive collimators, prevalent in radiation applications, employ dense materials like lead to attenuate non-parallel particles via photoelectric absorption or Compton scattering.^[3]^[15]^[11] The behavior of collimation differs between wave-like (e.g., light) and particle-like (e.g., photons, neutrons) propagation due to inherent physical limits. For waves, diffraction imposes a fundamental constraint, preventing perfect collimation; the output beam forms an Airy disk pattern, where the central spot size limits resolution to approximately $1.22 \lambda / D (with \lambda as wavelength and D as aperture diameter), causing unavoidable spreading even for ideal geometries. In contrast, for particles treated as classical trajectories, efficiency is governed by scattering cross-sections, which determine the probability of deflection within the collimator material; high cross-sections enhance absorption of off-axis particles but can introduce secondary scattering that degrades beam purity.^[16]^[17]^[11] Efficiency in collimators is evaluated through metrics that balance beam quality and throughput. The transmission rate measures the fraction of the input beam that passes through, often low (e.g., ~0.01% for gamma-ray collimators due to strict directional selection), reflecting the trade-off between collimation quality and intensity. A key performance metric is the collimation ratio L/D, where L is the collimator length and D the aperture diameter; higher values reduce the divergence angle \theta \approx D/L, indicating better collimation quality.^[18] These metrics guide design, with geometric efficiency further expressed as the ratio of detected events to source activity per unit area in extended sources.^[11]^[19]^[20]

Historical Development

Early Optical Collimators

The term "collimator" entered optics in the early 19th century, derived from the verb "collimate," stemming from a misreading of the Latin collineāre, meaning "to align in a straight line."^[7] The device's formal invention is credited to English physicist Henry Kater in 1825, who developed the floating collimator—a mechanism using a pivoted telescope to establish precise horizontal lines for astronomical instruments, replacing less accurate plumb lines.^[4] This innovation marked the transition from rudimentary alignment tools to dedicated optical systems for producing parallel light beams. Precursors to structured collimators appeared centuries earlier, with 11th-century Arab physicist Ibn al-Haytham (Alhazen) employing pinhole apertures in camera obscura experiments to demonstrate rectilinear light propagation, effectively collimating rays through a small opening to form inverted images.^[21] By the 17th century, Galileo's refracting telescopes incorporated simple apertures and convex lenses for sighting alignment, though without the parallel-beam focus of later designs; these early instruments relied on basic mechanical adjustments to direct light toward celestial objects. A pivotal advancement came in 1814 with Joseph von Fraunhofer's prism spectroscope, featuring a narrow adjustable slit that, paired with a distant light source or lens, served as an implicit collimator to deliver parallel rays onto a flint glass prism for dispersion analysis.^[22] Early optical collimators typically employed brass for durable tubes and adjustable apertures, providing mechanical stability, while optical glass formed slits and lenses to shape the beam.^[23] Refractive versions faced significant challenges from chromatic aberration, as varying refractive indices in glass caused different wavelengths to converge at distinct focal points, blurring spectral lines and reducing resolution in polychromatic sources.^[24] These foundational devices profoundly influenced scientific progress by facilitating accurate stellar positioning and enabling Fraunhofer's observation of over 570 dark absorption lines in sunlight—now known as Fraunhofer lines—revealing atomic signatures in solar and stellar atmospheres.^[25] Such capabilities underpinned advancements in spectroscopy, later extending collimation principles to radiation detection in the 20th century.

Evolution in Radiation Applications

The development of collimators for ionizing radiation began in the early 20th century, building on optical precedents to address the challenges of directing X-rays and radioactive emissions while minimizing exposure. In 1895, Wilhelm Conrad Röntgen employed lead shielding during his pioneering X-ray experiments to protect himself and focus observations, marking an initial step toward beam control mechanisms that evolved into formal collimators.^[26] By the 1910s, Marie Curie advanced radium therapy by supplying sources for treatments that utilized lead boxes with apertures to direct emissions toward targeted tissues, such as in early brachytherapy applications at institutions like Memorial Hospital.^[27] These rudimentary shielded applicators represented the first structured efforts to collimate radiation for therapeutic precision, reducing scatter and protecting surrounding areas.^[28] Mid-20th-century progress accelerated during and after World War II, driven by nuclear research needs. The Manhattan Project in the 1940s spurred innovations in gamma ray handling, including high-density materials for shielding and beam direction in experimental setups, though specific collimator designs remained classified. Post-war, neutron collimators emerged in reactor-based experiments at facilities like Oak Ridge National Laboratory, where the Graphite Reactor enabled initial neutron scattering studies in the late 1940s, requiring collimation to produce directed beams for diffraction analysis. These early neutron systems, often using lead or graphite channels, laid the groundwork for controlled beam extraction from reactors, supporting both scientific and industrial applications.^[29] Key milestones in the 1950s and 1960s further refined collimation for clinical use. The invention and patenting of the first multileaf collimator (MLC) occurred in 1959, allowing adjustable tungsten leaves to shape radiation fields in linear accelerators and enabling conformal therapy for irregular tumor geometries.^[30] This innovation, building on earlier conformation concepts by Takahashi in the 1950s, transitioned from manual blocks to mechanized systems. Concurrently, the International Atomic Energy Agency (IAEA) established foundational standards in its 1967 Basic Safety Standards for Radiation Protection, which mandated collimation techniques to limit stray radiation and ensure safe beam confinement in medical and industrial settings. From the 1970s onward, collimation shifted toward precision and dynamism, influenced by computing advancements. Static lead blocks gave way to computer-controlled dynamic systems, such as the tracking cobalt unit developed at the Royal Free Hospital and similar linac implementations at Massachusetts General Hospital, which adjusted beam shapes in real-time for improved dose conformity.^[30] This evolution, propelled by early intensity modulation ideas, enhanced therapeutic accuracy while adhering to IAEA protection guidelines, setting the stage for modern radiation delivery.

Optical Collimators

Design and Construction

Optical collimators are engineered to produce beams of parallel light rays from divergent sources, primarily through refractive or reflective optical elements. The core components include an objective lens or pinhole aperture that captures and focuses incoming light, a focal plane where the light source or pinhole is positioned to ensure parallelism, and an exit slit or aperture that defines the beam's shape and size.^[31]^[23] In many designs, achromatic doublets—comprising a convex crown glass lens and a concave flint glass lens—are integrated as the objective to correct chromatic aberrations, maintaining focus across a range of wavelengths by balancing dispersions based on Abbe numbers.^[32] Materials selection is critical for performance in specific spectral ranges; for visible light collimators, N-BK7 borosilicate crown glass is commonly used due to its low dispersion and high homogeneity, enabling precise refractive elements with refractive indices around 1.517.^[33] For ultraviolet or infrared applications, aluminum-coated mirrors serve as reflective alternatives to minimize chromatic issues, offering high reflectivity (>90%) while avoiding absorption in glass.^[34] Compact designs often incorporate fiber optic collimators, where graded-index or aspheric lenses couple light from optical fibers, reducing size and alignment complexity in integrated systems.^[31] Configurations vary to suit applications, with parallel beam setups—such as telecentric designs—ensuring rays remain perpendicular to the image plane for distortion-free imaging, achieved by placing the aperture at the lens's focal point.^[31] Converging configurations, in contrast, allow slight beam focus for coupling into subsequent optics, while adjustable iris diaphragms enable variable aperture control to optimize beam diameter and flux without redesign.^[35] Fabrication demands high precision to achieve low divergence; slits and apertures are produced via diamond-tipped precision grinding, attaining tolerances below 1 μm to prevent beam asymmetry.^[36] Anti-reflective coatings, typically multi-layer dielectric stacks, are applied to lens surfaces to exceed 95% transmission efficiency, reducing losses from Fresnel reflections in broadband systems.^[37] Key challenges in multi-element collimators include minimizing vignetting, where off-axis rays are clipped by apertures, leading to uneven illumination—addressed through optimized lens spacing and field stops.^[38] Ghosting from internal reflections in uncoated or poorly coated interfaces can introduce stray light artifacts, mitigated by high-quality AR coatings and tilted element orientations to deflect ghosts away from the beam path.^[39]

Applications in Imaging and Instrumentation

Optical collimators play a crucial role in telescopes by producing parallel light beams that enable precise alignment and infinity focus in eyepiece systems. In reflecting telescopes, collimators ensure that light rays from distant celestial objects remain parallel after reflection, facilitating sharp imaging without distortion. For instance, the Hubble Space Telescope employs specialized collimation optics in its alignment mechanisms to maintain the integrity of incoming starlight across its primary mirror, compensating for any spherical aberrations during pre- and post-servicing adjustments.^[40] Similarly, in microscopes, infinity-corrected optical systems use collimators to generate parallel beams from the objective lens, allowing intermediate components like prisms or filters to be inserted without altering focus, which is essential for high-resolution imaging of specimens at infinity conjugate.^[41] In spectroscopy and laser applications, collimators narrow divergent laser outputs into parallel beams, enhancing precision in interferometric setups. This collimation is vital for maintaining beam coherence over long paths, as seen in laser interferometry where reduced divergence minimizes phase errors and improves measurement accuracy. In Fabry-Pérot etalons, used for high-resolution wavelength selection in spectroscopic instruments, collimated input beams ensure uniform interference patterns across the etalon's parallel surfaces, enabling narrowband filtering with finesse values exceeding 100 in many configurations.^[42]^[34] Alignment tools such as laser levels and surveying instruments rely on optical collimators to project straight, parallel reference lines over extended distances. In laser levels, collimators transform the laser diode's output into a low-divergence beam, achieving horizontal or vertical alignments with errors below 0.2 mm/m in construction and surveying tasks. Automotive headlight systems incorporate collimator lenses to shape LED or halogen sources into uniform, parallel beams that provide consistent road illumination while complying with safety regulations like ECE standards for beam spread.^[31]^[43] In industrial settings, optical collimators enhance machine vision systems for defect detection by delivering uniform, collimated illumination that reduces shadows and glare on inspected surfaces. For example, telecentric collimators in vision setups project parallel light rays, enabling accurate edge detection and surface profiling with sub-pixel resolution in automated quality control. Barcode scanners utilize slit collimators to focus laser beams into narrow lines that scan codes efficiently, achieving read rates over 99% even on curved or damaged surfaces by maintaining beam uniformity across the scan field.^[44] Performance metrics for optical collimators emphasize beam uniformity and minimal divergence to ensure reliable applications. High-quality collimators achieve beam uniformity greater than 95% across the output aperture, minimizing intensity variations that could degrade imaging quality. Spot size reduction is typically to under 0.1 mm at the focus, while divergence angles are controlled to less than 1 mrad full angle, allowing beams to propagate over meters with negligible spread.^[31]^[45]

Radiation Collimators

Types for X-rays, Gamma Rays, and Neutrons

Collimators for X-rays, gamma rays, and neutrons are designed to account for the distinct interaction mechanisms and penetration depths of these ionizing radiations, primarily relying on absorption and geometric constraints rather than refraction. High-density materials like tungsten or lead are favored for X-rays and gamma rays due to their high atomic numbers, which enhance photoelectric absorption, while neutron collimators use materials with high neutron capture cross-sections such as boron or cadmium. These designs prioritize directional selection through apertures or channels, with efficiency governed by factors like hole geometry and material attenuation properties.^[46] X-ray collimators typically employ diverging cone configurations to match the natural spread of the beam from the source, often lined with copper or tungsten to minimize scatter and achieve precise beam shaping. The conical structure allows the beam to expand proportionally with distance, preventing unnecessary exposure outside the target area. For applications requiring parallel beams, such as in X-ray crystallography, Soller slits are utilized; these consist of closely spaced parallel foils or plates that restrict axial divergence while permitting transmission along the desired direction.^[47]^[48] Gamma-ray collimators are categorized into parallel-hole, pinhole, and cone-beam types, each optimized for specific energy ranges and source geometries using lead as the primary absorber due to its high density (11.34 g/cm³) and attenuation coefficient. Parallel-hole collimators feature hexagonal arrays of straight channels in lead, enabling uniform projection imaging by allowing only near-perpendicular gamma rays to pass, with typical hole diameters of 1-3 mm and lengths of 20-50 mm. In contrast, pinhole collimators use a single aperture (often 1-5 mm diameter) in a thick lead shield to form inverted magnified images, suitable for compact sources. Cone-beam variants extend parallel-hole designs with tapered channels to accommodate diverging sources, improving field coverage in rotational imaging setups.^[49]^[46]^[50] Neutron collimators leverage absorbers with high thermal neutron capture cross-sections, such as boron-10 in boron carbide (B₄C) or cadmium, arranged in layered or channeled structures to define beam direction in reactor environments. These materials effectively attenuate neutrons via (n,α) reactions in B₄C or (n,γ) in Cd, with B₄C preferred for its lower gamma production and mechanical stability. For cold neutrons (energies < 5 meV), mechanical velocity selectors, such as rotating choppers or helical rotors, monochromatize the beam by filtering neutrons based on velocity using time-of-flight principles.^[51]^[52] Design differences across these collimators stem from radiation-specific attenuation coefficients and geometric efficiencies. For gamma rays, lead's linear attenuation coefficient μ is approximately 62 cm⁻¹ at 100 keV, necessitating thicker septa (e.g., 0.2-0.5 mm) to minimize penetration compared to X-rays, where lower energies allow thinner linings. Geometric efficiency η, which quantifies the fraction of radiation passing through, is roughly proportional to (d/l)² for parallel-hole designs, where d is the hole diameter and l is the hole length, with more precise formulas incorporating septal thickness to balance resolution and throughput.^[53]^[54] Hybrid types, such as multi-leaf collimators (MLCs), integrate dynamic shaping capabilities using arrays of independently movable tungsten leaves (typically 5-10 cm long, 0.5-1 cm wide) to conformally adjust beam profiles in real-time, often combining parallel-hole principles with adaptive geometry for versatile radiation control.^[55]^[56]

Medical and Industrial Applications

In medical diagnostics, parallel-hole collimators are commonly employed in gamma cameras to acquire images of radioiodine uptake in the thyroid gland, enabling the assessment of thyroid function and detection of abnormalities such as nodules or cancer.^[57] These collimators consist of arrays of parallel channels that allow only photons traveling perpendicular to the detector to pass, improving spatial resolution for planar imaging of distributed radionuclides.^[58] For pediatric applications, pinhole collimators are preferred due to their ability to provide magnified images of small organs, such as the thyroid or heart, while facilitating dose reduction through higher sensitivity and shorter acquisition times compared to parallel-hole designs.^[59] This approach minimizes radiation exposure in children, who are more sensitive to ionizing radiation, by optimizing image quality at lower administered activities.^[60] In radiation therapy, multileaf collimators (MLCs) play a pivotal role in intensity-modulated radiation therapy (IMRT), where tungsten leaves dynamically shape the beam to conform high doses to irregular tumor volumes while sparing adjacent organs at risk, such as the spinal cord or lungs.^[61] This conformal delivery enhances tumor control probability and reduces toxicity by creating steep dose gradients, with thinner leaf widths (e.g., 5 mm or less) further improving conformity indices.^[62] For stereotactic radiosurgery, micro-collimators with leaf widths as small as 2.5 mm enable precise targeting of lesions under 1 cm in diameter, such as brain metastases, delivering ablative doses in single or few fractions while minimizing damage to surrounding healthy tissue.^[63] These systems, often integrated with linear accelerators, achieve sub-millimeter accuracy essential for hypofractionated treatments.^[64] Industrial applications of radiation collimators include non-destructive testing (NDT) for weld inspection, where X-ray collimators direct a focused beam to penetrate welds in pipelines or structures, revealing defects like cracks or porosity without disassembling components.^[65] This technique ensures structural integrity in critical infrastructure, with collimation limiting the beam to the weld area to enhance image contrast and reduce unnecessary exposure.^[66] In aerospace, neutron radiography employs collimators to shape thermal neutron beams for detecting material flaws, such as voids or inclusions in composite components or turbine blades, which are often invisible to X-rays due to similar attenuation coefficients.^[67] Collimators in these setups, typically made of cadmium or boron, define the beam geometry to achieve high-resolution images of hydrogen-rich defects like delaminations.^[68] Collimation is integral to safety standards in both medical and industrial settings, adhering to the ALARA (As Low As Reasonably Achievable) principle outlined by the U.S. Nuclear Regulatory Commission (NRC), which mandates techniques to minimize radiation exposure to workers and the public.^[69] By restricting the beam to the region of interest, collimators can reduce scatter dose by over 90% in radiographic procedures, thereby lowering overall patient and occupational exposure.^[70] NRC guidelines emphasize collimation as a primary control measure in NDT and therapy, integrated with shielding and distance to implement ALARA effectively.^[71] A notable case study involves the use of collimators in positron emission tomography (PET) scanners, particularly in hybrid systems, where pinhole or clustered designs augment electronic coincidence detection to improve spatial resolution for small-animal or preclinical imaging of metabolic processes.^[72] In these setups, physical collimation rejects non-coincident photons, enhancing the accuracy of annihilation event localization and enabling simultaneous PET/SPECT studies with reduced artifacts.^[73] This approach has been applied in oncology research to track tumor response, demonstrating up to twofold resolution gains over standard coincidence-only detection.^[74]

Performance Limitations and Spatial Resolution

Radiation collimators in single-photon emission computed tomography (SPECT) and similar applications face inherent limitations that impact overall system performance. One primary constraint is the penetration of photons through the collimator septa, particularly when using thin absorbers like lead for lower-energy photons, which reduces sensitivity by allowing off-axis radiation to reach the detector and degrade image contrast. For instance, septal penetration becomes more pronounced with insufficient septal thickness, leading to a loss of directional specificity and increased background counts that compromise quantitative accuracy. Additionally, geometric blurring arises from the finite size of the radiation source, where the projection of the source extent onto the detector plane introduces broadening in the point spread function, further limiting the ability to resolve fine details. Scatter and noise pose another significant challenge, as Compton scattering within the patient or surrounding materials produces lower-energy photons that contribute to background noise and reduce signal-to-noise ratio. This effect is exacerbated in collimators, where scattered photons can pass through the holes, increasing the overall background and blurring images. Shielding efficiency notably declines at photon energies above 1 MeV, where the probability of photoelectric absorption drops, allowing more penetration and scatter to occur despite thicker septa, thus necessitating specialized high-energy designs to maintain performance. Spatial resolution in parallel-hole collimators is quantitatively assessed using the full width at half maximum (FWHM) of the point spread function, approximated by the formula:

\text{FWHM} = d \left(1 + \frac{b}{a}\right) + t \left(\frac{L}{a}\right)

where d is the hole diameter, b is the source-to-collimator distance, a is the hole length, t is the effective source thickness contributing to blurring, and L is the total source-to-detector distance. This expression captures both the geometric contribution from hole geometry and the additional blurring from finite source size. A key trade-off exists between spatial resolution and sensitivity, with sensitivity S roughly proportional to $1/\text{FWHM}^2, meaning improvements in resolution (smaller FWHM) typically come at the expense of reduced photon detection efficiency, as narrower holes or longer lengths limit the solid angle acceptance. To mitigate these limitations, strategies include employing thicker materials such as tungsten or lead alloys to reduce septal penetration and scatter, though this increases weight and cost while potentially lowering sensitivity. Alternative approaches like coded aperture collimators can enhance resolution without the strict geometric constraints of parallel holes by using patterned masks for image reconstruction, offering better trade-offs in certain scenarios. Monte Carlo simulations are widely used for optimization, allowing detailed modeling of penetration, scatter, and resolution to iteratively design collimators that balance these factors. In clinical SPECT applications, such as myocardial perfusion imaging, typical spatial resolution ranges from 5-10 mm, highlighting the practical constraints even with optimized systems. These performance characteristics also influence collimator selection in radiation therapy for precise beam shaping, though imaging remains the primary focus.

Advanced and Specialized Collimators

Collimators in Particle Physics

In particle physics accelerators, collimators are essential for beam cleaning, where they intercept and remove halo particles—those oscillating at large amplitudes beyond the core beam—to protect downstream components such as superconducting magnets from damage. In the Large Hadron Collider (LHC) at CERN, the collimation system employs movable jaws constructed from materials like graphite, copper, or tungsten to achieve this, with primary collimators positioned close to the beam to scatter halo particles while secondary collimators absorb the resulting debris.^[75]^[76] This setup ensures that beam losses are localized and minimized, preventing quenching events in the superconducting circuits caused by excessive energy deposition.^[77] Collimation systems typically operate in a two-stage configuration: primary absorbers, often thin to promote scattering, increase the betatron amplitudes of halo particles, allowing secondary catchers—thicker jaws downstream—to efficiently capture them at optimal phase advances. For betatron cleaning, specialized crystal collimators using bent silicon crystals have been tested and implemented in the LHC, particularly for heavy-ion beams, to enhance halo deflection through channeling effects and improve overall cleaning performance.^[78]^[79] These multi-stage designs, including tertiary collimators for residual cleanup, are tailored to the accelerator's optics to constrain transverse particle motion effectively.^[80] Operating under high-luminosity conditions presents significant challenges, as intense beam interactions can lead to material degradation and thermal damage, potentially causing superconducting magnet quenches from localized losses exceeding 10^{-6} of the total beam intensity. Collimator jaws must exhibit high radiation hardness, with materials like molybdenum-graphite composites tested to withstand proton fluences of up to $2.8 \times 10^{18} protons/cm² without catastrophic failure, though ongoing upgrades address sublimation and mechanical robustness for the High-Luminosity LHC era.^[81] Prominent facilities employing these collimators include CERN's Super Proton Synchrotron (SPS), where they facilitate beam scraping for clean injection into the LHC and support antiproton production by managing halo in high-intensity proton beams incident on production targets. Similarly, at Fermilab's Tevatron collider, collimators were integral to beam scraping operations, using tungsten primary collimators to remove halo and maintain low backgrounds during proton-antiproton collisions.^[82]^[83] Performance benchmarks for these systems emphasize precision and reliability, achieving collimation efficiencies greater than 99.99% to localize over 99.9% of halo losses within the collimation regions, while jaw alignments are controlled to within 20-25 μm via beam-based procedures that monitor loss signals during incremental movements.^[78]^[84]

Emerging Technologies and Materials

Recent advancements in collimator design have leveraged liquid crystal technologies to enable adaptive optical systems capable of dynamic beam modulation. Liquid crystal spatial light modulators (SLMs) and Pancharatnam-Berry (PB) phase gratings facilitate beam steering and collimation in augmented reality (AR) and virtual reality (VR) displays by deflecting light with sub-millisecond response times, enhancing field-of-view through polarization multiplexing. These devices address vergence-accommodation conflicts by functioning as programmable lenses that map light to specific depths, improving wavefront correction in real-time optical applications.^[85] In radiation collimation, nanomaterials such as graphene-based nanocomposites have emerged as lightweight alternatives for shielding against gamma and X-ray radiation. These materials exhibit high attenuation coefficients due to their layered structure, enabling thinner shielding layers that maintain efficacy while reducing overall system weight. Similarly, carbon nanotube (CNT) arrays serve as collimators in vacuum ultraviolet applications, where vertically aligned CNT forests form channels that filter and direct beams with minimal scattering, offering robust performance in harsh environments like space. CNT-based shields protect electronics from radiation damage by strategically layering to preserve electrical properties under X-ray exposure, potentially enabling lighter spacecraft components.^[86]^[87]^[88] Computational integrations, particularly artificial intelligence (AI), have optimized multileaf collimator (MLC) trajectories in volumetric modulated arc therapy (VMAT) systems. Machine learning models predict fluence maps and MLC segments directly from patient data, reducing planning times from hours to minutes— for instance, from 110 minutes to 6.4 minutes in breast cancer cases—while ensuring conformal dose distributions. In neutron applications, 3D-printed boron carbide collimators enhance beam precision by enabling custom geometries that funnel neutrons to detectors with higher fidelity, as demonstrated in scattering experiments at facilities like Oak Ridge National Laboratory.^[89]^[90] Hybrid systems incorporating metamaterials and superconducting elements address sub-wavelength challenges across domains. Hyperbolic metamaterials (HMMs) enable subwavelength collimation in optics by coupling evanescent waves to propagating modes, achieving focusing beyond diffraction limits for applications in integrated photonics. For particle beams, superconducting magnets integrate with collimation systems to guide high-energy protons precisely, minimizing losses in accelerators like the Large Hadron Collider while supporting future high-luminosity upgrades. Machine learning further refines these hybrids by automating crystal collimator alignments, achieving over 95% precision in beam halo deflection at CERN.^[91]^[92]^[93] Looking ahead, trends emphasize machine learning for real-time collimator adjustments and sustainable materials. AI-driven models now optimize electromagnetic (EM) composite collimators under additive manufacturing constraints, tailoring wave propagation for efficient beam control. Recyclable composites, informed by automated biomateriomics platforms, promise eco-friendly alternatives to traditional heavy metals, reducing environmental impact in large-scale production. These developments collectively enhance collimator performance in multi-field applications, from medical imaging to space exploration.^[94]^[95]

References

[1]
Collimator - Definition and Applications - AZoOptics
A collimator is a device used for changing the direction of a light diverging from a point source into a parallel beam.<|control11|><|separator|>
[2]
What Does a Collimating Lens Do? - Shanghai Optics
Collimation optics is the process of aligning light beams in a parallel direction. A collimator that is used to narrow light beams in a parallel is called an ...
[3]
Beam Collimators - RP Photonics
The purpose of a beam collimator is essentially to transform a strongly diverging light beam into a collimated beam.
[4]
7 Facts About A Collimator - Warren Knight
Jan 17, 2022 · The first collimator was designed in the 1820s by English physicist Henry Kater. Kater's collimation design was known as a floating collimator, ...
[5]
https://warrenknight.com/7-facts-about-a-collimator/
[6]
COLLIMATE Definition & Meaning - Merriam-Webster
Oct 17, 2025 · Collimate comes from Latin collimāre, a misreading of the Latin word collineāre, meaning "to direct in a straight line." The erroneous collimāre ...
[7]
[PDF] Elementary Optical Systems Section 12 Objectives
Collimator. A collimator is a reversed objective. It creates a collimated beam from a source at the system front focal point, and the image of the source is ...
[8]
Medical Tungsten Shielding and Collimators - Wolfmet
In pre-molecular imaging a collimator is used to direct radiation emitted by the subject onto a detector, and to minimise the number of stray photons.
[9]
X-Ray Collimators: Purpose, Use and Technological Advances
Sep 9, 2024 · Reduced radiation exposure: By limiting the x-ray beam to the area of interest, collimators help minimise the patient's exposure to radiation.
[10]
The collimation system: defence against beam loss - CERN Courier
Aug 19, 2013 · As the closest elements to the circulating beams, the collimators provide passive machine protection against irregular fast losses and failures.
[11]
An active collimator system for a high-energy photon beam
Active collimators are designed to both collimate the tagged photon beam and suppress the background of secondary photons.Missing: passive | Show results with:passive
[12]
Collimator - an overview | ScienceDirect Topics
Rather than diverting the rays like a lens, the collimator forms an image by selecting only the rays traveling in (or nearly in) a specific direction, namely ...
[13]
Collimator Guide: How These Optical Devices Shape Light & Beams
Medical imaging systems rely on collimators to control radiation exposure and enhance image quality. These specialized devices play a vital role in diagnostic ...
[14]
Beam divergence - Schäfter+Kirchhoff GmbH
Beam divergence is the variation of beam diameter with distance. It depends on beam diameter at the collimator and wavelength. The formula is θ = 2λ/πØbeam.Missing: ≈ d/<|separator|>
[15]
Beam Focusing and Collimating - Newport
If we collimate the output from this source using a lens with focal length f, then the result will be a beam with a radius y2 = θ1f and divergence angle θ2 = y1 ...Missing: principle | Show results with:principle
[16]
Principle of Operation of Lens Collimation - Hyperion Optics
Nov 14, 2023 · The core principle of lens collimation is based on the phenomenon of light refraction. When light passes from one medium into another, its ...
[17]
https://www.hep.ph.ic.ac.uk/~hallg/UA9/Nuclear/Barlow_IPAC10.pdf
[18]
[PDF] Simulations of the LHC Collimation System
In this section we describe the scattering model of MER-. LIN, and present the differential cross sections relevant for proton scattering in a collimator.
[19]
A Simple Technique for Determining Basic Collimator Characteristics
The geometric efficiency, G, is an expression of the ratio of detected radioactivity to the amount of radioactivity contained in a unit area of an extended ...
[20]
Efficiency simulations for the beam collimation system of the Japan ...
Dec 18, 2008 · The collimation efficiency dependence on the aperture ratio. A value of 70% of the design component aperture size is almost comparable to size ...Missing: transmission | Show results with:transmission
[21]
VII. The description of a floating Collimator - Journals
Kater Henry. 1825VII. The description of a floating CollimatorPhil. Trans. R. Soc.115147–178http://doi.org/10.1098/rstl.1825.0009. Section. Abstract; Footnotes.Missing: invention | Show results with:invention
[22]
Ibn Al-Haytham: Father of Modern Optics - PMC - PubMed Central
He is known for the earliest use of the camera obscura and pinhole camera. As stated above, he contradicted Ptolemy's and Euclid's theory of vision that ...
[23]
Galileo and the Telescope | Modeling the Cosmos | Digital Collections
The story of Galileo's telescopic observations illustrates how a tool for seeing and collecting evidence can dramatically change our understanding of the cosmos ...Missing: collimators | Show results with:collimators
[24]
A Brief History of Spectral Analysis and Astrospectroscopy
He made such precise assessment possible when he invented a spectroscope in 1814. The light from the source passed through slits and was incident upon a flint ...
[25]
https://adsabs.harvard.edu/full/1987JBAA...97..339H
[26]
Chromatic Aberrations - Evident Scientific
Chromatic aberrations are wavelength-dependent artifacts that occur because the refractive index of every optical glass formulation varies with wavelength.
[27]
Joseph Fraunhofer (1787-1826) - NASA ADS
... collimator slit in front of the objective. He obtained a series of spectra and then discovered that closely ruled lines inscribed on a glass plate gave an ...
[28]
https://pmc.ncbi.nlm.nih.gov/articles/PMC5002019/
[29]
Hot Times in “Radium Hospital”: The History of Radium Therapy at ...
Sep 22, 2016 · Polish physicist Marie Curie and her husband, Pierre, discovered radium in 1898, refining it from pitchblende scooped from the Joachimsthal ...Missing: collimators | Show results with:collimators
[30]
The contribution of women to radiobiology: Marie Curie and beyond
In 1911, Marie Sklodowska-Curie was awarded her second Nobel Prize for the discovery of radium. Her pioneering work demonstrated that radiation is a powerful ...Missing: collimators | Show results with:collimators
[31]
A History of Neutron Scattering at ORNL
Jun 13, 2018 · Neutron scattering at ORNL began in the 1940s, with two facilities now operating. Wollan and Shull were pioneers, and the first neutron ...Missing: collimators | Show results with:collimators
[32]
P.R. Bell's Lead Collimator (early 1950s) | Museum of Radiation and ...
This lead collimator was donated by P. R. Bell who described it as the first one to be constructed for a medical scanner. Bell, who worked for most of his ...
[33]
[PDF] Historical perspective on IMRT - AAPM Summer School: June 2003
1959 Invention and patenting of the first multileaf collimator. 1960s Proimos developed gravity-oriented blocking and conformal field shaping. 1970s The Royal ...
[34]
Considerations in Collimation
### Summary of Design and Construction of Optical Collimators
[35]
Achromatic doublet design and optimization - Optics for Hire
Aug 26, 2024 · An achromatic doublet is a two-lens system (concave and convex) using flint and crown glass to reduce chromatic aberration by compensating ...Chromatic Aberration · Design Of Doublets · Correcting Chromatic...
[36]
Mounted Achromatic Doublets, AR Coated: 400 - 1100 nm - Thorlabs
These mounted achromatic doublets have AR coating for 400-1100 nm, multi-element design, threaded housing, and are optimized for 488, 707, and 1064 nm.Missing: fabrication techniques
[37]
Laser Diode Collimators - RP Photonics
These lenses convert divergent laser beams to well-collimated beams for use in laser scanning applications, laser material processing, and interferometry with ...Missing: converging | Show results with:converging
[38]
Adjustable Fiber Optic Collimators - Newport
Free delivery 30-day returnsOur adjustable fiber optic collimators allow the user to vary the beam for best collimation at the wavelength and the distance of interest.Missing: parallel telecentric converging
[39]
Precision Optical Polishing Techniques - Avantier Inc.
Transforming optical raw materials into functional components involves several steps: blank forming, rough grinding, fine grinding, polishing, and coating.Missing: slits | Show results with:slits
[40]
http://ui.adsabs.harvard.edu/abs/1994SPIE.2199..573H/abstract
[41]
[PDF] 19660010844.pdf - NASA Technical Reports Server
This form of vignetting can be eliminated by incorporating a field or Fresnel lens at the Focon input to bend the meridional ray from the lens along the axis ...Missing: challenges | Show results with:challenges
[42]
Ghost Images in Collimation Systems - LightTrans
The ghost image effects in a collimation lens system are investigated by checking the reflections between uncoated surfaces.Missing: challenges design vignetting element
[43]
Collimating the Hubble Space Telescope - NASA ADS
Abstract. Collimation techniques for the Hubble Space Telescope before and after the 1993 December servicing mission are discussed.Missing: microscopes | Show results with:microscopes
[44]
Infinity Optical Systems | Nikon's MicroscopyU
Infinity optical systems allow introduction of auxiliary components, such as differential interference contrast (DIC) prisms, polarizers, and epi-fluorescence ...
[45]
Etalons – Fabry--Pérot interferometer - RP Photonics
Etalons are monolithic interferometric devices containing two parallel reflecting surfaces. They can be used for wavelength tuning of lasers, for example.
[46]
LED collimator element for a vehicle headlight with a low-beam ...
The invention relates to a LED collimator element for a vehicle headlight with a low-beam function, which emits at least visible light of one color from at ...
[47]
https://myscope.training/XRD_Primary_optics
[48]
Collimated Beams - RP Photonics
Collimated beams are laser beams with weak divergence within some region of interest. This implies that they have a relatively large beam radius.
[49]
Review of SPECT collimator selection, optimization, and fabrication ...
This paper reviews methods for production, sensitivity maximization, and task-based optimization of collimation for both clinical and preclinical imaging ...Missing: transmission | Show results with:transmission
[50]
Primary optics - XRD - MyScope
The soller slits reduce the axial divergence of the X-ray beam to less than 6° (in some instruments even 4° or even 2°). Reducing the axial divergence will ...
[51]
[PDF] X-RAY POWDER DIFFRACTION - XRD for the analyst
This book is intended both for people new to the field of XRD analysis and for more experienced users to find new applications which might be helpful in daily ...
[52]
Scintillation Camera with Multichannel Collimators
Parallel-channel collimators with hexagonal arrays of round holes can be made by (a) drilling holes in a plate, (b) cementing together lengths of tubing, or (c) ...
[53]
Advances in Pinhole and Multi-Pinhole Collimators for Single ... - NIH
The purpose of this paper is to provide a review on recent researches in the pinhole and multi-pinhole collimators for SPECT imaging.
[54]
Characterization of plastic and boron carbide additive manufactured ...
Dec 5, 2017 · Neutron collimators are most often Soller collimators with a varying number of blades in the same frame to increase or decrease the collimation ...INTRODUCTION · ADDITIVE MANUFACTURED... · NEUTRON SCATTERING...
[55]
Focusing and imaging of cold neutrons with a permanent magnetic ...
Jan 10, 2020 · This paper reports the focusing and imaging properties of magnetic compound refractive lenses (MCRL) based on theoretical analysis and initial ...
[56]
X-Ray Mass Attenuation Coefficients - Lead - NIST
For lead, at 1.00000E-03 MeV, μ/ρ is 5.210E+03 cm²/g and μen/ρ is 5.197E+03 cm²/g. At 1.50000E-03 MeV, μ/ρ is 2.356E+03 cm²/g and μen/ρ is 2.344E+03 cm²/g.Missing: 100 | Show results with:100
[57]
[PDF] Imaging and detectors for medical physics Lecture 5: Gamma cameras
Collimator → geometric collimator efficiency. 2. Scintillator → ratio of 𝛾-rays recorded by the ... N = true count rate = number of scintillations / s. n ...
[58]
Optimizing leaf widths for a multileaf collimator - IOPscience
Apr 27, 2009 · The multileaf collimator (MLC) is becoming a standard accessory of modern linac in shaping radiation fields. However, for a given target ( ...
[59]
Delivery systems of intensity-modulated radiotherapy using ...
Abstract. Intensity-modulated radiotherapy (IMRT) using conventional multileaf collimators (MLCs) has gained much attention in the radiation therapy community.
[60]
Radioiodine Imaging for Differentiated Thyroid Cancer - PubMed
Summary: The first of the techniques is spot imaging of anatomical areas of interest using a gamma camera with a parallel-hole collimator. Spot images ...
[61]
Nuclear Medicine Instrumentation - StatPearls - NCBI Bookshelf
Nov 14, 2023 · Parallel hole collimators are the most frequently utilized type for gamma cameras. ... Imaging. J Med Phys. 2022 Jul-Sep;47(3):294-300 ...
[62]
Gamma Camera Imaging with Rotating Multi-Pinhole Collimator. A ...
May 12, 2021 · In this work, we propose and analyze a new concept of gamma ray imaging that corresponds to a gamma camera with a mobile collimator, ...
[63]
(PDF) Pediatric applications of pinhole magnification imaging
Aug 10, 2025 · This article reviews basic principles of pinhole magnification imaging and ways for optimizing image acquisition with this technique.
[64]
Dosimetric comparison using different multileaf collimeters in ...
Due to the significant anatomical variations inside the human bodies, it has always been a challenge to deal with the target conformity and organs at risk (OARs) ...
[65]
The effect of multi‐leaf collimator leaf width on VMAT treatment plan ...
Mar 13, 2025 · The prevailing understanding is that MLCs with thinner leaves provide a level of target conformity and organs at risk (OAR) sparing that is ...
[66]
On the Feasibility of Stereotactic Radiosurgery With 5.0 and 10.0 ...
Aug 7, 2019 · 5.0 and 10.0 mm MLC can be used in SRS/SRT for targets (PTV) diameter larger than 1 cm. For smaller targets, 2.5 mm MLC is clinically superior, 5.0 is ...
[67]
Commissioning of a micro multi-leaf collimator and planning system ...
Purpose: A computer controlled micro multi-leaf collimator, m3 mMLC, has been commissioned for conformal, fixed-field radiosurgery applications.
[68]
non-destructive testing (NDT) - Waygate Technologies - Baker Hughes
Radiographic testing (RT) is a non-destructive testing method using X-rays or gamma rays to examine internal structures of materials without causing damage. The ...
[69]
Collimator for a non-destructive testing device using gamma ...
The radiation emerging from the object to be inspected then impresses a radiographic film which, after chemical development, gives a negative image of the ...
[70]
A systematic review on neutron radiography: applications ...
Jul 28, 2025 · It has been very effective in imaging structural flaws, hydrogen entry, water retention, and corrosion in aerospace materials, fuel cells, ...
[71]
[PDF] APPLICATION OF NEUTRON RADIOGRAPHY IN AEROSPACE ...
In addition, some defects like cracks that might form during the material processing (casting, forging, machining and joining) could be visualized as marked in ...Missing: flaws | Show results with:flaws
[72]
ALARA - Nuclear Regulatory Commission
As defined in Title 10, Section 20.1003, of the Code of Federal Regulations (10 CFR 20.1003), ALARA is an acronym for "as low as (is) reasonably achievable," ...Missing: collimation | Show results with:collimation
[73]
[PDF] Effectiveness of Collimation for Reducing Patient Dose and Scatter ...
Apr 23, 2021 · The findings of this research showed a correlation between collimated field size and patient dose, as well as collimated field size and scatter.<|separator|>
[74]
Evidence on radiation dose reduction using rectangular collimation
Despite these, all 13 studies concluded that when using rectangular collimators, there was a reduction of radiation dose to the patient of at least 40%. The ...Missing: efficiency metrics transmission ratio
[75]
Enhanced PET resolution by combining pinhole collimation and ...
Oct 21, 2015 · A practical approach with clinical PET detectors is to combine multi-pinhole collimation with coincidence detection.
[76]
Performance Assessment of a Preclinical PET Scanner with Pinhole ...
Jun 5, 2014 · A recently developed preclinical PET system uses a clustered-pinhole collimator, enabling high-resolution, simultaneous imaging of PET and SPECT tracers.
[77]
Comparison of two small animal PET scanners: Pinhole collimation ...
Such a physical collimation technique strongly departs from traditional electronic collimation achieved via coincidence detection in PET.
[78]
[PDF] CHAPTER 18 BEAM CLEANING AND COLLIMATION SYSTEM
The possible options include consumable metallic collimators, a graphite material doped with copper, beryllium jaws, thick metallic coating and graphite jaws.
[79]
[PDF] Upgraded Control System for LHC Beam-Based Collimator Alignment
Each collimator installed for ring cleaning consists of two jaws, made of graphite, tungsten or copper, which have to be positioned around the beam at all ...
[80]
[PDF] COLLIMATORS AND CLEANING: COULD THIS LIMIT THE LHC ...
The LHC collimators are designed to restrict the me- chanical aperture in the machine and to capture (”clean”) the primary halo so that quenches of magnets are ...
[81]
[PDF] Lecture 4 - Collimation - U.S. Particle Accelerator School
Beam collimation is mandatory to reduce beam losses, protect components, and reduce radiation impact. It uses a primary and secondary collimator to increase ...
[82]
[PDF] Crystal collimation of heavy-ion beams at the Large Hadron Collider
May 1, 2025 · Ion fragments scattered out of the collimators in the betatron cleaning insertion risk quenching the cold dipole magnets downstream and may ...
[83]
[PDF] Radiation-induced Effects on LHC Collimator Materials ... - CERN
In this case, the MoGr samples experienced the effects of short- term proton irradiation (2.8 × 1018 p/cm2) and the effects of the neutron spectrum (3.2 × 1018 ...Missing: per | Show results with:per
[84]
[PDF] Collimation issues at the SPS and in the Transfer lines
Any beam-halo should be removed by beam cleaning before injection into the LHC to minimize the risk of quenches. For a quantitative estimate, we will assume ...
[85]
[PDF] Fermilab-Pub-11-378-APC August 2011 TEVATRON BEAM HALO ...
Over the next six and a half minutes collimators sequentially approach the beams and scrape them. The horizontal position of one of the collimators (D49H) is ...
[86]
[PDF] efficiency for the imperfect lhc collimation system
25 μm. Setting accuracy (prim) -1.0/+0.5 σ. Setting accuracy (sec). ≥ 소 0.5 σ and jaw surface (in terms of active jaw length). Further re- finements are ...
[87]
Advanced liquid crystal devices for augmented reality and virtual ...
May 30, 2022 · In this paper, we focus on advanced LC-based light engines and optical components for AR/VR applications.
[88]
Graphene-based nanocomposites as gamma- and X-ray radiation ...
Aug 16, 2024 · A recent review article discussed the topic of carbon-based (graphite, graphene oxide) materials for radiation shielding in X-ray and gamma ...
[89]
Carbon nanotube collimator as an vacuum ultraviolet window
Jun 13, 2024 · The CNT collimators are arrays of square channels of various dimensions and height with sidewalls composed of vertically aligned CNT forests.
[90]
Carbon nanotubes help space-bound electronics resist radiation ...
Dec 9, 2021 · They found that placing the shields both above and below the CNTs protected the electrical properties of the FETs against incoming X-ray ...Missing: dot EUV lithography
[91]
Artificial intelligence applications in intensity modulated radiation ...
In this review, we will focus on the most studied AI approach in intensity modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT)—machine ...
[92]
ORNL's new 3D printed collimator improves neutron scattering
Apr 4, 2024 · Neutron collimators play a key role in neutron scattering, funneling the desired neutrons to a detector after they have interacted with sample ...
[93]
Hyperbolic Metamaterials for Collimation and Subwavelength ...
Feb 27, 2020 · The HMMs can couple evanescent waves with high wave vectors into propagating modes, and as a result, they provide subwavelength focusing.
[94]
Superconducting magnets and technologies for future colliders
In this paper we review the implications for accelerator magnet R&D towards future colliders. We give first a brief overview of the future accelerator ...<|separator|>
[95]
Machine learning based crystal collimator alignment optimization
Sep 24, 2024 · In the CERN Large Hadron Collider (LHC), bent crystals are used to efficiently deflect beam halo particles toward secondary collimators used ...Missing: composites | Show results with:composites
[96]
None
Nothing is retrieved...<|control11|><|separator|>
[97]
An automated biomateriomics platform for sustainable ... - NIH
We outline an automated system for the discovery and characterization of novel, sustainable, and functional materials from input biomass.