High-energy Γ-ray Detectors Research Articles

Measuring space-time fuzziness with high energy γ-ray detectors

There are several suggestions to probe space-time fuzziness (also known as space-time foam) due to the quantum mechanics nature of space-time. These effects are predicted to be very small, being related to the Planck length, so that the only hope to experimentally detect them is to look at particles propagating along cosmological distances. Some phenomenological approaches suggest that photons originating from pointlike sources at cosmological distance experience path length fluctuation that could be detected. Also the direction of flight of such photons may be subject to a dispersion such that the image of a point-like source is blurred and detected as a disk. An experimentally accessible signature may be images of point-like sources larger that the size due to the Point Spread Function of the instrument. This additional broadening should increase with distance and photon energy. Some concrete examples that can be studied with the AGILE and FERMI-LAT γ -ray satellite experiments are discussed.

Observation and simulations of the backsplash effects in high-energy γ-ray telescopes containing a massive calorimeter

Beam test and simulation results are presented for a study of the backsplash effects produced in a high-energy γ-ray detector containing a massive calorimeter. An empirical formula is developed to estimate the probability (per unit area) of backsplash for different calorimeter materials and thicknesses, different incident particle energies, and at different distances from the calorimeter. The results obtained are applied to the design of the Anti-Coincidence Detector (ACD) for the Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST).

High-energy gamma-ray detection with the Alpha Magnetic Spectrometer on board the International Space Station

The Alpha Magnetic Spectrometer (AMS) is a large acceptance, superconducting magnetic spectrometer designed to search for anti-matter and to study, with high accuracy, the origin of dark-matter and the composition of cosmic rays. The results of a Monte Carlo (MC) simulation study of AMS as a high-energy γ-ray detector are presented. AMS will be able to provide accurate measurements of γ-ray spectra over a broad energy range (up to hundreds of GeV) with energy resolution of a few per cent and angular resolution of 0.018-1°. The acceptance of 0.04-0.13 m 2sr has been estimated with maximal opening angle being 20° to 42°. The study of the background events has been done, the irreducible background-to-signal ratio being at the level of a few per cent or below being. The γ-ray sky survey sensitivity of AMS is finally discussed.

Relativistic laser interactions with preformed plasma channels and gamma-ray measurements

The propagation of a 1-ps laser pulse at intensities exceeding 1019 Wcm−2 in a low-density plasma channel was experimentally tested. The channel was produced by a lower intensity preceding pulse of the same duration. Plasma electrons were accelerated during the propagation of the main pulse, and high energy γ-ray detectors were used to detect their bremsstrahlung emission. The γ-ray yield was studied for different channel conditions, by varying the delay between the channel forming pulse and the high intensity pulse. These results are correlated with the interferograms of the propagation region into the plasma.

Present status of liquid rare gas scintillation detectors and their new application to gamma-ray calorimeters

Scintillation from liquid rare gases has a fast decay component with a high photon yield which is comparable to that of NaI(Tl), although the wavelength is in the vacuum ultraviolet. On the basis of these properties, many investigators have tried to realize liquid rare gas scintillation detector. In particular, liquid Xe is expected to be an excellent detector medium for γ-rays because of its fast response, its large atomic number, and high density. However, it is very difficult to achieve sufficient light collection as scintillator, because the light emission are in vacuum ultraviolet. Recently, some groups have reported liquid Xe/Kr homogeneous scintillation calorimeters for high-energy γ-rays using reflectors method, but their energy resolution was not as high as expected. In this situation it seems that the realization of liquid rare gas detectors may not be easy. In this paper, we review the physical properties of scintillation from liquid rare gas, the scintillation yields, the decay time constants and attenuation lengths. We summarize the results obtained with liquid rare gas scintillation detector. The present status of development of liquid Kr/Xe homogeneous scintillation calorimeters by using reflected light is described. A new device which observes only direct light is proposed as high-energy γ-ray detector or homogeneous electromagnetic shower calorimeters for γ-rays.

High energy gamma ray observatories for the study of cosmic ray electrons above 1014 eV

Abstract We have studied in detail the possibility of detecting cosmic ray electrons of energy ≳10 14 eV using high energy γ-ray detectors. Such instruments would detect synchrotron γ-rays radiated by the electrons, while traversing the Earth's magnetic field. These radiated γ-rays are expected to be incident along a straight line in the detector for an unambiguous identification of an electron event. Our analysis shows that small γ-ray detectors such as those in SAS-2 and COS-B satellites cannot be used for this purpose. The high energy γ-ray detector to be flown on the GRO satellite may be able to detect electrons, if the energy spectrum of electrons at high energies is modified by the influence of a nearby source. Such exciting possibilities can be observed with large area γ-ray instruments, which are aslo capable of detecting γ-rays through Compton scattered electrons. We have, in this investigation, suggested ways of utilizing future large area γ-ray observatories to open up a new avenue for the study of ultra high energy cosmic ray electrons.

Gamma-ray astronomy and the study of electrons >1013 eV and bursts using an array of ?-ray detectors in space platform

We have discussed the possiblity of employing an array of high-energy γ-ray detectors in space platform in order to achieve higher sensitivity than by using a single detector. It is shown that such a detector system can be utilized for the study of faint galactic and extragalactic sources, and for deep survey of complex regions. The array can also be operated in the γ-ray burst mode to detect bursts. The energy spectrum of bursts can be obtained over a wide range from 0.1 MeV to 50 GeV, and their direction determined accurately. Further, the array can be used for the study of cosmic-ray electrons above 1013 eV, for which there is no other technique exists today to detect them. Detection of ultra-high energy electrons would open up a new dimension in the understanding of cosmic-ray propagation in the solar neighbourhood and of the local distribution of cosmic-ray sources.

Review of observational results on γ-ray background: (Invited discourse)

Recent observations in the X- and γ-Ray region of the electromagnetic spectrum have given strong evidence for the existence of an extragalactic intensity with a slowly steepening power law spectrum in the region 103 to 108 eV. Further data from the OSO-III high energy γ-Ray detector are in agreement with earlier published reports, and suggest that the γ-Rays from high galactic latitudes have a softer spectrum than those from the galactic plane.

Solar Gamma Rays and their Correlation with Space and Ground-Based Observations

Thus far, only two experiments have detected solar γ-radiation with energy significantly greater than 200 keV. In both events the γ-ray emission occurred during a solar flare. The first observation was in 1958 by Peterson and Winckler (1959), who recorded a burst of radiation that occurred in less than 18 sec from a class-2 solar flare. The radiation spectrum peaked in the 200- to 500-keV region. Recently, Cline et al. (1967) recorded in the OGO-3 satellite three rapid γ-ray bursts in the 80-keV to 1-MeV energy range and measured the integral energy spectrum. The measurements were made on July 7, 1966, during the first high-intensity flare (importance 3) of the new solar cycle. Many attempts have been made to measure higher energy γ-radiation from the quiet Sun and from solar flares, but no flux has been detected; this is primarily due to the fact that no high-energy γ-ray detectors have viewed a major solar flare during the maximum of the optical or microwave burst. However, theoretical estimates of the flux of solar γ-rays, based on a simple flare model, indicate a readily detectable flux from a major flare even to photon energies of 100 MeV. It is therefore important that experiments be performed during the coming maximum of the solar cycle to investigate this region of the electromagnetic spectrum.