Showing papers on "Collimated light published in 2023"

Modeling scatter through sides of island blocks used for intensity‐modulated bolus electron conformal therapy

Abstract: Abstract Purpose Passive Radiotherapy Intensity Modulators for Electrons (PRIME) devices are comprised of cylindrical tungsten island blocks imbedded in a machinable foam slab within the patient's cutout. Intensity‐modulated bolus electron conformal therapy (IM‐BECT) uses PRIME devices to reduce dose heterogeneity caused by the irregular bolus surface. Heretofore, IM‐BECT dose calculations used the pencil beam redefinition algorithm (PBRA) assuming perfect collimation. This study investigates modeling electron scatter into and out the sides of island blocks. Methods Dose distributions were measured in a water phantom at 7, 13, and 20 MeV for devices having nominal intensity reduction factors of 1.000 (foam only), 0.937, 0.812, and 0.688, corresponding to nominal island block diameters (dnom ) of 0.158, 0.273, and 0.352 cm, respectively. Pencil beam theory derived an effective diameter (dIS ) to account for in‐scattered electrons as a function of dnom and beam energy (Ep,0 ). However, for out‐scattered electrons, an effective diameter (dmod ) was estimated by best fitting measured data. Results In the modulated region (under island blocks, depth < R90), modified PBRA‐calculated dose distributions showed 2%/2 mm passing rates for dnom = 0.158, 0.273, and 0.352 cm of (100%, 100%, 100%) at 7 MeV, (100%, 100%, 93.5%) at 13 MeV, and (99.8%, 85.4%, and 71.5%) at 20 MeV. The largest dose differences (≤ 6%) occurred at the highest energy (20 MeV), largest dnom , shallowest depths (≤ 2 cm), and on central axis. Conclusions An equation for modeling island block scatter, dmod (dnom , Ep,0 ), has been developed for use in the PBRA, insignificantly impacting calculation time. Although inaccuracy sometimes exceeded our 2%/2 mm criteria, it could be clinically acceptable, as superficial dose differences often fall inside the bolus. Also, patient PRIME devices are expected to have fewer large diameter island blocks than did test devices. Inaccuracies are attributed to out‐scattered electrons having energy spectra different than the primary beams.

Effects of bowtie scatter on material decomposition in photon-counting CT

Abstract: Purpose: To investigate spectral distortion caused by bowtie (BT) scatter in photon-counting CT (PCCT) and its impact of the accuracy of material decomposition. Methods: GPU-accelerated Monte Carlo (MC) simulations of a PCCT scanner with 1 mm detector pixels, a 1- dimensional anti-scatter grid (ASG) with 30:1 grid ratio, and five energy channels per pixel (25/35/50/65/80keV) were performed. Beam collimation was varied 80 – 160 mm (at isocenter). X-ray tube voltage was 120 kVp. An ~80 mm thick Aluminum BT was placed 48 mm from the x-ray focal spot. Spectral and spatial distributions of scatter and Scatter-to-Primary ratio (SPR) of water cylinders (150 mm – 300 mm diameter) were compared for two MC simulation settings: (a) scatter occurs both in the BT and in the object (ground-truth); and (b) BT acts only as a beam shaper but does not cause scatter. Water cylinders with Calcium wedge inserts (5 mm – 25 mm Ca thickness) were used to evaluate material decomposition errors due to object and BT scatter using least-squares projection-domain decomposition. Results: Even with an 1D ASG, the low-energy channel SPRs for large objects (300 mm diameter) might be as high as 5 (at 80 mm collimation) – 10 (160 mm collimation). When BT scatter is ignored in scatter modeling, the SPRs are underestimated by 10% - 30%, with the relative error increasing with channel energy. Scatter introduces substantial biases in material decomposition: without any correction, the relative errors of Ca path length estimates range from 6%-10% for a 150 mm object and 80 mm collimation to 50%-100% for a 300 mm object at 160 mm collimation. Approximate correction using only object scatter reduces these biases to generally <5%, except for the largest phantom and collimation, where ignoring BT scatter leads to 6% - 12% underestimation of Ca thickness. Conclusions: Algorithmic scatter corrections will likely be necessary for precise PCCT material decomposition for body-sized objects and wide collimations. While adequate results can be obtained using simplified models that ignore BT scatter, achieving <10% decomposition accuracy might require incorporating BT scatter.

A Wide Energy Range and 4π-View Gamma Camera with Interspaced Position-Sensitive Scintillator Array and Embedded Heavy Metal Bars

Abstract: (1) Background: Gamma cameras have wide applications in industry, including nuclear power plant monitoring, emergency response, and homeland security. The desirable properties of a gamma camera include small weight, good resolution, large field of view (FOV), and wide imageable source energy range. Compton cameras can have a 4π FOV but have limited sensitivity at low energy. Coded-aperture gamma cameras are operatable at a wide photon energy range but typically have a limited FOV and increased weight due to the thick heavy metal collimators and shielding. In our lab, we previously proposed a 4π-view gamma imaging approach with a 3D position-sensitive detector, with which each detector element acts as the collimator for other detector elements. We presented promising imaging performance for 99mTc, 18F, and 137Cs sources. However, the imaging performance for middle- and high-energy sources requires further improvement. (2) Methods: In this study, we present a new gamma camera design to achieve satisfactory imaging performance in a wide gamma energy range. The proposed gamma camera consists of interspaced bar-shaped GAGG (Ce) crystals and tungsten absorbers. The metal bars enhance collimation for high-energy gamma photons without sacrificing the FOV. We assembled a gamma camera prototype and conducted experiments to evaluate the gamma camera’s performance for imaging 57Co, 137Cs, and 60Co point sources. (3) Results: Results show that the proposed gamma camera achieves a positioning accuracy of <3° for all gamma energies. It can clearly resolve two 137Cs point sources with 10° separation, two 57Co and two 60Co point sources with 20° separation, as well as a 2 × 3 137Cs point-source array with 20° separation. (4) Conclusions: We conclude that the proposed gamma camera design has comprehensive merits, including portability, 4π-view FOV, and good angular resolution across a wide energy range. The presented approach has promising potential in nuclear security applications.

Monte Carlo modeling of focused Very High Energy Electron beams as an innovative modality for radiotherapy application

Abstract: After the invention of the Linear Electron Accelerator for Research (CLEAR) based on the Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) at CERN, the development of an accurate and accessible high energy electron radiotherapy treatment is a major challenge in medical physics. The technological advances of the linear collider and the relativistic effects of Very High Energy Electron (VHEE) particles; have led researchers to propose a simple management of collimated beams in the energy range of 50–250 MeV to reduce scattering and enable irradiation of deep-seated tumor position. However, the measured entry and exit doses and lateral scattering for collimated VHEE beams treatment are very high compared with other treatment modalities. This task provides a new approach based on focused VHEE obtained by combining an accurate Monte Carlo (MC) simulation with a complex modeling electron transport with very high energy inside a water phantom. This focused VHEE is compared to stereotactic cyberknife, protontherapy and VHEE treatment using a collimator. The results demonstrated that radiotherapy with a focused VHEE beam of energy greater than 100 MeV can surround deep-seated and highly inhomogeneous tumors with great accuracy. It could represent a valid alternative for a better preservation of healthy tissues, since the dispersion of the dose over a large volume reduces the entry and exit dose. Moreover, this approach can be shaped or scanned to treat deep-seated tumors, as the dose will be concentrated into a small well-defined volumetric element.

Ultrashort laser pulses with chromatic astigmatism

Abstract: Ultrashort laser pulses are described as having chromatic astigmatism, where the astigmatic phase varies linearly with the offset from the central frequency. Such a spatio-temporal coupling not only induces interesting space-frequency and space-time effects, but it removes cylindrical symmetry. We analyze the quantitative effects on the spatio-temporal pulse structure on the collimated beam and as it propagates through a focus, with both the fundamental Gaussian beam and Laguerre-Gaussian beams. Chromatic astigmatism is a new type of spatio-temporal coupling towards arbitrary higher complexity beams that still have a simple description, and may be applied to imaging, metrology, or ultrafast light-matter interaction.

Large-scale particle shadow tracking and orientation measurement with collimated light

Abstract: Lagrangian particle tracking experiments are a key tool to understanding particle transport in fluid flows. However, tracking particles over long distances is expensive and limited by both the intensity of light and number of cameras. In order to increase the length of measured particle trajectories in a large fluid volume with minimal cost, we developed a large-scale particle-shadow-tracking method. This technique is able to accurately track millimeter-scale particles and their orientations in meter-scale laboratory fluid flows. By tracking the particles’ shadows cast by a wide beam of collimated light from a high-power LED, 2D particle position and velocity can be obtained, as well as their 3D orientation. Compared with traditional volumetric particle tracking techniques, this method is able to measure particle kinematics over a larger area using much simpler imaging and tracking techniques. We demonstrate the method on sphere, disk, and rod particles in a wavy wind-driven flow, where we successfully track particles and reconstruct their orientations.

Research on the Influence Model of Collimating Lens Aberrations in Autocollimation System Based on the Ray-Tracing Method

Abstract: An influence model of collimating lens aberrations in an autocollimation system based on the ray-tracing method is established. With the ray-tracing method, this model can accurately compute the direction and position of each light ray passing through the collimating lens in an autocollimation system, thereby obtaining the light-spot position of each light ray on the sensor and determining the systematic error caused by aberrations. Eventually, this model serves to compensate for the measurement error of autocollimators and improve the accuracy. Simulations and experiments demonstrate that the influence quantity of angular measurement value due to aberrations reaches 0.74 arcsec within the range of ±500 arcsec. Also, in a large-aberration situation, the measurement accuracy is promoted to 3.33 arcsec, approximately five times higher than that without compensation.

Collimation and cropping in diagnostic radiography: How concerned are we?

Abstract: This editorial examines current collimation and cropping practices in general radiography. We critically reflect on whether we are concerned by the practice of collimation creep amongst radiographers. Discussions around policy, evidence‐based practice and potential hypocrisies are outlined in this editorial piece.

A diffuse scattering model of ultracold neutrons on wavy surfaces

Abstract: Metal tubes plated with nickel-phosphorus are used in many fundamental physics experiments using ultracold neutrons (UCN) because of their ease of fabrication. These tubes are usually polished to a average roughness of 25-150 nm. However, there is no scattering model that accurately describes UCN scattering on such a rough guide surface with a mean-square roughness larger than 5 nm. We therefore developed a scattering model for UCN in which scattering from random surface waviness with a size larger than the UCN wavelength is described by a microfacet Bidirectional Reflectance Distribution Function model (mf-BRDF model), and scattering from smaller structures by the Lambert's cosine law (Lambert model). For the surface waviness, we used the statistical distribution of surface slope measured by an atomic force microscope on a sample piece of guide tube as input of the model. This model was used to describe UCN transmission experiments conducted at the pulsed UCN source at J-PARC. In these experiments, a UCN beam collimated to a divergence angle smaller than $\pm 6^{\circ}$ was directed into a guide tube with a mean-square roughness of 6.4 nm to 17 nm at an oblique angle, and the UCN transport performance and its time-of-flight distribution were measured while changing the angle of incidence. The mf-BRDF model combined with the Lambert model with scattering probability $p_{L} = 0.039\pm0.003$ reproduced the experimental results well. We have thus established a procedure to evaluate the characteristics of UCN guide tubes with a surface roughness of approximately 10 nm.

Metamaterial spectrometer on a chip for hyperspectral imaging and atmospheric sounding

Abstract: The monitoring of Earth’s atmosphere requires routine measurements of many gasses and aerosols. The most common technique to perform this task is hyperspectral imaging (HSI). However, with the push to integrate HSI sensing capabilities on small platforms, e.g. cubesats and UAVs, the development of smaller, cheaper, higher performing, and low power HSI systems is necessary. Current HSI systems are composed of a large and complex assortment of lenses, filters and cameras that are large, heavy, expensive, and intolerant to physical shocks—all things that make them challenging for use in space-based sensing and imaging applications. The metamaterial filter described in this work eliminates the need for many of the previously necessary optics because it can spectrally filter light independent of the lights angle of incidence—this allows for a focused beam of light to be filtered by the metamaterial. This is in distinct contrast to grating-based HSI systems where the spectrometer requires collimated light. Additionally, the metamaterial filter is designed to filter light only at the desired spectral bands; this is a great benefit for small-platform systems because of the substantially reduced data rate and required computational resources.

Uniformization of a large beam spot using sextupole magnets for a compact multiple-energy electron accelerator

Abstract: We have commissioned a multiple-energy electron accelerator that illuminates an 800 mm × 800 mm target. The energy of the beam ranges from 0.5 to 5 MeV. A beamline following the accelerator has horizontal and vertical sections that include an alpha dipole and a “focus sextupole”. In the horizontal section, the alpha magnet, having a bend angle of 270° and a field index of 0.8, provides both vertical collimation and energy selection. In the vertical section, a focus sextupole converts the initial Gaussian beam distribution to a uniform distribution in one dimension without beam loss. We used a scanning magnet just ahead of the target to expand the beam in the orthogonal dimension. Using the French code TraceWin, we simulate the beam dynamics in this beamline by integrating electron trajectories through field maps of the magnets. We have determined experimentally that the focus sextupole creates a horizontal strip beam on target having a current density uniformity of better than 90 %. By scanning this strip beam vertically, we have achieved a two-dimensional current density uniformity of better than 90 %.

Design of Optical Collimator System for Vehicle Speed Gun using Non-Imaging Optics

Abstract: Vehicle speed guns are usually used in normal sunlight conditions (daytime). If we want to use vehicle speed guns in low light conditions (nighttime), the illuminator is needed to provide sufficient light for the vehicle speed gun to take photos. The illuminator must fulfill two requirements: (i) using the infrared wavelength to ensure that the driver is not startled by dazzling eyes by the illuminator of the proposed speed gun system and (ii) high energy efficiency to make the illuminator compact leading to the use a small battery system to improve the portable of the proposed vehicle speed gun. In this study, an illuminator using a collimator system designed by using non-imaging optics is introduced. LEDs with infrared wavelength are chosen from the library of LightToolsTM, the structure of collimated is designed to transfer the illumination from the LEDs array to a square area of 3x3 m2 to cover the vehicle to detect the vehicle number plate. The design process is built based on the conservation of optical path length in the Matlab program. After that, the designed collimator is simulated in LightToolsTM software. The promising results of the simulation in LightToolsTM show that the collimator can efficiently transfer light from the LED array to the target area with a uniformity of about 70 % and optical efficiency of about 80 %.

Temporal Intensity Interferometry at a 0.5 m Telescope

Abstract: Intensity interferometry correlates light intensities rather than amplitudes of individual telescopes to recover the source geometry. While intensity correlations can alleviate the technical challenges of amplitude interferometry, and thus enable the realization of larger baselines and therefore higher resolution in astronomical imaging, this comes at the cost of greatly reduced sensitivity. We report the observation of photon bunching in the light of $\alpha$ Lyrae (Vega), measured with a telescope of merely 0.5m in diameter (Planewave CDK 20). The entire measurement setup, including collimation, optical filtering, and detection, was attached directly to the telescope without the use of optical fibers, facilitated by the large area of our single photon detectors. After a total exposure time of 32.4h over the course of six nights, a correlation signal with a contrast of $(9.5 \pm 2.7) \cdot 10^{-3}$ and a coherence time $0.34 \pm 0.12$ps was recovered, fitting well to preceding laboratory tests as well as expectations calculated from the optical and electronic characteristics of our measurement setup.

Study of a Compton backscattering wall defects detection device using the Monte Carlo method

Abstract: Abstract In view of the shortcomings of traditional wall defect detection methods, such as small detection range, poor accuracy, non-portable device, and so on, a wall defects detection device based on Compton backscattering technology is designed by Monte Carlo method, which is mainly used to detect the size and location information of defects in concrete walls. It mainly consists of two parts, the source container and the detection system: first, through the simulation and analysis of the parameters such as the receiving angle of the backscattered particles and the rear collimating material of the detector, the influence of the fluorescent X-ray peak of the detector collimating material on the backscattered particle counts is eliminated and the detected error is reduced; second, the ring array detector design, compared with single array detector and surface array detector, can facilitate real-time detection of defect orientation, expanding the single scan range and improving the detection efficiency. After simulation and comparative analysis, the relevant optimal parameters are obtained: the object is detected using a Cs-137 γ-ray source with an activity of 6 mCi, and a ring detector consisting of four 0.5-inch cube-shaped CsI scintillator detectors is placed at 150° to receive the backscattered photons. The simulation analysis using the Monte Carlo FLUKA program showed that the maximum depth of wall defect detection is 8 cm, the maximum error fluctuation range of defect depth and thickness is ±1 cm, the overall device weight is <20 kg, and the measurement time is <5 min.

Ghost imaging lidar system for remote imaging.

Abstract: Research towards practical applications of ghost imaging lidar system especially in longer sensing distance has been urgent in recent years. In this paper we develop a ghost imaging lidar system to boost an extension of remote imaging, where the transmission distance of the collimated pseudo-thermal beam can be improved hugely over long range and just shifting the adjustable lens assembly generates wide field of view suiting for short-range imaging. Based on the proposed lidar system, the changing tendency of illuminating field of view, energy density, and reconstructed images is analyzed and verified experimentally. Some considerations on the improvement of this lidar system are also discussed.

egs++: Optimization of Simulation Transport Parameters

Abstract: MC transport parameters used are common to all egs++ applications. The effect of each transport parameter need to understand to optimize the simulation process. Therefore, the purpose of this study was to investigate the efficiency of egs++ simulation for different transport parameters in water phantom. This water phantom has built using slab. Collimated source defined 100 cm above the phantom. The simulation parameters such as the efficiency, statistical uncertainty, and accuracy of selecting transport parameters such as electron and photon cut-off energies, spin effects, atomic relaxations, and bound Compton scattering was investigated. The selection of ECUT and PCUT greatly affects the simulation time. The simulation time, efficiency and energy fractions have same value for varied ECUT except for 0.521 MeV. The energy fraction have been shifted but the simulation time and efficiency were same. Turning on spin effects in this simulation increases simulation time by 25%. The simulation time increases by about 15% when relaxations are turned on. The more accurate result of deposited energy using EGSnrc algorithm is about 30% slower than the less accurate PRESTA-I algorithm. Therefore, The optimization of transport parameters is needed in the simulation of egs++ to provide the best efficiency.

Visualization and comparison of CT dose distribution between axial and helical acquisitions.

Abstract: BACKGROUND It is challenging to assess the accuracy of volume CT Dose Index (CTDIvol ) when the axial scan modes corresponding to a helical scan protocol is not available. An alternative approach was proposed to directly measure C T D I v o l H $CTDI_{vol}^H$ using helical acquisitions and relatively small differences (< 20%) from CTDIvol were observed. PURPOSE To visually demonstrate the 3D dose distribution for both axial and helical CT acquisitions and quantitively compare C T D I v o l H $CTDI_{vol}^H$ and CTDIvol . METHODS 3D dose distribution within the standard CTDI phantoms (16 and 32 cm diameter) from a single CT projection, Dp (x,y,z) was first generated using Monte Carlo simulation (GEANT4) with 9×108 photons per combination of tube voltage (80-140 kV), collimation width (1-8 cm), and z-axis location of the central ray of the x-ray beam, with a spatial resolution of 1 mm3 . These dose distributions from one single projection were analytically ensembled to simulate 3D dose volumes DA (x,y,z) and DH (x,y,z) for axial and helical scans, respectively, with different helical pitches (0.3-2) and scan lengths (100-150 mm). 2D planar dose distributions were obtained by integrating the inside 100 mm of the dose volumes. CTDIvol and C T D I v o l H $CTDI_{vol}^H\;$ were calculated using the planar dose data at corresponding pencil chamber locations and the percentage differences (PD) were reported. RESULTS High spatial resolution 3D CT dose volumes were generated and visualized. PDs between C T D I v o l H $CTDI_{vol}^H$ and CTDIvol had strong dependency on scan length and peripheral chamber locations, with subtle dependency on collimation width and pitch. PDs were mostly within the range of ± 3% for a scan length of 150 mm with four peripheral chamber locations. CONCLUSIONS With a scan length covering the entire phantom length, C T D I v o l H $CTDI_{vol}^H$ directly measured from helical scans can serve as an alternative to CTDIvol only if all four peripheral locations were measured.

The XY-Scanner for Absolute End-to-End Calibration of Fluorescence Detectors

Abstract: The precise determination of the energy scale is a key part of experiments in astroparticle physics. At the Pierre Auger Observatory, the energy scale is set by the calorimetric measurement of extensive air showers with fluorescence detectors. Thus, the absolute end-to-end calibration of the fluorescence detectors is of utmost importance. In the past, this calibration was performed by illuminating the whole optical system of a fluorescence telescope with a large-scale extended uniform light source of the same diameter as the telescope aperture. However, handling difficulties, excessive manpower requirements, and degradation of such a source led to the need for a different approach for the absolute end-to-end calibration. The fundamental idea of the novel approach is to significantly reduce the geometrical size of the calibration light source, which is a near-UV LED source implemented in a portable integrating sphere with specifically designed interior. This light source is moved over the aperture by a rail mechanism with two independent linear stages named the XY-Scanner. Calibration data are evaluated from a series of light source positions instead of illuminating the entire aperture at once. The absolute photometric determination of the light source emission intensity is performed in a dedicated laboratory setup with a measurement uncertainty of 3.5 %. The XY-Scanner mechanics installed at the aperture gives also the opportunity to install other, devices for instance a narrow, collimated beam source to investigate local impurities of the telescopes. This contribution gives an overview of this novel XY-Scanner calibration method and presents preliminary results and discusses plans for the future.

Design and Fabrication of Large Area Vat Photopolymerization 3D Printing System using a 32-inch Quasi-Collimated Visible Backlight Module with Local Dimming Control

Abstract: In this paper, we accomplished the first 32-inch liquid crystal display (LCD) type vat photopolymerization 3D printing system based on the quasi-collimated visible backlight module with local dimming control. The large building area (40x70cm) of the 3D printing system can greatly increase the size of printing objects and the production rate. We focused on the design of quasi-collimated backlights and analyzed their optical properties and the appearance of 3D printing objects fabricated by them. The optical performances of the quasi-collimated backlight using stacks of optical films feature no large angle leakage light, 86% intensity uniformity, and less than ±15° angular distribution of emitting light. After the optimization process by combining a variety of optical films, the uniformity, and collimation of the backlight module are greatly improved. Moreover, combining a local dimming algorithm with 3D printing technology can completely suppress unexpected photopolymerization residues, increase resin utilization rate, save energy, and greatly improve the probability of success in the 3D printing process, especially in large printing objects.

Dual-Band and Dual-Polarized Reflectarray for Intelligent Reflecting Surface Applications in Millimeter-Wave 5G

Abstract: In this work, a dual-band and dual-polarized reflectarray is proposed for non-tunable Intelligent Reflecting Surfaces (IRS) in millimeter-wave 5G. The reflectarray unit-cell has a dual-layer configuration, where the printed elements on each layer are designed to provide the required phase shifts at a different operating frequency (lower layer elements for 28 GHz and upper layer elements for 39 GHz). A 20 cm x 20 cm reflectarray panel has been designed to produce a collimated beam in dual-linear polarization at the 28 GHz and 39 GHz bands simultaneously. The proposed concept can be used to design passive IRS panels (without tunability) with dual-band operation, which can be used to improve coverage of dead zones or avoid obstacles that block direct communication links in millimeter-wave 5G networks.

Study and perspective on neutron beam divergence improvement achievable by the combination of two or more neutron collimating systems

Abstract: This communication presents the results obtained at an experimental campaign at PSI BOA beamline using the combination of the ANET Compact Neutron Collimator (CNC) with the actual BOA pin-hole system. Through extensive resolution campaigns, it has been possible to quantify and understand the effects of improvement on the beam divergence when combining the two collimating systems. A new theoretical approach to this problem is described and discussed. The effect is expected not to be limited to the specific case that has been studied at PSI BOA but to have a more general validity for neutron collimation systems.

In-orbit Performance of ME onboard Insight-HXMT in the first 5 years

Abstract: Introduction: The Medium Energy X-ray telescope (ME) is a collimated X-ray telescope onboard the Insight hard X-ray modulation telescope (Insight-HXMT) satellite. It has 1728 Si-PIN pixels readout using 54 low noise application-specific integrated circuits (ASICs). ME covers the energy range of 5-30 keV and has a total detection area of 952 cm2. The typical energy resolution of ME at the beginning of the mission is 3 keV at 17.8 keV (Full Width at Half Maximum, FWHM) and the time resolution is 255 us. In this study, we present the in-orbit performance of ME in its first 5 years of operation. Methods: The performance of ME was monitored using onboard radioactive sources and astronomical X-ray objects. ME carries six 241Am radioactive sources for onboard calibration, which can continuously illuminate the calibration pixels. The long-term performance evolution of ME can be quantified using the properties of the accumulated spectra of the calibration pixels. In addition, observations of the Crab Nebula and the pulsar were used to check the long-term evolution of the detection efficiency as a function of energy. Conclusion: After 5 years of operation, 742 cm2 of the Si-PIN pixels were still working normally. The peak positions of 241Am emission lines gradually shifted to the high energy region, implying a slow increase in ME gain of 1.43%. A comparison of the ME spectra of the Crab Nebula and the pulsar shows that the E-C relations and the redistribution matrix file are still acceptable for most data analysis works, and there is no detectable variation in the detection efficiency.

Two-dimensional numerical study of the effect of magnetic field on the evolution of laser-driven jets

Abstract: Astrophysical jets are highly collimated supersonic plasma beams distributed across various astrophysical backgrounds. The triggering mechanism, collimation transmission, and stability of jets have always been the focus of astrophysics research. In recent years, observations and laboratory research have found that the magnetic field plays a crucial role in jet collimation, transmission, and acceleration. In this paper, the two-dimensional numerical simulation of the jet in front of the CH plane target driven by an intense laser is carried out using the open-source MHD FLASH simulation program. The dynamics of jet evolution caused by the Biermann self-generated magnetic field, the external magnetic field with different directions, and initial strengths are systematically investigated and compared. Simulation results show that the Biermann self-generated magnetic field does not affect jet interface dynamics. The results show that the external magnetic field has a redirecting effect on the plasma outflow. The external magnetic field parallel to the direction of the plasma outflow center in front of the target is conducive to the generation and collimation of the jet. The evolution of the jet has gone through three stages: antimagnetic ellipsoid cavity, conical nozzle, and collimated jet. Its formation and evolution process results from competition between plasma thermal, magnetic, and ram pressure. In terms of force, plasma thermal pressure gradient and magnetic pressure forces play a decisive role in the jet evolution process. The presence of magnetic pressure significantly limits the radial expansion of the jet to achieve axial collimation transmission. The length-diameter ratio of the jet is positively correlated with the initial axial applied magnetic field intensity. In addition, we observed in the simulation that there are many node-like structures in the jet evolution zone, similar to the jet node in YSO. The results provide a reference for future experimental research related to jets and contribute to a deeper understanding of the evolution of celestial jets.