Uncertainty estimation of conventional neutron-spectrum unfolding codes with Monte Carlo based method
- Katsumi AOKI
- Katsumi AOKI (Kyushu University)
Unfolding method has been applied for neutron spectra derivation of Bonner sphere experiment, multiple-foil activation method and so on. Many types of unfolding techniques such as iterative approximation method, maximum entropy method, and stochastic methods have been developed. However, some of unfolding codes cannot analytically give uncertainty of the derived neutron spectrum. To overcome this situation, we have developed uncertainty estimation method based on Monte Carlo technique. For validation of the method, we applied our developing method to analysis of multiple-foil activation method. Experimental data was obtained at Cyclotron and Radioisotope Center (CYRIC), Tohoku University. Deuterons were accelerated to 20 MeV and bombarded on a thick carbon target to produce neutrons via the C(d, n) reaction. Multiple foils made of Al, Co, Fe, Mo, Ni, Zn, Zr, were irradiated by the neutrons to induce various activation reactions. In the multiple-foil activation method, an unfolding code derives a neutron spectrum from radioactivity induced by neutron irradiation and production rate functions of activation reactions. In our uncertainty estimation method, we considered only statistical uncertainty propagation of measured activity. First, measured activity is randomly changed by Gaussian distribution having statistical uncertainty, and then a neutron spectrum is derived by an unfolding code. This process is calculated iteratively and derived spectra. The spectra are statistically analyzed to estimate the uncertainty propagation. This method was applied to a few conventional unfolding codes, and we compared the propagated uncertainty to know properties of the unfolding codes. The details of developed program to estimate uncertainty of unfolded spectrum and the comparison result between codes will be reported in the presentation.