Precision measurement of the coherent neutron scattering length of 3He through neutron interferometry

Improved knowledge of the real part of the neutron scattering length of ³He is important for further development of nuclear few-body theory, as well as for a thorough understanding of neutron scattering off quantum liquids. The real part of the bound incoherent neutron scattering length b_i' has recently been measured directly with an experimental uncertainty of better than 1% by means of spin echo spectrometry. The uncertainty of the more fundamental bound multiplet scattering lengths b_±' is thus limited by today's 1.2% uncertainty of the spin-independent coherent part b_c'. Employing the skew-symmetric perfect crystal Si-interferometer at the S18 experimental site at ILL, Grenoble, we have re-measured the real part of the bound coherent neutron scattering length b_c' of ³He. Our result b_c' = 6.010(21)fm exhibits a significant deviation compared to the latest accepted value b_c' = 5.74(7)fm (H. Kaiser, H. Rauch, G. Badurek, W. Bauspiess, U. Bonse, Z. Phys. A 291, 231 (1979)). Including the known value of the incoherent neutron scattering length, we obtain new values for the real parts of the free singlet and triplet scattering lengths, a_-' = 7.573(30)fm and a₊' = 3.480(18)fm. Our result contravenes by more than 7 standard deviations the measurement of the same physical quantity that has recently been performed by a group at NIST in a very similar experiment (P.R. Huffman, D.L. Jacobson, K. Schoen, M. Arif, T.C. Black, W.M. Snow, S.A. Werner, Phys. Rev. C 70, 014004 (2004)) which yielded b_c' = 5.853(7)fm.     

Self-diffusion in liquid lithium from coherent quasielastic neutron scattering

Using the method of quasielastic coherent neutron scattering by liquid lithium, the temperature dependence of self-diffusion coefficient is investigated and compared with analogous data extracted by the incoherent scattering method.     

Role of IUC-DAEF in promoting neutron beam research in India

Inter University Consortium for Department of Atomic Energy Facilities (IUC-DAEF) is an autonomous institute of the University Grants Commission and provides an interface between the university fraternity and the institutions of Department of Atomic Energy. Mumbai Centre of IUC-DAEF promotes and supports the use of neutron facilities at Dhruva reactor by the university scientists. To augment the existing neutron scattering facilities, IUC-DAEF has developed a neutron beam line at Dhruva reactor. The present paper gives a brief survey of the activities and achievements of Mumbai Centre of IUC-DAEF.     

Basic to industrial research on neutron platform in Japan

The co-location of reactor- and accelerator-based neutron sources offers a great opportunity for complementary use of steady and pulsed neutron beams in a wide variety of neutron science and technology areas ranging from basic research to industrial applications. In Japan, such a balance of two kinds of neutron sources has a long tradition and now we are entering into a new era with the commissioning of the world’s most intense pulsed neutron beams at JSNS/J-PARC plus the existing JRR-3 reactor both co-located within 1 km of each other in Tokai. The joint operation of these neutron facilities in close proximity under a program called ‘neutron platform’, will allow neutron beam access not only to professional users, familiar with both pulsed and steady state techniques but also to first-time academics and industrial researchers to neutron scattering.      

Anomalous neutron scattering and ferroelectric soft modes

It is suggested that anomalous neutron scattering could prove a powerful experimental tool in studying ferroelectric phase transition, the sublattice displacements of the soft modes as well as their symmetry characteristics.     

Phase transitions in the H+-conducting perovskite ceramics by the quasi-elastic neutron and high-pressure Raman scattering

H⁺-containing lanthanide-doped perovskites A(Ba, Sr etc.)B(Zr, Ce, Ti etc.)O₃ are potential ceramic membranes for fuel cell and medium temperature water electrolysis (300–800 °C). The comparison studies of the hydrated and non-hydrated Yb-doped BaZrO₃ and SrZrO₃ were performed by thermal expansion, medium–high temperature neutron and room-temperature high-pressure Raman scattering. Neutron diffraction and elastic/quasi-elastic studies carried out for BaZrO₃ ceramic show the presence of the protons, their successive diffusion above ∼600 °C, and then their departure above 750 °C (under vacuum). Phase transitions and their modification by proton insertion are discussed. A high-pressure Raman study of SrZrO₃ performed at room temperature in the diamond anvil cell reveals the presence of two pressure-induced phase transitions at about 5 and 22 GPa and confirms that proton insertion modifies the phase transition sequences. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

第一讲中子散射与散裂中子源

中子散射是研究物质微观结构和动态的理想工具之一,广泛地应用于凝聚态物质研究和应用的众多学科领域.散裂中子源能是新一代的加速器基脉冲中子源,能为中子散射提供高通量的脉冲中子.文章简明地介绍了中子散射的特点和它作为物质结构和动态探针的优越性,以及散裂中子源的基本原理、发展状况和多学科的应用优势.我国计划建设的散裂中子源CSNS中,靶站将由多片钨靶、铍/铁反射体和铁/重混凝土生物屏蔽体组成.质子束功率100kW下,脉冲中子通量约为2.4×1016n/cm2/s.第一期将设计建造高通量粉末衍射仪、高分辨粉末衍射仪、小角散射仪、多功能反射仪和直接几何非弹性散射仪等五台典型的中子散射谱仪,以覆盖大部分的中子散射研究领域.     

Hydrostatic pressure and temperature dependence study of d-camphor and dl-borneole by neutron scattering

Abstract

Neutron scattering investigations have been performed down to helium temperatures under different hydrostatic pressures up to 330 MPa. Neutron diffraction (ND) and incoherent inelastic neutron scattering (IINS) spectra showed clearly the existence of a phase transition in d-camphor, which was not observed in dl-borneole. The ND spectra point to a possible cubic structure of the dl-borneole crystal down to helium temperatures. Pressure and temperature dependence of the IINS spectra assumed a glass-like transition from the dynamical to static orientational disorder of molecules in this crystal.     

利用中子散射探索生命世界中的物理奥秘

中子散射是利用入射中子与原子核发生碰撞以后中子动量与能量的改变来研究微观世界的一种技术。由于中子对氢原子的散射截面远大于其他元素的独特属性,使得中子散射在研究包含大量氢元素的生物大分子的结构以及动力学特性方面都有卓越的应用。文章对中子散射在生物方面的应用进行了探讨,重点介绍了中子衍射、结合衬度变换技术的小角中子散射、准弹性/非弹性中子散射和中子自旋回波技术,以及它们在研究生物大分子结构、动力学及其功能方面的应用。最后对中子散射未来在生命科学中探索新的物理现象进行了探讨和展望。     

Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published) at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom.     

Small-angle neutron scattering from micellar solutions

Micellar solutions are the suspension of the colloidal aggregates of the sur-factant molecules in aqueous solutions. The structure (shape and size) and the interaction of these aggregates, referred to as micelles, depend on the molecular architecture of the surfactant molecule, presence of additives and the solution conditions such as temperature, concentration etc. This paper gives the usefulness of small-angle neutron scattering to the study of micellar solutions with some of our recent results.     

Inelastic neutron scattering from superconducting rings

For the first time the differential cross section for the inelastic magnetic neutron scattering by superconducting rings is derived taking account of the interaction of the neutron magnetic moment with the magnetic field generated by the superconducting current. Calculations of the scattering cross section are carried out for cold neutrons and thin film rings from type-II superconductors with the magnetic fields not exceeding the first critical field.     

Bragg prism monochromator and analyser for super ultra-small angle neutron scattering studies

We have designed, fabricated and operated a novel Bragg prism monochromator-analyser combination. With a judicious choice of the Bragg reflection, its asymmetry and the apex angle of the silicon single crystal prism, the monochromator has produced a neutron beam with sub-arcsec collimation. A Bragg prism analyser with the opposite asymmetry has been tailored to accept a still sharper angular profile. With this optimized monochromator-analyser pair, we have attained the narrowest and sharpest neutron angular profile to date. At this facility, we have recorded the first SUSANS spectra spanning wave vector transfers Q ～ 10^?6 Å^?1 to characterize samples containing agglomerates up to tens of micrometres in size.     

VITESS polarized neutron suite: allows for the simulation of performance of any existing polarized neutron scattering instrument

As neutron simulations packages are used for analysis of the expected performance for practically all newly built neutron instruments, possibilities for simulations with polarized neutrons have been relatively underdeveloped.During the last years we developed a new approach for the representation of time-dependent magnetic fields (both in magnitude and direction) for the VITESS simulation package. This allowed us to simulate the neutron spin dynamics in practically all polarized neutron devices (RF neutron flipper, adiabatic gradient RF flipper, the Drabkin resonator, etc.). In this article the above-mentioned VITESS instrument components (modules) will be presented and the simulated performance of a number of polarized neutron scattering instruments (NRSE, MIEZE, SESANS, etc.) will be demonstrated.Thus, we practically complete the polarized neutron suite of the VITESS, which seems sufficient for the simulation of performance of any existing polarized neutron scattering instrument. Future work will be concentrated on developments of dedicated sample modules (kernels) to allow for virtual experiments with VITESS.     

Performance of ceramic anvils for high pressure neutron scattering

Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9?GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude.     

Small-angle neutron scattering study of dynamically polarized polyethylenes

We carried out a small-angle neutron scattering (SANS) study of dynamically polarized polyethylene (PE) samples doped with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The transmission of the PE with almost fully polarized neutrons (98.5%) increased with increasing the proton polarization, P. The incoherent scattering cross section decreased with increasing P. The effect of P on the polarized neutrons’ transmission and the incoherent scattering cross section agreed well with the theory. The q-dependence of the coherent scattering, which reflects a two-phase structure of PE composed of crystalline and amorphous domains, was kept unchanged by the proton polarization, but the intensity increased by a factor of 3 and 6 for P=+23% and −23%, respectively. The results mean that the contrast between the two phases was successfully enhanced by a dynamic nuclear polarization (DNP) technique. However, the enhancement is only 1/13–1/16 of the enhancement calculated by assuming a homogeneous polarization through the PE sample. The discrepancy suggests that P in amorphous domains (25%) should be higher than that in crystalline domains (22%) by 3%, which in turn may suggest the partial depolarization of proton spins on the way of the spin diffusion from amorphous domains, where TEMPO radicals localize, to crystalline domains.     

Small-angle neutron and dynamic light scattering study of gelatin coacervates

The state of intermolecular aggregates and that of folded gelatin molecules could be characterized by dynamic laser light and small-angle neutron scattering experiments, which implied spontaneous segregation of particle sizes preceding coacervation, which is a liquid-liquid phase transition phenomenon. Dynamic light scattering (DLS) data analysis revealed two particle sizes until precipitation was reached. The smaller particles having a diameter of ～50 nm (stable nanoparticles prepared by coacervation method) were detected in the supernatant, whereas the inter-molecular aggregates having a diameter of ～400 nm gave rise to coacervation. Small-angle neutron scattering (SANS) experiments revealed that typical mesh size of the networks exist in polymer dense phase (coacervates) [1]. Analysis of the SANS structure factor showed the presence of two length scales associated with this system that were identified as the correlation length or mesh size, ξ = 10.6 Å of the network and the other is the size of inhomogeneities = 21.4 Å. Observations were discussed based on the results obtained from SANS experiments performed in 5% (w/v) gelatin solution at 60°C (ξ = 50 Å, ζ = 113 Å) and 5% (w/v) gel at 28°C (ξ = 47 Å, ζ = 115 Å) in aqueous phase [2] indicating smaller length scales in coacervate as compared to sol and gel.     

中子散射在磁性材料研究中的应用

中子具有天然磁矩,穿透能力强且对轻元素敏感等独特的优势,是目前研究材料中磁结构最有力的工具。发展中子散射技术对开发新型磁性材料和研究磁性物理机理等方面具有重大意义。文章介绍了几种常用的中子散射技术(如粉末衍射、小角散射、反射等),并通过典型的实例来说明它们在磁性材料研究中的具体应用。针对国内介绍中子反射技术的资料相对较少,尤其是极化中子反射技术在精确定量表征薄膜磁性大小和分布方面的研究极度匮乏的现状,文章重点介绍了这一特色技术以及应用实例。     

中国先进研究堆中子散射科学平台介绍

中子散射技术作为人类认知世界不可或缺的独特手段,多年来在诸多领域得到了广泛应用并成绩显著。文章以新建成的中国先进研究堆中子散射科学平台谱仪为例,较为详细地介绍了中子散射技术和谱仪的基本原理和特点,并对其未来的应用进行了展望。     

中国先进研究堆中子散射科学平台介绍

中子散射技术作为人类认知世界不可或缺的独特手段,多年来在诸多领域得到了广泛应用并成绩显著。文章以新建成的中国先进研究堆中子散射科学平台谱仪为例,较为详细地介绍了中子散射技术和谱仪的基本原理和特点,并对其未来的应用进行了展望。