Early detection can be very effective, hence the importance of x-ray diagnostics. A mammogram cannot diagnose a malignant tumor, only give evidence of a lump or region of increased density within the breast. X-ray absorption by different types of soft tissue is very similar, so contrast is difficult; this is especially true for younger women, who typically have denser breasts. For older women who are at greater risk of developing breast cancer, the presence of more fat in the breast gives the lump or tumor more contrast.
MRI Magnetic resonance imaging has recently been used as a supplement to conventional x rays to improve detection and eliminate false positives.
Figure 6. The relative absorption of the x rays along different directions is computer analyzed to produce highly detailed images. Three-dimensional information can be obtained from multiple slices.
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Figure 7. This three-dimensional image of a skull was produced by computed tomography, involving analysis of several x-ray slices of the head. A standard x ray gives only a two-dimensional view of the object.
Dense bones might hide images of soft tissue or organs. If you took another x ray from the side of the person the first one being from the front , you would gain additional information. While shadow images are sufficient in many applications, far more sophisticated images can be produced with modern technology. An array of many detectors on the other side of the patient registers the x rays. The system is then rotated around the patient and another image is taken, and so on. The x-ray tube and detector array are mechanically attached and so rotate together.
Complex computer image processing of the relative absorption of the x rays along different directions produces a highly-detailed image. Different slices are taken as the patient moves through the scanner on a table. Multiple images of different slices can also be computer analyzed to produce three-dimensional information, sometimes enhancing specific types of tissue, as shown in Figure 7. Hounsfield UK and A. Since x-ray photons are very energetic, they have relatively short wavelengths. For example, the Thus, typical x-ray photons act like rays when they encounter macroscopic objects, like teeth, and produce sharp shadows; however, since atoms are on the order of 0.
The process is called x-ray diffraction , because it involves the diffraction and interference of x rays to produce patterns that can be analyzed for information about the structures that scattered the x rays. Perhaps the most famous example of x-ray diffraction is the discovery of the double-helix structure of DNA in by an international team of scientists working at the Cavendish Laboratory—American James Watson, Englishman Francis Crick, and New Zealand—born Maurice Wilkins. Using x-ray diffraction data produced by Rosalind Franklin, they were the first to discern the structure of DNA that is so crucial to life.
There is much debate and controversy over the issue that Rosalind Franklin was not included in the prize. Figure 8. X-ray diffraction from the crystal of a protein, hen egg lysozyme, produced this interference pattern.
X Rays: Atomic Origins and Applications | Physics
Analysis of the pattern yields information about the structure of the protein. This process is known as x-ray crystallography because of the information it can yield about crystal structure, and it was the type of data Rosalind Franklin supplied to Watson and Crick for DNA. Not only do x rays confirm the size and shape of atoms, they give information on the atomic arrangements in materials. For example, current research in high-temperature superconductors involves complex materials whose lattice arrangements are crucial to obtaining a superconducting material.
These can be studied using x-ray crystallography. Historically, the scattering of x rays from crystals was used to prove that x rays are energetic EM waves. This was suspected from the time of the discovery of x rays in , but it was not until that the German Max von Laue — convinced two of his colleagues to scatter x rays from crystals. If a diffraction pattern is obtained, he reasoned, then the x rays must be waves, and their wavelength could be determined. The experiments were convincing, and the Nobel Prize in Physics was given to von Laue for his suggestion leading to the proof that x rays are EM waves.
In , the unique father-and-son team of Sir William Henry Bragg and his son Sir William Lawrence Bragg were awarded a joint Nobel Prize for inventing the x-ray spectrometer and the then-new science of x-ray analysis.
Applications of Soft X-Ray Imaging to Materials Science
The elder Bragg had migrated to Australia from England just after graduating in mathematics. He learned physics and chemistry during his career at the University of Adelaide. The younger Bragg was born in Adelaide but went back to the Cavendish Laboratories in England to a career in x-ray and neutron crystallography; he provided support for Watson, Crick, and Wilkins for their work on unraveling the mysteries of DNA and to Max Perutz for his Nobel Prize-winning work on the structure of hemoglobin. Here again, we witness the enabling nature of physics—establishing instruments and designing experiments as well as solving mysteries in the biomedical sciences.
Certain other uses for x rays will be studied in later chapters. X rays are useful in the treatment of cancer because of the inhibiting effect they have on cell reproduction. X rays observed coming from outer space are useful in determining the nature of their sources, such as neutron stars and possibly black holes. Created in nuclear bomb explosions, x rays can also be used to detect clandestine atmospheric tests of these weapons. X rays can cause excitations of atoms, which then fluoresce emitting characteristic EM radiation , making x-ray-induced fluorescence a valuable analytical tool in a range of fields from art to archaeology.
Skip to main content. Atomic Physics. Search for:. Show the x-ray characteristic energy. Specify the use of x rays in medical observations. Explain the use of x rays in CT scanners in diagnostics. Example 1. Strategy How do we calculate energies in a multiple-electron atom? Discussion This large photon energy is typical of characteristic x rays from heavy elements. Conceptual Questions Explain why characteristic x rays are the most energetic in the EM emission spectrum of a given element. Why does the energy of characteristic x rays become increasingly greater for heavier atoms?
Observers at a safe distance from an atmospheric test of a nuclear bomb feel its heat but receive none of its copious x rays. Why is air opaque to x rays but transparent to infrared? Lasers are used to burn and read CDs. Explain why a laser that emits blue light would be capable of burning and reading more information than one that emits infrared.
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Crystal lattices can be examined with x rays but not UV. CT scanners do not detect details smaller than about 0. Is this limitation due to the wavelength of x rays? A color television tube also generates some x rays when its electron beam strikes the screen. What is the shortest wavelength of these x rays, if a When Stanford University physics professor Fernando Sanford created his "electric photography" he also unknowingly generated and detected X-rays. From to he had studied in the Hermann Helmholtz laboratory in Berlin, where he became familiar with the cathode rays generated in vacuum tubes when a voltage was applied across separate electrodes, as previously studied by Heinrich Hertz and Philipp Lenard.
Starting in , Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube with a "window" in the end made of thin aluminum, facing the cathode so the cathode rays would strike it later called a "Lenard tube".