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The scintillation and Cherenkov responses of plastic Cherenkov radiators containing different wavelength-shifting fluors in varying concentrations have been studied in beams of low energy protons and pions. For cosmic ray applications, where large Cherenkov to scintillation ratios are desired, the optimum fluor concentrations are 0.000025 by weight or less.
Previous treatments of Cherenkov radiation, electromagnetic and gravitational, by tachyons were in error because the prescription employed to cut off the divergent integral over frequency is not a Lorentz invariant procedure. The resulting equation of motion for the tachyon is therefore not covariant. The proper procedure requires an extended, deformable distribution of charge or mass and yields a particularly simple form for the tachyon's world line, one that could be deduced from simple invariance considerations. It is shown that Cherenkov radiation by tachyons implys their ultimate annihilation with an antitachyon and demonstrates a disturbing property of tachyons, namely the impossibility of specifying arbitrary Cauchy data even in a purely classical theory.
The primary goal of this research project was to further extend the use of advanced heteroepitaxial-semiconductor crystal growth techniques such as molecular beam epitaxy (MBE) and to demonstrate significant gains in UV/blue photonic detection by designing and fabricating atomically-tailored heteroepitaxial GaAlN/GaInN photocathode device structures. This NASA Explorer technology research program has focused on the development of photocathodes for Cherenkov and scintillation radiation detection. Support from the program allowed us to enhance our MBE system to include a nitrogen plasma source and a magnetic bearing turbomolecular pump for delivery and removal of high purity atomic nitrogen during GaAlN/GaInN film growth. Under this program we have also designed, built and incorporated a cesium activation stage. In addition, a connected UHV chamber with photocathode transfer/positioner components as well as a hybrid phototube stage was designed and built to make in-situ quantum efficiency measurements without ever having to remove the photocathodes from UHV conditions. Thus we have constructed a system with the capability to couple atomically-tailored MBE-grown photocathode heterostructures with real high gain readout devices for single photon detection evaluation.
We report on measurements of (11-18)-cm wavelength radio emission from interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield Accelerator.
This paper describes the concept of a large gamma-ray imaging telescope system (GRITS) which will provide sufficient sensitivity for the identification of faint objects to be catalogued by the Gamma-Ray Observatory. The technique used in this telescope for the detection of gamma rays is based on the conversion of the incident gamma ray into an electron-positron pair which subsequently produces Cherenkov radiation. The gamma ray is identified by a unique signature based on a sequence of time-delayed coincidence events. The GRITS telescope will use the extended Shuttle external tank, ET, as the pressure vessel necessary for the gas-Cherenkov process. Astronauts from the Shuttle or the Space Station performing EVA will convert ET to an autonomous spacecraft and install the telescope inside the ET.
The third High Energy Astronomy Observatory satellite (HEAO-3) carries a particle telescope for the detection of highly charged cosmic ray nuclei. These nuclei, which have Z equal to or greater than 28, are much rarer than the lower charged nuclei in the cosmic radiation. As a consequence, this particle telescope was required to have a large collecting area as well as an ability to resolve individual elements. This paper describes the telescope, composed of large area parallel plate ionization chambers, multiwire ion chamber hodoscopes and a Cherenkov radiation detector. The resulting telescope has a total geometry factor of 59,000 sq cm sr and is capable of measuring the charges of nuclei in the range Z = 14-120.
Intensities of auroral and magnetospheric hiss generated by the Cherenkov radiation process of electrons in the lower magnetosphere were calculated with respect to a realistic model of the earth's magnetosphere. In this calculation, the magnetic field was expressed by the Mead-Fairfield Model, and a static model of the iono-magnetospheric plasma distribution was constructed by accumulated data obtained by recent satellite observations. The energy range of hiss producing electrons and the frequency range of produced VLF in the computation are 100 eV to 200 keV, and 2 to 200 kHz, respectively. The maximum hiss intensity produced by soft electrons is more than one order higher than that of hard electron produced hiss. Higher rate of hiss occurrence in the daytime side, particularly in the soft electron precipitation zone in the morning sector, and less association of auroral hiss in nighttime sectors must be, therefore, due to the local time dependence of the energy spectra of precipitating electrons rather than the difference in the geomagnetic field and in the geoplasma distributions.
The Cherenkov detector designed and built for the LEAP (Low Energy AntiProton) experiment utilized a novel design to achieve appreciable sensitive area (02. sq m) with a refractive index of 1.25 in a magnetic fringe field region (500-1000 Gauss). The weight was held to only 64 kg by using 16 unshielded Hamamatsu R2490-01 photomultiplier tubes, each aligned with its local magnetic field. A filling and reservoir system for the highly volatile FC-72 liquid Cherenkov radiator also presented many design challenges. Relativistic particles yielded about 72 photoelectrons, total.
Upward-going showers in the atmosphere can be detected by an orbiting satellite with appropriate instrumentation. If the method only uses directional Cherenkov radiation, it is difficult to discriminate the red shower events from the background noises of very short pulse. A spectroscopic polychromatic optical design can intentionally blur the focusing of photons at shorter wavelengths (300 - 330 nm), spreading the image size to 2 x 2 or 3 x 3 pixels. False triggers due to random chance coincidence of noises can be drastically reduced with a spectroscopic polychromatic, refractive telescope.
We investigate the capability of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA)in performing Target-of-Opportunity (ToO) neutrino observations. POEMMA is a proposed space-based probe-class mission for ultra high-energy cosmic ray and very-high-energy neutrino detection using two spacecraft, each equipped with a large Schmidt telescope to detect optical and near-ultraviolet signals generated by extensive air showers (EASs). POEMMA will be sensitive to Cherenkov radiation from upward-moving EASs initiated by tau neutrinos interacting in the Earth. POEMMA will be able to quickly re-point (90◦in 500 s) each of the two spacecraft to the direction of an astrophysical source, which in combination with its orbital speed will provide it with unparalleled capability to follow up transient alerts. We calculate POEMMA’s transient sensitivity for two observational configurations for the satellites (ToO-stereo and ToO-dual for smaller and larger satellite separations, respectively) and investigate the impact of variations arising due to POEMMA’s orbital characteristics on its sensitivity to tau neutrinos in various regions of the sky. We explore separate scenarios for long (∼105−6s) and short (∼103s) duration events, accounting for intrusion from the Sun and the Moon in the long-duration scenario. We compare the sensitivity and sky coverage of POEMMA for ToO observations with those for existing experiments (e.g., IceCube, ANTARES, and the Pierre Auger Observatory) and other proposed future experiments (e.g., GRAND200k).For long bursts, we find that POEMMA will provide a factor of&7 improvement in average neutrino sensitivity above 300 PeV with respect to existing experiments, reaching the level of model predictions for neutrino fluences at these energies and above from several types of long-duration astrophysical transients (e.g., binary neutron star mergers and tidal disruption events). For short bursts, POEMMA will improve the sensitivity over existing experiments by at least an order of magnitude forEν∼>100 PeV in the “best-case” scenario. POEMMA’s orbital characteristics and rapid re-pointing capability will provide it access to the full celestial sky, including regions that will not be accessible to ground-based neutrino experiments. Finally, we discuss the prospects for POEMMA to detect neutrinos from candidate astrophysical neutrino sources in the nearby universe. Our results demonstrate that with its improved neutrino sensitivity at ultra-high energies and unique full-sky coverage, POEMMA will be an essential, complementary component in a rapidly expanding multi-messenger network.
A proposed radiation-detecting apparatus would provide information on the kinetic energies, directions, and electric charges of highly energetic incident subatomic particles. The apparatus was originally intended for use in measuring properties of cosmic rays in outer space, but could also be adapted to terrestrial uses -- for example, radiation dosimetry aboard high-altitude aircraft and in proton radiation therapy for treatment of tumors.
A solid-state radiation detector includes a pattern of conductive metal on a zinc oxide substrate. The pattern provides an arrangement of interdigitated electrode fingers. The wide band gap substrate is sensitive to UV light, which can cause a conductivity change in the substrate. The electrode fingers are configured to sense a difference in substrate conductivity resulting from UV light. The detector has a fast response time, which enables it to detect Cherenkov light. The compact detector provides savings on size, weight, and required power. Thus, the solid-state detector can be used to replace photomultiplier tubes in Cherenkov detectors. The features of the novel detector allow for an improved system to detect and monitor UV radiation, especially during deep space missions.
A range-energy experiment was built to measure the isotopic composition of galactic cosmic rays. An enrichment of neutron rich isotopes, 22Ne and (25Mg + 26Mg) in particular, when compared to the solar composition is shown. A rich statistics measurement of these and other neutron-rich isotopes in the galactic flux yields information to the source of these particles. A computer simulation of the experiment was used to estimate the instrument resolution. The Cherenkov detector light collection efficiency, was calculated. Absorption of light in the radiator was considered to determine the optimum Cherenkov medium thickness. The experiment will determine the isotopic composition for the elements neon through argon in the energy range 300 to 800 MeV per nucleon.
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The recent Fermi detection of the globular cluster (GC) 47 Tucanae highlighted the importance of modeling collective gamma-ray emission of millisecond pulsars (MSPs) in GCs. Steady flux from such populations is also expected in the very high energy (VHE) domain covered by ground-based Cherenkov telescopes. We present pulsed curvature radiation (CR) as well as unpulsed inverse Compton (IC) calculations for an ensemble of MSPs in the GCs 47 Tucanae and Terzan 5. We demonstrate that the CR from these GCs should be easily detectable for Fermi, while constraints on the total number of MSps and the nebular B-field may be derived using the IC flux components.
Spontaneous emission of radiation with frequencies near the electron plasma frequency is studied for a plasma which consists of both thermal and runaway electrons. It is found that a substantial enhancement of the spontaneous radiation intensity can occur in this frequency regime via a Cherenkov resonance with the runaway electrons. Numerical analysis indicates that, for reasonable estimates of densities and energies, the plasma-frequency radiation can attain levels greater than the peak thermal emission at the second gyroharmonic.
The detection of the Crab Nebula via the Cherenkov imaging technique places TeV astronomy on a secure observational footing. The motivation for TeV observations, a discussion of the atmospheric Cherenkov technique, the experimental details of the Crab Nebula detection, and its scientific implications are presented. The present dilemma of VHE/UHE astronomy is that the Crab appears to be the only source whose showers match theoretical expectations. The situation will be clarified as improved ground-based detectors come on-line with sensitivities matching those of the GRO (Gamma Ray Observatory) instruments.
A particle detector is provided, the particle detector including a spherical Cherenkov detector, and at least one pair of detector stacks. In an embodiment of the invention, the Cherenkov detector includes a sphere of ultraviolet transparent material, coated by an ultraviolet reflecting material that has at least one open port. The Cherenkov detector further includes at least one photodetector configured to detect ultraviolet light emitted from a particle within the sphere. In an embodiment of the invention, each detector stack includes one or more detectors configured to detect a particle traversing the sphere.