Goals. An Art and a Science. Principles of Imaging Science I (RAD119) Radiography as art Scientific method Natural science

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1 Principles of Imaging Science I (RAD119) Physics Fundamentals & Atomic Structure Goals Understand the structure of matter and the fundamentals of electromagnetic radiation. Understand the concept of x-ray production, how x-rays interact with matter, the quantity and quality of the x-ray beam, and demonstration of anatomic structures in the radiographic image (radiograph) An Art and a Science Radiography as art Scientific method Natural science o Physical science: non-living matter Physics o Biological science: living matter Anatomy and Physiology 1

2 Matter and Energy Physics studies relationships between matter and energy Matter o Mass and occupies space Energy is force used to do work Matter Matter Anything that occupies space, has shape or form, and has mass States of matter: Solid, liquid, gas Mass Amount or quantity of matter in an object. Does not change with a change in the form Does not change with gravitational force Air has mass, but much less than a rock that has the same volume because the particles of matter in air are more widely spaced. Fundamental Unit - Atom Composed of smaller units protons, neutrons, and electrons Atomic Theory Basic building blocks of matter Atom is unique and characteristic of a certain type of matter o Hydrogen atom is different from an atom of Barium or Calcium Atoms cannot be seen o Scientists theorized about its structure and function based on experimentation 2

3 Atomic Structure Nucleus Small, dense center Contains nucleons protons and neutrons Electrons Orbit nucleus Bohr Atom Basic structure of atoms is comparable to our solar system An atom is mostly empty space the space between the electrons and the nucleus is like the space between the earth and sun Atom is comprised of a small, dense, positive nucleus and negative electrons revolving in orbit around the nucleus Bohr Atom 3

4 Basic Atomic Particles Proton Positive charge Represents the Atomic Z# Distinguishes elements by number of protons in the nucleus Change the Z#, change the element! Basic Atomic Particles Neutron Neutral charge Stability of nucleus Serve in the role in radioactive atoms (isotopes) Electron Negative charge Electrical stability maintained through equal number of protons and electrons Atomic Mass Unit (amu) Unit used to measure atomic mass. It is not a metric unit, based on the standard of the carbon-12 atom. The equivalent mass in kilograms notes the small size of an atomic mass unit 4

5 Electrons Electrons (-) charge Subatomic particle Small quantity of mass Located outside nucleus in orbital shells Stable atoms have equal electrons as protons Electron shells Ordered from the first shell (K) to the last shell (Q) Electron Shells Represent the energy levels Maximum number of electrons in each shell based upon 2n 2 K shell: Shell #1 = 2 electrons (innermost) L shell: Shell #2 = 8 electrons (2)(2) 2 M shell: Shell #3 = 18 electrons (2)(3) 2 Q shell: Shell # 7 = 98 electrons (2)(7) 2 A maximum of 8 electrons may comprise the outermost shell of any atom (valence shell) Electron Shell Maximum Shell Number Number of Shell Symbol Principle Electrons Quantum # 1 K 2 2 L 8 3 M 18 4 N 32 5 O 50 6 P 72 7 Q 98 Factoid: The largest naturally occurring atom, uranium, has a total of 92 electrons in its seven shells. Even in this atom, shells 5, 6, and 7 are not completely filled. 5

6 Forces Nuclear Binding Energy Holds protons and neutrons together in the nucleus Sum of the strong nuclear forces that attract and pull the protons and neutrons together in the nucleus Measure of the amount of energy needed to split the atom If a particle shot at the atom strikes the nucleus with the energy equal to the nucleus's binding energy, the atom could break up or "split." Forces Centripetal force Maintains electron in orbit preventing it from flying away from the nucleus Center seeking force Balances the force created by the electron velocity Forces Centrifugal force Maintains electron at a distance from the nucleus while moving around the nucleus Out from center force 6

7 Forces Electron Binding Energy (BE) Maintains electrons in their shells Dependent upon: Proximity to nucleus Higher BE closer to nucleus Total # electrons in the atom Higher BE in larger atoms Most of the BE comes from the force of attraction between the electrons and protons Electron Binding Energy (E b ) Energy needed to eject electron from atom TUNGSTEN (E b )Comparison 7

8 Electron Binding Energy CHARGE & IONS Neutral atoms: equal # of electrons and protons Balanced or stable If an electron is added or removed the atom is no longer neutral: it becomes electrically charged. Negative ion - An atom with an extra electron Positive ion - - An atom that has one fewer electrons than protons IONS 8

9 IONS Ionization Adding or removing an electron from its shell An atom in which this has occurred is called an ion. If an electron is added, termed a negative ion (-1 charge) If an electron is removed, termed a positive ion (+1 charge) Ionization Positive or Negative Ion?? 9

10 ATOMIC NUMBER & ATOMIC MASS NUMBER ATOMIC NUMBER Definition: Equal to the number of protons in the nucleus of an atom Element s Z number ATOMIC MASS NUMBER Definition: Equal to the number of protons and neutrons in an atom Element s A number May be measured using amu (atomic mass unit) ATOMIC MASS NUMBER & ATOMIC NUMBER Both the A number (atomic mass number) and Z number (atomic number) are often given to represent an element Y as follows: A Y Z Periodic Table of Elements Arranged based on increasing atomic # Groups are vertical columns Represent same # electrons in outermost shell Similar chemical characteristics Group I, II: Light metals Groups III VI: Non-metals Group VII: Halogens Group VIII: Noble gases Periods are horizontal rows Represent the total number of electron shells Interpretation of Table 10

11 Periodic Table of Elements Non-Metals Periodic Table of Elements Periodic Table of Elements No set ratio of neutrons to protons in atoms Larger and more stable the atom, the higher its ratio of neutrons to protons. Many stable atoms with a low atomic number have about the same number of neutrons and protons. Heavier elements may have almost twice as many neutrons as protons. greater strong nuclear force is needed to help stabilize such atoms to keep the nucleus from breaking up. 11

12 Nuclear arrangements Isotope Atoms with same atomic number Unstable isotopes often have a deficient or excess number of neutrons. This causes them to spontaneously change from one element to another. Considered radioactive, referred as radioisotopes Isobar Atoms with same atomic mass Isotone Atoms with same neutron number Nuclear Arrangements Nuclear Arrangements 12

13 Combination of Atoms Atoms of different elements may combine to form molecules Ionic Bonding occurs when an electron from one atom transfers to another atom Sodium Chloride (NaCl) Combination of Atoms Covalent Bonding occurs when two atoms share some of the same electrons which revolve around both nuclei Water (H 2 O) Video 13