How is x ray generated

X-rays are alternating electric and magnetic waves that are traveling in perpendicular planes. But to make things simpler in the figures we will draw just a single wave as that is easier to visualize. Electromagnetic waves have fundamental properties — repeating peaks and valleys with certain: amplitude and a frequency directly related to the Energy, and inversely related to the wavelength.

The waves repeat and the distance for the wavelength to repeat. Therefore, the distance from one valley to the next valley is the wavelength. Likewise, the distance from one peak to the next peak is also the wavelength.

The plots in the wave figure show the height or amplitude of the wave as a function of time. So, longer wavelengths have lower frequencies because they have less peaks in a given time.

Electromagnetic waves with higher frequencies have proportionally higher energies. What if we compare the two waves and ask which has the higher energy?

The wave with the shorter wavelength, will have higher frequency. Since we know that the energy scales directly with the frequency we know that the wave that has the shorter wavelength will have higher energy. For instance, violet light has a shorter wavelength than red light and thus violet light has higher energy.

Likewise, a 60keV x-ray photon and a 30 keV x-ray photon have the same relationship where the wavelength of the 60keV x-ray is smaller. The same principles apply when comparing electromagnetic radiation at different parts of the spectrum. If you are familiar with light being much more intense by a light bulb or heat being much hotter right near a fire this is because of the inverse square law.

The number of x-ray photons that pass through a given point depends on distance between source and detector. If we think about the fact that x-rays travel straight lines like particles, they will spread out more with greater distances.

For example, if we increase the distance three times between source and detector the strength of beam will decrease nine times. Fluoroscopy: Uses x-rays and a fluorescent screen to obtain real-time images of movement within the body or to view diagnostic processes, such as following the path of an injected or swallowed contrast agent.

For example, fluoroscopy is used to view the movement of the beating heart, and, with the aid of radiographic contrast agents, to view blood flow to the heart muscle as well as through blood vessels and organs. This technology is also used with a radiographic contrast agent to guide an internally threaded catheter during cardiac angioplasty, which is a minimally invasive procedure for opening clogged arteries that supply blood to the heart.

Radiation therapy in cancer treatment: X-rays and other types of high-energy radiation can be used to destroy cancerous tumors and cells by damaging their DNA.

The radiation dose used for treating cancer is much higher than the radiation dose used for diagnostic imaging. Therapeutic radiation can come from a machine outside of the body or from a radioactive material that is placed in the body, inside or near tumor cells, or injected into the blood stream.

Click here for more information on radiation therapy for cancer. When used appropriately, the diagnostic benefits of x-ray scans significantly outweigh the risks. X-ray scans can diagnose possibly life-threatening conditions such as blocked blood vessels, bone cancer, and infections. However, x-rays produce ionizing radiation—a form of radiation that has the potential to harm living tissue. This is a risk that increases with the number of exposures added up over the life of the individual.

However, the risk of developing cancer from radiation exposure is generally small. In general, if imaging of the abdomen and pelvis is needed, doctors prefer to use exams that do not use radiation, such as MRI or ultrasound. However, if neither of those can provide the answers needed, or there is an emergency or other time constraint, an x-ray may be an acceptable alternative imaging option. Children are more sensitive to ionizing radiation and have a longer life expectancy and, thus, a higher relative risk for developing cancer than adults.

Parents may want to ask the technologist or doctor if their machine settings have been adjusted for children. These electrons are then directed into the main storage ring.

When radiation is emitted, the electrons loose energy. The electrons are reenergized by resonating rf cavities located in the straight parts of the storage ring. Two types insertion devices, devices to send radiation beams towards an instrument, are used in the straight parts of the storage ring to boost the flux of radiation.

Wigglers are a series of electromagnetic plates with opposite charge. Undulators are similar to wigglers with lower energy applied to the plates, but the plates are spaced to give optimum intensity to particular wavelengths and their harmonics. The main problem limiting brightness in laboratory-based X-ray sources is the removal of heat.

A new type of X ray source, that offers a novel solution to this problem, uses a liquid metal, gallium anode. A Swedish company, Excillum , is currently producing these sources. A new type of tube that utilizes carbon nanotubes as the cathode are most likely to be developed as portable and miniature X-ray sources. X Rays for medical use are generally produced by one of two methods.

Diagnostic X rays for examining bones and teeth are usually produced by sealed tube equipment with a tungsten target. X Rays for CT computed tomography scans and radiation therapy are produced by a linear accelerator, linac.

Electrons from an electron gun are accelerated through the linac by a series of charge plates. These electrons then collide with a target giving off Bremsstrahlung. The medical X rays from sealed tube equipment have typical energies of kev.

The X rays from CT or tomography equipment typically have energies around Mev. Most X-ray tubes used for diffraction studies have targets anodes made of copper or molybdenum metal. The characteristic wavelengths and excitation potentials for these materials are shown below.

Copper radiation is preferred when the crystals are small or when the unit cells are large. A copper source is preferred for most types of powder diffraction. Chromium anodes are sometimes used to enhance anomalous scattering effects for some macromolecular samples. The scintillation point detectors, often used in small molecule diffraction, have somewhat higher quantum efficiencies for molybdenum radiation than for copper radiation.

Because the diffraction spots are closer together for molybdenum radiation than for copper radiation, molybdenum is the preferred radiation source when using area detectors to study small molecules. The solid angle coverage of most area detectors is such that with molybdenum radiation, it is usually possible to collect an entire data set with the detector sitting at a single position.

However, because a brighter incident beam of X-rays is produced from a copper tube than from a molybdenum tube at the same power level, very small crystals of even strongly absorbing materials will often yield better diffracted intensities from copper radiation than from molybdenum radiation.

Occasionally, other types of target materials, e. Cr, Fe, W, or Ag, are chosen for specialized diffraction experiments. Sources with Cr or Fe targets are often chosen when protein crystals are very small or when anomalous differences need to be enhanced. When samples are very strongly absorbing or when extremely high resolution data are needed then X-ray tubes with sources such as W or Ag are usually selected. Nearly all of the data collection experiments require that the energy of the X-ray radiation be limited to as narrow a band of energies and hence wavelengths as possible.

Using a narrow wavelength band of X rays significantly reduces the fluorescent radiation given off by the sample and makes absorption corrections much simpler to perform. Also, typical data collection methods require that the incident beam be a parallel beam of photons. To assure that the beam is as parallel as possible lacking divergence , the incident beam path is collimated to produce an incident beam that is about 0. When the energy of a photon beam is just above the excitation potential or absorption edge of a material, that material strongly absorbs the given photon beam.

The linear absorption coefficient depends on the substance, its density, and the wavelength of radiation. An alternative way to produce an X-ray beam with a narrow wavelength distribution is to diffract the incident beam from a single crystal of known lattice dimensions. X-Ray photons of different wavelengths are diffracted from a given set of planes in a crystal at different scattering angles according to Bragg's Law.

Therefore a narrow band of wavelengths can be chosen by selecting a particular scattering angle for the monochromator crystal. Crystal monochromators need to have the following properties.

The crystal must have a strong diffracted intensity at a reasonably low scattering angle for the wavelength of the radiation being considered.

The mosaicity of the crystal, which determines the divergence of the diffracted beam and the resolution of the crystal, should be small. A variety of geometries are possible for crystal monochromators. Most monochromators are cut with one face parallel to a major set of crystal planes.

Some monochromators are cut at an angle to the major set of planes in order to produce a diffracted beam with a smaller divergence. By properly curving the monochromator crystal, the diffracted beam may be focused onto a very small area. This curving may be achieved either by bending or grinding or both bending and grinding. Curved monochromators are usually reserved for special applications such synchrotrons.

Graphite crystals cut on the face are the most common crystals used as monochromators in X-ray diffraction laboratories. Other special purpose monochromator materials include germanium and lithium fluoride.

In all commercially available single-crystal instruments, the monochromator is placed in the incident beam path. Powder diffraction instruments with a point detector typically place a monochromator in the diffracted beam path to remove any fluorescent radiation from the sample. Crystal monochromators systematically alter the polarization of the incident beam, requiring different geometric corrections be applied to the intensity data.

Collimators are objects inserted in the incident- or diffracted-beam path to shape the X-ray beam.