Optimization of a Bonse-Hart Ultra-Small-Angle Neutron Scattering facility by elimination of the rocking-curve wings
Optimization of a Bonse-Hart Ultra-Small-Angle Neutron Scattering facility by elimination of the rocking-curve wings
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DOI：
10.1107/s0021889896014343
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发表时间：
1997-06-01
影响因子：
6.1
通讯作者：
Triolo, R
中科院分区：
文献类型：
--
作者：
Agamalian, M;Wignall, GD;Triolo, R
高通量同位素反应堆(HIFR)的ORNL超小角中子散射(USANS)设施最近进行了升级，采用Bonse-Hart技术。单色仪和分析仪均采用了Si(111)三反弹槽切单晶。分析器摆动曲线的总宽度约为1.6‘’，初级中子束的波长为2.59埃。已经证明，由于硅对中子的低吸收，在沟道切割晶体的壁内传播和绕射的中子通常会污染摇摆曲线的两翼。这种寄生强度已经通过在长壁上切割一条槽和插入一个镉吸收件(0.6毫米厚)来消除。这一改进有效地将摇摆曲线的翅膀抑制了两个数量级以上，从而极大地提高了衍射仪的灵敏度。升级后的设备已经用几个样品进行了测试，其中包括光学显微镜确定的半径为2.50×10(4)埃的聚苯乙烯乳胶。根据USANS数据计算的平均半径为2.48×10(4)埃，与独立确定的尺寸非常一致。升级后的USANS设施的最小可达散射向量为Q(Min)类似或等于2×10(-5)埃(-1)，这对应于2pi/q(Min)的最大可分辨实空间维度类似或等于3×10(5)埃(30微米)。
The ORNL Ultra-Small-Angle Neutron Scattering (USANS) facility at the High Flux Isotope Reactor (HIFR) has been recently upgraded, using the Bonse-Hart technique. Si(111) triple-bounce channel-cut single crystals have been used for both the monochromator and analyzer. The total width of the rocking curve of the analyzer is about 1.6 '' and the wavelength of the primary neutron beam is 2.59 Angstrom. It has been demonstrated that, owing to the low neutron absorption of silicon, the wings of the rocking curve are generally contaminated by neutrons propagating and diffracting inside the walls of channel-cut crystals. This parasitic intensity has been eliminated by the cutting of a groove in the long wall and the insertion of a cadmium absorber (0.6 mm thick). This modification effectively suppresses the wings of the rocking curve by over two orders of magnitude and thus dramatically improves the sensitivity of the diffractometer. The upgraded facility has been tested with several samples, including a polystyrene latex with a radius of 2.50 x 10(4) Angstrom as determined by optical microscopy. The average radius calculated from USANS data is 2.48 x 10(4) Angstrom in excellent agreement with independently determined dimensions. The minimum accessible scattering vector of the upgraded USANS facility is Q(min) similar or equal to 2 x 10(-5) Angstrom(-1), which corresponds to a maximum resolvable real-space dimension of 2 pi/Q(min) similar or equal to 3 x 10(5) Angstrom (30 mu m).