How X-Rays Work

How Rays Work

How Rays Work Click here to print this article As with many of mankinds monumental discoveries ray technology was invented completely by accident In 1895 German physicist named Wilhelm Roentgen made the discovery while experimenting with electron beams in gas discharge tube Roentgen noticed that fluorescent screen in his lab started to glow when the electron beam was turned on This response in itself wasnt so surprising fluorescent material normally glows in reaction to electromagnetic radiation but Roentgens tube was surrounded by heavy black cardboard Roentgen assumed this would have blocked most of the radiation Roentgen placed various objects between the tube and the screen and the screen still glowed Finally he put his hand in front of the tube and saw the silhouette of his bones projected onto the fluorescent screen Immediately after discovering rays themselves he had discovered their most beneficial application Roentgens remarkable discovery precipitated one of the most important medical advancements in human history ray technology lets doctors see straight through human tissue to examine broken bones cavities and swallowed objects with extraordinary ease Modified ray procedures can be used to examine softer tissue such as the lungs blood vessels or the intestines Now well find out exactly how rays machines pull off this incredible trick As it turns out the basic process is really very simple Whats an Ray rays are basically the same thing as visible light rays Both are wavelike forms of electromagnetic energy carried by particles called photons see How Light Works for details The difference between rays and visible light rays is the energy level of the individual photons This is also expressed as the wavelength of the rays Our eyes are sensitive to the particular wavelength of visible light but not to the shorter wavelength of higher energy ray waves or the longer wavelength of the lower energy radio waves Visible light photons and ray photons are both produced by the movement of electrons in atoms Electrons occupy different energy levels or orbitals around an

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atoms nucleus When an electron drops to lower orbital it needs to release some energy it releases the extra energy in the form of photon The energy level of the photon depends on how far the electron dropped between orbitals See this page for detailed description of this process When photon collides with another atom the atom may absorb the photons energy by boosting an electron to higher level For this to happen the energy level of the photon has to match the energy difference between the two electron positions If not the photon cant shift electrons between orbitals The atoms that make up your body tissue absorb visible light photons very well The energy level of the photon fits with various energy differences between electron positions Radio waves dont have enough energy to move electrons between orbitals in larger atoms so they pass through most stuff ray photons also pass through most things but for the opposite reason They have too much energy They can however knock an electron away from an atom altogether Some of the energy from the ray photon works to separate the electron from the atom and the rest sends the electron flying through space larger atom is more likely to absorb an ray photon in this way because larger atoms have greater energy differences between orbitals the energy level more closely matches the energy of the photon Smaller atoms where the electron orbitals are separated by relatively low jumps in energy are less likely to absorb ray photons The soft tissue in your body is composed of smaller atoms and so does not absorb ray photons particularly well The calcium atoms that make up your bones are much larger so they are better at absorbing ray photons In the next section well see how ray machines put this effect to work Other Ray Uses The most important contributions of ray technology have been in the world of medicine but rays have played crucial role in number of other areas as well rays have been pivotal in research involving quantum mechanics theory crystallography and cosmology In the industrial world ray scanners are often used to detect minute flaws in heavy metal equipment And ray scanners have become standard equipment in airport security of course The Ray Machine The heart of an ray machine is an electrode pair cathode and an anode that sits inside glass vacuum tube The cathode is heated filament like you might find in an older fluorescent lamp The machine passes current through the filament heating it up The heat sputters electrons off of the filament surface The positively charged anode flat disc made of tungsten draws the electrons across the tube The voltage difference between the cathode and anode is extremely high so the electrons fly through the tube with great deal of force When speeding electron collides with tungsten atom it knocks loose an electron in one of the atoms lower orbitals An electron in higher orbital immediately falls to the lower energy level releasing its extra energy in the form of photon Its big drop so the photon has high energy level it is an ray photon The free electron collides with the tungsten atom knocking an electron out of lower orbital higher orbital electron fills the empty position releasing its excess energy as photon Free electrons can also generate photons without hitting an atom An atoms nucleus may attract speeding electron just enough to alter its course Like comet whipping around the sun the electron slows down and changes direction as it speeds past the atom This braking action causes the electron to emit excess energy in the form of an ray photon The free electron is attracted to the tungsten atom nucleus As the electron speeds past the nucleus alters its course The electron loses energy which it releases as an ray photon The high impact collisions involved in ray production generate lot of heat motor rotates the anode to keep it from melting the electron beam isnt always focused on the same area cool oil bath surrounding the envelope also absorbs heat The entire mechanism is surrounded by thick lead shield This keeps the rays from escaping in all directions small window in the shield lets some of the ray photons escape in narrow beam The beam passes through series of filters on its way to the patient camera on the other side of the patient records the pattern of ray light that passes all the way through the patients body The ray camera uses the same film technology as an ordinary camera but ray light sets off the chemical reaction instead of visible light See How Photographic Film Works to learn about this process Generally doctors keep the film image as negative That is the areas that are exposed to more light appear darker and the areas that are exposed to less light appear lighter Hard material such as bone appears white and softer material appears black or gray Doctors can bring different materials into focus by varying the intensity of the ray beam Contrast Media In normal ray picture most soft tissue doesnt shows up clearly To focus in on organs or to examine the blood vessels that make up the circulatory system doctors must introduce contrast media into the body Contrast media are liquids that absorb rays more effectively than the surrounding tissue To bring organs in the digestive and endocrine systems into focus patient will swallow contrast media mixture typically barium compound If the doctors want to examine blood vessels or other elements in the circulatory system they will inject contrast media into the patients bloodstream Contrast media are often used in conjunction with fluoroscope In fluoroscopy the rays pass through the body onto fluorescent screen creating moving ray image Doctors may use fluoroscopy to trace the passage of contrast media through the body Doctors can also record the moving ray images on film or video Are Rays Bad For You rays are wonderful addition to the world of medicine they let doctors peer inside patient without any surgery at all Its much easier and safer to look at broken bone using rays than it is to open patient up But rays can also be harmful In the early days of ray science lot of doctors would expose patients amd themselves to the beams for long periods of time Eventually doctors and patients started developing radiation sickness and the medical community knew something was wrong The problem is that rays are form of ionizing radiation When normal light hits an atom it cant change the atom in any significant way But when an ray hits an atom it can knock electrons off the atom to create an ion an electrically charged atom Free electrons then collide with other atoms to create more ions An ions electrical charge can lead to unnatural chemical reactions inside cells Among other things the charge can break DNA chains cell with broken strand of DNA will either die or the DNA will develop mutation If lot of cells die the body can develop various diseases If the DNA mutates cell may become cancerous and this cancer may spread If the mutation is in sperm or an egg cell it may lead to birth defects Because of all these risks doctors use rays sparingly today Even with these risks ray scanning is still safer option than surgery ray machines are an invaluable tool in medicine as well as an asset in security and scientific research They are truly one of the most useful inventions of all time For more information on rays and ray machines check out the links on the next page Lots More Information Related stuff dewsoftoverseas com Articles How Light Works How Atoms Work How Magnetic Resonance Imaging MRI Works How Nuclear Medicine Works How Ultrasound Works How Diagnosing Heart Disease Works How Cancer Works Do certain radio wave frequencies pose health risks How far does ultraviolet light penetrate into the body More Great Links Rays Another Form of Light Rays Fluoroscope Rays the invisible phenomenon Physics of Radiology An Inexpensive ray Machine The interaction of radiation with matter Medical Imaging Techniques Generation and Properties of rays Introduction to ray Diffraction Overview of ray Computed Tomography History of ray Radiation expert warns of danger from overuse of medical rays