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The potential of KD 2 PO 4 (or DKDP) crystal as a terahertz generator is demonstrated, despite its extremely strong terahertz absorption. By combining the Cherenkov radiation scheme and surface-emitting geometry, femtosecond Ti:sapphire laser pulses of ∼ 200 − 300 μ J energy were converted to broadband (∼ 4 THz bandwidth) terahertz transients with the efficiency of ∼ 8 × 10 − 6 . The transients produced electro-optic signals of a ∼ 0.15 modulation depth and ∼ 10 3 dynamic range in a 1-mm thick ZnTe detector crystal. This suggests DKDP as a potential generator crystal for terahertz time-domain spectroscopy. From our measurements, we estimated the nonlinear coefficient d 36 ≈ 3 pm/V of DKDP for optical rectification, which is an order of magnitude larger than the value known from second-harmonic-generation experiments. At the same time, the obtained value of d 36 is an order of magnitude smaller than the value calculated from the clamped electro-optic coefficient r 63 for the MHz frequency range. At high pump intensities, we observed multiple filamentation of the pump beam and white light generation, spatially separated from terahertz generation. [ABSTRACT FROM AUTHOR]

Ground-based observations of Very High Energy (VHE) gamma rays from extreme astrophysical sources are significantly influenced by atmospheric conditions. This is due to the atmosphere being an integral part of the detector when utilizing Imaging Atmospheric Cherenkov Telescopes (IACTs). Clouds and dust particles diminish atmospheric transmission of Cherenkov light, thereby impacting the reconstruction of the air showers and consequently the reconstructed gamma-ray spectra. Precise measurements of atmospheric transmission above Cherenkov observatories play a pivotal role in the accuracy of the analysed data, among which the corrections of the reconstructed energies and fluxes of incoming gamma rays, and in establishing observation strategies for different types of gamma-ray emitting sources. The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the Cherenkov Telescope Array Observatory (CTAO), both located on the Observatorio del Roque de los Muchachos (ORM), La Palma, Canary Islands, use different sets of auxiliary instruments for real-time characterisation of the atmosphere. In this paper, historical data taken by MAGIC LIDAR (LIght Detection And Ranging) and CTAO FRAM (F/Photometric Robotic Telescope) are presented. From the atmospheric aerosol transmission profiles measured by the MAGIC LIDAR and CTAO FRAM aerosol optical depth maps, we obtain the characterisation of the clouds above the ORM at La Palma needed for data correction and optimal observation scheduling. [ABSTRACT FROM AUTHOR]

Monitoring of the anthropogenic radionuclides (90Sr, 135Cs and 137Cs) in different components such as spinach, milk, meat, soil and the grass is important for the environmental radiological survey. Nuclear weapons testing in the atmosphere, nuclear power plant accidents and leaks from the nuclear fuel cycle are the main sources of these radionuclides. The amounts of 90Sr/90Y detected in the environment are mostly due to fallout from nuclear weapons testing. Because of its long physical (28.5 years) and biological half-lives (approximately 12 years) and high fission yield, the measurement of 90Sr is also necessary for radiation protection purposes. It accumulates in bone tissue when ingested by humans through the food chain, and 90Y, a daughter nuclide of 90Sr, emits high-energy beta particles, raising the risk of bone cancer. Strontium has been widely measured in milk samples by using various classical methods. In this study, the procedure we used is based on the separation of 90Y by HDEHP extraction and counting the Cherenkov radiation using a liquid scintillation spectrometer, Quantulus 1220. Prior to analyses, spiked milk samples were dried and prepared as milk powder. The microwave ashing programme was optimised, and recovery of the radiochemical separation steps was tested for spiked milk powder samples before routine analysis. This method is found to be applicable for the routine analysis of 90Sr in milk samples after validation of the method by measuring IRMM milk powder samples, too. A lower limit of detection of about 0.02 Bq.kg−1 was obtained for samples in the case of 84–99% Y chemical yield, 1.45 cpm reagent blank, 4 × 60 minutes counting time and about 83.5 ± 2.1% counting efficiency. [ABSTRACT FROM AUTHOR]

In this article, the test particle method is used in order to calculate the Cherenkov radiation of runaway electrons. We have applied the dielectric tensor for hot magnetized plasma to derive the wave frequency of Cherenkov radiation due to particle resonance with the warm electrostatic waves. The electric field from the Cherenkov radiation is numerically calculated to model the radiation reaction force as a correction to the Coulomb logarithm in the collisional drag force. Then, the behavior of the correction term in strongly and weakly magnetized regimes is investigated. It is shown that both magnetic field strength and the speed of runaway electrons significantly modify the correction term. [ABSTRACT FROM AUTHOR]

The harmonic modulation of coherent systems gives rise to a wealth of physical phenomena, e.g., the AC-Stark effect and Mollow triplets, with important implications for coherent control and frequency conversion. Here, we demonstrate a novel regime of temporal coherence in oscillators harmonically driven at extreme energy modulation amplitudes relative to the modulation quantum. The studies were carried out by modulating a confined exciton-polariton Bose-Einstein condensate (BEC) by an acoustic wave. Features of the new regime are the appearance, in the spectral domain, of a comb of resonances termed acceleration beats with energy spacing tunable by the modulation amplitude and, in the time domain, of temporal correlations at time scales much shorter than the acoustic period, which also depend on the modulation amplitude. These features are quantitatively accounted for by a theoretical framework, which associates the beats with accelerated energy-change rates during the harmonic cycle. These observations are underpinned by the high sensitivity of the BEC energy to the acoustic driving, which simultaneously preserves the BEC's temporal coherence. The acceleration beats are a general feature associated with accelerated energy changes: analogous features are thus also expected to appear under highly accelerated motion e.g., in connection with Cherenkov and Hawking radiation. The authors demonstrate a novel regime of coherent harmonic modulation yielding resonances (termed acceleration beats) with energy spacing and temporal correlations controlled by the modulation amplitude. These features are associated with accelerated energy-change rates during the harmonic cycle. [ABSTRACT FROM AUTHOR]

It is shown that a thin film nanocomposite (NC) coating the radiator enhances the electromagnetic radiation in a particular band. The parameter enhancement in a rigid radiator is done with a metal strip, which is not suitable for a flexible substrate radiator. The NC, i.e. carbon nanotubes-iron-nickel-cobalt (CNT-FeNiCo) nanocomposite, proposed in the radiator design has good electric, magnetic and mechanical characteristics suitable for a flexible radiator. The NC film coated on a shorter radiating strip improves the upper band radiation of a dual-band radiator. The bandwidth of the upper band in the NC-coated radiator is enhanced by 102.50% with a good improvement in the gain and radiation efficiency. The concentration and distribution of CNTs in the antenna substrate coating changes the dielectric constant of the substrate, which can be tailored for specific antenna requirements. Unique properties of the CNT-FeNiCo NC synthesized for radiator fabrication are considered. A uniform NC coating is applied in accordance with the thickness and concentration to enhance the electrical conductivity and mechanical properties. The proposed radiator produces a 2.30–4.10 GHz (1.80 GHz) bandwidth in the lower band and 4.75–6.35 GHz (1.60 GHz) in the upper band, which covers the ISM, WLAN, WiMAX, WiFi and 5G bands. [ABSTRACT FROM AUTHOR]

A novel approach for generation of the multiple three‐directional and controllable beams from a cubical electromagnetic (EM) wave radiator is proposed in this paper. This cubical radiator is a multiple‐mode EM resonator, which is formed by a cubical metal cavity. Three resonant modes are excited in this cavity resonator by a feeding slot. Besides the feeding slot, a few additional slots are opened on the side wall(s) of the cavity to act as the EM wave radiation elements. Various combinations of radiation slots contribute to different beam directions, for example, side‐direction (single radiation slot), edge‐direction (two radiation slots), and vertex‐direction of the cavity (three radiation slots). More combinations of these slots are further studied in the cases of side + edge and edge + vertex to illustrate the diversity in the directions of the produced EM beams. To validate the predicted results, two prototypes are fabricated and measured to display their far‐field radiation patterns. The measured results agree well with the full‐wave simulated ones, thereby demonstrating the possibility of a large number of the flexible EM beams, as well as the capability of the controllable beam directions. [ABSTRACT FROM AUTHOR]

Objective. Prompt gamma timing (PGT) uses the detection time of prompt gammas emitted along the range of protons in proton radiotherapy to verify the position of the Bragg peak (BP). Cherenkov detectors offer the possibility of enhanced signal-to-noise ratio (SNR) due to the inherent physics of Cherenkov emission which enhances detection of high energy prompt gamma rays relative to other induced uncorrelated signals. In this work, the PGT technique was applied to 3 semiconductor material slabs that emit only Cherenkov light for use in a full scale system: a 3 × 3 × 20 mm3 TlBr, a 12 × 12 × 12 mm3 TlBr, and a 5 × 5 × 5 mm3 TlCl. Approach. A polymethyl methacrylate (PMMA) target was exposed to a 67.5 MeV, 0.5 nA proton beam and shifted in 3 mm increments at the Crocker nuclear laboratory (CNL) in Davis, CA, USA. A fast plastic scintillator coupled to a photomultiplier tube (PMT) provided the start reference for the proton time of flight. Time of flight (TOF) distributions were generated using this reference and the gamma-ray timestamp in the Cherenkov detector. Main results. The SNR of the proton correlated peaks relative to the background was 20, 29, and 30 for each of the three samples, respectively. The upper limit of the position resolutions with the TlCl sample were 2 mm, 3 mm, and 5 mm for 30k, 10k, and 5k detected events, respectively. The time distribution of events with respect to the reference reproduced with clarity the periodicity of the beam, implying a very high SNR of the Cherenkov crystals to detect prompt gammas. Background presence from the neutron-induced continuum, prompt gammas from deuterium, or positron activation were not observed. Material choice and crystal dimensions did not seem to affect significantly the outcome of the results. Significance. These results show the high SNR of the pure Cherenkov emitters TlBr and TlCl for the detection of prompt gammas in a proton beam with current of clinical significance and their potential for verifying the proton range. The accuracy in determining shifts of the BP was highly dependent on the number of events acquired, therefore, the performance of these detectors are expected to vary with different beam conditions such as current, pulse repetition, and proton bunch width. [ABSTRACT FROM AUTHOR]

The polarization modulation of Cherenkov diffraction radiation facilitates intriguing potentials to explore material properties and advanced technologies such as free-electron lasers; however, it is still challenging to achieve polarization modulation. Here, we propose versatile on-chip silicon-patterned silicon-nitride photonic integrated waveguides to produce a direction-dependent polarization modulator for Cherenkov diffraction radiation. The radiation angle can be manipulated arbitrarily by arranging the period of the grating and the propagation direction of the electron beam. Furthermore, the polarization and the number of output directions of the radiation can be controlled by the gradient metasurfaces. In particular, the linear, left-, and right-handed circular polarized Cherenkov diffraction radiation could be generated in separate radiation directions. Our results pave the way to modulate the polarization of free-electron radiation and further promote the development of on-chip light sources. [ABSTRACT FROM AUTHOR]

Background: The interest of using fiber Bragg gratings (FBGs) dosimeters in radiotherapy (RT) lies in their (i) microliter detection volume, (ii) customizable spatial resolution, (iii) multi‐point dose measurement, (iv) real‐time data acquisition and (v) insensitivity to Cherenkov light. These characteristics could prove very useful for characterizing dose distributions of small and nonstandard fields with high spatial resolution. Purpose: We developed a multi‐point FBGs dosimeter customized for small field RT dosimetry with a spatial resolution of ∼$\sim$1 mm. Methods: The 3 cm‐long multi‐point dosimeter is made by embedding a 80 μm$\umu{\rm {m}}$ silica fiber containing an array of thirty (30) co‐located ∼$\sim$ 1 mm‐long fs‐written FBGs inside a plastic cylinder with an UV curing optical adhesive. With its higher thermal expansion coefficient, the plastic cylinder increases the sensitivity of the dosimeter by stretching the fiber containing the FBGs when the temperature rises slightly due to radiation energy deposition. Irradiations (2000 MU at 600 MU/min) were performed with a Varian TrueBeam linear accelerator. Results: The dose profile of a 2 ×$ \times$ 2 cm2$^{2}$ 6 MV beam was measured with a mean relative difference of 1.8% (excluding the penumbra region). The measured output factors for a 6 MV beam are in general agreement with the expected values within the experimental uncertainty (except for the 2 ×$\,\times $ 2 cm2$^{2}$ field). The detector response to different energy of photon and electron beams is within 5% of the mean response (0.068±0.002$0.068\pm 0.002$ pm/Gy). The calorimeter's post‐irradiation thermal decay is in agreement with the theory. Conclusions: An energy‐independent small field calorimeter that allows dose profile and output factor measurements for RT using FBGs was developed, which, to our knowledge, has never been done before. This type of detector could prove really useful for small field dosimetry, but also potentially for MRI‐LINAC since FBGs are insensitive to magnetic fields and for FLASH since FBGs have been used to measure doses up to 100 kGy. [ABSTRACT FROM AUTHOR]

The Tunka Advanced Instrument for Gamma- and cosmic-ray Astronomy (TAIGA) is a multicomponent experiment for the measurement of TeV to PeV gamma- and cosmic rays. Our goal is to establish a novel hybrid direct air shower technique, sufficient to access the energy domain of the long-sought Pevatrons. The hybrid air Cherenkov light detection technique combines the strengths of the HiSCORE shower front sampling array, and two ∼4 m class, ∼9.6° field of view Imaging Air Cherenkov Telescopes (IACTs). The HiSCORE array provides good angular and shower core position resolution, while the IACTs provide the image shape and orientation for gamma-hadron separation. In future, an additional muon detector will be used for hadron tagging at ≥100 TeV energies. Here, only data from the first IACT of the TAIGA experiment are used. A randomforest algorithm was trained using Monte Carlo (MC) simulations and real data, and applied to |$85\, \mathrm{h}$| of selected observational data tracking the Crab Nebula at a mean zenith angle of 33.5°, resulting in a threshold energy of 6 TeV for this data set. The analysis was performed using the gammapy package. A total of 163.5 excess events were detected, with a statistical significance of 8.5 σ. The observed spectrum of the Crab Nebula is best fit with a power law above 6 TeV with a flux normalization of (3.20 ± 0.42) · 10−10 TeV−1 cm−2 s−1at a reference energy of |$13\, \mathrm{TeV}$| and a spectral index of −2.74 ± 0.16. [ABSTRACT FROM AUTHOR]

Regular measurements of radio emission produced by relativistic air shower particles were started at the Yakutsk array in 1986. After monitoring of the background noise in the array area, the frequency of 30–35 MHz was chosen, because noise level is minimal in this frequency range. During this time, air showers with highest energies of 100 EeV were registered. By means of hybrid measurements of charged particles, Cherenkov light and radio emission, it was shown that signal amplitude proportional to air shower energy and shape of lateral distribution at sea level correlates with the depth of maximum development. By these characteristics, the atomic weight of primary particles that generated air shower is estimated within QGSjetII-04 framework simulation. [ABSTRACT FROM AUTHOR]

This work investigates the proposed enhanced efficacy of photodynamic therapy (PDT) by activating photosensitizers (PSs) with Cherenkov light (CL). The approaches of Yoon et al. to test the effect of CL with external radiation were taken up and refined. The results were used to transfer the applied scheme from external radiation therapy to radionuclide therapy in nuclear medicine. Here, the CL for the activation of the PSs (psoralen and trioxsalen) is generated by the ionizing radiation from rhenium-188 (a high-energy beta-emitter, Re-188). In vitro cell survival studies were performed on FaDu, B16 and 4T1 cells. A characterization of the PSs (absorbance measurement and gel electrophoresis) and the CL produced by Re-188 (luminescence measurement) was performed as well as a comparison of clonogenic assays with and without PSs. The methods of Yoon et al. were reproduced with a beam line at our facility to validate their results. In our studies with different concentrations of PS and considering the negative controls without PS, the statements of Yoon et al. regarding the positive effect of CL could not be confirmed. There are slight differences in survival fractions, but they are not significant when considering the differences in the controls. Gel electrophoresis showed a dominance of trioxsalen over psoralen in conclusion of single and double strand breaks in plasmid DNA, suggesting a superiority of trioxsalen as a PS (when irradiated with UVA). In addition, absorption measurements showed that these PSs do not need to be shielded from ambient light during the experiment. An observational test setup for a PDT nuclear medicine approach was found. The CL spectrum of Re-188 was measured. Fluctuating inconclusive results from clonogenic assays were found. [ABSTRACT FROM AUTHOR]

Summary: This article presents a highly compact printed radiator for direct broadcast satellite (DBS) systems that exhibits good gain and left‐handed circular polarization. The inferred pattern is accomplished by etching two isosceles triangles, one from each of the four corners of a square. From the center of the newly acquired structure, a circular geometric design is made up of 16 isosceles‐scaled triangles has been etched. This arrangement induces resonance in the antenna, aligning it with the desired frequency. The proposed antenna is designed using PCB laminated Rogger 5880 material and simulated in a CST EM simulator. The antenna under consideration exhibits a significant size reduction, achieving a miniaturization ratio of 21.03%. The LHCP antenna resonated at 12.61 GHz and offered a decent LHCP gain of 7.95 dBic. It gives 0.56 GHz CP bandwidth, which covers the DBS service band entirely. It also provides 96.43% radiation efficiency and 44.27 dB/m correction factor, respectively. All the measured findings of the prototype agree with its simulated one. [ABSTRACT FROM AUTHOR]

The International Journal of Molecular Sciences has published a special issue on "Materials for Photobiology," which explores the interactions between light and living organisms. The issue includes articles and reviews on the latest advances in light-responsive materials for photobiology, with applications in cancer therapy, microbial infections, aesthetic dentistry, and neurological disorder treatment. The articles cover topics such as nanoprodrugs for combined chemo-photodynamic therapy, selective modulators for breast cancer treatment, bichromophoric systems for bioimaging, and the use of photodynamic therapy for cancer and antimicrobial treatment. The issue also discusses the potential of photobiomodulation therapy in various medical fields, including neurology. The studies published in the journal focus on the use of light-responsive materials in photobiology and related biomedical areas, with the hope of inspiring further developments in the field. [Extracted from the article]

NUSES is a pathfinder satellite project hosting two detectors: Ziré and Terzina. Ziré focuses on the study of protons and electrons below 250 MeV and MeV gamma rays. Terzina is dedicated to the detection of Cherenkov light produced by ultra-high-energy cosmic rays above 100 PeV and ultra-high-energy Earth-skimming neutrinos in the atmosphere, ensuring a large exposure. This work mainly concerns the description of the Cherenkov camera, composed of SiPMs, for the Terzina telescope. To increase the data-taking period, the NUSES orbit will be Sun-synchronous (with a height of about 550 km), thus allowing Terzina to always point toward the dark side of the Earth's limb. The Sun-synchronous orbit requires small distances to the poles, and as a consequence, we expect an elevated dose to be received by the SiPMs. Background rates due to the dose accumulated by the SiPM would become a dominant contribution during the last two years of the NUSES mission. In this paper, we illustrate the measured effect of irradiance on SiPM photosensors with a variable-intensity beam of 50 MeV protons up to a 30 Gy total integrated dose. We also show the results of an initial study conducted without considering the contribution of solar wind protons and with an initial geometry with Geant4. The considered geometry included an entrance lens as one of the options in the initial design of the telescope. We characterize the SiPM output signal shape with different μ-cell sizes. We describe the developed parametric SiPM simulation, which is a part of the full Terzina simulation chain. [ABSTRACT FROM AUTHOR]

For the perturbative model of a plane gravitational wave on a flat background of Minkowski space-time, electromagnetic radiation from a charged cloud in the field of a gravitational wave, detected by a remote observer, was found. It is shown that the charge density in the cloud does not change, and the radiation is generated by currents induced by the gravitational wave. The angular distribution of the radiation is obtained. If the refractive index of the cloud medium is greater than unity, Cherenkov-type radiation is generated. [ABSTRACT FROM AUTHOR]

This paper presents the results of the sky survey with the TAIGA–HiSCORE installation, an array of 120 wide-angle Cherenkov light detectors spread over an area of 1 km2. Data analysis is made for 2 winter seasons (2019–2021) at cosmic ray energies above 200–500 TeV. A modified method of background estimation is tested. Signal significance is estimated using classical Li-Ma method. [ABSTRACT FROM AUTHOR]

Recent theoretical studies have suggested the existence of a lower‐dimensional version of the Cherenkov radiation, known as "flatland Cherenkov radiation" (FCR). FCR is generated by leakage from a surface‐wave waveguide while being entirely confined in a plane. Here, a metasurface platform is proposed for generating and observing FCR, which is characterized by alternated regions of capacitive and inductive surface impedance, supporting transverse electric (TE) and magnetic (TM) surface waves (SWs), respectively. For experimental demonstration, a microwave setup is presented, and measured results are compared with numerical simulations and theoretical predictions. The study shows that the phase velocities of different SWs can be controlled by structural designs, and suitably fast TE SWs can excite FCR in the form of slower TM SWs. FCR has unique properties such as directionality, tunability, and subwavelength confinement. The proposed platform has important potential to enable nanophotonic applications based on 2D optics, such as agile waveguiding and scanning. [ABSTRACT FROM AUTHOR]

Classical Cherenkov radiation is a celebrated physics phenomenon of electromagnetic (EM) radiation stimulated by an electric charge moving with constant velocity in a three-dimensional dielectric medium. Cherenkov radiation has a wide spectrum and a particular distribution in space similar to the Mach cone created by a supersonic source. It is also characterized by the energy transfer from the charge's kinetic energy to the EM radiation. In the case of an electron beam passing through the middle of an EM waveguide, the radiation is manifested as collective Cherenkov radiation. In this case, the electron beam can be viewed as a one-dimensional non-neutral plasma, whereas the waveguide can be viewed as a slow wave structure. This collective radiation occurs, in particular, in traveling wave tubes (TWTs), and it features the energy transfer from the electron beam to the EM radiation in the waveguide. Based on a first principles Lagrangian field theory, we develop a convincing argument that the collective Cherenkov effect in TWTs is, in fact, a convective instability, that is, amplification. We also recover Pierce's theory as a high-frequency limit of our generalized Lagrangian theory. Finally, we derive for the first time expressions identifying low- and high-frequency cutoffs for amplification in TWTs. [ABSTRACT FROM AUTHOR]

Cosmic rays are a very valuable tool of multi‐messenger astrophysics, as they provide a very different picture of the sky. During the past decades, a large number of active astrophysical objects in our Galaxy and beyond have been discovered through the detection of gamma‐rays with Cherenkov telescopes. Cosmic rays, neutrinos have been successfully supplementing the astronomical view. Also, cosmic rays may offer to investigation of the elementary particle properties. Neutrino telescope detects the Cherenkov radiation generated in water or ice by the passage of relativistic charged particles produced by neutrino collisions with nucleons in the detector volume. Some alternative approaches have been proposed. One of them is using earth matter or mountains as a target volume for the conversion of neutrinos to leptons which then initiate extensive air showers (EAS) in the atmosphere, then showers can be detected by the Cherenkov telescope. Investigations with SHALON Cherenkov telescope have included observations of EAS from the sub‐horizontal direction Θ=97°$$ \Theta ={97}^{{}^{\circ}} $$. Five EAS of ∼10 TeV energies were detected with SHALON from the sub‐horizontal directions in the conditions with the zero expected number of showers. These events may be caused by the decay of a long‐lived penetrating particle entering the atmosphere from the ground and decaying in front of the telescope. As a possible explanation, two scenarios with an unstable neutrino of mass m≈0.5$$ m\approx 0.5 $$ GeV and cτ≈30$$ c\tau \approx 30 $$ m is discussed. Remarkably, one of these models has been proposed to explain an excess of electron‐like neutrino events at MiniBooNE. [ABSTRACT FROM AUTHOR]

The IceCube Neutrino Observatory instruments about 1 km 3 of deep, glacial ice at the geographic South Pole. It uses 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. An unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. We examine birefringent light propagation through the polycrystalline ice microstructure as a possible explanation for this effect. The predictions of a first-principles model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties include not only the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube light-emitting diode (LED) calibration data, the theory and parameterization of the birefringence effect, the fitting procedures of these parameterizations to experimental data, and the inferred crystal properties. [ABSTRACT FROM AUTHOR]

Astrophysical very high energy (VHE) gamma-rays (with energies >30 GeV) are believed to result almost exclusively from the interactions of populations of highly relativistic particles with ambient matter or photon fields. The study of these VHE photons therefore allows us to examine the processes of particle acceleration in the Universe, and the extreme environments in which they occur. Gamma-rays are also highly directional, making them useful for studying the origin, acceleration, propagation, and composition of cosmic rays. This study uses the Monte Carlo method to simulate the process of extensive air showers being initiated when primary incident γ -rays with energies ranging from 10 GeV to 5 TeV interact with the atmosphere. The ultimate goal is to investigate and analyze the properties and lateral density distributions of Cherenkov light at different altitudes. The simulation considers various energies and zenith angles. The results show that a hump in the lateral density distribution of Cherenkov light is a distinctive feature of a γ -initiated shower, with the hump becoming less prominent at higher energy levels and altitudes. These significant findings not only facilitate better fitting of experimental data obtained from actual extensive air showers but also assist with estimating readings from detectors, thus advancing our understanding of these processes. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally that a recently proposed structure comprising a tens of microns thick layer of LiNbO 3 sandwiched between two totally reflecting Si prisms can serve as an efficient Cherenkov-type optical-to-terahertz converter of femtosecond laser pulses from an optical oscillator. Using Ti:sapphire laser pulses of 3.75 nJ energy as a pump, we achieved a conversion efficiency of 2.3 × 10 − 5 , which exceeds the efficiency of the conventional collinear scheme with a ZnTe crystal by an order of magnitude. The converter can be used as a reliable radiation source for performing terahertz time-domain spectroscopy. [ABSTRACT FROM AUTHOR]

In this Letter, we present a multistage smart radiator with a gradient emittance that gradually increases with increasing temperature in the spectral range of 2.5–15 μm. Such smart radiator is a relatively simple multilayered structure composed of three phase change materials (PCMs): VO2, GST, and IST. The smart radiator achieves multistage manipulation of emittance through phase transitions of PCMs, with the largest emittance tunability of ∼0.85. The underlying mechanism involves manipulating the Fabry–Pérot resonance and antireflection. Additionally, the emittance is found to be relatively insensitive to polarization and incident angles. The proposed multistage smart radiator exposes excellent potential for exploitation in thermal management and energy conservation. [ABSTRACT FROM AUTHOR]

Background: Plastic scintillating detectors (PSD) have gained popularity due to small size and are ideally suited in small‐field dosimetry due to no correction needed and hence detector reading can be compared to dose. Likewise, these detectors are active and water equivalent. A new PSD from Blue Physics is characterized in photon beam. Purpose: Innovation in small‐field dosimetry detector has led us to examine Blue Physics PSD (BP‐PSD) for use in photon beams from linear accelerator. Methods: BP‐PSD was acquired and its characteristics were evaluated in photon beams from a Varian TrueBeam. Data were collected in a 3D water tank. Standard parameters; dose, dose rate, energy, angular dependence and temperature dependence were studied. Depth dose, profiles and output in a reference condition as well as small fields were measured. Results: BP‐PSD is versatile and provides data very similar to an ion chamber when Cerenkov radiation is properly accounted. This device measures data pulse by pulse which very few detectors can perform. The differences between ion chamber data and PSD are < 2% in most cases. The angular dependence is a bit pronounces to 1.5% which is due to PSD housing. Depth dose and profiles are comparable within < 1% to an ion chamber. For small fields this detector provides suitable field output factor compared to other detectors and Monte Carlo (MC) simulated data without any added correction factor. Conclusions: The characteristics of Blue Physics PSD is uniquely suitable in photon beam and more so in small fields. The data are reproducible compared to ion chamber for most parameters and ideally suitable for small‐field dosimetry without any correction factor. [ABSTRACT FROM AUTHOR]

It is shown that the breaking of azimuthal symmetry during the oblique entry of relativistic particles into a thin target leads to oscillations of the spectral-angular density of polarized Cherenkov radiation along the azimuthal angle. The effect of modulation of the angular distribution of Cherenkov radiation can be observed in quartz glass on individual spectral lines in the optical and near ultraviolet ranges. The interference maxima have a small angular width not exceeding 10–2 rad. The effect can be used in the diagnostics of the angular characteristics of beams of accelerated relativistic particles. [ABSTRACT FROM AUTHOR]

The JEM-EUSO program aims to study ultra-high energy cosmic rays from space. To achieve this goal, it has realized a series of experiments installed on the ground (EUSO-TA), various on stratospheric balloons (with the most recent one EUSO-SPB2), and inside the International Space Station (Mini-EUSO), in light of future missions such as K-EUSO and POEMMA. At nighttime, these instruments aim to monitor the Earth's atmosphere measuring fluorescence and Cherenkov light produced by extensive air showers generated both by very high-energy cosmic rays from outside the atmosphere and by neutrino decays. As the two light components differ in duration (order of microseconds for fluorescence light and a few nanoseconds for Cherenkov light) they each require specialized sensors and acquisition electronics. So far, the sensors used for the fluorescence camera are the Multi-Anode Photomultiplier Tubes (MAPMTs), while for the Cherenkov one, new systems based on Silicon PhotoMultipliers (SiPMs) have been developed. In this contribution, a brief review of the experiments is followed by a discussion of the tests performed on the optical sensors. Particular attention is paid to the development, test, and calibration conducted on SiPMs, also in view to optimize the geometry, mass, and weight in light of the installation of mass-critical applications such as balloon- and space-borne instrumentation. [ABSTRACT FROM AUTHOR]

This work presents the development of a 64-channel application-specific integrated circuit (ASIC), implemented to detect the optical Cherenkov light from sub-orbital and orbital altitudes. These kinds of signals are generated by ultra-high energy cosmic rays (UHECRs) and cosmic neutrinos (CNs). The purpose of this front-end electronics is to provide a readout unit for a matrix of silicon photo-multipliers (SiPMs) to identify extensive air showers (EASs). Each event can be stored into a configurable array of 256 cells where the on-board digitization can take place with a programmable 12-bits Wilkinson analog-to-digital converter (ADC). The sampling, the conversion process, and the main digital logic of the ASIC run at 200 MHz, while the readout is managed by dedicated serializers operating at 400 MHz in double data rate (DDR). The chip is designed in a commercial 65 nm CMOS technology, ensuring a high configurability by selecting the partition of the channels, the resolution in the interval 8–12 bits, and the source of its trigger. The production and testing of the ASIC is planned for the forthcoming months. [ABSTRACT FROM AUTHOR]

We explore, both theoretically and experimentally, the potential of semiconductor materials for the Cherenkov scheme of terahertz generation on the example of GaP crystal pumped by femtosecond laser pulses of 1.54 μ m wavelength. We use a convenient scheme with a focused-to-a-line laser beam which is introduced into the crystal by oblique incidence at the Brewster angle on the crystal front face and propagates in the crystal at the Cherenkov angle to its normal. A half of the generated Cherenkov wedge impinges normally the rear face of the crystal and generates an output terahertz beam with a plane wavefront. The whole generation process is simulated by FDTD method. In experiments, the laser pulses of 140 fs duration and 10 μ J energy were converted to wideband (~2.5 THz bandwidth) terahertz radiation with the efficiency of ~3 × 10 − 5 , which exceeds the efficiency of the standard collinear scheme by at least an order of magnitude. [ABSTRACT FROM AUTHOR]

High peak power, tunable, narrowband terahertz emitters are becoming sought after given their portability, efficiency, and ability to be deployed in the field for industrial, medical, and military applications. The use of accelerator systems producing THz frequencies via Cherenkov radiation, generated by passing an electron beam through a slow-wave wakefield structure, is a promising method to meet future THz requirements. To date, efforts have been dedicated to analysis and design of sources utilizing laser seeded bunched electron beam drivers with relativistic energies beyond 5 MeV. Presented here is a wakefield THz generation scheme based on passing a long quasi-dc nonrelativistic beam (200 keV) through a dielectric loaded traveling wave structure. Reduced energy allows for compactness and portability of the accelerator as the size and weight of the dielectric slow-wave structure is vanishingly small compared to the accelerator unit. The presented scheme can serve as a tunable high peak power THz source operated between 0.4 and 1.6 THz and produces power gain by a factor of five with an average efficiency of 6.8%. [ABSTRACT FROM AUTHOR]

Vavilov–Cherenkov radiation (CR), an electromagnetic radiation emission that occurs when a charged particle in a medium moves faster than the speed of light in the same medium, plays an important role in many areas of physics such as nuclear physics. Recently, CR has been investigated in photonics and plasmonics in the perspective of its application in velocity-dependent particle detection to enhance current particle detectors, thanks to the flexibility that offer integrated devices. In this contribution, the description of the excitation of eigenmodes in different integrated photonic and plasmonic structures by a uniformly moving charged particle is numerically presented. The CR that arise from such an interaction is described within the framework of an eigenmode analysis and validated with source and field propagation with the use of the finite-difference time-domain method. Integrated nanophotonics could provide a promising platform for the investigation of the interaction between electrons and photons on-chip. [ABSTRACT FROM AUTHOR]

Paper contains the first results on the development of a SPHERE-3 telescope for the primary cosmic ray studies in 1–1000 PeV energy range using reflected and direct Cherenkov light generated by extensive air showers. It also sheds some light on the development of our new approach to the design of the new telescope. [ABSTRACT FROM AUTHOR]

Next-generation large-scale neutrino detectors, from Eos, at the 1 t scale, to Theia, at the 10 s-of-kt scale, will utilize differences in both the scintillation and Cherenkov light emission for different particle species to perform background rejection. This manuscript presents measurements of the scintillation light yield and emission time profile of water-based liquid scintillator samples in response to α radiation. These measurements are used as input to simulation models used to make predictions for future detectors. In particular, we present the timing-based particle identification achievable in generic water-based scintillator detectors at the 4 t, 1 kt, and 100 kt scales. We find that α / β discrimination improves with increasing scintillation concentration and we identify better than 80% α rejection for 90% β acceptance in 10% water-based liquid scintillator, at the 4 t scale. [ABSTRACT FROM AUTHOR]

Particle identification at the Super Charm-Tau factory experiment will be provided by a Focusing Aerogel Ring Imaging CHerenkov detector (FARICH). Silicon photomultipliers used for the Cherenkov light detection generate a lot of noise hits that must be mitigated to reduce both the data flow and negative effects on particle velocity resolution. In this work we present our approach to filtering signal hits, inspired by object detection techniques for computer vision. Several ML-based approaches to the FARICH reconstruction problem in different settings are also discussed. [ABSTRACT FROM AUTHOR]

To date, 10 dynamic, total-body (DTB) [18F]FDG-PET/CT datasets (60 min acquisition) from 2 PET/CT systems were included: 5 healthy controls (HC) acquired on an uEXPLORER and 5 HC on a Siemens Biograph Vision PET/CT system. P28 Design of a generic method for single acquisition dual-tracer PET imaging Nasrin Taheri1,2*, Benjamin Le Crom2, Caroline Bouillot3, Michel Chérel1, Nicolas Costes3, Sé... 1CRCINA, INSERM, CNRS, Université d'Angers, Université de Nantes, Nantes, France; 2Nuclear Me... Correspondence: Nasrin Taheri (Nasrin.taheri@chu-nantes.fr) I EJNMMI Physics i 2023, B 10(1): b P28 B Context b Total body Positron Emission Tomography (PET) opens an area of feasible large axial single PET acquisition with quasi-simultaneous dual-tracer injection. LB1 Parameterised Geant4 simulation for total body PET research Benjamin M Wynne1*, Matthew Needham1, Adriana S Tavares2,3 1School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK; 2Edinburgh Imaging,... Correspondence: Benjamin M Wynne (b.m.wynne@ed.ac.uk) I EJNMMI Physics i 2023, B 10(1): b LB1 B Introduction b Total-body positron emission tomography (PET) imaging has the potential to transform medical care of a number of diseases and augment our knowledge of systems biology. P24 Evaluation of CT dose reduction scanning a whole-body phantom with the Biograph Vision Qu... Samaneh Mostafapour1, James Hamill2, Adriaan A. Lammertsma1, Charalampos Tsoumpas1 1Medical Imaging Center, University Medical Center Groningen, Groningen, Netherlands; 2Siemen... Correspondence: Samaneh Mostafapour (s.mostafapour@umcg.nl) I EJNMMI Physics i 2023, B 10(1): b P24 B Background b Low-dose CT can provide about 1-3 mSv of the total delivered radiation dose during a typical PET-CT scan. [Extracted from the article]

We investigate, both numerically and theoretically, laser-driven generation of intense terahertz (THz) waves embedded in external magnetic (B) fields in excess of 100 T. Depending on the interaction geometry and the B-field orientation, one-dimensional particle-in-cell simulations reveal that two distinct mechanisms can operate as efficient laser-to-THz converters. At nonrelativistic laser intensities, photocurrents induced by two-color laser pulses are shown to supply THz field strengths < 10 GV m - 1 for B fields parallel to the laser propagation axis. The THz field can be intensified when using circularly polarized pump pulses. By contrast, when the B field is perpendicular to the laser propagation axis, ponderomotive effects are found to prevail at relativistic intensities, leading to the emission of much stronger THz fields ( > 30 GV m - 1 ) via Cerenkov wake radiation. Laser-to-THz conversion efficiencies above 10 - 3 are predicted, together with full transmission of the THz waves across the rear plasma boundary, provided that the ratio of the electron cyclotron and plasma frequencies exceeds unity. The main trends revealed by the simulations are interpreted in light of simple analytical models. [ABSTRACT FROM AUTHOR]

Cherenkov radiation occurs only when a charged particle moves with a velocity exceeding the phase velocity of light in that matter. This radiation mechanism creates directional light emission at a wide range of frequencies and could facilitate the development of on-chip light sources except for the hard-to-satisfy requirement for high-energy particles. Creating Cherenkov radiation from low-energy electrons that has no momentum mismatch with light in free space is still a long-standing challenge. Here, we report a mechanism to overcome this challenge by exploiting a combined effect of interfacial Cherenkov radiation and umklapp scattering, namely the constructive interference of light emission from sequential particle-interface interactions with specially designed (umklapp) momentum-shifts. We find that this combined effect is able to create the interfacial Cherenkov radiation from ultralow-energy electrons, with kinetic energies down to the electron-volt scale. Due to the umklapp scattering for the excited high-momentum Bloch modes, the resulting interfacial Cherenkov radiation is uniquely featured with spatially separated apexes for its wave cone and group cone. [ABSTRACT FROM AUTHOR]

Based on the reversed Cherenkov radiation excited in metamaterials, a novel S-band reversed Cherenkov radiation amplifier (RCRA) with two output ports is proposed in this paper. Its metamaterial slow-wave structure (MSWS) consists of a hollow circular waveguide periodically loaded with all-metal double-ridge complementary electric split-ring resonators (CeSRRs). The CeSRR exhibits subwavelength and strong resonance characteristics, which lead to miniaturization and high interaction impedance of the MSWS. The period of the MSWS is optimized using the phase velocity jump technique to further increase the output power and electronic efficiency. The simulation results demonstrate that when the microwave signal of 7.8 W at 2.286 GHz is inputted at port 2, the output power at port 1 is 307 W, and the saturated output power and saturated gain at port 3 are 5.48 kW and 28.47 dB, respectively. Notably, the total electronic efficiency of the RCRA is predicted as 33.84%. The RCRA features high electronic efficiency and miniaturization and may meet special application scenarios that require two output microwave signals at the same frequency. [ABSTRACT FROM AUTHOR]

Electroforming of metal–insulator–metal (MIM) diodes is a non-destructive dielectric breakdown that results in a conducting filament in the insulator and changes the high resistance of the as-prepared MIM diode into a low-resistance state. It is a critical step in the development of conducting states between which switching can occur in memristors or resistive switching memories. Electroforming of Al–Al2O3–Ag diodes in vacuum results in the formation of a conducting Al2O3 filament. There are Ohmic contacts at the Al–Al2O3 and Al2O3–Ag interfaces. Electronic processes develop, such as voltage-controlled negative resistance in the current–voltage (I–V) characteristics, electron emission into vacuum (EM), and electroluminescence (EL). I–V curves, EM, and EL of three electroformed Al–Al2O3–Ag diodes with anodic Al2O3 thicknesses between 36 nm and 49 nm have been measured with 20 mV resolution between voltage steps. Periodic voltage structure occurs for the three electronic processes for applied voltages between the voltage threshold for EL, ∼2 V, and the maximum applied voltage, 11 V. The voltage peak period, 60 mV to 70 mV, is the same as the range of LO phonon energies of anodic Al2O3. The proposed mechanism is Čerenkov phonon generation by ballistic electrons whose velocity exceeds the velocity of sound in Al2O3. The phonons, in turn, modify the motion and number of electrons that are emitted into vacuum, that are responsible for EL radiation, and that contribute to conduction through the diode. The occurrence of LO phonons shows that the conducting filament is Al2O3, not Ag or Al. The phenomena may provide a new method of generating terahertz radiation. [ABSTRACT FROM AUTHOR]

Cerenkov radiation from radiopharmaceuticals (18F-FDG) serves as an internal light source to excite UV-responsive silicon nanocrystals for near-infrared luminescence imaging that offers deeper tissue penetration and high signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

The therapeutic efficacy of photodynamic therapy is limited by the ability of light to penetrate tissues. Due to this limitation, Cerenkov luminescence (CL) from radionuclides has recently been proposed as an alternative light source in a strategy referred to as Cerenkov radiation‐induced therapy (CRIT). Semiconducting polymer nanoparticles (SPNs) have ideal optical properties, such as large absorption cross‐sections and broad absorbance, which can be utilized to harness the relatively weak CL produced by radionuclides. SPNs can be doped with photosensitizers and have ≈100% energy transfer efficiency by multiple energy transfer mechanisms. Herein, an optimized photosensitizer‐doped SPN is investigated as a nanosystem to harness and amplify CL for cancer theranostics. It is found that semiconducting polymers significantly amplify CL energy transfer efficiency. Bimodal positron emission tomography (PET) and optical imaging studies show high tumor uptake and retention of the optimized SPNs when administered intravenously or intratumorally. Lastly, it is found that photosensitizer‐doped SPNs have excellent potential as a cancer theranostics nanosystem in an in vivo tumor therapy study. This study shows that SPNs are ideally suited to harness and amplify CL for cancer theranostics, which may provide a significant advancement for CRIT that are unabated by tissue penetration limits. [ABSTRACT FROM AUTHOR]

LB1 Parameterised Geant4 simulation for total body PET research Benjamin M Wynne1*, Matthew Needham1, Adriana S Tavares2,3 1School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK; 2Edinburgh Imaging,... Correspondence: Benjamin M Wynne (b.m.wynne@ed.ac.uk) I EJNMMI Physics i 2023, B 10(1): b LB1 B Introduction b Total-body positron emission tomography (PET) imaging has the potential to transform medical care of a number of diseases and augment our knowledge of systems biology. P21 A deep learning method for the recovery of standard-dose imaging quality from ultra-low-d... Song Xue3*, Hong Zhu5, Rui Guo2, Hasan Sari3,4, Clemens Mingels3, Konstantinos Zeimpekis3, Ge... 1Department of Nuclear Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Med... Correspondence: Song Xue (song.xue@dbmr.unibe.ch) I EJNMMI Physics i 2023, B 10(1): b P21 B Introduction b Recent development in positron emission tomography (PET) dramatically increased the effective sensitivity by increasing the geometric coverage leading to total-body PET imaging. P24 Evaluation of CT dose reduction scanning a whole-body phantom with the Biograph Vision Qu... Samaneh Mostafapour1, James Hamill2, Adriaan A. Lammertsma1, Charalampos Tsoumpas1 1Medical Imaging Center, University Medical Center Groningen, Groningen, Netherlands; 2Siemen... Correspondence: Samaneh Mostafapour (s.mostafapour@umcg.nl) I EJNMMI Physics i 2023, B 10(1): b P24 B Background b Low-dose CT can provide about 1-3 mSv of the total delivered radiation dose during a typical PET-CT scan. To date, 10 dynamic, total-body (DTB) [18F]FDG-PET/CT datasets (60 min acquisition) from 2 PET/CT systems were included: 5 healthy controls (HC) acquired on an uEXPLORER and 5 HC on a Siemens Biograph Vision PET/CT system. [Extracted from the article]

This work is devoted to several translation-invariant models in nonrelativistic quantum field theory (QFT), describing a nonrelativistic quantum particle interacting with a quantized relativistic field of bosons. In this setting, we aim at the rigorous study of Cherenkov radiation or friction effects at small disorder, which amounts to the metastability of the embedded mass shell of the bare nonrelativistic particle when the coupling to the quantized field is turned on. Although this problem is naturally approached by means of Mourre's celebrated commutator method, important regularity issues are known to be inherent to QFT models and restrict the application of the method. In this perspective, we introduce a novel non-standard procedure to construct Mourre conjugate operators, which differs from second quantization and allows to circumvent many regularity issues. To show its versatility, we apply this construction to the Nelson model with massive bosons, to Fröhlich's polaron model, and to a quantum friction model with massless bosons introduced by Bruneau and De Bièvre: for each of those examples, we improve on previous results. [ABSTRACT FROM AUTHOR]

Free‐electron radiation is a fundamental photon emission process that is induced by fast‐moving electrons interacting with optical media. Historically, it has been understood that, just like any other photon emission process, free‐electron radiation must be constrained within a finite time interval known as the "formation time," whose concept is applicable to both Cherenkov radiation and transition radiation, the two basic mechanisms describing radiation from a bulk medium and from an interface, respectively. Here, this work reveals an alternative mechanism of free‐electron radiation far beyond the previously defined formation time. It occurs when a fast electron crosses the interface between vacuum and a plasmonic medium supporting bulk plasmons. While emitted continuously from the crossing point on the interface—thus consistent with the features of transition radiation—the extra radiation beyond the conventional formation time is supported by a long tail of bulk plasmons following the electron's trajectory deep into the plasmonic medium. Such a plasmonic tail mixes surface and bulk effects, and provides a sustained channel for electron–interface interaction. These results also settle the historical debate in Ferrell radiation, regarding whether it is a surface or bulk effect, from transition radiation or plasmonic oscillation. [ABSTRACT FROM AUTHOR]

Objective. This study aimed at investigating through Monte Carlo simulations the limitations of a novel hybrid Cerenkov-scintillation detector and the associated method for irradiation angle measurements. Approach. Using Monte Carlo simulations, previous experimental irradiations of the hybrid detector with a linear accelerator were replicated to evaluate its general performances and limitations. Cerenkov angular calibration curves and irradiation angle measurements were then compared. Furthermore, the impact of the Cerenkov light energy dependency on the detector accuracy was investigated using the energy spectra of electrons travelling through the detector. Main results. Monte Carlo simulations were found to be in good agreement with experimental values. The irradiation angle absolute mean error was found to be less than what was obtained experimentally, with a maximum value of 1.12° for the 9 MeV beam. A 0.4% increase of the ratio of electrons having an energy below 1 MeV to the total electrons was found to impact the Cerenkov light intensity collected as a function of the incident angle. The effect of the Cerenkov intensity variation on the measured angle was determined to vary according to the slope of the angular calibration curve. While the contribution of scattered electrons with a lower energy affects the detector accuracy, the greatest discrepancies result from the limitations of the calculation method and the calibration curve itself. Significance. A precise knowledge of the limitations of the hybrid detector and the irradiation angle calculation method is crucial for a clinical implementation. Moreover, the simulations performed in this study also corroborate hypotheses made regarding the relations between multiple Cerenkov dependencies and observations from the experimental measurements. [ABSTRACT FROM AUTHOR]

Background: Fiber optic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. Purpose: The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4:Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). Methods: A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. Results: The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. Conclusions: Photoluminescence (PL) of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber (OF) are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD. [ABSTRACT FROM AUTHOR]