RT 101 - PRE-LIMS (reviewer).pdf

THE ATOMS: HISTORY, MODELS, & STRUCTURE Atoms - The basic of all matters - The smallest unit of matter - “Basic building blocks of matter” “All things can be classified as matter or energy” Without atom radiologic technology won’t exist What is matter? Anything that occupies space an...

THE ATOMS: HISTORY, MODELS, & STRUCTURE Atoms - The basic of all matters - The smallest unit of matter - “Basic building blocks of matter” “All things can be classified as matter or energy” Without atom radiologic technology won’t exist What is matter? Anything that occupies space and has mass All matter is composed of atoms. Greek Atom matter was composed of four substances: Earth, Water, Air, Fire Dmitri Mendeleev (Russian Scholar) - introduced the first periodic table of elements. (After 50 years of Dalton’s work) ⤴ John Dalton (English School Teacher) In 1808, he published a book showing that elements could be classified according to atomic mass. He said that: ↪ an element is composed of identical atoms. ↪ Atoms are different for every element. Dalton Atom: the “eye and hook affair” Atoms are made up of eyes and hooks The numbers of eyes and hooks are different for each element. J.J (Joseph John) Thomson Thomson Atom: the “plum pudding” model. Plums represented negative electric charges (electrons) Pudding a shapeless mass of uniform positive electrification. Number of electric charges (electrons) = quantity of positive electrification. Rutherford Atom: Nuclear model In 1911, Ernest Rutherford introduced the nuclear model, which described the atom as containing a small, dense, positively charged center surrounded by a negative cloud of electrons. Nucleus - the center of the atom ← by Rutherford Bohr Atom: “miniature solar system” In 1913, Neils Bohr described the atom as being a “miniature solar system” where electrons revolved around the nucleus in prescribed orbits or energy levels. The atoms contains a small, dense, positively charged nucleus surrounded by negatively charged electrons that revolve in fixed, well-defined orbits around the nucleus. 3 Fundamental Particles of Atom: 1. Electron (-) ↪ very small particles that carry one unit of negative electric charge. ↪ revolve in fixed orbits. 2. Proton (+) ↪ carries one unit of positive charge. 3. Neutron ↪ carries no charge; electrically neutral. Nucleons - particles that compose the nucleus (proton + neutron) Nucleus Electron Proton Neutron Location electron shells nucleus nucleus −31 −27 −27 Mass in kg 9.109 x 10 1.673 x 10 1.675 x 10 Mass in amu 0.000549 1.00728 1.00867 Charge -1 +1 0 THE ATOM: STRUCTURE, NOMENCLATURE COMBINATIONS Parts of Atom: Electron shells Nucleus Components of the Atom: electrons neutrons protons What is the difference between atoms and elements? Atom - make up elements Element - is composed of only one type of atom Molecules - are combinations of atoms. Ex. H2O Hydrogen + Hydrogen + Oxygen = H2O Compound: Chemical compound - is any quantity of one type of molecule atomic mass (protons + neutrons) → A X ← chemical symbol atomic number (number of protons) → Z Elements are arranged according to their atomic number. Isotopes - Atoms that have the same atomic number, but different atomic mass number Ex. 130 132 134 136 138 Ba Ba Ba Ba Ba 56 56 56 56 56 Isobar - Atoms that have the same atomic mass number, but different atomic numbers. Ex. 143 143 143 143 143 N P Cl K Ca 7 15 17 19 20 Isotone - Atoms that have the same number of neutrons but different numbers of protons. Ex. 120 110 112 114 115 N P Cl K Ca 7 15 17 19 20 102-7 110-15 112-17 114-19 115-20 = 95 =95 =95 =95 =95 Isomer - Atoms that have the same atomic number and the same atomic mass number. Ex. Tc-99m Tc-99 ↓ Emits 140 - keV gamma ray Arrangement Atomic Number Atomic Mass Number Neutron Number Isotope Same Different Different Isobar Different Same Different Isotone Different Different Same Isomer Same Same Same THE ATOMIC STRUCTURE In a neutral atom, the total number of electrons in the orbital shells is exactly equal to the number of protons in the nucleus. All neutral atoms have the same number of protons and electrons. Ionized - If an atom has an extra electron, or has had an electron removed. Ionization - is the removal or addition of an orbit electron from an atom. Ex. 5 protons - 6 electrons = -1 ← the charge of the atom 5 proton - 4 electrons = 1 ← the charge of the atom  Shell Shell Number of Number Symbol Electrons 1 K 2 2 L 8 3 M 18 4 N 32 5 O 50 6 P 72 7 Q 98 2 Formula: 2(𝑛) Ex. maximum number of electrons that can exist in the: O shell = 5 N shell = 4 2 2 2 2 2(𝑛) = 2(5) 2(𝑛) = 2(4) = 2(25) = 2(16) = 50 electrons = 32 electrons 2 In the formula 2(𝑛) physicists call the shell number 𝑛 the principal quantum number. Why is the principal quantum number important? There is a relationship between the number of shells in an atom and its position in the periodic table of elements. The columns in the periodic table represent the groups to which the elements belong. (↓) The rows represent the periods to which the elements belong to. (→) The number of the outermost electron shell is equal to its period in the periodic table. Ex.: Oxygen has 8 electrons. 2 occupy the K shell, and 6 occupy the L shell. The L shell is the 2nd orbital shell from the nucleus. Aluminum has the following electron configurations: K shell = 2 electrons, L shell = 8 electrons, M shells = 3 electrons. Aluminum belongs to the 3rd period. Centripetal force - or the “center-seeking” force; keeps an electron in its orbit. Opposite charges attract and like charges repel. Centrifugal force - or the “flying-out-from-the-center” force; allows the electrons to maintain their distance from the nucleus while traveling in a circular or elliptical path. Electron Binding Theory ↪ the strength of the attachment of an electron to the nucleus. ↪ the closer an electron is to the nucleus, the more tightly it is bound. K-shell electrons = have higher binding energy (than L-shell electrons or any electron shells) Not all k-shell electrons of all atoms are bound with the same binding energy. The greater the number of electrons in an atom, the more tightly it is bound. The larger and more complex the atom, the higher the electron binding energy for electrons in any given shell. Electrons of atoms with many protons = more tightly bound to the nucleus than those of small atoms. It generally takes more energy to ionize a large atom than a small atom. RADIATION: THE BASICS Two parts of Radiation: Non-ionizing & Ionizing Non-ionizing Radiation - refers to radiation which do not contain enough energy to cause ionization in matter – that is, to completely remove an electron from an atom. When passing through matter, it only contains enough energy to cause excitation in an atom. Ex. Radio waves, Microwaves, Infrared, & Ultraviolet Ionizing Radiation - refers to radiation which contains enough energy that during an interaction with an atom, it can remove tightly bound electrons from an orbit, causing the atom to become charged or ionized. Two Kinds of Ionizing Radiation: Electromagnetic & Particulate Electromagnetic: X-rays & Gamma Rays X-rays - are produced when an inner shell orbital electron is removed and the rearrangement of electrons results with the release of characteristic x-ray energy. X-rays may also be produced by the sudden slowing down of charged particles in the vicinity of the nucleus. Two Kinds of X-ray Radiation: Characteristics Radiation - is emitted when an inner-shell electron (such as from the K-shell) is ejected, and an electron from a higher energy shell (such as the L-shell) fills the resulting vacancy/void. For example: In a tungsten atom, the K-shell electron has a binding energy of about 69.5 keV. When a photon or particle with energy greater than or equal to this binding energy (e.g., 70 keV) interacts with the atom, it can eject the K-shell electron, creating a vacancy. An electron from the L-shell (or another outer shell) drops down to fill this vacancy, releasing energy as characteristic radiation. And this process continues as other outer-shell electrons fill remaining vacancies, producing additional X-rays until the atom stabilizes. Bremsstrahlung Radiation (Brems Radiation) slowed down radiation; “braking radiation” ← from the German word. ↪ Is produced when high-speed projectile electrons are slowed down or deflected as they pass near the nucleus of an atom, typically in the anode of an X-ray tube. ↪ The electrostatic attraction between the electron and the nucleus causes the electron to deviate from its path and decelerate. This loss of kinetic energy is released as an X-ray photon, with energy equal to the amount of kinetic energy lost, in accordance with the law of conservation of energy. Simplified: occurs when a high-speed electron is slowed down or deflected by the electric field of the protons in the atomic nucleus. As the electron loses energy, it emits this energy in the form of X-rays. Gamma Rays Gamma radiation is a product of radioactive atoms that undergo gamma decay. A nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation (photons). The number of protons (and neutrons) in the nucleus does not change in this process, so the parent and daughter atoms are the same chemical element. ← If the parents decays, the daughter replaces it. Particulate: Alpha, Beta, Neutron, & Proton Alpha Particles - are produced by the alpha decay of a radioactive nucleus. Because the nucleus is unstable, a piece of it is ejected, allowing the nucleus to reach a more stable state. Beta Particles - forms when a neutron changes into a proton and a high-energy electron (beta minus particle). The proton stays in the nucleus but the electron is ejected from the atom as a beta particle. Neutrons In nuclear fission, an unstable atom splits into two or more smaller pieces that are more stable, and releases energy in the process. The fission process also releases extra neutron, which can then split additional atoms, resulting in a chain reaction that releases a lot of energy. n = neutron Protons - are produced in particle accelerator which produce a beam of charged particles that serve a variety of uses such as: research. ← Degree of Penetration Extra Notes: Electromagnetic Particulate Gamma Rays : Useful for Imaging : not useful for imaging : used for Nuclear Medicine : Orbit shell : Nucleus RADIOACTIVITY Atoms - are neutral if they have an equal number of protons and electrons. However, some atoms exist in an abnormally excited state characterized by an unstable nucleus. Radioactive Disintegration (or Radioactive Decay) - The process by which, in order to reach stability, the nucleus spontaneously emits particles and energy and transforms itself into another atom. Things to remember: 1. Radionuclides: - are the atoms involved in radioactive decay. - the only nuclei that undergo radioactive decay 2. Nuclide - any nuclear arrangement. Why does radioactivity occur? Every atom seeks to be as stable as possible. Therefore, in order to become stable, a radioactive atom emits particles and energy in order to become stable. Nuclear Stability Number of Neutrons When a nucleus contains too few or too many neutrons, the atom can disintegrate radioactively, bringing the number of neutrons and protons into a stable and proper ratio. Radioisotopes: may be artificially produced there are two primary sources of naturally occurring radioisotopes: - some originated at the time of the earth’s formation. - others are continuously produced in the upper atmosphere through the action of cosmic radiation. artificially produced in nuclear reactors or particle accelerators artificially produced radioisotopes have been identified for nearly all elements. Ex. 127 128 129 130 131 132 133 134 Ba Ba Ba Ba Ba Ba Ba Ba Radioisotopes can decay to stability in: Alpha Emission, Beta Emission Alpha Emission An alpha particle consists of: two protons and two neutrons bound together; its atomic mass is 4. A nucleus must be extremely unstable to emit an alpha particle, but when it does, it loses two units of positive charge and four units of mass. The transformation is significant because the resulting atom is not only chemically different but it is also lighter by 4 atomic mass units. Example: Radium-226 starts with 88 protons and 138 neutrons. Radium-226 undergoes alpha decay, meaning it releases an alpha particle (which contains 2 protons and 2 neutrons) to form a different element. After losing 2 protons and 2 neutrons, the original radium atom changes into a new element, Radon-222. Now, it has 86 protons and 136 neutrons. In short: Radium-226 becomes Radon-222 and gives off an alpha particle. Beta Emission occurs much more frequently than alpha emission. During beta emission, an electron created in the nucleus is ejected from the nucleus and escaped from the atom. The result is the loss of a small quantity of mass and one unit of negative electric charge from the nucleus of the atom. Simultaneously, a neutron undergoes conversion to a proton. Therefore, the result of beta emission is to increase the atomic number by one. This nuclear transformation results in the changing of an atom from one type of element to another. Extra: To Achieve Stability: An unstable nucleus will emit particles or energy, such as alpha or beta particles, to become stable.