Detection of correlated fission fragments with a twin Frisch-grid ionization chamber

Abstract

Twin Frisch-grid ionization chambers (TFGICs) have been widely used in the measurement of total kinetic energy (TKE), angular distribution, mass, and charge of the correlated fission fragments. To study these correlated fission parameters, we have developed a TFGIC with a digital acquisition system for use at both the Chinese Mianyang research reactor (CMRR) and neutron science facility in the Institute of Nuclear Physics and Chemistry (INPC), as well as the China Spallation Neutron Source (CSNS). The distribution of the electric field was investigated with Garfield toolkit, the results showed that the ratio of the electric field of the collect region to the drift region (Ec /Ed ) must be greater than a critical value Z (1.78). An individual experiment, carried out with a compound alpha source (241Am and 243Am), was used to validate the preliminary performance of this detector. The effects of the electric field on the anode pulse height agreed well with the simulation results. Furthermore, the results also indicated that the energy resolution of (68.40 ± 1.07) keV at 5.39 MeV (243Am) and (69.67 ± 1.09) keV at 5.49 MeV (241Am) could be achieved. An initial in-beam fission experiment of 235U reaction with 14 MeV neutrons was also performed to test the setup, and the results showed that the reconstructed emission angle could achieve a resolution of 0.221 ± 0.002 on the difference of the cosines determined from both halves of TFGIC. The present work primarily reported the development of a TFGIC with a digital acquisition system in INPC.