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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

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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

oHydrogen 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

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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

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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

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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 2n2

• 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

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.

Shell

Number

Principle

Quantum #

Shell Symbol Number of

Electrons

1 K 2

2 L 8

3 M 18

4 N 32

5 O 50

6 P 72

7 Q 98

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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”

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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 (Eb)

• Energy needed to eject

electron from atom

TUNGSTEN

(Eb)Comparison

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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

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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??

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ATOMIC NUMBER & ATOMIC MASS NUMBER

ATOMIC NUMBER ATOMIC MASS NUMBER

• Definition: Equal to the

number of protons in

the nucleus of an atom

• Element’s “Z 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

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Periodic Table of Elements

Non-Metals

Periodic Table of Elements http://www.periodicvideos.com/#

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.

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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

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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 (H2O)

Video