Emfietzoglou Dimitris, Cucinotta Francis A, Nikjoo Hooshang
Medical Physics Laboratory, University of Ioannina Medical School, 451 10 Ioannina, Greece.
Radiat Res. 2005 Aug;164(2):202-11. doi: 10.1667/rr3399.
We present a complete yet computationally simple model for the dielectric response function of liquid water over the energy-momentum plane, which, in contrast to earlier models, is consistent with the recent inelastic X-ray scattering spectroscopy data at both zero and finite momentum transfer values. The model follows Ritchie's extended-Drude algorithm and is particularly effective at the region of the Bethe ridge, substantially improving previous models. The present development allows for a more accurate simulation of the inelastic scattering and energy deposition process of low-energy electrons in liquid water and other biomaterials. As an example, we calculate the stopping power of liquid water for electrons over the 0.1-10 keV range where direct experimental measurements are still impractical and the Bethe stopping formula is inaccurate. The new stopping power values are up to 30-40% lower than previous calculations. Within the range of validity of the first Born approximation, the new values are accurate to within the experimental uncertainties (a few percent). At the low end, the introduction of Born corrections raises the uncertainty to perhaps approximately 10%. Thus the present model helps extend the ICRU electron stopping power database for liquid water down to about two orders of magnitude with a comparable level of uncertainty.
我们提出了一个完整且计算简单的液态水在能量 - 动量平面上的介电响应函数模型，与早期模型相比，该模型在零动量转移值和有限动量转移值下均与最近的非弹性X射线散射光谱数据一致。该模型遵循里奇扩展的德鲁德算法，在贝塞脊区域特别有效，显著改进了先前的模型。目前的进展使得能够更准确地模拟低能电子在液态水和其他生物材料中的非弹性散射和能量沉积过程。例如，我们计算了液态水在0.1 - 10 keV范围内电子的阻止本领，在此范围内直接实验测量仍然不切实际，且贝特阻止公式不准确。新的阻止本领值比先前计算低30% - 40%。在第一玻恩近似的有效范围内，新值在实验不确定度（百分之几）内是准确的。在低端，引入玻恩修正会使不确定度增加到大约10%。因此，本模型有助于将国际辐射单位与测量委员会（ICRU）关于液态水的电子阻止本领数据库扩展到低约两个数量级，且具有相当的不确定度水平。
