Accurate bound coherent neutron scattering lengths, bc, of important isotopes

中子散射长度b是中子与原子核相互作用强度的量度。它们是物质的基本性质，大多数中子散射技术依赖于准确的b值。令人惊讶的是，中子散射长度通常只有中等精度或较差的精确度，或者根本没有实验确定。本研究项目的目的是利用中子衍射以非常高的精度确定重要稳定同位素的热中子的束缚相干散射长度。待检测的同位素和天然同位素混合物有：6Li、7Li、NatLi、114Cd、NatCd、123Te、Natte、141Pr(=NatPr)、142Li、143Nd、144Nd、145Nd、146Nd、148Nd、150Nd、NatNd、147Sm、147Sm、152Sm、154Sm、NatSm、151Eu、153Eu、NatEu、177Hf、NatHf、185Re、187Re、NatRE、203Tl、205Tl、NatTl。这将为用户群体提供从凝聚态到核物理和生物学等不同领域的大量中子实验所需的基本和重要数据。首先，发展了一种用中子衍射法确定束缚相干中子散射长度的稳健而又准确的方法。在确定散射长度方面，中子衍射法比其他方法(有时更准确)更有优势，它只依赖于相对值而不是绝对值，而且不容易出现系统误差。因此，它是一种稳健但相当准确(1%)的方法，非常适合重新确定重要同位素的散射长度。由同位素富集物合成了LiF、LiBaF3、CdF2、TeO2、LnN和LnOCl(Ln=Pr、Nd、Sm、Eu)、ReO_3、TlCl等合适的材料。对这些材料的中子粉末衍射实验进行了优化，以获得准确的强度测量，并对衍射数据进行了Rietveld精化处理。统计和一致性检查完成了中子散射长度的确定。大多数中子实验是在法国格勒诺布尔的劳厄-朗之万研究所进行的，并与其合作进行。在德国慕尼黑Garching的MLZ、瑞士维利根的PSI和澳大利亚卢卡斯高地的ANSTO收集了更多的中子衍射数据。对于选定的化合物，如LiF、LiBaF3和REO_3，使用单晶衍射和中子干涉法等替代方法。

Neutron scattering lengths b are the measure of the strength of the interaction between neutrons and the nucleus of an atom. They are fundamental properties of matter, and most neutron scattering techniques rely on accurate b values. Surprisingly, neutron scattering lengths are often only known with moderate or poor accuracy or have not been determined experimentally at all. The aim of this research project is to determine bound coherent scattering lengths for thermal neutrons of important stable isotopes with very high accuracy using neutron diffraction. The isotopes and natural isotope mixtures to be examined are: 6Li, 7Li, natLi, 114Cd, natCd, 123Te, natTe, 141Pr (= natPr), 142Nd, 143Nd, 144Nd, 145Nd, 146Nd, 148Nd, 150Nd, natNd, 147Sm, 147Sm , 152Sm, 154Sm, natSm, 151Eu, 153Eu, natEu, 177Hf, natHf, 185Re, 187Re, natRe, 203Tl, 205Tl, natTl. This will provide the user community with fundamental and important data needed for a plethora of neutron experiments in diverse fields ranging from condensed matter to nuclear physics and biology. First, a robust yet accurate method for determining bound coherent neutron scatter lengths by neutron diffraction is developed. Neutron diffraction has the advantage over other (sometimes more accurate) methods of determining the scattering length that it only relies on relative and not on absolute values and is less prone to systematic errors. It is therefore a robust but fairly accurate (< 1%) method and well suited to redetermining the scattering lengths of important isotopes. Suitable materials like LiF, LiBaF3, CdF2, TeO2, LnN and LnOCl (Ln = Pr, Nd, Sm, Eu), ReO3, TlCl are synthesized from isotopically enriched materials. Neutron powder diffraction experiments on these materials are optimized for accurate intensity measurements and diffraction data are analyzed by Rietveld refinement. Statistical and consistency checks complete the neutron scattering length determination. Most neutron experiments are performed at and in collaboration with the Institut Laue-Langevin in Grenoble, France. Additional neutron diffraction data are collected at MLZ, Garching, Munich, Germany, at PSI, Villigen, Switzerland, and at ANSTO, Lucas Heights, Australia. Alternative methods such as single crystal diffraction and neutron interferometry are used for selected compounds such as LiF, LiBaF3 and ReO3.