2 X-ray Modality
2.1 Brief History
On Friday evening, November 8, 1895 Wilhelm Conrad Röntgen discovered a “new kind of ray” that penetrated matter. Röntgen, a 50-year old professor of physics at Julius
Maximilian University of Wurzburg, named the new kind of ray X-strahlen, or “X-rays”
(“X” for unknown). Röntgen was looking for the “invisible high-frequency rays” that
Hermann Ludwig Ferdinand von Helmholtz had predicted from the Maxwell’s theory of electromagnetic radiation. Röntgen’s discovery was submitted for publication on
December 28, 1895 and was published on January 5, 1896.
Röntgen developed the first X-ray pictures on photographic plates, and one of the first materials tested was human tissue. The most famous picture was an image of his wife’s hand with a ring on her finger (Figure 2-1).
Figure 2-1 The first reported image of human tissue. Mrs. Röntgen’s hand with a ring, taken in
1895.
In 1901 Röntgen received the Nobel Prize for Physics, which was the first Nobel Prize in physics ever awarded.
The first medical use of the X-ray was on January 13, 1896 by Drs. Ratcliffe and HallEdwards, in which they showed the location of a small needle in a woman’s hand. As a
______________
Page 1 of 34
Ch. 2 consequence, Dr. J.H. Clayton performed the first X-ray guided surgery nine days after the publication of the existence of X-rays.
2.2 X-ray Physics
An X-ray is electromagnetic (EM) radiation similar to light, radio waves, and TV waves.
Electromagnetic radiation has energy, which is often measured in units of electron volts.
An electron volt (eV) is the energy required to move a quantum of charge through 1 volt of potential energy. A quantum of charge is 1.60x10-19 coulombs, or the charge of one single electron. Table 2-1 shows some of the components of the EM spectrum, their frequency, wavelength, energy, and use.
Table 2-1 Electromagnetic Wave Spectrum (from [Enderle et al.])
Figure 2-2 graphically shows the electromagnetic spectrum and the corresponding energy of each component.
______________
Page 2 of 34
Ch. 2
Figure 2-2 The Electromagnetic Spectrum. The photon energies are given in electron volts (eV).
Planck showed that the relationship between energy and frequency for EM waves is given by
E = hf
(2.1)
where E is energy (keV), h is Planck’s constant (4.13x10-18 keV s, or 6.63x10-34 J s), and f is the frequency (Hz). (1 eV=1.6x10-19 joules)
At least in a vacuum, all EM waves propagate at the same speed, which is known as the speed of light (c = 3.0x108 m s-1). An important relationship between the speed of light and the frequency of the EM radiation is given by c=λf (2.2)
where λ is the wavelength (m).
X-rays are also characterized as particles. This is a wonderful example of the duality of nature – energy can be viewed simultaneously as both a wave and a particle. Viewed as a particle, an X-ray particle with velocity v (m s-1) and mass m (kg) has a momentum p (kg m s-1) given by
=
p mv
= mc
(2.3)
These X-ray particles are called photons, and these photons are delivered in packets called quanta. If the particle energy is greater than the binding energy of the electron, then the photons are capable of ionizing atoms. For example, when a hydrogen atom with its electron in the lowest energy configuration gets hit by a photon (light wave) and is boosted to the next lowest energy level, the energy levels are given by
En = −
______________
13.6 eV n2
Page 3 of 34
Ch. 2 where n is the energy band of the atom. The energy difference between the lowest (n=1) and second lowest (n=2) levels corresponds to a photon with wavelength 1216 angstroms
(1 angstrom=0.1 nanometers). Thus, to ionize hydrogen, one would need a photon of
1216 angstroms. Of course, other atoms have different binding energies. There is no unique energy that defines the threshold for ionizing human tissue because human tissue is not composed of only one element.
Diagnostic radiation is typically in the range of 100 nm to about
Related Documents: Electron and Energy Essay example
and then the electron transport system is what generates the load of ATP. the Krebs cycle in general what happens is that pyruvate from glycolysis out in the cytoplasm as it starts to enter into the mitochondria enzymes will take off a couple of high energy electrons and then onto an electron carrier called NAD positive. Then add 2 electrons it becomes negatively charged and then takes a nearby positively charged hydrogen ion, and becomes NADH. So NADH is a full high energy electron carrier full…
CHAPTER 5 NOTES - ELECTRONS IN ATOMS I. MODELS OF THE ATOM A. The Development of Atomic Models 1. At Rutherford's time electrons were thought to be particles and light was thought to be a wave - these theories explained many properties. 2. In the early 1900s it was discovered that electrons have certain wave properties and light has certain particle-like properties. 3. Electrons and light both have dual wave-particle natures. II. THE BOHR MODEL A. Bohr Model of the…
Atomic Structure Chapter 1 Atomic Par2cles Atoms No. of electrons in each energy level • Electrons occupy the lowest possible energy level in an atom. Electron Configura2on Bohr Model – electrons travelling in fixed circular paths (INACCURATE) • It is not possible to specify exact loca2on of electron in atom – • Only the probability of loca2ng an electron in a given region of space. Ionisa'on Energies • An ion is a charged atom! • Atoms form charged ions by the gain or…
Emma Lang Electrons and the Bright-Line Spectrum Purpose: The purpose of this lab is to observe the bright-line spectrum of the elements Mercury and Helium and calculate the frequency and energy of each photon of light given off by the specific element. Introduction: In 1909 a scientist named Rutherford fired alpha particles which were positively charged through gold foil. He discovered 99.99% of the particles went straight through the gold foil and only .01% of the particles were deflected…
Energy level -can be thought of as a region of space near a nucleus that may be empty or may contain electrons -electrons in energy levels nearest the nucleus have the lowest energy -electrons in energy levels farther away from the nucleus have more energy -electron in the lowest energy levels are the most tightly held in the atom because they are closest to the positively charged nucleus -the number of electrons that can exist in the different energy levels varies. The lowest energy level…
important: Hydrogen, Carbon, Nitrogen and O Oxygen • Four types of atoms comprise 96% of the matter in living organisms: – Hydrogen, _______, ________, and _______. Valence Electrons 1) valence 2) filled 3)bonding An atom is happiest when it's valence shell is full • Atoms often have unpaired electrons in their _________ (outermost) shells. • Atoms are most stable when their valence shells are _____. • Atoms can interact with each other in ways that help fill their valence shells…
metal. They have an electron configuration of 1s2, 2s1 in order to satisfy the octet rule. It has one electron in its outer shell. Therefore, its position is in group 1. 2. Sodium: Na Sodium is also present in group1 since it has similar properties to that of Na. It has an electron configuration of 1s2, 2s2, 2p6,3s1.The two electrons fill the 1stsub shell, 8 electrons fill the 2nd and 1 electron fill the outermost shell due to octet rule. Due to the presence of single electron on the outermost…
Chapter 8 Photosynthesis Chapter 8 Section 1 Energy and Life Autotrophs and Heterotrophs Plants and some other types of organisms are able to use light energy from the sun to produce food. Autotrophs Organisms such as plants, which make their own food. Heterotrophs (Impalas and Leopard) Other organisms, such as animals, cannot use the sun's energy directly. To live, all organisms, including plants, must release the energy in sugars and other compounds Autotrophs…