基于复合结构的气体电子倍增器增益模拟和实验研究

气体电子倍增器(GEM)作为高性能的微结构气体探测器在高能物理相关领域内得到了广泛的研究和应用.其中增益是GEM探测器基本性能研究中的一个重要参数,该值的精确测量至关重要.增益的测量一般采用电流测量或者能谱测量方法,但均存在精度较低或者过程繁琐的问题,且无法精确测量低增益值.针对GEM探测器增益的精确测量,本文提出了一种由GEM探测器与微网结构气体探测器(MM)级联构成的复合结构探测器(GEM-MM).利用GEM-MM结构以相对方法实现GEM增益的精确测量.该方法既可以省去传统方法中复杂的电子学标定过程,同时不需要进行原初电离电子数的估算,保证了增益的精确测量,并且可以实现GEM低增益的测量.基于GEM-MM测量GEM增益的原理,本文首先对GEM-MM电荷输运过程进行了模拟研究,优化了合适的工作电压.比较了三种不同类型和配比工作气体下GEM增益模拟结果,并在Ar/iC_4H_(10)(95/5)气体中测量了单层GEM在3—24范围内的有效增益.不同Penning系数下GEM增益的模拟结果表明,Penning系数为0.32时GEM增益的模拟结果与实验测量结果符合得很好.由此可以确定一个大气压下的Ar/iC_4H_(10)(95/5)气体中,Penning系数为0.32±0.01.

Measurement and simulation of the hybrid structure gaseous detector gain

As one of the most popular micro pattern gaseous detectors, gas electron multiplier (GEM) has been extensively studied and applied in recent years. The studies of the detector gain measurement and simulation are important, especially on a low gain scale. Traditionally, the gain measurement is realized by measuring the current or the pulse height spectrum. The former needs complicated electronic chain calibration and the latter needs necessarily to calculate the primary electron number. In this paper, an alternative method to determine the effective gain of GEM is introduced. The GEM gain can be precisely achieved through a gaseous detector of hybrid structure which combines GEM with micro-mesh gaseous structure (MM). The hybrid structure is called GEM-MM for short. The GEM-MM detector consists of drift cathode, standard GEM foil, stainless steel micro mesh, and readout anode. In this detector, the space between the cathode and the GEM foil is called drift gap and the other space between the GEM foil and the mesh is named transfer gap. When the X-rays irradiate into the gas volume of GEM-MM, the primary ionization occurs in both regions. Photoelectrons in the drift gap transfer from the drift region to amplification sensitive areas of the GEM and the MM detector while those in the transfer region are only amplified by the MM detector. In the energy spectrum of ⁵⁵Fe, there is a clear energy profile including two sets of peaks. The gain of GEM can be easily obtained from the energy spectrum. Meanwhile, detailed simulations are carried out with Garfield++ software package. Simulation of the electron transport parameters has been optimized. and the gains of GEM detector are also calculated for three different gas mixtures. Experimental results of the gains ranging from 3 to 24 are obtained. The gains of GEM under different working voltages are studied precisely from the spectrum measurements. The Penning transfer rate could reach 0.32±0.01 when the simulated value matches the measurement within 1σ error.