The dosimetric properties of a gamma-radiation field can be measured by a dose-rate meter or by a gamma-spectrometer with spectrum-dose conversion.One of the spectrum dose conversion methods is to evaluate the radiation dosedirectly from integrating the observed pulse height spectrum weighted by a G(E) function

instead of making spectrum analysis.In this paper

energy spectra of 11 single energy point sources in 0.1–2.5 MeV are simulated by using Monte Carlo software MCNP5 for NaI(Tl) detectors of Φ 75 mm×75 mm

Φ 50 mm×50 mm and Φ 25 mm×25 mm.The energy spectra are used as standard spectrum to calculate the G(E) value

so as to calculate corresponding doses.Comparing the results with theoretical value

the error is less than 1.5%.Finally

the G(E)-based γ dose rate of radiation field agreed well(within 5%) with the dose rate measured by a dosimeter.