Cosmic-ray intensities under sea-water at depths down to 1400 m

There is a disagreement between the muon energy spectrum observed at seal-level and the one evaluated from the depth-intensity relation of cosmic rays below ground by using the theoretical expression for energy loss of the muon traversing the rock. As the cause of this fact, one can point out following two reasons: uncertainties in the determination of the compositions of the rocks or imperfection of the theoretical expression for energy loss. To decide this point, the cosmic-ray intensities have been measured at various depths up to 1380 m in the ocean where the composition of the water is well known and the uniformity is well certified. The observed result is in excellent agreement with the sea-level energy spectrum in the corresponding energy region, the current energy loss formula being taken into account. From this fact, it is pointed out that the previous observations of range spectra underground suffered from ambiguities due to uncertainties in the composition of the rocks.