| This project designed a kind of portable ionization chamber detectors to measure uranium and plutonium emitted gamma-ray spectrum, which used high-pressure xenon (HPXe) (pressure >40 atm) as the medium of ionization chamber work.Because uranium and plutonium in nuclear materials gamma-ray energy is relatively concentrated—mainly in 0.1～2MeV, and their branching ratios are relatively small and spectrum are complex, the detectors for these ray detection require higher energy resolution and efficiency. Meanwhile, the portable spectrometer detectors are required to keep stable performance in different environmental conditions.We passed a lot of literature investigation found that the HPXe ionization chamber with high-pressure Xe as the working medium can be used as the portable spectrometer detectors. First, the resolution of HPXe ionization chambers with Frisch grid at 0.662MeV and 1.117MeV gamma-ray leads to 2.0% and 1.0% , superior to the use of NaI detectors and compound semiconductor detector; Secondly, Xenon as a detection medium is quite efficient due to its relatively higher atomic number and cross sections, ionization chamber flexible structure can be produced various size and shape to meet the needs of the detection efficiency; Third, the HPXe ionization chambers energy linear and the resolution and the efficiency for ambient temperature changes are insensitive, so the performance is stably.However, the existing detectors of HPXe gridded ionization chamber also have their shortcoming:Grid of acoustic noise and vibration sensitive impact the detectors' energy resolution. Among the parallel plate and cylindrical structure chambers with shielding mesh for the measurement of the energy spectrum , the cylindrical gridded ionization chamber own simple structure, but increasing the size of the district so electrode system changes, grid strength weakened, while working voltage, high voltage power supply is not easy integration; Generaly, the parallel plate gridded ionization chamber have the high detection efficiency and energy resolution capability of their flexible structure of the advantages , the grid can easily fixed, but it is very difficult to take into account the detection efficiency and energy resolution of the requirements of larger exterior dimensions. They work for laboratory work, unfit for portable spectrometer.Against both of the above advantages, we design a new electrode structure, it has the merits both of parallel plate ionization chamber in the energy resolution skills and grid structure and cylindrical gridded ionization chamber flexibility in the size of sensitive areas and easy to carry. The basic structure based on a gridded parallel plate ionization chamber forms, using electrode array structure to increase the sensitivity and size of area to improve detection efficiency. Design of the ionization chamber volume is about 4000cm~3, the effective volume of the sensitive area is 2000cm~3 and sensitive area is 500cm~2. In addition, we use MCNP Monte Carlo procedure calculate and study the main performance parameters of the ionization chambers. The main results are1) Completion of the HPXe gridded array-pole ionization chamber electrode system architecture design;2) Completion of the HPXe gridded array-pole ionization chamber sealed shell structure design;3) Completion of the basic parameters calculating related electronic system of HPXe gridded array-pole ionization chambers;4) Using MCNP Monte Carlo procedure to calculate the ionization chamber effect after the gamma-ray passed through the wall material;5) Using MCNP Monte Carlo procedure to calculate the ionization chamber of uranium, plutonium nuclear materials mainly ray detection efficiency;...
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