Search Results (11)

Semiconductor detectors for high-energy sensing ($X/\gamma$-rays) play a critical role in fields such as astronomy, particle physics, spectroscopy, medical imaging, and homeland security. The increasing need for precise detector characterization highlights the importance of developing advanced digital twins, which help optimize the design and performance of imaging systems. Current simulation frameworks primarily focus on modeling electron–hole pair dynamics within the semiconductor bulk after the photon absorption, leading to the current signals at the nearby electrodes. However, most simulations neglect charge diffusion and Coulomb repulsion, which spatially expand the charge cloud during propagation due to the high complexity they add to the physical models. Although these effects are relatively weak, their inclusion is essential for achieving a high-fidelity replication of real detector behavior. There are some existing methods that successfully incorporate these two phenomena with minimal computational cost, including those developed by Gatti in 1987 and by Benoit and Hamel in 2009. The present work evaluates these two approaches and proposes a novel Monte Carlo technique that offers higher accuracy in exchange for increased computational time. Our new method enables more realistic performance predictions while remaining within practical computational limits. Full article

The history of Compton cameras began with the detection of radiation sources originally for applications in astronomy. A Compton camera is a promising γ-ray detector that operates in the wide energy range of a few tens of keV to MeV. The γ-ray detection method of a Compton camera is based on Compton scattering kinematics, which is used to determine the direction and energy of the γ-rays without using a mechanical collimator. Although the Compton camera was originally designed for astrophysical applications, it was later applied in medical imaging as well. Moreover, its application in environmental radiation measurements is also under study. Although a few review papers regarding Compton cameras have been published, they either focus very specifically on the detectors used in such cameras or the particular applications of Compton cameras. Thus, the aim of this paper is to review the features and types of Compton cameras and introduce their applications, associated imaging algorithms, improvement scopes, and their future aspects. Full article

A space-based detector dedicated to measurements of $\gamma$-rays and charged particles has to achieve a balance between different instrumental requirements. A good angular resolution is necessary for the $\gamma$-rays, whereas an excellent geometric factor is needed for the charged particles. The tracking reference technique of $\gamma$-ray physics is based on a pair-conversion telescope made of passive material (e.g., tungsten) coupled with sensitive layers (e.g., silicon microstrip). However, this kind of detector has a limited acceptance because of the large lever arm between the active layers, needed to improve the track reconstruction capability. Moreover, the passive material can induce fragmentation of nuclei, thus worsening charge reconstruction performances. The Tracker-In-Calorimeter (TIC) project aims to solve all these drawbacks. In the TIC proposal, the silicon sensors are moved inside a highly-segmented isotropic calorimeter with a couple of external scintillators dedicated to charge reconstruction. In principle, this configuration has a good geometrical factor, and the angle of the $\gamma$-rays can be precisely reconstructed from the lateral profile of the electromagnetic shower sampled, at different depths in the calorimeter, by silicon strips. The effectiveness of this approach has been studied with Monte Carlo simulations and validated with beam test data of a small prototype. Full article

Unlike blazars, radio galaxies have jets that are misaligned relative to our line-of-sight. This misaligned geometry provides us with a unique view of both the jet and super massive black hole. To date, four radio galaxies have been detected at TeV energies with an additional two active galactic nuclei shown to exhibit both radio galaxy and BL Lac-type properties. TeV observations of radio galaxies have revealed these objects to be fascinating, displaying ultra-fast variability and often relatively hard spectral energy distributions. This work aims to provide a review of the current state of radio galaxy observations within the context of very-high-energy $\gamma$-ray astronomy, while also highlighting that radio galaxies are excellent targets for multi-wavelength observations. A number of motivations for the continued study of radio galaxies are provided, and these are discussed with a focus on the key observational results, including implications for future observations with next-generation instruments soon to be operational. Full article

Thirty years after the discovery of the first very-high-energy $\gamma$-ray source by the Whipple telescope, the field experienced a revolution mainly driven by the third generation of imaging atmospheric Cherenkov telescopes (IACTs). The combined use of large mirrors and the invention of the imaging technique at the Whipple telescope, stereoscopic observations, developed by the HEGRA array and the fine-grained camera, pioneered by the CAT telescope, led to a jump by a factor of more than ten in sensitivity. The advent of advanced analysis techniques led to a vast improvement in background rejection, as well as in angular and energy resolutions. Recent instruments already have to deal with a very large amount of data (petabytes), containing a large number of sources often very extended (at least within the Galactic plane) and overlapping each other, and the situation will become even more dramatic with future instruments. The first large catalogues of sources have emerged during the last decade, which required numerous, dedicated observations and developments, but also made the first population studies possible. This paper is an attempt to summarize the evolution of the field towards the building up of the source catalogues, to describe the first population studies already made possible, and to give some perspectives in the context of the upcoming, new generation of instruments. Full article

The evolution of extensive air shower detection as a technique for $\gamma$-ray astronomical instrumentation for the last three decades is reviewed. The first discoveries of galactic PeVatrons by the Large High Altitude Air Shower Observatory demonstrate the importance of this technique in ultra-high energy $\gamma$-ray astronomy. Utilizing this technique, the origins of high energy cosmic rays may be discovered in the near future. Full article

A neutron star was first detected as a pulsar in 1967. It is one of the most mysterious compact objects in the universe, with a radius of the order of 10 km and masses that can reach two solar masses. In fact, neutron stars are star remnants, a kind of stellar zombie (they die, but do not disappear). In the last decades, astronomical observations yielded various contraints for neutron star masses, and finally, in 2017, a gravitational wave was detected (GW170817). Its source was identified as the merger of two neutron stars coming from NGC 4993, a galaxy 140 million light years away from us. The very same event was detected in $\gamma$-ray, X-ray, UV, IR, radio frequency and even in the optical region of the electromagnetic spectrum, starting the new era of multi-messenger astronomy. To understand and describe neutron stars, an appropriate equation of state that satisfies bulk nuclear matter properties is necessary. GW170817 detection contributed with extra constraints to determine it. On the other hand, magnetars are the same sort of compact object, but bearing much stronger magnetic fields that can reach up to 10${}^{15}$ G on the surface as compared with the usual 10${}^{12}$ G present in ordinary pulsars. While the description of ordinary pulsars is not completely established, describing magnetars poses extra challenges. In this paper, I give an overview on the history of neutron stars and on the development of nuclear models and show how the description of the tiny world of the nuclear physics can help the understanding of the cosmos, especially of the neutron stars. Full article

The field of ground-based $\gamma$-ray astronomy has made very significant advances over the last three decades with the extremely successful operations of several atmospheric Cherenkov telescopes worldwide. The advent of the imaging Cherenkov technique for indirect detection of cosmic $\gamma$ rays has immensely contributed to this field with the discovery of more than 220 $\gamma$-ray sources in the Universe. This has greatly improved our understanding of the various astrophysical processes involved in the non-thermal emission at energies above 100 GeV. In this paper, we summarize the important results achieved by the Indian $\gamma$-ray astronomers from the GeV-TeV observations using imaging Cherenkov telescopes over the last two decades. We mainly emphasize the results obtained from the observations of active galactic nuclei with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) telescope, which has been operational since 1997 at Mount Abu, India. We also discuss the future plans of the Indian $\gamma$-ray astronomy program with special focus on the scientific objectives of the recently installed 21 m diameter MACE (Major Atmospheric Cherenkov Experiment) telescope at Hanle, India. Full article

High-energy neutrino astronomy is a fascinating new field of research, rapidly developing over recent years. It opens a new observation window on the most violent processes in the universe, fitting very well to the concept of multi-messenger astronomy. This may be exemplified by the recent discovery of the high-energy neutrino emissions from the $\gamma$-ray loud blazar TXS 0506+056. Constraining astrophysical neutrino fluxes can also help to understand the long-standing mystery of the origin of the ultra-high energy cosmic rays. Astronomical studies of high-energy neutrinos are carried out by large-scale next-generation neutrino telescopes located in different regions of the world, forming a global network of complementary detectors. The Baikal-GVD, being currently the largest neutrino telescope in the Northern Hemisphere and still growing up, is an important constituent of this network. This paper briefly reviews working principles, analysis methods, and some selected results of the Baikal-GVD neutrino telescope. Full article

Precise measurements of the energy spectra and of the composition of cosmic rays in the PeV region could improve our knowledge regarding their origin, acceleration mechanism, propagation, and composition. At the present time, spectral measurements in this region are mainly derived from data collected by ground-based detectors, because of the very low particle rates at these energies. Unfortunately, these results are affected by the high uncertainties typical of indirect measurements, which depend on the complicated modeling of the interaction of the primary particle with the atmosphere. A space experiment dedicated to measurements in this energy region has to achieve a balance between the requirements of lightness and compactness, with that of a large acceptance to cope with the low particle rates. CaloCube is a four-year-old R&D project, approved and financed by the Istituto Nazionale di Fisica Nucleare (INFN) in 2014, aiming to optimize the design of a space-borne calorimeter. The large acceptance needed is obtained by maximizing the number of entrance windows, while thanks to its homogeneity and high segmentation this new detector achieves an excellent energy resolution and an enhanced separation power between hadrons and electrons. In order to optimize detector performances with respect to the total mass of the apparatus, comparative studies on different scintillating materials, different sizes of crystals, and different spacings among them have been performed making use of MonteCarlo simulations. In parallel to simulations studies, several prototypes instrumented with CsI(Tl) (Caesium Iodide, Tallium doped) cubic crystals have been constructed and tested with particle beams. Moreover, the last development of CaloCube, the Tracker-In-Calorimeter (TIC) project, financed by the INFN in 2018, is focused on the feasibility of including several silicon layers at different depths in the calorimeter in order to reconstruct the particle direction. In fact, an important requirement for $\gamma$ -ray astronomy is to have a good angular resolution in order to allow precise identification of astrophysical sources in space. In respect to the traditional approach of using a tracker with passive material in front of the calorimeter, the TIC solution can save a significant amount of mass budget in a space satellite experiment, which can then be exploited to improve the acceptance and the resolution of the calorimeter. In this paper, the status of the project and perspectives for future developments are presented. Full article

CdTe/CZT based spectroscopic two-dimensional (2D)/three-dimensional (3D) imagers when operated in the Compton regime can work as high performance scattering polarimeters, for high-energy astrophysics. Polarimetry in high-energy astrophysics has been little explored. To date, X- and γ-ray source emissions have been studied almost exclusively through spectral, imaging, and timing analysis. Polarization measurements provide two additional observational parameters: the polarization angle and the level of linear polarization. These additional parameters should allow for a better discrimination between the physical mechanisms of different emission models characterizing a celestial object. Therefore, polarimetry will play a strategic role in new instrumentations for future high-energy astronomy missions. 2D and 3D CZT/CdTe spectroscopic imagers provided with coincidence readout logic can efficiently handle scattering events to perform simultaneously polarization, spectroscopy, imaging, and timing measurements. Herein, we describe the results obtained, both experimentally and by MC simulations, with CdTe/CZT pixel detector prototypes in high-energy polarimetry. We give an overview on the achievable polarimetric performance with spectroscopic imagers and on how these performances are affected by detector configuration parameters. Finally, we address the perspective of scattering polarimetry opened by the recent implementation of new high energy focusing optics, as broadband Laue lens, in next generation of hard X- and soft γ-ray astronomy instrumentation. The unprecedented sensitivity achievable by these telescopes will definitely open the window of polarimetry in this high-energy range. Full article