The absolute intensities of cosmic-ray muon

by Kong, Fung-luen

Abstract of thesis entitled " The Absolute Intensities of Cosmic-ray Muons "

submitted by Kong Fung Luen, Doreen for the degree of Master of Philosophy

at the University of Hong Kong in November, 1976.

The absolute vertical cosmic-ray muon intensities at sea-level have been ~easured by the

air Cerenkov method. The Cerenkov light generated

by muons above threshold energy in a vertical air column of height about 4.4 metres was 'collected by a'mirror-and-photomultiplier system. The aperture was defined by two large circular scintillators and the muon events extracted by an additional scintillator under a lO~cm lead absorber. A movable ceiling was incorporated to vary the muon path length so as to determine the detectable threshold energy.

This method has the advantage that it does not involve any correction for the multiple scattering, the use of muon range-energy tables or magnetic deflection, which are required in other absolute intensity measurements. In the present

measurement, the thick solid medium usually employed for muon energy or momentum determination was replaced by a simple column of air, thus eliminating the loss of particles due to multiple scattering and the fluctuation of energy loss due to zigzag motion and straggling.

Two points of integral intensities are obtained: the value at 4.81 GeV is (2.59?.lO)xlO-3 cm-2sr-ls-l and the value at 5.485 GeV is ?1.95?.07)xlO-3cm-2sr-ls-l. The first datum is slightly higher than Allkofer's curve and other

contemporary measurement while the second datum is quite consistent with results obtained by other workers.