Electron Physics - Case Study Example

TAQ Excitation is the process if giving an electron in an atom at a certain energy level some extra amount of energy for it to move or jump up to the next higher energy level. After the excitation of an electron, it falls back to its original energy level, shell or orbital, and emits a photon of electromagnetic radiation, which equals to the amount of energy that was applied to cause excitation. The frequency of the photon is proportional to the amount of energy it possesses and thus higher frequency photons including X-rays have high levels of energy and radio waves have low energy. K shell refers to the lowest energy level, and the L level is the level that is above the K shell. Relative large amount of energy is needed for the excitation of electrons, and the excitation occurs when the surrounding temperature is raised to several million degrees or when a material is bombarded with electrons at the speed of light. The excitation of electrons in X-ray tubes is through bombardment to release photons. TAQ 2 Bremsstrahlung radiation occurs when electrons travel through a vacuum and enter a solid material to spontaneously release high energy photons which result in loss of energy and slowed speed of the electrons. The number of photon energy that is released by the electron equals to its motion or kinetic energy that is released. Spectrum of a radiation source is a graph that shows the relationship between the radiation intensity or power and the wavelength of radiation. Continuous spectrum indicates that the source emits power over the wavelength for the range on the graph. The graph can be used to change the X-ray output by varying the potential difference and the current. Current is proportional to the X-ray intensity, and an increase in the potential difference increases the frequency and lowers the intensity.(Continuous spectrum, Electron Physics and X-ray tomography, Pdf) X-ray spectrum graph for a copper target TAQ 3 (X-ray tube, Electron Physics and X-ray tomography, Pdf) The tube is enclosed by a high quality glass, and there is a vacuum inside the tube. The small filament is made up of tungsten and receives a small current that lights it up just as the ordinary bulb of a torch. A large potential difference is applied to the anode, positively charged electrode, near the filament so that it directs a stream of electrons from the white hot filament at a speed close to the speed of light. The process of directing the electrons from a hot filament is referred to as Thermionic emission. A part of the anode acts as a target and is mainly made of tungsten or molybdenum and it is where electrons hit as they come from the filament to produce X-rays. Tungsten and molybdenum are preferred because of the high temperatures involved in the process though there is a mechanism of cooling that helps improve the efficiency of the tubes. TAQ 4 (X-ray spectrum graph, Electron Physics and X-ray tomography, Pdf) When the voltage that speeds up the movement of electrons form the filament to the target is increased, the speed of the electrons increases and they have more energy thus they produce X-ray photons with high energy through Bremsstrahlung radiation. Most of the electrons produced possess energy that is enough to release X-ray photons, so the process becomes more efficient. When the tungsten target is operated at three different potential differences, the results in the spectrum graph show that peak of the hump moves upwards in the left direction as the voltage is increased with the excitation lines staying in their original positions. The peak moves up and to the left because as the voltage is increased more X-ray photons are released, which have low frequencies and high energies and the result is that the peak of the hump shifts to the left and to a lower value of the wavelength or high frequency. A change in the voltage has no effect on the wavelengths. Also, when voltage is increased while using different materials, the peak of the hump moves upwards in the left direction but along different excitation lines. When the current flowing in the filament is altered, it changes the filament temperature which determines the number of electrons that are emitted. Thus, a change in current has no effect on the wavelength but it results into an increase in the intensity as shown in the graph. (Dependence of spectrum on current, Electron Physics and X-ray tomography, Pdf) TAQ 5 Scatter refers to a way of interaction between the X-rays and their atoms when X-ray photons bounce off the atoms after they have failed to be absorbed or changed in form. It is only their direction of travel that is altered Photoelectric effect is the process by which an X-ray photon hits its atom to give up energy and release an electron from the atom. The X-ray photon is then absorbed and disappears completely. The electrons released by photoelectric effect are of beta radiation travelling at high speeds and are harmful to human tissue. Compton Scattering is the process by which an X-ray photon is deflected from an atom to change its direction while releasing an electron from the atom. The process uses some of the X-ray photon energy to pull an electron from the atom and thus results in the reduction of frequency. Compton scattering also releases electrons that are dangerous to human tissue. Pair production is a rare process whereby an X-ray photon hits a particle and stops completely releasing all its energy which is then converted to production of two new particles, which include electron and a positron, the antimatter equivalent of the electron. TAQ 6 At photon energy of 10keV Simple scattering and Compton scattering occur at low photon energies, but the amount of scatter is independent of the material used. The low photon energies are used in X-rays that do not require much penetration such as mammography. At photon energy of 30keV The photoelectric effect occurs at voltages that are lower than the Pair production voltages and higher than the voltages for scattering. It is the main absorption process for normal X-rays used in diagnostics. At photon energy of 4MeV Pair production occurs with the highest frequency photons and thus requires photons with high photon energies. It happens with frequency values that are higher than the values used for normal X-ray photography, but the occurrence is on the same extent to the absorbing material. Beam hardening Attenuation occurs when the strength of a beam of X-ray photons is reduced as a result of absorption or scatter. Attenuation depends on photon energy and density of the material used. Absorption of X-rays is more in denser materials than in less dense materials to cause more beam attenuation. Beam hardening is the effect that occurs since normal X-ray beams have a range of photon energies and are referred to as an increase in the effective energy of X-ray beams as they penetrate the attenuating materials. The X-ray beams as they pass soft materials they absorb lower photon energies more than the higher photon energies resulting into more penetration and the beam becomes harder. TAQ 7 A chest X-ray requires high voltages of about 80kV or more for obese patients as more photon energy is required to penetrate the X-rays the patient and reach their underneath film. The number of X-rays photon is controlled by the tube current, the electrical current through a tungsten filament. The formation of a good image requires a large tube current of about 400mA. The amount of X-rays reaching the film is determined by the exposure time. A higher exposure time gives an image that is as twice the radiation as much as the image resulting from half of the exposure time. The tube current is multiplied by the exposure time to give a figure in milliamp seconds. The patient puts on an X-ray gown and removes metallic objects such as jewelry around the neck and chest since they can block penetration of the X-rays. The patient takes a deep breath and holds to inflate the lungs to maximum during the scan so as to increase the visibility of the tissues within the chest. Chest X-ray procedures can be done from the back or the side known as lateral chest X-ray. Other angles are added to interpret certain areas of the chest. The X-ray is taken and recorded on X-ray film for interpretation in a developing machine by a radiologist (How is the chest X-ray procedure performed n.d.). Different body parts absorb X-rays depending on their densities, and this is the basis of recognition for abnormalities. In a chest scan, the density of calcium in the spine and ribs blocks most of the X-rays to leave white areas on the film. When the X-rays fail to penetrate, the spots are left darkened. Fluids, mainly water, in the stomach and liver block few X-rays and thus they look darker than the bones. The density of fat is lower than that of water and thus the image appears darker than the stomach or liver image but it is only noticeable for a trained eye. The lung air spaces allow most of the X-rays and thus the image appears black (Linton, 1995 p. 6). Multi beam radiotherapy procedure Multi beam radiotherapy is the process of minimizing the radiation that is received by healthy tissue around the tumour to ensure a large dose to the tumour. It uses high energy equipment known as Linac or Linear accelerator that directs radiation to the desired body part. The linear accelerator applies small voltages many times to the same electrons and accelerates them to mega electron volts. The electrons are then allowed to hit the target, molybdenum or tungsten, to produce higher energy photons than those produced in normal X-ray tubes. The X-ray beam is then shaped to fit the tumour through adjustments of diaphragms and depending on the purpose. For the purposes of destroying the tumour completely, the radiation is delivered in one beam. In this case, the healthy tissue between the skin and the tumour receives large radiation and increases the side effects and the likelihood of causing new cancer. To prevent this, the X-ray beam is moved around the body to reach the tumour from different angles. Multi beam radiotherapy equipment The equipment, linear accelerator, generates high energy photons which are directed to the area to be treated. The equipment can also use electrons to treat the area that are close to the skins surface. The Intensity modulated radiation therapy allows for the treatment of healthy tissue. The machine has multi-leaf collimators, which change the shape of the beam so that the machine does not treat in square or rectangular shapes (Radiotherapy n.d.). References Electron physics and X-ray Tomography, Pdf How is the chest X-ray procedure performed? - Chest X-Ray: Get Facts about Imaging the Human Trunk, n.d,.MedicineNet, Available from . [12 May 2014] Linton OW, 1995, Medical Applications of -rays, p. 5, Pdf Radiotherapy - Radiation Therapy - MyRadiotherapy.com, n.d., Radiotherapy Treatment Machines, Available from [12 May 2014] Read More