Jakubowski Klaudiusz, Bevitt Joseph J, Howell Nicholas, Dobie Chris, Sierro Frederic, Garbe Ulf, Olsen Scott, Stopic Attila, Franklin Daniel R, Tran Linh T, Rosenfeld Anatoly, Guatelli Susanna, Safavi-Naeini Mitra
Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW, 2234, Australia.
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Sci Rep. 2025 Apr 2;15(1):11233. doi: 10.1038/s41598-025-96164-7.
In this work, we extend our previously published Monte Carlo simulation model of the Dingo thermal neutron beamline at the Australian Centre for Neutron Scattering model by (1) including a sapphire crystal filter in the model, and (2) utilising the NCrystal package to simulate thermal neutron interactions with the crystalline structure. In addition to previous experimental measurements performed in the beamline's high-resolution mode, the beam was experimentally characterised in its high-intensity mode upstream from the sample stage (at the tertiary shutter wall exit) and these measurements were used as inputs for the model. The planar neutron distributions were optimised at both the sample stage and tertiary shutter wall exit, and model predictions were validated against experimental gold wire activation measurements. For both configurations-with and without the sapphire filter-we measured neutron fluxes, and performed neutron activation analysis using 11 materials to improve the accuracy of the neutron spectrum in the model relative to the original version. Using the optimised spectrum, we simulated out-of-beam neutron spectra that were further used as the initial input in unfolding code to explore the capability of the current solution to accurately reproduce the experimental results. The normalised neutron planar distribution from the simulation was on average within 2% at the centre, and 6% and 24% at the penumbra of the experimental results at the tertiary shutter wall exit and sample stage, respectively. The specific activities predicted by the refined model were within an average of 13% and 5% of the experimentally measured activities with and without the sapphire filter, respectively. We observed a decrease of around 45% in thermal neutron flux when the sapphire filter is used, which has been reproduced by the model. The maximum value of the logarithm of the ratio of simulated to experimental out-of-beam neutron spectra across 8 locations was 0.6 compared to 2.0 in the previous work, resulting in an average normalised root mean squared error between the unfolded spectrum and experimental measurements of 5% and 9% with and without the filter, respectively. Without the sapphire filter, the optimised predicted in-beam neutron spectrum consists of around 59% thermal, 21% epithermal and 20% fast neutrons, while the addition of the filter provides an almost pure (approximately 98%) thermal neutron beam.
在这项工作中，我们扩展了之前发表的澳大利亚中子散射中心丁戈热中子束线的蒙特卡罗模拟模型，具体做法是：（1）在模型中加入蓝宝石晶体滤波器；（2）利用NCrystal软件包模拟热中子与晶体结构的相互作用。除了之前在束线高分辨率模式下进行的实验测量外，还在样品台上游的高强度模式下（在三级快门壁出口处）对束流进行了实验表征，并将这些测量结果用作模型的输入。在样品台和三级快门壁出口处对平面中子分布进行了优化，并根据实验金线活化测量结果对模型预测进行了验证。对于有无蓝宝石滤波器这两种配置，我们都测量了中子通量，并使用11种材料进行中子活化分析，以提高模型中中子能谱相对于原始版本的准确性。利用优化后的能谱，我们模拟了束外中子能谱，并将其进一步用作解卷积代码的初始输入，以探索当前解决方案准确再现实验结果的能力。模拟得到的归一化中子平面分布在三级快门壁出口和样品台处，中心位置平均在实验结果的2%以内，半影区分别为6%和24%。改进后的模型预测的比活度分别在有和无蓝宝石滤波器时实验测量比活度的平均13%和5%以内。我们观察到使用蓝宝石滤波器时热中子通量下降了约45%，模型也再现了这一结果。在8个位置上，模拟束外中子能谱与实验能谱之比的对数最大值为0.6，而在之前的工作中为2.0，有和无滤波器时解卷积能谱与实验测量结果之间的平均归一化均方根误差分别为5%和9%。没有蓝宝石滤波器时，优化后的束内中子能谱由约59%的热中子、21%的超热中子和20%的快中子组成，而加入滤波器后可提供几乎纯的（约98%）热中子束。
