Cerenkov Light Pulse Research Articles

Photocathodes for the Detection of Cerenkov Radiation in Deep-Water Neutrino Telescopes

The results from a comparative assessment of the applicability of various vacuum photodetectors with different types of photocathodes to next-generation neutrino telescopes are presented. It is shown how the spectrum of Cerenkov radiation is altered during its propagation through the waters of Lake Baikal and the Mediterranean Sea. The effect exerted by the dispersion of the medium on the duration of a Cerenkov light pulse is studied.

Primary composition of cosmic rays near 1017eV

Measurements of the Cerenkov light pulse shape in cosmic-ray showers of energy approximately 1017-1018 eV are reported. These are interpreted with the aid of detailed computer simulations to give estimates of the mean value and fluctuations in the atmospheric depth of shower maximum. Implications for the primary mass composition and the model of hadronic interactions are discussed briefly.

A new upper limit on optical bursts from primordial black hole explosions

Two wide-angle photomultiplier systems were simultaneously operated over a baseline of nearly 30 km in a search for cosmic optical bursts of fractional microsecond time-scale. In 74 hours of overlapping observation, one event was recorded coincident to 1 ms as against the corresponding accidental coincidence value of 0.14 from Cerenkov light pulses from unrelated cosmic ray showers. The possible cosmic origin of this event, including that from primordial black-hole explosions, is discussed and the corresponding upper limits derived.

A nonrandom component in cosmic rays of energy ≥ 1014 eV

We have been studying1 the distribution of the arrival times of atmospheric Cerenkov light pulses, initiated by cosmic rays of energy ≥1014 eV. We have now detected a nonrandom component for tune separations <40 s, and here we discuss the possibility that it has a point-source origin.

The primary cosmic-radiation spectrum from 1012 eV to 1015 eV from atmospheric Črenkov-radiation measurements

A measurement of the primary spectrum of the cosmic radiation in the energy range of 5·1011 eV to ∼5·1015 eV has been made, employing the detection of atmospheric Cerenkov-light pulses produced in extensive air showers. Through the use of an all linear system and an extensive series of calibration, the uncertainties of previous measurements have been removed. The relation between the Cerenkov pulseheight spectrum and the primary cosmic-ray spectrum was investigated through the use of Monte Carlo air shower simulations designed specifically for interpretation of the results of this experiment, covering primary energies from 1011 eV to 1013 eV. These indicate that, due to large fluctuations in shower development, the technique is relatively insensitive to the spectrum of primaries at energies of 1011 eV to 1013 eV. The simulations also indicate a decrease in the importance of fluctuations with increasing primary energy. The measured spectral index shows an increase at ∼1.5·1015 eV. The physical implications of this bending are discussed.

Direct observation of individual cosmic ray showers

THE detection of the cores and directions of large cosmic ray showers became possible in the late 1950s as a result of the combination of the techniques of density sampling, using an array of particle detectors to find the shower centre of symmetry1 and fast timing using spaced scintillation counters to fix the shower arrival direction2. Previous Cerenkov light measurements in extensive air showers have concentrated on the gross properties of the light flux on the ground using a similar approach to the particle measurements. It has been suggested by Fomin and Khristiansen3 and Efimov et al.4. that the full-width half maximum (FWHM) of pulses of Cerenkov light may depend on the longitudinal development of the shower, and so on the atomic mass number of the primary. We have gone further and used precise measurements of the detailed shape of the Cerenkov light pulses recorded by several well spread simple detectors to reconstruct accurately an image of the shower in Cerenkov light. This has been done without the usual prerequisite of first determining the shower's axis of symmetry and arrival direction. The data so obtained may be of use in studies of the average shower characteristics, the search for extreme fluctuations and, we hope, for the labelling of individual showers with an indication of the mass of their primary.

Nuclear Radiation Measurement Using Cerenkov Light Generated in a Light Guide

Cerenkov light pulses were generated in one end of 100-m lengths of multi-fiber cable and a single strand of graded index fibers by a 50-ps burst of 18-MeV electrons. Pulse dispersion in this length was between 3.5 and 2.9 ns for the cabled fibers and 4.1 ns in the single fiber. By narrow band optical filtering, the dispersion was reduced to values between 610 and 246 ps in the cable and 400 ps for the single fiber. Cerenkov sensitivity was measured for two of the fibers and found to be 6 × 1013 photons/sec and 6 × 1012 photons/ sec for 50 ps electron bursts of 10 A/cm2 and 6 A/cm2 respectively. In terms of time response and sensitivity it appears feasible to design a nuclear explosive diagnostic system utilizing Cerenkov radiation generated in and transmitted by cables of graded index fibers.

Cerenkov pulse dispersion in two low-loss fibers

We have measured the material and mode dispersion of a 50-psec Cerenkov light pulse generated in 500-m lengths of low-loss graded and step-index Corning fibers. The initial 15.7-nsec full width at half-maximum (FWHM) transmitted pulse in the graded fiber was reduced to less than 2 nsec with narrow-band optical filtering. Parallel measurements in the step-index fiber gave a value of less than 4 nsec for an initial 16.3-nsec FWHM pulse. Fluorescence induced in the fiber by the electron radiation was less than 1% of the amplitude of the transmitted Cerenkov light in the graded fiber and approximately 2% in the step fiber.

Photomultiplier Counters in High-Energy Physics Experiments

Techniques in the use of photomultipliers in high-energy nuclear physics are presented by the description of experiments that have been prominent recently. The applications involve the use of photomultipliers with attendant amplification at the limit of present possibilities of time resolution. Such applications include measurements of time of flight, measurement of lifetime of heavy unstable particles, and the elimination of background effects in the pulsed radiation fields of high-energy accelerators. The need for the development of large fast-rising signals from events of small light output, such as Cerenkov light pulses, is made apparent, and a discussion of the performance desired from electron multipliers in view of contemplated experiments is presented.