Experimental Study for Pion Distribution in the Nuclear Surface

为了研究相干介子的产生，研制了对核力的近程分量敏感的探测系统。在该反应中，动能为400 MeV的质子束发射出的虚介子经过核介质的传播，从核子散射而成为实介子。探测器系统样机已搭建完成，并计划于2004年进行测试实验。(1)气电子倍增器（GEM）检测器的研制气电子倍增器检测器由阴极电极、GEM电极和读出板组成。GEM电极具有非常小的孔，并且在电极的两侧施加高电压。空穴附近电场的快速变化引起电子放大。产生的电子被收集到制作在读出板上的条带中。我们测量了增益与气体类型和混合物的关系，发现与Ar + co2相比，Ar + c4h2o获得了更高的增益。(2)高速读出电子器件的发展读出卡由前置放大器、缓冲器和多路复用器组成。来自许多通道的信号被放大，并存储在缓冲器中。缓冲后的模拟信号通过多路复用器以10mhz的速度传输到ADC模块。增益和整形时间可以通过在读出卡的寄存器中设置值来调节。我们开发了现场可编程G门阵列电子器件，将数据加载到寄存器中设置读出卡。

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.