## Doctoral Dissertations

Spring 1990

Dissertation

Physics

#### Degree Name

Doctor of Philosophy

James M Ryan

#### Abstract

We report the results of ground level neutron measurements in the energy range of 10-170 MeV by the neutron double scatter telescope developed at the University of New Hampshire. Measurements were carried out at different altitudes and latitudes for the first time using the same telescope, yielding better correction values for comparison of fluxes measured at different altitudes and latitudes. The measurements were performed at four different locations in the U.S.A.: Leadville (3.1 km) and Boulder (1.66 km), Colorado in the rigidity range of 2.97 to 2.90 GV; Mt. Washington (1.85 km) and Durham (24 m), New Hampshire in the rigidity range of 1.43 to 1.61 GV.

The data from the zenith angle range of 15 to 45 degrees and from 10 to 170 MeV have been analysed. The zenith angle dependence of differential neutron flux in the total energy range was found to have a cos$\sp{n}$ $\theta$ dependence with n = 2.6 $\pm$ 0.2. The integrated flux over the upper hemisphere shows a flat energy spectrum in the 10-60 MeV range and from 60 to 170 MeV falling of as E$\sp{-\alpha}$ with $\alpha$ = 0.6 $\pm$ 0.1. The e-folding depth was found to be $\lambda$ = (123 $\pm$ 29) g/cm$\sp2$ with the neutron count rate at sea level (Durham) being (0.03 $\pm$ 31%). We find that latitude correction applied to upper atmospheric neutrons is larger than that for ground level neutrons. Over the 1.56 GV range of these measurements the flux change after altitude correction is $\sim$21%.

We also describe the instrument, the details of the measurements and the methods of analysis.

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