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• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 物理代写|高能物理代写High Energy Physics代考|Total Cross-Section and Absorption Coefficient per Unit Mass

Given the three processes discussed above, we can visualize the total result by introducing the linear attenuation coefficient as follows. We consider a beam initially with $N_0$ photons crossing a material of density $\rho$. There is a certain probability of interaction with the matter, which means that on average $N$ of them will survive after traveling a distance $x$, where
$$N=N_0 \mathrm{e}^{-\mu x},$$
and the quantity $\mu$ with dimensions of (length $)^{-1}$ is a linear attenuation coefficient that depends on the energy and the material. Multiplying and dividing by $\rho$ in the argument of the exponential, we define $\mu / \rho$ as the attenuation coefficient per unit mass, generally expressed in $\mathrm{cm}^2 \mathrm{~g}^{-1}$. If all the processes contribute to absorbing photons, the total attenuation coefficient results from the sum of each of them.
Figure $2.7$ shows the regions where each of these processes dominates. (There is also coherent Rayleigh scattering, but it is never important in high energy Astrophysics, although it is responsible for the blue color of Earth’s sky.) We see that the lighter the element, the broader the energies at which the Compton effect is dominant. Pair creation and the photoelectric effect will be important only at high and low energies.

As a result of the different energy dependencies, the curves for the attenuation coefficient per unit mass behave as shown in Fig. 2.8. Although calculated for $\mathrm{Pb}$, the shape is similar for any other element or compound substance. Thus, we can discuss the construction of photon detectors, whose interactions with matter we now know, and choose materials and configurations according to the range of energies we wish to observe. Essentially all these detectors need to be operated in space, since attenuation by the atmosphere, described by the same formalism, is otherwise inevitable. Note that all instruments already built and operated have used one of the forms of absorption discussed above.

## 物理代写|高能物理代写High Energy Physics代考|Relevant Processes for High-Energy Photons

While we have been discussing the fate of photons that find matter in their path, it is equally important to worry about the emission of photons by matter. In fact, this is precisely what we observe from high energy astrophysical sources. Thus, knowing the mechanisms of radiation emission is equivalent to obtaining a diagnosis of the physical conditions of the environment in which it originates.

Basically, the emission processes are classified as coherent or incoherent. The former have a very particular physical characterization: the particles emit collectively and the final amplitude reflects this collective character; usually it is proportional to the square of the number of emitters $N^2$. Incoherent processes, on the other hand, sum up random amplitudes of particles that emit individually, without correlation with their neighbors. We can study different astronomical sources by understanding the types of emission they produce.

# 高能物理代考

## 物理代写|高能物理代写高能物理代考|单位质量的总截面和吸收系数

$$N=N_0 \mathrm{e}^{-\mu x},$$

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

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