双臂 XRD：原理与模型边界
本应用是参考 Bruker D8 θ–θ 双臂结构制作的独立教学仿真，不连接真实设备。设备外观、机械细节、光束亮度、动画速度和保护门联锁均为示意，不代表真实设备或安全培训认证。X 射线不可见；入射和出射束为伪色可视化，亮度随相对模拟信号非线性变化，束宽不是经过计算的仪器发散或聚焦。
测角几何
样品表面水平、中心固定；光源及探测器位于同一垂直散射平面，以样品中心为共同旋转中心。对称扫描时两臂分别与样品表面形成 θ，散射角为 2θ。使用单一波长，2d sinθ = λ。动画加速播放；估算时间为点数乘以每点计数时间，不包含机械运动、检测器窗口、准备和通信等时间。
粉末谱与强度
复用本站晶体衍射实验室的随机粉末计算：立方 SC、BCC、FCC、金刚石型结构为等权标量点散射体，枚举允许反射，采用文献所述理想 Lorentz–polarization 因子和 2θ 方向面积归一高斯峰形。背景和曲线标度是固定示意值；输出为相对强度，不是探测器计数，也未模拟计数噪声或计数时间与强度的关系。峰宽由用户指定，并非从粒径计算。未考虑真实原子散射因子、Kα 双峰、温度因子、吸收、择优取向、样品位移、仪器展宽或探测器响应。
适用范围
不能据此作物相鉴定、定量组成、Rietveld 精修或真实上机参数判断；布拉格公式显示的是当前角度所对应的晶面间距，不能单凭该值说明当前一定存在反射。内置安全状态仅是操作流程动画，实际 X 射线安全须遵循实验室与设备制造商的规程。
检查与依据
开发中以几何对称、角度范围、扫描点数及布拉格峰位数值测试检查模型。下列资料为几何和粉末计算依据；这些检查不是仪器厂商或领域专家认证。
Dual-arm XRD: scientific basis and limits
This is an independent educational simulation inspired by the Bruker D8 θ–θ arrangement; it does not connect to hardware. Enclosure, mechanical details, beam brightness, playback speed and interlock are illustrative and do not constitute equipment or safety training certification. X-rays are invisible: both beams use false colour, brightness changes nonlinearly with the relative simulated signal, and beam width is not a calculated divergence or focus.
Goniometer geometry
The sample surface remains horizontal and its centre stationary. Source and detector rotate in a vertical scattering plane around the common sample centre. In a symmetric scan both arms make θ to the sample plane and the scattering angle is 2θ. A single wavelength is used: 2d sinθ = λ. Animation runs faster than the simulated measurement; estimated time is point count × dwell, excluding motion, detector window, preparation and communication.
Powder profile and intensity
The existing crystal lab random-powder calculation is reused. Cubic SC, BCC, FCC and diamond prototypes use equal scalar point scatterers; allowed reflections are enumerated with an ideal Lorentz–polarization factor and area-normalized Gaussian peaks on the 2θ axis. Background and display scale are illustrative; output is relative intensity, not detector counts. Count noise and the relation between dwell and intensity are not modelled. Peak width is user supplied, not inferred from crystallite size. Atomic form factors, Kα doublet, thermal factors, absorption, preferred orientation, sample displacement, instrumental broadening and detector response are omitted.
Interpretation
Do not use the simulation for phase identification, quantitative composition, Rietveld refinement or setting a real instrument. The spacing shown corresponds to the current Bragg angle and does not by itself mean a reflection exists. The virtual interlock is an animation; actual X-ray safety follows laboratory and manufacturer procedures.
Checks and references
Development checks include symmetric geometry, angular bounds, scan point count and numerical Bragg-peak benchmarks. These checks are not manufacturer or domain-expert certification.