Honkimäki Veijo, Suortti Pekka
European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France.
J Synchrotron Radiat. 2007 Jul;14(Pt 4):331-8. doi: 10.1107/S0909049507014744. Epub 2007 Jun 14.
The response of an intrinsic Ge detector in energy-dispersive diffraction measurements with synchrotron radiation is studied with model calculations and diffraction from perfect Si single-crystal samples. The high intensity and time-structure of the synchrotron radiation beam leads to pile-up of the output pulses, and the energy distribution of the pile-up pulses is characteristic of the fill pattern of the storage ring. The pile-up distribution has a single peak and long tail when the interval of the radiation bunches is small, as in the uniform fill pattern, but there are many pile-up peaks when the bunch distance is a sizable fraction of the length of the shaping amplifier output pulse. A model for the detecting chain response is used to resolve the diffraction spectrum from a perfect Si crystal wafer in the symmetrical Laue case. In the 16-bunch fill pattern of the ESRF storage ring the spectrum includes a large number of ;extra reflections' owing to pile-up, and the model parameters are refined by a fit to the observed energy spectrum. The model is used to correct for the effects of pile-up in a measurement with the 1/3 fill pattern of the storage ring. Si reflections (2h,2h,0) are resolved up to h = 7. The pile-up corrections are very large, but a perfect agreement with the integrated intensities calculated from dynamical diffraction theory is achieved after the corrections. The result also demonstrates the convergence of kinematical and dynamical theories at the limit where the extinction length is much larger than the effective thickness of the perfect crystal. The model is applied to powder diffraction using different fill patterns in simulations of the diffraction pattern, and it is demonstrated that the regularly spaced pile-up peaks might be misinterpreted to arise from superlattices or phase transitions. The use of energy-dispersive diffraction in strain mapping in polycrystalline materials is discussed, and it is shown that low count rates but still good statistical accuracy are needed for reliable results.
利用模型计算以及完美硅单晶样品的衍射，研究了本征锗探测器在同步辐射能量色散衍射测量中的响应。同步辐射束的高强度和时间结构会导致输出脉冲堆积，堆积脉冲的能量分布具有储存环填充模式的特征。当辐射束团间隔较小时，如均匀填充模式，堆积分布有一个单峰和长尾巴，但当束团间距为整形放大器输出脉冲长度的相当一部分时，会有许多堆积峰。使用检测链响应模型来解析对称劳厄情况下完美硅晶体薄片的衍射谱。在欧洲同步辐射装置（ESRF）储存环的16束团填充模式下，由于堆积，谱中包含大量“额外反射”，通过与观测能谱拟合来优化模型参数。该模型用于校正储存环1/3填充模式测量中的堆积效应。硅的（2h,2h,0）反射可分辨到h = 7。堆积校正非常大，但校正后与动力学衍射理论计算的积分强度完全吻合。结果还证明了在消光长度远大于完美晶体有效厚度的极限情况下，运动学理论和动力学理论的收敛性。该模型应用于粉末衍射，在衍射图样模拟中使用不同的填充模式，结果表明规则间隔的堆积峰可能会被误解释为来自超晶格或相变。讨论了能量色散衍射在多晶材料应变映射中的应用，结果表明为获得可靠结果需要低计数率但仍要有良好的统计精度。
