Boron-lined ionization chambers （BLICs） have gradually become one of radiation detectors which are used to monitor the neutron/y-ray mixed field with large flux around reactors in recent years. In this paper a BLIC with high sensitivity is fabricated and the internal structure is detailed. By using a weak current amplifier with an accuracy of fA, the leakage current of the BLIC is less than 1.0 pA when the high voltage is below 700 V; under the irradiation by the Am-Be neutron source, on the I-V curve of the BLIC there appears a current plateau with a length of 500 V and a slope of 3.72 x 10- 4 V- 1; when the operating voltage is 400 V, the leakage current of the BLIC is 0.4 pA. Experiments show that neutron signal current measured by the BLIC depends on the relative position of the BLIC with repect to the radiation source; a maximum of 2.0 pA is obtained when the source is 8 cm away from the bottom of the hole in the paraffin moderator. Under the exposure by 137Cs and 9~Sr, T-ray signal current measured by the BLIC is 1.0--2.0 pA, but the current plateau is not obvious in T-ray field. The neutron sensitivity of the BLIC reaches a level of 1.0x 10-15 Acm2s and the T-ray sensitivity reaches a level of 9.0x 10-22 Acm2s.eV-1. The BLIC shows small leakage current, high sensitivity, and good plateau characteristics, which can be used to monitor the neutron/T-ray mixed field around reactors.%近年来，涂硼电离室已逐渐成为核反应堆周围大通量中子，1，射线混合场监测的辐射探测器之一．研制了一种高灵敏度涂硼电离室，并给出了其内部结构．用fA级弱电流放大器测得：当涂硼电离室的工作电压在700V以下时，漏电流小于1．0pA；用Am-Be中子源辐照时测得涂硼电离室的电流曲线坪长为500V坪斜为3．72X10-4V-1：当涂硼电离室的工作电压为400V时，对应漏电流为0．4pA．测试表明涂硼电离室中子信号电流与辐照源的相对位置有关，将Am-Be中子源置于距石蜡慢化体底部8cm时，测得中子信号电流最大值为2．0pA．用137Cs和90sr辐照时测得涂硼电离室v射线信号电流为1．0-2．0pA，但在1，射线场中坪特性不如中子场中坪特性明显．电离室中予探测灵敏度达1．0×10-15Acm2S量级，1，射线探测灵敏度达9．0×10-22Acm2S．eV-1量级．这种涂硼电离室漏电流小、灵敏度高、坪特性好，可用于反应堆周围的中子/γ射线混合场测量．
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