Large Cosmic-ray Showers Research Articles

The mass composition of primary cosmic rays of energy 6×1015-2×1018eV

Measurements of the mean and fluctuation in the depth of cascade maximum of large cosmic-ray showers are reported. These are compared with computer simulation predictions for iron nucleus and proton primaries incorporating a range of models of the hadronic interaction. The authors conclude that the primary composition comprises predominantly iron-like nuclei at 1016 eV with an increasing proportion of lighter nuclei at higher energies.

The average depth of cascade maximum in large cosmic-ray showers from particle measurements

Measurements of the angle of muons to the shower-core direction and the spread in angle of muons in extensive cosmic-ray showers of energy greater than 1017 eV are reported. These measurements, along with measurements of the lateral structure function of deep-water detectors and muon density detectors, are compared with rigorous computer simulations. The data are used to derive the average depth of electron cascade maximum as a function of primary particle energy.

Computer simulations of atmospheric Čerenkov radiation in large cosmic-ray showers

The computations of Protheroe and Turver (1) have been extended to include the Cerenkov light in showers incident at zenith angles up to 60°. We use results from a wide range of scaling-based models to demonstrate the existence of a unique model-independent relationship between a range of observable Cerenkov parameters and the depth of the electron cascade maximum.

Photoproduction in large cosmic-ray showers

The authors examine the importance of the photoproduction of pions as a source of low-energy muons in cosmic-ray air showers of the highest energy. Results of detailed calculations of the characteristics of this additional muon component are presented. The consequences for the interpretation of experiments which are sensitive to low-energy muons in high-energy extensive air showers such as existing experiments to measure muon core angles, shower particle arrival times and the primary energy spectrum are discussed.

Computer simulations of Čerenkov light from large cosmic-ray showers

Detailed computer simulations have been made for the air Cerenkov radiation produced in large cosmic-ray showers. The hadron cascade employed in the air shower simulation incorporates Feynman scaling; primary particles ranging in mass from protons to iron nuclei are considered. The simulation results compare well with recent measurements of the average characteristics of Cerenkov light from large cosmicray showers made with a synchronized array of fast photomultipliers at the Haverah Park EAS array; satisfactory overall agreement is found between the observations and the predictions for showers of primary energy (≈2·1017÷≈2·1018) eV having their electron cascade maximum at depths in the atmosphere of (≈680÷≈770) g cm−2. For the cascade model employed here these depths of maximum arise for a heavy primary mass composition.

Ĉerenkov radiation in large cosmic-ray air showers

A synchronized array of fast photomultipliers has been used to reconstruct the image in Ĉerenkov light of individual large cosmicray showers high in the atmosphere. The details of the images are in agreement with simulations based upon conservative models for cascade development. Observation of the fluctuations of the image between showers may enable the mass of the energetic cosmic rays to be determined.

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.

Optical Cerenkov emission from large cosmic ray air showers (computer simulation)

Computer simulations of the optical Cerenkov emission from large cosmic ray showers indicate that the form of the lateral distribution of photons is sensitive to the longitudinal development of the electron cascade and so to the nature of the primary particle. The breadth of the computed distribution of photons, confirmed by measurements made at the Haverah Park air shower array, suggest the possibility of detection of the largest air showers widely separated, simple detectors.

Atmospheric Signals Caused by Cosmic-Ray Showers

It is suggested that large cosmic-ray showers can be detected by the electrical signal produced when the ionization of the shower nullifies the electric field of the earth. The signal should have two components, a very short but small signal due to the motion of free electrons, and a slow but possibly large component due to the motion of the ions. The energy of the signal is stored in the earth's electrical field until it is released by the ionization. An estimate is made of the size and duration of the signals which indicates that they may be detectable, especially in the case of the slow signal which may have a time of rise of the order of a fraction of a second.

Theoretical Calculations on Extensive Atmospheric Cosmic-Ray Showers

Large cosmic-ray showers in air, investigated with ionization chambers and coincidence counters, have been explained hitherto as originating from primary electrons of very high energy. In recent experiments at an altitude of 3100 meters Lewis measured the frequency of coincident bursts in two unshielded ionization chambers. The theoretical cumulative frequency $H(P,D)$ of such coincidences is calculated as a function of the electron density $P$ and the separation $D$ of the chambers for this altitude and for sea level. The cumulative size-frequency distribution $H(P)$ for bursts in a single chamber is also computed. All calculations are based on the cascade theory of showers and the theory of the multiple scattering of electrons. The theoretical frequencies compared with those of experiments show (1) a much smaller absolute value, (2) a much slower drop as the chambers are separated, (3) a different form for the cumulative size-frequency distributions, and (4) a smaller increase with altitude. It is pointed out that the large number of narrow showers of high energy observed must originate much nearer to the chamber than the top of the atmosphere if they are to be explained by the cascade theory. It is concluded that the assumption of primary electrons is of little help in explaining the experimental results.

Radio echoes and cosmic ray showers

It is suggested that the origin of some of the transient ionic clouds, generally assumed to be responsible for the low level sporadic radio reflexions, may be due to large cosmic ray showers. It is shown that cascade cosmic ray showers of sufficient energy to produce some of these radio reflexions certainly exist, but there is insufficient published evidence to decide whether any of the echoes already observed are actually due to such showers. More conclusive evidence could be obtained from the frequency-size distribution of the radio echoes observed from a horizontal or vertically directed beam.

Large Cosmic Ray Showers and Mesons

IT has been pointed out recently by Bhabha, Carmichael and Chou1 that a meson may produce a large cosmic ray shower by knocking on an atomic electron in a close collision; this electron then produces a shower by the ordinary cascade process. Previously, Bhabha2 had come to the conclusion that large knock-on showers are comparatively unimportant; but he had based his argument on the assumption that the scattering of mesons by electrons could be described by the Dirac relativistic theory. However, Massey and Corben3 have shown that the effect of the spin of the meson is greatly to increase the scattering for high energies of the incident meson and the knocked-on electron. Using Massey and Corben's formula, Bhabha, Carmichael and Chou have shown that the experimental results of Carmichael and Chou4 can be reasonably well explained, whereas the previous theory predicted too few large showers.

Investigation of Cosmic Ray Showers of Atmospheric Origin, using Two Cloud Chambers

USING two simultaneously operated cloud chambers, we have investigated the occurrence of large cosmic ray showers originating high in the atmosphere1, and the transition behaviour of these showers in absorbing material. The cloud chambers were 28 cm. in diameter with an illuminated depth of 4 cm. (chamber I) and 8 cm. (chamber II) respectively. The counters used to select showers and so to operate both chambers were all situated around chamber I, there being none around chamber II. The whole apparatus was situated beneath a light roof.

Nature of Extensive Cosmic Ray Showers

THE counter experiments of Auger, Maze and Grivet-Meyer1, and those of Kolhorster, Matthes and Weber2, indicate the existence of very large cosmic ray showers, extending over an area of many square metres, and consisting of several thousand particles. In order to obtain information about the constituents of these showers, a cloud chamber with a 2 cm. lead plate across its centre, situated in a room with a light roof, has been used in a magnetic field of 800 gauss. The chamber was controlled by the five-fold coincidences of counters, distributed so that the outer counters were separated by 5 metres. With this counter arrangement the chamber took, on the average, 0·2 photographs per hour.