γ全谱法测定空气吸收剂量率的M-C法应用

Application of Monte Carlo method in determination of air absorbed dose rate from a full γ-ray spectrum

γ辐射场剂量的测量可以通过γ剂量率仪或谱-剂量转换的方法来实现。其中一种谱-剂量转换方法为γ全谱法(G(E)函数),即通过建立能谱转换函数G(E),把测得的能谱直接换算成剂量,G(E)函数的系数可通过标准源刻度获得,但标准源及其能量分布会受实际条件限制。我们采用蒙特卡罗方法,在0.1–2.5 MeV能量范围内较均匀地选择了11个能量点,用MCNP5软件模拟了不同尺寸NaI(Tl)晶体的响应能谱,并把它们作为标准谱求解得到了G(E)函数;最后利用该G(E)函数计算各模拟能谱的剂量,并与理论计算值进行比较,平均误差<4%。

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.