Experimental Study for Pion Distribution in the Nuclear Surface

该探测器系统是为了研究相干π介子的产生而研制的，它对核力的短程分量很敏感。在该反应中，动能为400 MeV的质子束发射出的虚π介子通过核介质的传播，被核子散射，成为真实的π介子。探测器系统样机的建造已经完成，定于2004年进行测试实验。(1)气体电子倍增探测器的研制气体电子倍增探测器由阴极、GEM电极和读出板组成。GEM电极具有非常小的孔，并且在电极的两侧上施加高电压。空穴附近电场的快速变化引起电子放大。我们测量了增益与气体种类和混合气体的关系，发现Ar + C_4H_1O比Ar + CO_2有更高的增益。(2)高速读出电子学的发展读出卡由前置放大器、缓冲器和多路复用器组成。来自多个通道的信号被放大，并存储在缓冲器中。缓冲后的模拟信号通过10 MHz的多路复用器传输到ADC模块。增益和整形时间可以通过设置读出卡寄存器中的值进行调整。我们开发了现场可编程门阵列的电子学，将数据加载到寄存器中以设置读出卡。

The detector system was developed to study the coherent pion production, which will be sensitive to the short range component of the nuclear force. In this reaction, the virtual pion emitted from proton beam with kinetic energy 400 MeV will become real pion by scattered from nucleon through the propagation of nuclear medium. The construction of the prototype of detector system was completed, and the test experiment is scheduled in 2004.(1) Development of Gas Electron Multiplier (GEM) DetectorThe gas electron multiplier detector consists of cathode electrode, GEM electrodes, and readout board. The GEM electrode has very small holes, and the high voltage is applied on both sides of electrode. The rapid change of electric field near the hole causes the electron amplification. The produced electrons are collected into the strips fabricated on the readout board.We measured the gain dependence on the gas type and mixture, and found that we got a high gain with Ar + C4H1O, compared with Ar + C02.(2) Development of High Speed Readout ElectronicsThe readout card consists of the pre-amplifier, buffering, and multiplexer. The signals from many channels are amplified, and stored in the buffer. The buffered analogue signal is transferred to ADC module through the multiplexer with the speed of 10 MHz. The gain and shaping time can be adjusted by setting the value in the register of the readout card. We developed the electronics with Field Programmable G ate Array to load the data into the register to set the readout card.