Cerenkov Events Research Articles

First Cerenkov charge-induction (CCI) TlBr detector for TOF-PET and proton range verification

Thallium bromide (TlBr) is a semiconductor material and, simultaneously, a good Cerenkov radiator. The performance of a TlBr detector that integrates two different readouts, the charge induction readout and the detection of Cerenkov light, was evaluated. A TlBr detector with dimensions of 4 × 4 × 5 mm3, with a monolithic cathode and an anode segmented into strips, was manufactured. One of the bare and polished 4 × 4 mm2 faces of the detector was coupled to a silicon photomultiplier (SiPM) to read out the Cerenkov light. Simultaneous timing and energy resolutions of <400 ps full width at half maximum (FWHM) and ~8.5% at 511 keV were measured using the Cerenkov detection and charge induction readouts, respectively. A coincidence time resolution of 330 ps was obtained when selecting Cerenkov events with amplitudes above 70 mV. The combination of both readouts showed the potential to resolve the depth-of-interaction (DOI) positioning, based on the improvement of energy resolution when selecting events with similar electron drift times. This manuscript sets the stage for a new family of semiconductor detectors that combine charge induction readout with the Cerenkov light detection. Such detectors can provide, simultaneously, outstanding timing, energy, and spatial resolution, and will be an excellent fit for applications that require the detection of high-energy gamma photons with high timing accuracy, such as time-of-flight positron emission tomography (TOF-PET) and prompt gamma imaging (PGI) to assess the particle range in hadron therapy.

Cerenkov Events Seen by The TALE Air Fluorescence Detector

Cerenkov Events Seen by The TALE Air Fluorescence Detector

Comment on “T[CLC]e[/CLC]V Cerenkov Events as Bose-Einstein Gamma Condensations”

The idea that the TeV air showers, thought to be produced by gamma rays greater than 10 TeV from Markarian 501, can be mimicked by coherent bunches of sub-TeV photons is reexamined, focusing on fundamental considerations. In particular, it is shown that the minimum spot size of a beam of photons arriving at Earth is on the order of a few kilometers unless a lens with certain characteristics is placed between the TeV laser and Earth. The viability of the production mechanism of coherent bunches of TeV photons proposed by M. Harwit et al. is also reassessed.

T[CLC]e[/CLC]V Cerenkov Events as Bose-Einstein Gamma Condensations

The recent detection of gamma radiation from Mrk 501 at energies as high as ~25 TeV suggests stringent upper bounds on the diffuse, far-infrared, extragalactic radiation density. The production of electron-positron pairs through photon-photon collisions would prevent gamma photons of substantially higher energies from reaching us across distances of order 100 Mpc. However, coherently arriving TeV or sub-TeV gamma rays—Bose-Einstein condensations of photons at these energies—could mimic the Cerenkov shower signatures of extremely energetic gamma rays. To better understand such events, we describe their observational traits and discuss how they might be generated.

An upper limit on TeV gamma rays from Geminga

Atmospheric Cerenkov events recorded by the Gulmarg gamma-ray telescope between December 1984 and December 1985 have been systematically searched for both steady and time-dependent photon emissions from the enigmatic 2CG catalogue source Geminga at energies above 6 TeV. Having found none at the authors sensitivity level, upper limits are derived on both the emission modes which, while comparing favourably with those obtained at Whipple Observatory and Ooty, are significantly below the flux values quoted for this source by the Tian-Shan group.

Pulse Shape Discrimination in a Portable Beta-Gamma Dose Rate Meter

A portable beta-gamma dose rate instrument capable of tissue-equivalent dose rate measurements in mixed beta-gamma fields has been developed and tested. The detector is a 5 mg/cm2-thick plastic scintillator with a 4 mg/cm2-window and a 1 cm-thick lucite light pipe to achieve the backscatter geometry required for this application. Pulse shape discrimination techniques are used to minimize contributions from Cerenkov events within the lucite light pipe, photomultiplier tube glass, and direct interaction within the photomultiplier tube dynode structure. The response of the prototype instrument has been demonstrated to be independent of beta end-point energy to a precision of ± 5% from 150 keV to 2.9 MeV and 1 mRem/h to 200 Rem/h. Response to gamma radiation in the energy range >400 keV is also accurate, but low energy photon response (<100 keV) is considerably lower than expected.

Photon Counting with Fiber-Optic Coupled Scintillators

By coupling a scintillation crystal to a photomultiplier with fiber optics, one can place the detector in areas not normally accessible to a crystal-photomultiplier combination. Although fiber optics provide a flexible optical coupling, serious light losses cause about a factor of 10 reduction in the light intensity reaching the photomultiplier. Most of the light loss is due to the small acceptance angle of the fiber optics with transmission losses and crystal aperture losses playing secondary roles. Attention to the design and to the selection of the crystals and fiber optics help to optimize the light collection efficiency. The light losses lower the scintillation intensity from low-energy (10 to 40 keV) radiation into the region where photomultiplier noise becomes important (3.5 - 18 photoelectron equivalents). This noise consists of Cerenkov events, faceplate scintillations, electroluminescence, afterpulses and thermionic emissions. For effective low background counting this noise must be reduced. A combination of pulse-shape discrimination, magnetically limiting the photocathode area and shielding were effective in reducing the background rate from 513±3 counts/minute to 10.0±0.5 counts/minute in the energy range from 6.5 to 40 keV. By coincidence counting, in the same energy region, a background rate of 1.60±0.28 counts/minute was obtained.