Using Monte Carlo Method To Simulate The Data Of ～(137)Cs Window In The NaI(Tl) Multi-channel Gamma Spectrum

This paper is about using Monte Carlo method to simulate the gamma photon's response through the NaI(Tl) crystal detector. In this paper, the Monte Carlo method and Monte Carlo method's application in nuclear physics are introduced, the Monte Carlo method's realization in computer and a kind of Monte Carlo computer software —MCNP-4B —are clearly described. In the end of the paper, simulating the different energy gamma photon's response through the nude NaI(Tl) crystal detector and getting the response in 137Cs window from the different kinds of radionuclide, such as the response of 238U, 232Th, 40K and 137Cs itself in 137Cs window, getting the response in NaI(Tl) multi-channel gamma spectrum from different nuclides.When the gamma photon through the NaI(Tl), in the multi-channel gamma spectrum, on the condition of no polarization efficient, there will be exist four action types ,such as Photoelectricity, Compton scatter, Pair production, and Three production. Using the MCNP-4B to simulate the gamma photon particle transporting through the NaI(Tl), when the gamma photon energy exceed 2m0c2, there will produce pair production, when the gamma photon energy exceeds 4m0c2, there will produce Three production. In this paper, the gamma photon energy less than 10MeV, so in the procession of simulating, the former three actions are considered.Using MCNP-4B to simulate gamma photon's response of the Cs window in the NaI(Tl) multi-channel gamma spectrum. In the 137Cs window, it mainly includes nature background ,all kinds of nature radionuclides, the nature background can be measured by instrument. Using the point source to simulate the nature radionuclide response in the Cs window when simulating the contribution of 238U, 232Th,40K in 137Cs window. The 137Cs window is from 0.550MeV to 0.760Mev, using Monte Carlo method — MCNP-4B — to simulate the response of gamma photon through the NaI(Tl), getting the data from all kinds of radionuclide in 137Cs window. When processing the data in 137Cs window, it should subtract the nature background and the response of 238U,232Th,40K, then the result is from the 137Cs itself in the 137Cs window. In this method, simulating the data of 137Cs window within the NaI(Tl) multi-channel gamma spectrum is finished.