| Summary: | A double-grid ionization chamber(GIC) based on the 10B(n,α)7Li and 6Li(n,α)T nuclear reaction has been developed for neutron energy spectrum measurement in the energy region below 150 keV of CSNS/Back-n by time of flight method. According to the strong adjoint gamma-flash features, the structure design of thin window and thin bottom lining is adopted. In view of the characteristics of strong gamma-flash neutron beam, the structure design of thin bottom lining is adopted. Garfield++, SRIM and Simcenter Magnet Electric simulation programs are used to simulate the working parameters such as working gas, electrode spacing and electric field distribution of the GIC. CF4, which has fast electron drift speed and small diffusion coefficient and great organizing ability, is selected as the working gas for the CSNS/Back-n beam test with cathode-grid and grid-anode spacing of 20 mm and 5 mm, respectively. The collecting area within 74 mm can be considered as the uniform electric field area, and the relative deviation of the field strength is not more than 0.03%. The performance of the GIC was tested by α source. The GIC has good energy resolution for 239Pu/241Am/244Cm mixed α surface source with CF4. And the best energy resolution is 2.4%@5.48 MeV. Compared with the measured results of the parallel-plate chamber and the silicon microstrip detector, the advantages of energy resolution of the GIC developed in this work are verified.
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