The angular distnbution of muons observed deep underground (10788 ft, or 8.89 X 10' g~r n -~ standard rock) has been measured with a 174-m' liquid scintillation detector in conjunction with 48384 neon flash tubes. The data are fitted by a curve giving the vertical intensity of muons vs vertical depth h, asern-' sec-' sr-', and y = (7.58 k0.09) X lo4 g cm ' . The constant term, representing the measured depth-independent flux of muons produced in the surrounding rock by interactions of cosmic-ray neutrinos generated in the earth's atmosphere, has the value I,!;' = (2.23 t 0 . 2 0 ) X 10-13 crn-'sec-'sr-'. This observed flux is in fair agreement with that predicted assuming a cosmic-ray neutrino flux which is a composite of several theoretical estimates. Thus the flux of muons from extraterrestrial neutrinos is < 1 0 -'~c m -~ sec-'sr-'. A Z Z E N I T H D I R E C T I O NFIG. 1. The scintillation-detector array and the angular coordinate system.

To obtain information concerning the energy dependence of the average number of evaporation neutrons produced by a nucleon incident on a neutron monitor, measurements were obtained with a multiplicity detector operated during the epoch of solar minimum aboard the U.S. Naval Oceanographic Office worldwide survey aircraft (Project MAGNET). The latitude and altitude variations of events with different multiplicities were determined. The data indicate, for example, that over the range of threshold rigidity 3–13 GV, the latitude effect for threefold events is 1.7 ± 0.1. This is intermediate between the corresponding results obtained with the conventional neutron monitor and a semicubical meson telescope that was also carried aboard the aircraft. The atmospheric attenuation length for high-multiplicity events is less than for events in which a single neutron is detected, consistent with a slightly increasing inelastic nucleon–nucleus cross section as the nucleon energy increases toward 1 GeV.

No abstract

Observations of the intensity of the nucleonic component have been obtained with an airborne neutron monitor aboard the U.S. Naval Oceanographic Of[ice Project Magnet aircrs/t in a worldwide survey extending from the equator to the north and south geomagnetic poles. The data were reduced to a standard pressure altitude (500 mm of Hg), and the effects of temporal variations were removed by a normalization procedure involving four groundbased neutron monitor stations distributed over a wide range of latitude. Representation of the results in the form of an isocosm map revealed general agreement with the Quenby and Wenk calculations of threshold rigidities. Discrepancies are attributable to the inexactness of the approximation adopted for taking into account the effects of the penumbra. The location of the cosmic-ray equator, determined at seven points, was in accordance with calculations using the sixth-order expansion of the geomagnetic potential. The variation in intensity along the equator was in agreement with earlier results obtained during a different phase of the solar cycle. Measurements in the arctic and antarctic regions reveal that, during a period of extreme solar cycle modulation, the intensities in the northern and southern polax caps were equal within less than 0.5%. The latitude dependence of the atmospheric attenuation length of the nucleonic component, L, was determined from observations of the dependence of intensity upon altitude. In the plateau region, the mean value of L was 136.1 ñ 0• g/cm •. L increased by about 11% over the range of threshold rigidity from 2.5 to 16 Gv. The absorption mean free path, X,, deduced from L, was 160 g/cm • in the plateau region. Calculations based on currently accepted models of nuclear collision and of the process of nucleon propagation through the atmosphere yielded a value for the interaction length, X•, of about 80 g/cm •. This increased to 85 g/cm • when the effects of charge exchange were considered.

No abstract