MCNP simulation of detection efficiency of NaI and measuration of natural radionuclide contents in soil in the northeast China

Using the standard earth sample, the full-energy peak detection efficiency of NaI(Tl) detector for γ rays with the biggest branching ratio emitted from the isotopes of ⁴⁰K, ²²⁶Ra, ²³²Th, ²³⁸U in earth was measured. And the same efficiency also simulated with the code of MCNP. The results obtained by both methods matched well and the difference between the two results was no more than 5 percent. To calculate the maximum error induced by the variation of detection efficiency from the difference of the density of earth samples, the detection efficiency under the different density of earth samples was investigated with MCNP code. Based on the work mentioned above, some typical samples of earth and architectural materials were measured. Compared with data form literature, the results were reasonable and had some reference value in this field. (authors)