The dose assessment for cosmic rays has depended on analytical calculations and simulations, since the radiation has relatively high energy and is hardly distinguishable from other environmental radiations. Meanwhile, the neutron monitor selectively detects cosmic neutrons by shielding neutrons from the lithosphere, and also has great advantage at statistical reliability of the cosmic ray measurement that can, therefore, measure small effects in detail. In the present study, the method of dose assessment for cosmic rays in Korea was analyzed with the real time measured data from the neutron monitor. The main results of this study are listed below:
? the standard 18-tube NM64 neutron monitor was successfully introduced for the first time in Korea;
? the reliability and performances of the cosmic neutron detection system were confirmed through evaluations of the barometric pressure correlation and the periodic modulations of cosmic rays and;
? the formulas of the ambient dose conversion coefficient for cosmic ray at various altitudes of Korea were established.

In order to verify the performance of the neutron monitor, located in Daejeon, Korea (latitude: 36.39 , longitude: 127.37 , altitude: 200 m),
the effect of the barometric pressure was evaluated. The diurnal and 27-day variations were analyzed with the pressure corrected data through fast Fourier transformation and ordinary harmonics analysis. Furthermore, the performance of the introduced detector was verified by an observation of Forbush decrease phenomena, in comparison with the interplanetary magnetic field and Oulu neutron monitor.
Response characteristics were studied through various physics models in Monte-Carlo simulation codes and then, the response function was acquired. To estimate the integral response, energy spectra of protons and
neutrons were obtained analytically and experimentally. Subsequently, the estimated count-rate was calculated by multiplying the energy spectrum by the response function. In both cases, estimated count rate and real count rate did not show much difference. Spectrum changes of cosmic ray according to main parameters were analyzed and then, the relationship between expected count-rate and the ambient dose was simplified by two parameters, relative humidity and atmospheric pressure. Therefore, the conversion formula for the count-rate to the ambient dose was established.