Collimator Structure Research Articles

Collimation principles of a hollow X-ray microbeam for high-contrast cytoplasm irradiation.

A Monte Carlo simulation was used to assess the performance of a collimated hollow X-ray microbeam for subcellular cytoplasm irradiation. A high-Z coaxial collimation structure with an inner core for nucleus shielding was investigated. Two key performances, the extraction efficiency (cytoplasm dose per unit incident fluence) and the dose contrast (cytoplasm-to-nucleus dose ratio), were evaluated regarding the influences of the material, geometry and physical arrangements of the collimator, target dish and incident beam source. Simulation results demonstrate that a gold coaxial structure with a practical collimation geometry of a 1-mm length, 10-μm inner diameter and 200-μm outer diameter, with the top exit closely attached (with a minimized air gap) to the bottom of a cell dish with a 3-μm thick Mylar film is recommended for cytoplasm irradiation of adherent mammalian cells. For a synchrotron source in the energy range < 10keV, a dose contrast of approximately 100 can be achieved. For a bremsstrahlung source <30-kV tube voltage, a dose contrast of approximately 50-100 can still be achieved. General principles are summarized with further explanations of the performance of the hollow X-ray microbeam.

The effect of the tongue and groove of the multileaf collimator on dose distribution: examination of results of measurements and treatment planning system

Multileaf collimators play an important role in the field of radiotherapy and are widely used today. The effect of multileaf collimator structure on dose distribution should be well investigated and whether treatment planning systems reflect these effects on dose distribution should be examined. In our study, we examined the effect of tongue-and-groove on irregular fields and intensity-modulated radiotherapy plan. We also investigated the depth dependence of the tongue-and-groove effect. All fields are created in RayStation treatment planning system. Data obtained from treatment planning systems were compared with data obtained with 2-dimensional dose-measuring devices. We found the tongue-and-groove effect consistent in both measurements in single field measurements. We calculated dose reductions due to tongue-and-groove effect between 6% and 14%. When we examined the tongue-and-groove effect at different depths, we observed that the tongue-and-groove effect decreased as the depth increased. Although the tongue-and-groove effect did not create significant results on the dose distribution in multi-field use, we observed that this effect could occur at the edge of the field. Dose differences due to multileaf collimator structure should be examined by clinics. In addition, the extent to which treatment planning system takes these effects into account should be checked with some measurements. Otherwise, undesirable dose differences may be seen in the patient.

Development of a diverging collimator for environmental radiation monitoring in the industrial fields

Environmental radiation monitoring is required to protect from the effects of radiation in industrial fields such as nuclear power plant (NPP) monitoring, and various gamma camera systems are being developed. The purpose of this study is to optimize parameters of a diverging collimator composed of pure tungsten for compactness and lightness through Monte Carlo simulation. We conducted the performance evaluation based on spatial resolution and signal-to-noise ratio for point source and obtained gamma images and profiles. As a result, optimization was determined at a collimator height of 60.0 mm, a hole size of 1.5 mm, and a septal thickness of 1.0 mm. Also, the full-width-at-half-maximum was 3.5 mm and the signal-to-noise ratio was 53.5. This study proposes a compact 45° diverging collimator structure that can quickly and accurately identify the location of the source for radiation monitoring.

Improved Design and Thermo-Mechanical Verification of Deflection Magnet Beam Collimator of EAST-NBI System

The deflection magnet (DM) is the most important component of the Neutral Beam Injection (NBI) system of Experimental Advanced Superconducting Tokamak (EAST), which can magnetically deflect the un-neutralized charged particles after the neutralized process of the beam is extracted from the ion source, and then form a neutral beam injected into the tokamak. Under the operating conditions of the NBI system, by using the thermocouple monitoring system in the experiment, it can be found that the currently operating DM beam collimator has a quite high temperature rise. It is necessary to redesign the DM beam collimator to improve its heat transfer performance. The parallel arrangement of multiple rows of tubes is proposed as the basic method for the redesign of the beam collimator of DM, the thermal-fluid-structure analysis model of this redesign model is established and its temperature field, pressure field and stress field are analyzed. Taking the surface temperature of the beam collimator, the overall dimension after the total tube combination and the pressure drop of the whole structure of collimator as the optimization objectives, and setting the fluid velocity, the tube’s inner diameter and the number of tube rows as the design variables, the optimized design scheme of the beam collimator structure is obtained. From the results of simulation, the new structure can better meet the operation requirements of DM, and its maximum temperature rise is well controlled, which is expected to meet the long pulse operation requirements of the NBI system. The proposed simulation and design optimization method can provide a certain reference for the design and optimization of other high-heat-flux structures in complex large-scale neutral beam systems in the future.

A collimator design method for the tomographic gamma scanning system with a fan-shaped NaI(Tl) detector array

The detection speed of the tomographic gamma scanning (TGS) system with a detector array is faster than the single detector system. The NaI(Tl) detector is inexpensive and can work at room temperature, making it ideal for use in the TGS system with a fan-shaped detector array. The collimator of the TGS system is one of the critical elements to ensure the reconstructed image's quality. In addition to providing good detection efficiency of the detector while improving the system's spatial resolution, a proper collimator structure may also reduce cross-interference between segments. We propose a collimator design method for the TGS system with a fan-shaped NaI(Tl) detector array and combine it with the Monte Carlo method to optimize the collimator. We get the collimator aperture size and shape of the TGS system through the simulation results. Simultaneously, according to the detectors' equiangular sector arrangement limitation, we propose setting up a fan-shaped shield with adjustable depth and height at the detector collimator's front. The cross-interference between segments is effectively reduced without reducing the current segment's detection efficiency. The transmission image reconstruction shows that the collimator designed by this method can be used in the TGS system with the fan-shaped NaI(Tl) detector array.

High-endurance micro-engineered LaB6 nanowire electron source for high-resolution electron microscopy

The size tunability and chemical versatility of nanostructures enable electron sources of high brightness and temporal coherence, both of which are important characteristics for high-resolution electron microscopy1-3. Despite intensive research efforts in the field, so far, only conventional field emitters based on a bulk tungsten (W) needle have been able to yield atomic-resolution images. The absence of viable alternatives is in part caused by insufficient fabrication precision for nanostructured sources, which require an alignment precision of subdegree angular deviation of a nanometre-sized emission area with the macroscopic emitter axis4. To overcome this challenge, in this work we micro-engineered a LaB6 nanowire-based electron source that emitted a highly collimated electron beam with good lateral and angular alignment. We integrated a passive collimator structure into the support needle tip for the LaB6 nanowire emitter. The collimator formed an axially symmetric electric field around the emission tip of the nanowire. Furthermore, by means of micromanipulation, the support needle tip was bent to align the emitted electron beam with the emitter axis. After installation in an aberration-corrected transmission electron microscope, we characterized the performance of the electron source in a vacuum of 10-8 Pa and achieved atomic resolution in both broad-beam and probe-forming modes at 60 kV beam energy. The natural, unmonochromated 0.20 eV electron energy loss spectroscopy resolution, 20% probe-forming efficiency and 0.4% probe current peak-to-peak noise ratio paired with modest vacuum requirements make the LaB6 nanowire-based electron source an attractive alternative to the standard W-based sources for low-cost electron beam instruments.

7.1: Invited Paper: Establishment and Simulation Optimization of Optical Fingerprint Recognition Structure in LCD Screen

This paper reports a new type of liquid crystal screen which has an in‐screen optical fingerprint recognition collimation structure. The collimator structure in the TFT&amp;CF glass in the screen has different opening size and height. Through simulation, the SNR(Signal to Noise Ratio)&amp;CR(contrast ratio) evaluation criteria were obtained to judge the fingerprint identification accuracy of the collimating structure. Compared with the unoptimized structure, the optimized collimation layer improves the accuracy of fingerprint identification.

Measurement of absorbed dose rate in water phantom maintained at body temperature by 60Co irradiator – comparison of experimental results and Monte Carlo simulation

To analyze the biological effects of radiation, it is important that the conditions of in vitro experiments match closely with those of in vivo experiments. In this study, we constructed an irradiation system to conduct irradiation experiments under conditions similar to those of in vivo experiments. The Dongnam Institute of Radiological and Medial Sciences has a gamma irradiator including 60Co radioisotope for research purposes and accreditation for standard calibration of the ion chamber. The temperature of the water phantom was maintained the same as that of the normal human body, and the physical dosimetry was carried out accurately using the ion chamber with traceability. We report the measurement of lateral profiles, depth profiles, and absorbed dose rate in water, Dw, at the irradiation location of the blood samples using a farmer-type ion chamber. We simulated the source, collimator, irradiator, phantom, and extra structure of the gamma irradiation system using the Monte Carlo code and compared the simulated and the experimental results. The experimentally and theoretically evaluated dose rates were 0.2975 ? 0.0055 Gymin?1 (at coverage factor k = 2) and 0.2978 ? 0.0052 Gymin?1 (at coverage factor k = 2) at source-to-surface distance of 100 cm and 5 gcm?2 depth in the water phantom, respectively. Blood irradiation will be conducted in vitro, under conditions similar to in vivo conditions, to provide the dose-response curve based on dosimetry with traceability.

Conceptual design of a collimator for the neutron emission profile monitor in JT-60SA using Monte Carlo simulations.

Materials and structures of a collimator for a new neutron emission profile monitor in JT-60SA are examined through Monte Carlo simulations using the Monte Carlo N-Particle transport code. First, the shielding properties of various material combinations are compared in order to determine a combination with high shielding performances against both neutrons and gamma-rays. It is found that a collimator consisting of borated polyethylene and lead has a high shielding performance against neutrons. Moreover, a high shielding performance against gamma-rays is obtained when a lead pipe with a radial thickness of 0.01 m is inserted into a collimation tube. Second, we demonstrate that it is possible to improve the spatial resolution to a desired level by installing a thin tubular extension structure that fits into the limited space available between the main collimator block and the tokamak device. Finally, the collimator structures that meet both the targeted spatial resolutions (<10% of the plasma minor radius) and the targeted counting rate (105 cps order) are discussed.

Chandra Monitoring of the J1809–1917 Pulsar Wind Nebula and Its Field

Abstract PSR J1809–1917 is a young (τ = 51 kyr) and energetic ( erg s−1) radio pulsar powering an X-ray pulsar wind nebula (PWN) that exhibits morphological variability. We report on the results of a new monitoring campaign by the Chandra X-ray Observatory (Chandra), carried out across six epochs with a ∼7 week cadence. The compact nebula can be interpreted as a jet-dominated outflow along the pulsar’s spin axis. Its variability can be the result of Doppler boosting in the kinked jet, whose shape changes with time (akin to the Vela pulsar jet). The deep X-ray image, composed of 405 ks of new and 131 ks of archival Chandra data, reveals an arcminute-scale extended nebula (EN) whose axis of symmetry aligns with both the axis of the compact nebula and the direction toward the peak of the nearby TeV source HESS J1809–193. The EN’s morphology and extent suggest that the pulsar is likely moving through the ambient medium at a transonic velocity. We also resolved a faint 7′ long nonthermal collimated structure protruding from the PWN. It is possibly another instance of a “misaligned outflow” (also known as a “kinetic jet”) produced by high-energy particles escaping the PWN’s confinement and tracing the interstellar magnetic field lines. Finally, taking advantage of the 536 ks exposure, we analyzed the point sources in the J1809 field and classified them using multiwavelength data. None of the classified sources in the field can reasonably be expected to produce the extended TeV flux in the region, suggesting that PSR J1809–1917 is indeed the counterpart to HESS/eHWC J1809–193.

42‐2: Establishment and Simulation Optimization of Optical Fingerprint Recognition Structure in LCD Screen

This paper reports a new type of liquid crystal screen which has an in‐screen optical fingerprint recognition collimation structure. The collimator structure in the TFT&amp;CF glass in the screen has different opening size and height. Through simulation, the SNR( Signal to Noise Ratio )&amp;CR(contrast ratio) evaluation criteria were obtained to judge the fingerprint identification accuracy of the collimating structure .Compared with the unoptimized structure, the optimized collimation layer improves the accuracy of fingerprint identification.

Detection of voluminous gamma-ray source with a collimation beam geometry and comparison with peak efficiency calculations of EXVol

In this study, we expanded the performance of the existing EXVol code and performed empirical experiments and calculations. A high-resolution gamma spectroscopy system was constructed, and a standard point source and a standard volume source were measured with an HPGe detector with 43.1% relative efficiency. EXVol was verified by quantitative comparison of the detection efficiencies determined by measurements and calculations.To introduce the concept of the detector scanning that occurs in the actual measurement into the EXVol code, a collimator was placed between the source and detector. The detection efficiency was determined in the asymmetric arrangement of the source and detector with a collimator. A collimator made of lead with a diameter of 15 mm and a thickness of 50 mm was installed between the source and the detector to determine the detection efficiency at a specific location. The calculation result was contour plotted so that the distribution of detection efficiency could be visually confirmed. The relative deviation between the measurements and calculations for the coaxial and asymmetric structures was 10%, and that for the collimation structure was 20%. The results of this study can be applied to research using γ-ray measurements.

Laboratory study of non-ideal effects in magnetically collimated astrophysical outflows

Central outflow’s collimation by magnetic field is an important theoretical mechanism for explaining the astrophysical objects’ morphology formation, and its credibility has been tested in many laser plasma experiments in a dimensionless manner. This article introduces integrated simulation and experiment work based on the present laboratory magnetically collimated jet framework, to explore how non-ideal terms’ strength including radiative cooling and magnetic diffusion from different targets can affect the outflow shape. The interaction between outflow from a target with low atomic number and external field satisfies the ideal magneto-hydrodynamic conditions, and the outflow shape results in diamagnetic cavity and jet; on the other hand, a heavy element target brings strong magnetic diffusion that destroys the collimation structure, together with the stagnation of outflow introduced by radiative cooling, and outflow shape results in weakly collimated hemisphere near the target and a detached magnetized density clump. The detailed dimensionless analysis shows that the large-scale dissipation of jets in young stellar objects can possibly be an analog of the laboratory jet’s magnetic diffusion breakup, also similar structures like the loosely collimated lobes and bright ansaes in planetary nebula can be observed in highly diffusive laboratory outflows. This article shows for the first time that a series of non-relativistic astronomical outflows’ dynamic behaviors can be explained by the non-ideal magneto-hydrodynamic evolution of laboratory plasmas.

200 MeV proton irradiation of the oxide-dispersion-strengthened copper alloy (GlidCop-Al15)

In search to identify extremely stable materials to perform the collimation function of the 7-TeV proton beam halo at the Large Hadron Collider (LHC), oxide dispersion strengthened (DS) copper alloys were explored. These internally oxidized copper alloys known as GlidCop are also leading candidates for high heat flux applications in fusion reactors and as divertor and first wall structure in ITER. These considerations have led to an extensive body of research on neutron-induced changes in the microstructure and physio-mechanical properties. This study focused primarily on the damage induced by 200 MeV protons on as wrought and cold-worked GlidCop Al15 DS copper ally selected as a candidate material of the LHC beam collimation structure to damage levels up to ∼10 displacements-per-atom (dpa) and irradiation temperatures up to ∼600 °C. For reference, low dose spallation neutron damage at sub-zero irradiation temperature was included in the study. Proton irradiation effects on dimensional stability, mechanical behavior, electrical resistivity and X-ray diffraction-based microstructural changes are presented in the paper. GlidCop Al15 exhibited excellent thermal stability and superior to pure Cu resistance to conductivity loss. Proton irradiation-induced hardening and embrittlement at distinct irradiation temperature regimes were shown to follow similar trends to what was reported under neutron exposure to even higher dpa damage. At Tirr ∼600 ± 20 °C the cold-worked DS copper alloy exhibited softening accompanied by elongation reduction while at Tirr ∼200 ± 10 °C the as-wrought experienced hardening with elongation increase. High resolution X-ray diffraction revealed that even low-dose neutron irradiation has a strong influence on the size and distribution of dispersed Al2O3 particles.

Study of a multi-pinhole collimation system based small-angle neutron scattering instrument at the Compact Pulsed Hadron Source

The neutron flux of the Compact Pulsed Hadron Source (CPHS) is about 2–3 orders of magnitude lower than that of large neutron sources, which means that the beam intensity should be improved to achieve good statistics. Multi-pinhole collimation can be used to obtain a lower Q with an acceptable beam intensity in a very small angle neutron scattering (VSANS) instrument and a higher beam intensity for a larger sample size in a small-angle neutron scattering (SANS) instrument. A new nine-pinhole structure is used in a SANS instrument at CPHS to achieve an acceptable range and resolution of Q and a higher beam intensity compared to single-pinhole collimation. The crosstalk issue associated with multi-pinhole collimation is addressed using an optimized algorithm to achieve a higher safety margin and a larger pinhole size with a higher beam intensity at the sample. Different collimator aperture structures are compared on the basis of their noise production. Experiments are performed to verify the theory of calculating reflection noise from the inner surface of the collimator's aperture and parasitic noise from the beveled collimator structure. From a simulated SANS experiment using cold neutrons in the SANS instrument, it is clarified that multi-pinhole collimators with an opening angle on the downstream side have better performance than those with an opening angle on the upstream side and straight-cut collimators. Compared with a single-pinhole collimation system, a nine-pinhole collimation system increases the intensity at the sample by approximately sevenfold when the sample size is increased by 20-fold for CPHS-SANS, and the signal-to-noise ratio is improved by exploiting a specific collimator aperture structure. Our goal is to install a multi-pinhole collimator based SANS instrument at CPHS in the future, and it is hoped that these results will serve to promote the utilization of multi-pinhole collimation systems at other facilities.

Serendipitous Discovery of an Optical Emission-line Jet in NGC 232

Abstract We report the detection of a highly collimated linear emission-line structure in the spiral galaxy NGC 232 through the use of integral field spectroscopy data from the All-weather MUse Supernova Integral field Nearby Galaxies survey. This jet-like feature extends radially from the nucleus and is primarily detected in [O iii]λ5007 without clear evidence of an optical continuum counterpart. The length of the radial structure projected on sky reaches ∼3 kpc, which makes NGC 232 the second-longest emission-line jet reported. The ionized gas presents extreme [O iii]/Hβ and [N ii]/Hα line ratios, increasing along the jet-like structure. We discuss three possible scenarios to explain the observed structure: (i) direct ionization of infalling material from the intergalactic medium by the AGN, (ii) photoionization by an undetected optical counterpart of the radio jet, and (iii) fast shock ionization due to the lateral expansion of the radio jet across the interstellar medium. Our analysis favors in situ ionization.

Thin-film camera using luminescent concentrators and an optical Söller collimator.

This article reports our investigation of the potential of optical Söller collimators in combination with luminescent concentrators for lens-less, short-distance, and shape-independent thin-film imaging. We discuss optical imaging capabilities and limitations, and present first prototypes and results. Modern 3D laser lithography and deep X-ray lithography support the manufacturing of extremely fine collimator structures that pave the way for flexible and scalable thin-film cameras that are far thinner than 1 mm (including optical imaging and color sensor layers).

H2in low-ionization structures of planetary nebulae

We report the detection of near-IR H$_2$ emission from the low-ionization structures (knots) in two planetary nebulae. The deepest ever, high-angular resolution H$_2$ 1-0 S(1) at 2.122$\mu$, H$_2$ 2-1 S(1) at 2.248$\mu$ and Br$\gamma$ images of K 4-47 and NGC 7662, obtained using the Near InfraRed Imager and Spectrometer (NIRI) at Gemini-North, are analyzed here. K 4-47 reveals a remarkable highly collimated bipolar structure not only in the optical but also in the molecular hydrogen emission. The H$_2$ emission emanates from the walls of the bipolar outflows and also from the pair of knots at the tip of the outflows. The H$_2$ 1-0 S(1)/2-1 S(1) line ratio ranges from ~7 to ~10 suggesting the presence of shock interactions. Our findings can be explained by the interaction of a jet/bullet ejected from the central star with the surrounding asymptotic giant branch material. The strongest H$_2$ line, v=1-0 S(1) is also detected in several low-ionization knots located at the periphery of the elliptical planetary nebula NGC 7662, but only four of these knots are detected in the H$_2$ v=2-1 S(1) line. These four knots exhibit an H$_2$ line ratio between 2 and 3.5, which suggests that the emission is caused by the UV ionizing flux of the central star. Our data confirms the presence of H$_2$ gas in both fast- and slow-moving low-ionization knots, which has only been confirmed before in the nearby Helix nebula and Hu 1-2. Overall, the low-ionization structures of planetary nebulae are found to share similar traits to photodissociation regions.

Magnetic Dissipation in Relativistic Jets

The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets involve magnetohydrodynamical (MHD) processes. We have investigated the magnetic dissipation mechanism in relativistic jets via relativistic MHD simulations. We found that the relativistic jets involving a helical magnetic field are unstable for the current-driven kink instability, which leads to helically distorted structure in relativistic jets. We identified the regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated to the kink unstable regions and correlated to the converted regions of magnetic to kinetic energies of the jets. We also found that an over-pressured relativistic jet leads to the generation of a series of stationary recollimation shocks and rarefaction structures by the nonlinear interaction of shocks and rarefaction waves. The differences in the recollimation shock structure due to the difference of the magnetic field topologies and strengths may be observable through mm-VLBI observations and space-VLBI mission.

Optimizing modelling in iterative image reconstruction for preclinical pinhole PET

The recently developed versatile emission computed tomography (VECTor) technology enables high-energy SPECT and simultaneous SPECT and PET of small animals at sub-mm resolutions. VECTor uses dedicated clustered pinhole collimators mounted in a scanner with three stationary large-area NaI(Tl) gamma detectors. Here, we develop and validate dedicated image reconstruction methods that compensate for image degradation by incorporating accurate models for the transport of high-energy annihilation gamma photons. Ray tracing software was used to calculate photon transport through the collimator structures and into the gamma detector. Input to this code are several geometric parameters estimated from system calibration with a scanning 99mTc point source. Effects on reconstructed images of (i) modelling variable depth-of-interaction (DOI) in the detector, (ii) incorporating photon paths that go through multiple pinholes (‘multiple-pinhole paths’ (MPP)), and (iii) including various amounts of point spread function (PSF) tail were evaluated. Imaging 18F in resolution and uniformity phantoms showed that including large parts of PSFs is essential to obtain good contrast-noise characteristics and that DOI modelling is highly effective in removing deformations of small structures, together leading to 0.75 mm resolution PET images of a hot-rod Derenzo phantom. Moreover, MPP modelling reduced the level of background noise. These improvements were also clearly visible in mouse images. Performance of VECTor can thus be significantly improved by accurately modelling annihilation gamma photon transport.