The Telescope System With Multi-channel Measurement ~ From 9be At (n, X¦Á) Reaction Of Double Differential Cross Section

The double differential cross section (DDX) of neutrons or charged particles emission from fast neutron induced reactions is one of the most important nuclear data used in nuclear engineering design and in the study of nuclear reactions mechanism. In this thesis the measurement of DDX is described in detail for the ~9Be(n,xα) reaction at En=14.8 MeV by using multitelescope system.The performance of the structure materials will be bad for the bubbles and the bulges induced by the m-particles emission from the (n,α) reactions and be frangible for the protons from the (n,p) reactions, so in nuclear engineering design it is of considerable interest to investigate the energy and angular distributions of chargedparticles from neutron induced reactions. Moreover, in the theoretical study of nuclear reaction, the consideration of Pauli effect and the quantum numbers of J andπin the exciton state density make it possible to describe the processes of nuclear reactions with the pre-equilibrium exciton model and the unified Hauser-Feshbach model theory with the conservation of momentum and parity. Now the theoretical models are still in developing and improving, so more experimental data are needed for examing their calculations.Up to now, the experimental data are scarce because of the small DDX of charged particles emission from the nuclear reactions induced by fast neutron, and meanwhile the energy losses are considerable when the charged particles pass through the sample. In general, the DDX can be measured in activation method or in the direct method. In activation method the measurement system is simple and convenient, but it is only available to those nuclides with appropriate half-lives. In addition, this method is only suitable to measure the total cross sections, not the energy and angular distributions of the particles emission. The direct way can overcome these shortcomings, but the measurement is very difficult.The multitelescope system described in this thesis is a cylindrical multiwire proportional chamber in connection with a central CsI(T1) scintillator. The system has many merits as the following: (1) Allowing simultaneously the measurement of charged particle spectra at 16 reaction angles from 31°～161°with the angular resolution of 13°. (2) Measuring the background and the effect at the same time. (3) More raction events can be gotten with the thick sample of ~9Be. (4) Powerful ability of the particle identification via the dE-E detector system and via pulse shape discrimination. Therefore, this system can greatly limit the background and reduce the measuring time.The Monte-Carlo method was widely used in the data processes such as the simulation of the geometry and the distribution of the neutron flux along the ring of the sample. Moreover, the Monte-Carlo method was also used to simulate the whole experimental procedure to get the simulation spectra which can be compared directly with the measurement spectra. Finally, an iteration method was discussed to improve the DDX for the simulation procedure. The iteration method given in this thesis is very valuable in analysis the data measured with thick sample.