X-ray interactions with matter Essay Example

X X-ray interactions with matter Paper X-ray interactions with matter Paper This document presents the interactions of x-ray with matter. It talks about the five types of x-ray interactions with matter, photoelectric absorption, compton scattering, pair production, coherent interaction, and photodisintegration. Each of this x-ray interactions are discussed in a manner that it can be understood by the general public. This document also dwells on the various exposure factors involve in radiography. It also provides a brief discussion of the attenuation that occurs when a photon travels through the matter. X-ray is a form of Photon that is created when energetic electron interacts with matter at the atomic level. Photons end their lives when they collide with electrons and transfer their energy. Like other forms of photons, x-rays possess intrinsic energy that may be imparted to the matter they interacts with. Interaction takes place as either absorption (transfer of energy from the X-ray photon to the absorbing material) or scattering (in which the X-ray photon is â€Å"redirected† by interaction with the scattering material) (Connolly, 2007). X-ray has been used extensively in medical imaging which sometimes brings wonders to a number of people of how x-rays are able to penetrate solid objects and produce images of the internal structure. Photoelectric Absorption occurs when a photon hits the atom of matter and all of its energy is transferred to the electron which is then knocked out of its orbital. The atom becomes ionized due to the loss of an electron. The photon, which is a form of energy, completely disappears as it transfers all its energy to the electron knocking it out of the orbital. The electron is ejected from the atom by the transformation of energy from light to kinetic energy and begins to pass through the surrounding matter. The electron rapidly loses its energy and moves only a relatively short distance from its original location. The photons energy is, therefore, deposited in the matter close to the site of the photoelectric interaction (Sprawls, 2006). The energy transfer is a two-step process. The photoelectric interaction in which the photon transfers its energy to the electron is the first step. The depositing of the energy in the surrounding matter by the electron is the second step. The transfer of energy is depicted by figure 1 to figure 2. Figure 1. Before Collision Figure 2. After Collision Photoelectric interaction normally occurs with electrons that has relatively high binding energy. It is most probable when the electron binding energy is only slightly less than the energy of the photon. If the binding energy of the electron is greater than the photon then photoelectric interaction cannot occur. This is because the interaction can only occur if the photon has sufficient energy to knock and overcome the binding energy, thus removing the electron from the atom. Compton Effect Compton effect occurs when a photon hits the atom of matter and only a portion of its energy is transferred to the electron. The photon still leaves the vicinity of the interaction in a direction different from the original path of the photon. This is illustrated in figure 3. The atom also becomes ionized due to the loss of an electron. The Relativistic energy and momentum are conserved in this process1 and the scattered x-ray photon has less energy and therefore greater wavelength than the incident photon (Connolly, 2007). The photon that leaves the vicinity of the interaction may interact further with the nearby atoms until it looses all its energy or escapes the matter and goes outside.

Carl Ritter - German Founder of Modern Geography

Carl Ritter - German Founder of Modern Geography German geographer Carl Ritter is commonly associated with Alexander von Humboldt as one of the founders of modern geography. However, most acknowledge Ritters contributions to the modern discipline to be somewhat less significant than those of von Humboldt, especially as Ritters life-work was based on the observations of others. Childhood and Education Ritter was born on August 7, 1779, in Quedlinburg, Germany (then Prussia), ten years after von Humboldt. At the age of five, Ritter was fortunate to have been chosen as a guinea pig to attend a new experimental school which brought him into contact with some of the greatest thinkers of the period. In his early years, he was tutored by the geographer J.C.F. GutsMuths and learned the relationship between people and their environment. At the age of sixteen, Ritter was able to attend a university by receiving tuition in exchange for tutoring a wealthy bankers sons. Ritter became a geographer by learning to observe the world around him; he also became an expert at sketching landscapes. He learned Greek and Latin so that he could read more about the world. His travels and direct observations were limited to Europe, he was not the world traveler that von Humboldt was. Career In 1804, at the age of 25, Ritters first geographical writings, about the geography of Europe, were published. In 1811 he published a two-volume textbook about the geography of Europe. From 1813 to 1816 Ritter studied geography, history, pedagogy, physics, chemistry, mineralogy, and botany at the University of Gottingen. In 1817, he published the first volume of his major work, Die Erdkunde, or Earth Science (the literal German translation for the word geography.) Intended to be a complete geography of the world, Ritter published 19 volumes, consisting of over 20,000 pages, over the course of his life. Ritter often included theology in his writings for he described that the earth displayed evidence of Gods plan. Unfortunately, he was only able to write about Asia and Africa before he died in 1859 (the same year as von Humboldt). The full, and lengthy, title of Die Erdkunde is translated to The Science of the Earth in Relation to Nature and the History of Mankind; or, General Comparative Geography as the Solid Foundation of the Study of, and Instruction in, the Physical and Historical Sciences. In 1819 Ritter became a professor of history at the University of Frankfurt. The following year, he was appointed to be the first chair of geography in Germany - at the University of Berlin. Though his writings were often obscure and difficult to understand, his lectures were very interesting and quite popular. The halls where he gave lectures were almost always full. While he held many other simultaneous positions throughout his life, such as founding  the Berlin Geographical Society, he continued to work and lecture at the University of Berlin until his death on September 28, 1859, in that city. One of Ritters most famous students and ardent supporters was Arnold Guyot, who became a professor of physical geography and geology at Princeton (then the College of New Jersey) from 1854 to 1880.