基于玻璃毛细管的大气环境MeV质子微束的产生与测量 : [Production and measurement of MeV proton microbeams in atmospheric environment based on glass capillary]

• 本文采用玻璃毛细管产生了大气环境中工作的2.5 MeV质子外束微束, 并对束斑直径及能量分布随玻璃毛细管与束流方向之间角度(倾角)变化进行测量. 测量结果表明, 在玻璃毛细管轴向与束流方向一致时(倾角为0°), 产生的微束中存在保持初始入射能量的直接穿透部分以及散射部分, 其中直接穿透的质子占比最大, 束斑直径也最大. 随着玻璃毛细管倾角的增大, 当其大于几何张角时, 束斑直径变小, 产生的微束全部为能量减小的散射部分, 直接穿透质子消失. 我们对质子在玻璃毛细管内传输时的内壁散射过程进行了模拟计算及离子轨迹分析, 发现大角度的散射部分决定了形成的外束微束斑外围轮廓, 而束斑中心区域由不与毛细管内壁产生任何作用的直接穿透离子构成, 其大小由玻璃毛细管出口直径以及几何容许张角决定. 采用玻璃毛细管产生的外束微束具有产生简单廉价, 微束区域定位简单的特点, 有望在辐射生物学、医学、材料等领域得到广泛应用.

• Traditionally, ion microbeam is produced by focusing or/and collimating to reduce the beam size to submicron level. The traditional setup for producing the microbeam consists of an expensive focusing and collimating system with a large space, based on electromagnetic fields. Meanwhile, the microbeam obtained through pure collimation of metal micro-tubes is limited by the fabrication processing, i.e. the size of beam spot is largely limited to a few microns and its manufacture is not as simple as that of a glass capillary. Inspired by early studies of the guiding effect, the use of inexpensive and easy-to-make glass capillaries as the tool for ion external microbeam production has become a new direction.In this work, we use a glass capillary with an open outlet (108 μm in diameter), which serves as a vacuum differential and collimating component, to produce a 2.5 MeV-proton microbeam directly from the linear accelerator into the atmosphere for measurements. We measure the beam spot diameter and energy distribution of the microbeam as a function of the tilt angle of the capillary. We also conduct calculations and ion trajectory analysis on the scattering process of 2.5 MeV protons on the inner walls.The measurement results show that when the tilt angle is around 0°, there are a direct transmission part that maintains the initial incident energy, and a scattering part with the energy loss in the microbeam. It is found that the proportion of directly transmitted protons and the beam spot size are highest near zero tilt angle. As the tilt angle increases, the beam spot diameter decreases; when the tilt angle is greater than the geometric angle, all the microbeams come from the scattering with the energy loss. The simulation combined with the ion trajectory analysis based on the scattering process can explain the experimental results. It is found that the large angle scattering determines the entire external microbeam spot, and the central region of the beam spot is composed of directly penetrating ions, whose size is determined by the geometric shape of the glass capillary, i.e. the outlet diameter and aspect ratio.The natural advantage of producing external micobeames easily and inexpensively through glass capillaries is their relative safety and stable operation, and the last but not least point is to simply locate the microbeams on the sample without complex diagnostic tools. The microbeams are expected to be widely used in fields such as radiation biology, medicine, and materials.

Subject headings

NATURVETENSKAP  -- Fysik -- Acceleratorfysik och instrumentering (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Accelerator Physics and Instrumentation (hsv//eng)

Keyword

ions external microbeam

MeV protons

conical glass capillary

离子外束微束

MeV质子

锥形玻璃毛细管

Publication and Content Type

ref (subject category)

art (subject category)