Based On The ¹³⁷Cs Dry Storage Radioactive Source Spectroscopy Study Of The Dosimetry

Dry storage γ radioactive source is often used to scale nuclear detector,calibrate γ dosimeter.But because of the structural features of dry storage radioactive source,the radioactive source does not only radiate γ ray,but also make Compton plateau with shielding material after the ray,which will generate backscattering photon.Usually,the standard dosemeter is calibrated through the γ ray of the known energy,taking no account of the effect of backscattering photon. Though the energy of backscattering photon is lower than the photon of the principal ray,but the fluence percentage between backscattering and the principal ray photon is not exact.Using this type of storage radioactive source to calibrate dosemeter will have some errors,which is disadvantageous in scaling detector and calibrating γ dosemeter.This thesis use the Monte Carlo Simulation and experiments to confirm of the exist backscattering peak of the present dry storage radioactive source,and give two ways to and analyse its results.Caculating results of the Monte Carlo Simulation suggest:measuring position from 1meter to 6.8meter,when there is a wall,the minium of back-scattered energy area accounts 9.33% of the main ray,and the maximum is 13.32%,while there is no wall,the minimum is 8.82%,the maximum is 9.33%.This passage adopts two methods to deduct Compton plateau to analyse the backscattering peak in the energy spectrum measured by experiments.one is the Compton plateau that simulates the monoenergetic photon in the HPGe detectors.The other is by using the theory deducing experiment to measure the fluence percentage between backscattering photon and the photon of the principal ray,and then deduct the Compton plateau according to this percentage.By constract,I adopt the latter method to deduct the Compton plateau in the energy spectrum measured by experiments.Utilizing the caculated intrinsic efficiency of the detector and the energy spectrum measured by experiments after deducting the Compton plateau,we will acquire the energy fluence spectrum of the radiative source,and find that the fluence percentage of backscattering and principal ray at 6meter is 9.1%. This result suggests that the experiment data well inosculate data of the Monte Carlo Simulation.Utilizing the energy spectrum measured by experiments of the 137 Cs and the external photons of the different energies in the ICRP74 report,we caculate the percentage between the fluence caused by backscattering ray and fluence caused by principal ray.The result suggests,the low-energy sector of the energy spectrum measured by experiments in the HPGs detector mainly is the Compton plateau, the percentage of the dose caused by backscattering and principal ray is 3%or so.If we need higher dose accuracy,we should consider more about the dose caused by backscattering.