M G Thompson

Precise measurement of the vertical muon spectrum in the range 20-500 GeV/c

The 300 ton cosmic ray spectrograph (MARS) has been used to measure the vertical momentum spectrum of cosmic ray muons in the momentum range 20-500 GeV/c at sea level.

Mars II: The operation and elements of the spectrograph

Abstract The method of operation of the spectrograph - MARS - is described. The limitations of the triggering system, and of the method of storage of data from the flash-tubes are discussed. The momentum selector incorporated in the spectrograph is considered in detail, and it is shown that there is no rejection of events by the device due to the production of bursts in the iron blocks or to air showers incident upon the apparatus. The events are also considered by equipment which, if the data in the event is suitable, calculates the deflection of the particle traversing the spectrograph using the information available from the momentum selector.

The sea-level muon spectrum and charge ratio and their relationship with high-energy accelerator data

The sea-level muon spectrum and charge ratio have been calculated using the available high-energy accelerator data. The calculated muon spectrum is inconsistent with a primary nucleon spectrum of the form AE- gamma but is consistent with a spectrum of the form A(E- gamma 1+X0E- gamma 2). Consideration of the sea-level muon spectron and the primary iron spectrum suggests a primary nucleon spectrum 1.73 (E-2.70+or-0.05+1.35* 10-3*E-2.00+or-0.10)s-1 sr-1 cm-2 GeV-1. This spectrum is in better agreement with the observed muon charge ratio than a spectrum with a single exponent, but the predicted ratio is 7%in excess of the measured ratio at a sea-level momentum of 10 GeV/c, and this is attributed to a breakdown in the limiting fragmentation hypothesis or a difference in the charge distribution of secondaries between nucleon and nucleus targets. The predicted and observed variation of the ratio are in good agreement assuming that the spectrum of nuclei (Z approximately 26) cuts off in the region of 104GeV.

The Durham extensive air shower array — II: Data analysis

Abstract Air shower data registered by the small air shower array at Durham are digitised and stored within 2 ms of an air shower event occurring. The data are decoded and particle densities and the times of arrival of the particles at the detectors are determined. The size, core position and arrival direction of the shower responsible for the event are calculated using the versatile and comprehensive CERN minimising package MINUIT. An event takes on the average 2 s to analyse.

MARS I: THE GEOMETRICAL CHARACTERISTICS OF THE DURHAM MAGNETIC AUTOMATED RESEARCH SPECTROGRAPH.

Abstract The new 300 t vevertical spectrograph of the University of Durham are described. The spectrograph utilises neon flash-tubes for particle trajectory defining purposes and the data from the tubes are fed directly into an on-line computer. The m.d.m. of the spectrograph is 5850 GeV/c, and the ratio of the rms scattering angle to the magnetic deflection is 10%. A momentum selector is incorporated in the instrument with a low momentum cut off of approximately 200 GeV/c. The value of ʃB d l is 8.09×10 6 G cm , and each of the two sides of the spectrograph has an acceptance of (408±2) cm2sr for particles of infinite momentum. The rate of transversal of muons through each side of the instrument is in excess of 2×104 per day.

AN ANALYSIS OF THE CHARACTERISTICS OF A NEON-ALCOHOL SPARK CHAMBER

The characteristics of a spark chamber containing a neon-alcohol mixture are described with particular reference to the variation of efficiency with the parameters of the pulse and the determination of the spark formation time. An interpretation of the characteristics is made on the basis of a model for spark formation and the validity of the mechanism is examined by an internal comparison of the data. The results are used to derive the electron drift velocity as a function of field over the range of E/p from 0.05 to 4 v cm-1(mmHg)-1 and to determine the probability of a single electron initiating a spark. Measurements are also reported on the geometrical properties of the sparks and conditions are studied both for minimizing the angle between the direction of a particle trajectory and the ensuing spark, and for reducing the error in location of the trajectory.

The Durham extensive air shower array — I: A description

Abstract An extensive air shower array characteristic radius 60 m has been built, and is in operation at Durham, England, 40 m above sea level. The array incorporates 14 plastic and 8 liquid scintillation counters having areas varying from 2 m2 to 0.26 m2. The fast timing technique is used to determine the arrival directions of the showers. The array is sensitive to showers of size 105−3 × 106 particles. Near the centre of the array are situated the 300 t Durham muon spectrograph and the Durham flash-tube chamber. The data are stored in an on-line computer attached to the apparatus.

Cosmic ray showers produced by muon bremsstrahlung

A number of groups have observed air showers in the atmosphere at large zenith angles. The possibility of explaining these showers in terms of muon bremsstrahlung is examined; the expected shower size spectrum for this process is calculated and the method enables the sensitivity of shower frequency to high-energy muon intensity to be examined rather simply. Some problems associated with comparison of prediction with the experimental results are indicated. A tentative comparison indicates that when allowance is made for the effect of uncertainties in recorded shower size it is likely that the majority of the showers can be explained by muon bremsstrahlung.

ABSOLUTE INTENSITIES OF COSMIC RAY MUONS ABOVE 3.48 AND 7.12 GeV/c.

The new Durham spectrograph MARS has been used to determine absolute intensities of cosmic ray muons in the near vertical direction with momenta above 3.48 and 7.12 GeV/c. The intensities are found to be close to those previously reported by Aurela and Wolfendale in 1967, the present intensities being higher by some (7.7 ± 1.3)% and (1.7 ± 1.4)%, at the respective momenta. Comparison is also made with the results of other recent measurements.

ELECTRON ATTACHMENT IN A NEON SPARK CHAMBER

Measurements of the efficiency of a neon spark chamber, as a function of the amount of air contaminating the chamber, are reported. The results are shown to be consistent with the discharge model postulated by Burnham et al., and yield a value for the probability of attachment per collision for thermal electrons in air of 6.6 × 10-5.