Wang C L, Clonts L G, Diawara Y, Hannan B W, Hodges J P
Instrument and Source Design Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Rev Sci Instrum. 2013 Jan;84(1):013308. doi: 10.1063/1.4789497.
Misassignment of neutron position (ghosting) produces artifacts which have been observed in wavelength-shifting (WLS) fiber detectors developed for time-of-flight (TOF) neutron powder diffraction. In position-sensitive detectors (PSDs) with WLS fiber encoding, thermal and cold neutrons interact with a monolithic (6)LiF/ZnS:Ag scintillator screen, and scintillation photons are generated and transported through the crossed fibers to photomultipliers (PMTs). The neutron position is determined by photon counts in the PMTs within a preset time window. Ghosting occurs when neutrons hit the group boundaries of two neighboring PMTs for x-position multiplexing, which is modeled as resulting from a long travel length (about 3-5 mm) of a small number of scintillation photons. This model is supported by the change observed in aperture images when the threshold number for photon-pulses was adjusted for neutron event determination. When the threshold number of photon-pulses was set above 10 for each PMT, the ghost peaks in the aperture images and TOF spectra of powder diffraction were strongly suppressed or completely eliminated, and the intrinsic background levels of the WLS detectors were significantly reduced. Our result indicates that WLS fiber detector is a promising alternative for (3)He PSDs for neutron scattering.
中子位置误分配（重影）会产生伪影，这种伪影在为飞行时间（TOF）中子粉末衍射开发的波长转换（WLS）光纤探测器中已被观察到。在采用WLS光纤编码的位置敏感探测器（PSD）中，热中子和冷中子与单片（6）LiF/ZnS:Ag闪烁体屏相互作用，产生闪烁光子，并通过交叉光纤传输到光电倍增管（PMT）。中子位置由预设时间窗口内PMT中的光子计数确定。当用于x位置复用的中子击中两个相邻PMT的组边界时，就会出现重影，这被建模为少量闪烁光子的长传播长度（约3 - 5毫米）导致的结果。当为中子事件确定调整光子脉冲的阈值数量时，孔径图像中观察到的变化支持了这一模型。当为每个PMT将光子脉冲的阈值数量设置高于10时，粉末衍射的孔径图像和TOF光谱中的重影峰被强烈抑制或完全消除，并且WLS探测器的固有背景水平显著降低。我们的结果表明，WLS光纤探测器是用于中子散射的3He PSD的一种有前途的替代方案。
