大学物理实验报告英文版--X光.doc

Experiment report of X-ray Principle: When we speak of attenuation of x-rays, we mean the decrease in intensity that occurs when the radiation passes through matter. This attenuation is caused mainly by the two effects: scattering and absorption. Although absorption and attenuation are different physical phenomena, the transilluminated object is often referred to -inaccurately- as an absorber; this should more properly be termed an attenuator. However, this description will follow the traditional usage in some places and refer to absorbers instead of attenuators. The scattering of x-ray quanta at the atoms of the attenuator material causes a part of the radiation to change direction. This reduces the intensity in original direction. This scattering can be either elastic or entail an energy loss or shift in wavelength, i.e. Inelastic scattering. When x-ray hits a fluorescence material, it excites the material, making fluorescence lights. This is the principle of a fluorescence screen. When x-ray is used in imaging, the transmitted light will carry interior information of the object. A more sophisticated x-ray detector is the so-called Geiger-Muller counter, an instrument for detecting the presence of and measuring ionizing radiation such as the x-rays. It converts the intensity of the x-ray into counting rates. We will use such a device in our lab. Attenuation of x-rays: When passing through a material, x-ray can be attenuated by EM interactions. For a slab of thickness x, the transmission (defined as the ratio of the transmitted radiation to the incoming), . μ is the attenuation coefficient, with a dimension of 1/distance. μis a character of the material, and it varies, for example, as a function of atomic number. We will study this dependence in this lab. Bragg Diffraction Like normal lights, when x-ray transmit through material with regular optical pattern (e.g. lattice), diffraction will happen if the wavelength of the x-ray is close to the lattice space. Such