Study On The Techniques Of γ Dose Determination By γ Spectrum

Usingγspectrometry for radiation environmental assessment can measure radionuclides in the soil, while the air absorbed dose rate measured for parallel multi-parameter measurement, do not have to use the dose rate meter, is an efficient and economical way. The subject of the research results from home and abroad, using the whole spectrum method to measure air absorbed dose rate, on the measurement and theoretical analysis of the NaI(Tl) crystal detector energy spectrum characteristics, build energy spectrum dose conversion function , named G (E) function. Solving G(E) function in the least square method, select uranium, thorium model, K model, and uranium, thorium and potassium mixed model, and artificial radionuclides 60Co, 137Cs to obtain the standard spectrum. Put G(E) function estimated dose results calculated with the Beck formula results to compare, then measurement data of the function in radioactive standard model and field is to verify the accuracy, analysis error causes. In addition, different size NaI(Tl) detector for differentγ-ray energy point source equipment spectrum are simulated by Monte Carlo software MCNP and build up their energy spectrum dose conversion function. Research results are as follows:(1) On comparison of two multi-channel spectrometer, the relative dose error of G (E) function calculation of the uranium, thorium and potassium and the mixed model is related to the value k,when k = 3, the relative error square S in 2%, when k = 2, S is about 5%,Therefore, k greater the relative error smaller, more accurate dose estimates, the best k value is the number of standard sources reduced one. (2) Through the radioactive standard model and natural radiation validation measurements, the relative dose error of Beck formula estimating about 20%, while the use of G(E) function when the relative error below 5%, shows that the full spectrum method more accurate than the Beck Formula ofγdose measurement.(3) Different standard source selection results on the conversion of dose different, Only the standard source of uranium, thorium, potassium and mixed model, the relative error of dose of the four models calculated about 2%, the relative error of calculated dose in the background model and somewhere of campus respectively were 4.2%, 10.86%, After increase the two artificial sources 60Co, 137Cs equipment spectrum to standard spectrum, the relative error of the four models calculated dose about 1%, the relative error of calculated dose in the background model and somewhere of campus respectively were 0.096%, 4.57%,γair absorbed dose rate values could be determined more accurate.(4) Simulate different size NaI (Tl) crystal detector of 11γ-ray energy point source instrument spectrum as a standard spectrum by the Monte Carlo software MCNP, no matter what the size of the NaI(Tl) crystal detector, the larger of k value, the smaller the relative error, when k = 10, the average relative deviation S are below 1.5% by G (E) function method .