Doppler broadening as a lower limit to the angular resolution of next-generation Compton telescopes
Doppler broadening as a lower limit to the angular resolution of next-generation Compton telescopes
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多普勒展宽是下一代康普顿望远镜角分辨率的下限
DOI：
10.1117/12.461177
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
G. Kanbach
中科院分区：
文献类型：
--
作者：
A. Zoglauer;G. Kanbach
通过康普顿效应探测伽马射线的望远镜的角分辨率基本上被限制在几百keV以下，因为目标电子在其原子内具有不可确定的动量，这引入了康普顿电子和散射光子的反冲能量的不确定性。与静止目标的标准康普顿方程相比，能量和动量方程中的这一附加分量导致角分辨率的多普勒展宽。对于低光子能量、高散射角和散射材料的高Z，分辨率的劣化最显著。即使所有其他参数（例如能量和位置）都以高精度测量，康普顿望远镜的角分辨率也存在这种物理限制。对于不同的康普顿散射材料，如硅，锗和氙，这是在目前的望远镜设计中使用的，最好的可能的角分辨率作为光子能量和散射角的函数进行计算。在所有散射角度和能量上求平均值，硅的多普勒限制角分辨率比锗的好约1.6倍，比氙的好约1.9倍。观察从Z=1到90的材料的多普勒极限，对于碱金属和碱土金属可以达到最好的角分辨率，对于具有填充的p轨道（稀有气体）和d轨道（例如Pd和Au）的元素最差。在所有可能用于下一代康普顿望远镜的半导体中，硅似乎是最好的选择。
The angular resolution of a telescope which detects gamma-rays via the Compton effect is fundamentally limited below a few hundred keV by the fact that the target electrons have an indeterminable momentum inside their atoms which introduces an uncertainty in the recoil energy of the Compton electron and the scattered photon. This additional component in the energy and momentum equation results in a Doppler broadening of the angular resolution compared to the standard Compton equation for a target at rest. The deterioration in resolution is most pronounced for low photon energy, high scatter angle, and high Z of the scatter material. This physical limit to the angular resolution of a Compton telescope is present even if all other parameters (e.g. energy and position) are measured with high accuracy. For different Compton scatter materials such as silicon, germanium and xenon, which are used in current telescope designs, the best possible angular resolution as a function of photon energy and scatter angle is calculated. Averaged over all scatter angles and energies, the Doppler-limited angular resolution of silicon is a factor of ~1.6 better than that of germanium and a factor of ~1.9 better than that of xenon. Looking at the Doppler limit of materials from Z=1 to 90 the best angular resolution can be reached for alkaline and alkaline earth metals, the worst for elements with filled p-orbitals (noble gases) and d-orbitals (e.g. Pd and Au). Of all semiconductors which might be used in a next generation Compton telescope, silicon seems to be the best choice.