Magazù Salvatore, Migliardo Federica, Benedetto Antonio
Dipartimento di Fisica, Università di Messina, Messina, Italy.
Rev Sci Instrum. 2011 Oct;82(10):105115. doi: 10.1063/1.3641870.
The main aim of this paper is to present the scientific case of the resolution elastic neutron scattering (RENS) method that is based on the collection of elastic neutron scattering intensity as a function of the instrumental energy resolution and that is able to extract information on the system dynamical properties from an elastic signal. In this framework, it is shown that in the measured elastic scattering law, as a function of the instrumental energy resolution, an inflection point occurs when the instrumental energy resolution intersects the system relaxation time, and in an equivalent way, a transition in the temperature behavior of the measured elastic scattering law occurs when the characteristic system relaxation time crosses the instrumental energy resolution time. With regard to the latter, an operative protocol to determine the system characteristic time by different elastic incoherent neutron scattering (EINS) thermal scans at different instrumental energy resolutions is also proposed. The proposed method, hence, is not primarily addressed to collect the measured elastic scattering intensity with a great accuracy, but rather relies on determining an inflection point in the measured elastic scattering law versus instrumental energy resolution. The RENS method is tested both numerically and experimentally. As far as numerical simulations are concerned, a simple model system for which the temperature behavior of the relaxation time follows an Arrhenius law, while its scattering law follows a Gaussian behavior, is considered. It is shown that the system relaxation time used as an input for the simulations coincides with the one obtained by the RENS approach. Regarding the experimental findings, due to the fact that a neutron scattering spectrometer working following the RENS method has not been constructed yet, different EINS experiments with different instrumental energy resolutions were carried out on a complex model system, i.e., dry and D(2)O hydrated lysozyme, in an extended temperature range. The resulting temperature behavior of the system relaxation time, obtained with RENS method, agrees very well with the one obtained in literature, for the same system, following the quasi-elastic neutron scattering (QENS) approach. The proposed scientific case puts into evidence the challenges of an RENS spectrometer working by varying the instrumental energy resolution; in particular, in comparison with QENS, the proposed RENS method requires a smaller amount of sample, which is an important point in dealing with biological and exotic systems; it is not affected by the use of model functions for fitting spectra as in QENS, but furnishes a direct access to relevant information.
本文的主要目的是阐述分辨率弹性中子散射（RENS）方法的科学原理。该方法基于收集作为仪器能量分辨率函数的弹性中子散射强度，并且能够从弹性信号中提取有关系统动力学性质的信息。在此框架下，研究表明，在测量的弹性散射定律中，作为仪器能量分辨率的函数，当仪器能量分辨率与系统弛豫时间相交时会出现一个拐点，同样地，当特征系统弛豫时间超过仪器能量分辨率时间时，测量的弹性散射定律的温度行为会发生转变。关于后者，还提出了一种通过在不同仪器能量分辨率下进行不同的弹性非相干中子散射（EINS）热扫描来确定系统特征时间的操作方案。因此，所提出的方法并非主要致力于高精度地收集测量的弹性散射强度，而是依赖于确定测量的弹性散射定律相对于仪器能量分辨率的一个拐点。RENS方法通过数值模拟和实验进行了测试。就数值模拟而言，考虑了一个简单的模型系统，其弛豫时间的温度行为遵循阿仑尼乌斯定律，而其散射定律遵循高斯行为。结果表明，用作模拟输入的系统弛豫时间与通过RENS方法获得的弛豫时间一致。关于实验结果，由于尚未构建遵循RENS方法工作的中子散射光谱仪，因此在一个复杂的模型系统（即干燥的和D₂O水合的溶菌酶）上，在较宽的温度范围内进行了具有不同仪器能量分辨率的不同EINS实验。用RENS方法得到的系统弛豫时间的温度行为与在文献中使用准弹性中子散射（QENS）方法对同一系统得到的结果非常吻合。所提出的科学原理证明了通过改变仪器能量分辨率工作的RENS光谱仪所面临的挑战；特别是，与QENS相比，所提出的RENS方法所需的样品量更少，这在处理生物和特殊系统时是一个重要的点；它不像QENS那样受用于拟合光谱的模型函数的影响，而是能直接获取相关信息。
