Attenuation of neutrons in the atmosphere and a thick carbon target

A neutron beam dump experiment has been carried out using the accelerator b eam at RCNP, Osaka University. Neutrons with energies T-n = 100-400 MeV wer e allowed to bombard a carbon target (density 1.8 g/cm(3)) which had a thic kness varying from 0 to 300 cm, and the attenuation of the neutrons was mea sured in the range from 0 to 540 g/cm(2), The experimental data were well r eproduced by the Monte Carlo calculation by the Shibata model. Using these results, the attenuation of neutrons in the Earth's atmosphere was obtained by means of a simulation. The results are useful not only for cosmic ray e xperiments but also for radiation protection experiments since the target d oes not contain hydrogen. (C) 2001 Elsevier Science B.V. All rights reserve d.