北京师范大学大气颗粒物外束PIXE分析系统

AN EXTERNAL BEAM PIXE SYSTEM FOR THE ANALYSIS OF AIRBORNE PARTICLE IN BEIJING NORMAL UNIVERSITY

北京师范大学串列加速器实验室建立了大气颗粒物外束PIXE分析系统,并利用标准样品获得了16种大气颗粒物常见元素的外束PIXE分析系统刻度因子.对Z≥15的大多数元素,刻度因子的重复性较好,相对标准偏差在2%左右.通过降低样品与探测器Be窗之间空气层的有效厚度来削弱空气对低能X射线的吸收作用并降低空气中Ar元素的峰面积,可使标准样品中Mg的探测限由9 157ng.cm-2降至331ng.cm-2,Al的探测限由645ng.cm-2降至191ng.cm-2.大气颗粒物样品中Al及原子序数高于Al的元素外束PIXE的探测限约为内束PIXE的2～6倍.

An external beam PIXE system for the analysis of airborne particles was set up in the Tandem Accelerator Lab,Beijing Normal University.Calibration factors for 16 elements of common atmospheric concern were obtained by calibration against standard samples in an external beam of the PIXE system.For most elements with Z≥15 the relative standard deviations of repeatedly determined calibration factors are generally within ± 2%.By reducing the equivalent thickness of air layer between sample and the ＂Be＂ window of detector,absorption of X-ray by air and the peak area of Ar were restrained.Thus the detection limit for Mg in standard samples was lowered from 9157 ng·cm-2 to 331 ng·cm-2,and Al from 645 ng·cm-2 to 191 ng·cm-2.For the elements with Z≥15 the detection limits for airborne particles in external beam PIXE system were 2~6 times higher than those in internal beam PIXE system.