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THERMAL AND EPITHERMAL NEUTRON FLUENCE RATE GRADIENT MEASUREMENTS BY PADC DETECTORS IN LINAC RADIOTHERAPY TREATMENTS-FIELD

机译:LINAC放射治疗处理中PADC探测器的热敏和膜状中子流量梯度测量

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LINAC VARIAN 2100 is where energetic electrons produce Bremsstrahlung radiation, with energies above the nucleon binding energy (E≈5.5MeV). This radiation induce (y,n) and (e,e'n) reactions mainly in the natural tungsten target material (its total photoneutron cross section is about 4000 mb in a energy range from 9-17 MeV). These reactions may occur also in other components of the system (e.g. multi leaf collimator). During radiation treatment the human body may receive an additional dose inside and outside the treated volume produced by the mentioned nuclear reactions. We measured the neutron density at the treatment table using nuclear track detectors (PADC-NTD). These covered by a boron-converter are employed, including a cadmium filter, to determine the ratio between two groups of neutron energy, i.e. thermal and epithermal. The PADC-NTD detectors were exposed to the radiation field at the iso-center during regular operation of the accelerator. Neutron are determined indirectly by the converting reaction ~(10)B(n,a)~7Li the emerging charged particle leave their kinetic energy in the PADC forming a latent nuclear track, enlarged by chemical etching (6N, NaOH, 70°C). Track density provides information on the neutron density through calibration coefficient (-1.6 10~4 neutrons /track) obtained by a californium source. We report the estimation of the thermal and epithermal neutron field and its gradient for photoneutrons produced in radiotherapy treatments with 18 MV linear accelerators. It was obsered that photoneutron production have higher rate at the iso-center.
机译:LINAC 2100 VARIAN是其中高能电子产生轫致辐射,与核子结合能(E≈5.5MeV)以上的能量。这种辐射诱发(Y,N)和(e,e'n)反应主要在天然钨靶材料(其总光中子横截面是约在9-17从一兆电子伏的能量范围4000 MB)。可以在系统(例如多叶准直器)的其它部件也发生这些反应。在放射治疗人体可接收额外的剂量内外由所提到的核反应产生经处理的体积。我们利用核轨道检测器(PADC-NTD)测量的中子密度在治疗台。这些通过硼 - 转换器覆盖的采用,包括镉滤波器,以确定两组中子能量,即热和超热的之间的比率。所述PADC-NTD探测器加速器的常规操作期间暴露于在等中心的辐射场。中子由转换反应〜(10)乙间接地确定(N,A)〜7Li的新兴的带电粒子离开其动能在PADC形成潜核轨道,通过化学蚀刻扩大(6N,加入NaOH,70℃) 。磁道密度提供了关于由锎源获得通过校准系数的中子密度(-1.6 10〜4中子/轨道)的信息。我们报告的热和超热中子场的用于放射治疗的治疗产生具有18 MV线性加速器光中子的估计及其梯度。据obsered该中子产量都在等中心率较高。

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