To accurately and speedily determine a background counting rate.

This method for estimating the background counting rate comprises: an observation process S3 for actually measuring the background (BG) counting rate and determining an observed value of the BG counting rate; a first simulation process S4 for determining a pseudo BG counting rate by generating virtual radiation transmitted through a shielding body to be BG in a virtual three-dimensional model of a radiation detector and the shielding body; a second simulation process S5 for determining a pseudo BG counting rate by generating virtual radiation transmitted through the shielding body to be BG in a virtual three-dimensional model of an object to be measured, the radiation detector, and the shielding body; a correction coefficient computing process S6 for determining a correction coefficient on the basis of the BG counting rates determined in the first simulation process and the second simulation process; and a correction process S7 for correcting the observed value through the use of the correction coefficient. In the first and second simulation processes S4 and S5, the virtual radiation is generated from inside an virtual three-dimensional model of the shielding body.

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