Purpose

The possibility to calibrate microdosimetric spectra using the proton- and electron-edge was proposed many years ago. It consists of two steps: first identifying the edge and a marker point on it and then ascribing the correct lineal energy value to the position of the edge in the event size spectrum. The purpose of this work is to rigorously study the marker identification for the proton-edge in the mini-TEPC spectra measured in neutron and in clinical proton fields, and the correspondent lineal energy value to assign to it.

Materials and methods

Microdosimetric measurements were performed with a cylindrical miniaturized tissue-equivalent proportional-counter (mini-TEPC) in neutron and gamma rays radiation fields at the CN accelerator of the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (LNL-INFN) and in the clinical 62 MeV proton beam of the Southern National Laboratories of INFN (LNS-INFN). The fitting of the proton-edge region of the microdosimetric spectra with a Fermi-like function was studied in both neutron and proton fields to identify the most precise marker point. The lineal energy value to ascribe to it was determined starting from the maximum energy deposit in protons obtained in FLUKA simulations.

Results

Both in neutron radiation field and in clinical proton beams the flex and the intercept of the tangent through the inflection point are determined with similar precision. The flex was chosen as the most suitable marker of the proton-edge in sealed detectors because it is known to be less sensitive to pressure variations. The lineal energy value to ascribe to the flex position for 0.75 μm of propane depends on the irradiation geometry: 194 keV/μm for isotropic radiation fields and 165 keV/μm for mono-directional radiation fields orthogonal to the axis of the cylinder. The calibration values for the proton-edge have been converted in water by means of the mean stopping power ratio of water and propane for protons obtaining 171 keV/μm for isotropic radiation fields and 145 keV/μm for mono-directional radiation fields.

中文翻译：

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通过质子边缘技术对微型TEPC进行线性能量校准

目的

多年前提出了使用质子和电子边缘校准微剂量光谱的可能性。它包括两个步骤：首先识别边缘和边缘上的标记点，然后将正确的线性能量值赋予事件大小谱中的边缘位置。这项工作的目的是严格研究在中子和临床质子场中测量的微型TEPC光谱中质子边缘的标记识别，以及对应的线性能量值。

材料和方法

在意大利国家核物理研究所莱格纳罗国家实验室（LNL-INFN）的CN加速器的中子和伽马射线辐射场中，使用圆柱形微型组织当量比例计数器（mini-TEPC）进行微剂量测量，并在是美国国家科学研究院南部国家实验室（LNS-INFN）的临床62 MeV质子束。在中子和质子场中都研究了具有费米样功能的微剂量光谱的质子边缘区域的拟合，以确定最精确的标记点。归因于它的线性能量值是从在FLUKA模拟中获得的质子的最大能量沉积量开始确定的。

结果

在中子辐射场和临床质子束中，通过拐点的切线的挠曲和截距都以相似的精度确定。弯曲被选为密封检测器中质子边缘的最合适标记，因为已知它对压力变化不那么敏感。归因于0.75μm丙烷的弯曲位置的线性能量值取决于辐照几何形状：各向同性辐射场为194 keV /μm，正交于圆柱体轴的单向辐射场为165 keV /μm。质子边缘的校准值已经在水中通过质子的水和丙烷的平均停止功率比进行了转换，质子分别在各向同性辐射场中获得171 keV /μm，在单向辐射场中获得145 keV /μm。