FTO质子照相中扩束器的设计

 为了达到最佳的扩束效果和充分利用束流，从多次库仑散射角、能量损失和透射率这三个方面确定扩束器的材料类型。对均方根多次库仑散射(MCS)、质子能量损失和质子的透过率的研究都表明单位面质量下材料原子序数越大，扩束效果越好。再结合成本和适用性确定扩束器的材料为钨。同时，从探测器接收到的质子通量均匀而噪声影响小的角度，确定了扩束器的厚度。研究结果为：没有准直器的情形下，扩束器的厚度为3.1 cm；准直器角度为3.0 mrad时，扩束器厚度为2.4 cm。

Diffuser design for FTO's proton radiography

In order to achieve the best expanding effeciency of the diffuser and to use most protons to radiate the French Test Object, the material is chosed from three aspects. They are MCS (multiple Coulomb scattering) angle, energy loss and penetration rate for proton per unit areal mass. The analyzed results of these aspects show that the bigger the atomic number is, the higher the efficiency is. The material is determined to be tungsten considering cost and applicability. The thickness of the diffuser is designed according to the demands of uniform proton flux distribution and small noise. As a result, the diffuser thicknesses are 3.1 cm without collimator and 2.4 cm with 3.0 mrad collimator.