Chapter 3 Fundamentals of Physics & Chapter 4 The Atom

1. Chapter 3 Fundamentals of Physics & Chapter 4 The Atom • Physics is the study of the interaction of matter & energy. • Physicist strive for simplicity. There are three base quantities. • Mass • Length • Time.

2. Base Quantities Support Derived Quantities • From the base quantities, derived quantities are formed. • For radiology there are special quantities. • Exposure • Dose • Dose equivalent • Activity

3. Units of Measure • Every measurement has two parts: a magnitude and a unit. • Four systems of units • MKS (meters, kilograms, seconds) • CGS ( centimeters, grams, seconds) • British (Foot, Pound, Seconds) • International (SI) (Meter, Kilogram, Seconds)

4. Standards of Mass and Time • Mass: The kilogram is the unit for Mass. Mass is not weight. • For weight: The Newton or British Pound are used. • Time: Time is measured in seconds

5. Systems of Units • The pound is actually a unit of force but is related to mass. • The SI has four additional base units. There are special derived units and special units for derived quantities & special quantities.

6. British Exposure Dose Dose Equivalent Activity SI C/kg Air Kerma (Gya) J/kg Gray (Gyt) J/kg Seivert (Sv) s-1 Becquerel (Bq) SI units for Radiologic Quantities

7. Direction of Motion • Mechanics deals with the motion of objects. • Motion of an object is described by the use of two terms: • Velocity or speed or how fast the object is moving. • Acceleration or the rate of change of velocity. • Velocity of light c= 3 x 108m/s

8. Velocity or Speed • Velocity is how fast an object is moving or the rate of change of position in time. The metric measure is kilometers per hour or meters per second. • V= Distance / Time • Average velocity is determined by adding the initial velocity and final velocity and dividing by 2.

9. Acceleration • Acceleration is the rate of change of velocity. It is measured in m/s2. • Acceleration is velocity divided by time or distance divided twice by time • If velocity is constant, the acceleration would be zero.

10. Newton’s Laws of Motion • Newton’s First Law: A body will remain at rest or continue moving with a constant velocity in a straight line unless acted on by an external force. The Law of Inertia

11. Newton’s Laws of Motion • Newton’s second law define force: The force (F) acting on an object with acceleration (a) is equal to the mass (m) multiplied by the acceleration. Force is mass times acceleration. • SI unit is Newton • CGS unit is dyne. (1N=103 dyne) • F=ma

12. Newton’s Laws of Motion • Newton’s Third Law: To every action there is an equal and opposite reaction.

13. Weight WT = mg • Weight (WT) is a force on a body caused by gravity. This rate is called the acceleration of gravity (g) • The value for earth are: • SI g= 9.8 m/s2 • CGS g= 980 cm/s2 • British g= 32 ft/s2

14. Momentum p = mv • Momentum is represented by p • Momentum is the product of mass and velocity. • The greater the velocity of an object, the more momentum the object possesses. • The conservation of momentum law states the total momentum before any interaction is equal to the total momentum after the interaction.

15. Work = fd • Work done on an object is the force applied times the distance over which it is applied. • The SI unit is joule (j) • The CGS unit is erg • An object held motionless has no work according to the physics term.

16. Power P=Work/t • Power is the rate of doing work. • The SI term for power is watt (W) or Joules/ second. • The British term is horsepower (hp) • 1 hp= 746 w • 1000 W= 1 kilowatt (kW)

17. Energy • Energy is the ability to do work. Energy may be transformed from one form to another but it cannot be created or destroyed. The units for energy and work are the same. • To make x-ray, electrical energy is converted heat and x-rays in the x-ray tube.

18. Mechanical Energy • There are two types of mechanical energy. • Kinetic Energy (KE) or energy in motion • KE = 1/2 mv2 • Kinetic energy is dependent upon the mass of the object and the square of the velocity. • Potential Energy (PE) or stored energy of position or configuration. • PE= mgh where h is the height above the earth’s surface.

19. Heat • Heat is a form of energy important to radiology. Excessive heat will damage x-ray tubes. • Heat is the amount of kinetic energy of the random disordered motion of molecules. The unit for heat is calorie.

20. Heat • 1 calorie equals the amount of heat needed to raise the temperature of 1 g of water 1 degree C. • Heat is transferred three ways. • Conduction • Convection • Thermal reaction

21. Heat • Conduction is the transfer of heat by molecular motion. • Convection is the mechanical transfer of hot molecules in a gas or liquid from one place to another.

22. Heat • Thermal reaction is the transfer of heat through space that depends upon the temperature of the object. • X-ray tubes use thermal reaction for cooling. • Thermal radiation is the transfer of heat by the emission of infrared radiation. It is that red glow that come off very hot objects.

23. Temperature units • There are three scales of temperature • Fahrenheit (°F) Tf= 9/5Tc -32 • Celsius (°C) Tc= 5/9Tf +32 • Kelvin (K) Tk = Tc +273

24. Chapter 3 The Atom • One of sciences most pronounced and continuing investigation has been determining the structure of matter. • The Greek used the term atom to describe the smallest part of the four substances of matter. They were air, fire water earth. • This persisted until 1808.

25. The Atom • Today there are over 100 elements: 92 are naturally occurring and over 15 have been artificially produced • In 1808, John Dalton showed that elements could be classified according to integral values of atomic mass.

26. The Atom through the Ages

27. The Elements • In the middle of the 19th century, a Russian scholar Dmitri Mendeleev was credited with showing that if the elements were arranged in the order of increasing atomic mass, a periodic repetition of similar chemical properties occurred. His work resulted in the Periodic Table of the Elements

28. The Atom • In the late 1890’s J.J. Thompson theorized that the atom was like a plumb pudding where the plumbs represent negatively charged electron and the pudding was a shapeless mass of positive electrification. • In 1911 Earnest Rutherford disproved Thompson’s model of the atom.

29. The Atom • The Rutherford atom has a small positively charged nucleus and a cloud of negatively charged electrons. • In 1913 Neils Bohr improved upon Rutherford’s description of the atom as a miniature solar system. His method still works though quantum mechanics model is more accurate.

30. The Molecule • Atoms of various elements combine to form molecules. A measurable quantity of one type of molecules is called a chemical compound. Molecules make structures.

31. Fundamental Particles • The atom as described by Bohr consists of orbiting negatively charges electrons and a nucleus containing protons and neutrons which are made of quarks bound together by gluons.

32. Fundamental Particles • The fundamental particles of the atoms are electrons, protons and neutrons. • Atomic particles are so small, they are expressed in atomic mass units. • 1 amu = 1/12 the mass of a carbon 12 atom.

33. Atomic Structure • The nucleus of the atom contains 99.98% of the mass of a element. The nucleus contains nucleons called protons and neutrons. The neutron has no charge while the protons carry a positive charge. • The electrons carry a negative charge and are arranged in shell. The arrangement of shells determine how the atom reacts chemically or how it combines with other atoms to form molecules.

34. Atomic Structure • The number of protons determines the chemical element. • Atoms with a different number of neutrons are called isotopes. • The electrons are arranged in shells given codes K, L,M,N,.. To represent the electron binding energies. K being the innermost shell. • Electrons closer to the nucleus have higher binding energies. • Electrons farther away from the nucleus have greater potential energy.

35. Atomic Structure • Atoms are electrically neutral. Because the number of electrons and protons are equal. • The positive charge of the nucleus provided a binding force for the atom. • If the atom has an extra electron or an electron is removed, it is said to be ionized. • Ionized atoms are no longer electrically neutral. • Ionization is possible only with addition or loss of electrons. A change in protons would change the element. A change in neutrons would not cause ionization.

36. Electron Arrangement • Physicist call the shell number n the principle quantum number. • The maximum number of electrons that can exist in each shell increases with the distance of the shell from the nucleus. • The number can be calculated by the expression 2n2 where n is the shell number.

37. Electron Arrangement • The number of electrons in the outermost shell of an atom is equal to its group in the periodic table. • The number of electrons in the outermost shell determines the valence of a atom.

38. Electron Arrangement • No outer shell can contain more than 8 electrons. • All atoms that have one electron in the outer shell fall in group one of the periodic table and two electrons fall in group two. • This orderly progression is interrupted in the 4th period. Instead of adding another electron to the outer shell, one is added to the inner shell. These are called transitional elements.

39. Electron Arrangement • Shell notation of the electron arrangement of an atoms not only identifies the relative distance of an electron from the nucleus but indicates the relative binding energy by which the electron is bound to the nucleus. • The centripetal force or the force of attraction of the negative charge of the electron and the positive charge of the nucleus balances the centrifugal force or the force of the electron velocity to keep the electrons in precise orbits.

40. Electron Binding Energy • The strength of the attachment of the electron to the nucleus is called the electron binding energy or Eb. • The electron closer to the nucleus is more tightly bound than the outer shell electron. • Not all K-shell electrons are bound with the same binding energy. The greater the total number of electrons, the more tightly each is bound.

41. Electron Binding Energy • The larger and more complex atoms have higher Eb than smaller atoms because of the greater number of protons. • It take more energy to ionize these larger atoms. • Carbon is one of the important components of human tissue. As with other tissue atoms, Eb is approximately 10 eV. Yet is take about 34eV to ionize tissue atoms. The 34 eV is called the ionization potential. The difference 24 eV causes multiple excitations resulting in heat.

42. Atomic Nomenclature • Often elements are identified by an alphabetic abbreviation called the atomic symbol. • The chemical properties are determined by the number and arrangement of electrons. In the neutral atom, the number of electrons and protons are the same. This is called the atomic number or Z.

43. Atomic Nomenclature • The number of protons and number of neutrons in the nucleus of the atoms is called the atomic mass number or A. • The atomic mass number and the precise mass number are not equal. The actual precise atomic number (amu) is determined by actual measurement.

44. The Tungsten Atom

45. Isotopes • Atoms that have the same atomic number but different atomic mass numbers are isotopes. • Barium has an atomic number of 56. Its atomic mass number is 138 and is based upon the average of the seven isotopes of barium. Each has a different atomic mass but reacts chemically the same.

46. Isobars • Isobars are atoms that have different numbers of protons and neutrons but the same number of nucleons. • Isobaric radioactive transitions from parent atom to daughter atoms result in the release of a beta particle or positron. The parent atom and the daughter atoms are of different elements.

47. Isotones & Isomers • Atoms with the same number of neutrons but different number of protons are isotones. • Isomers have the same atomic number and the same atomic mass number.

48. Characteristics of Various Nuclear Arrangements

49. Combinations of Atoms • Atoms of various elements may combine to form structures called molecules. • A compound is any quantity of one type of molecule.

50. Radioactivity • Some atoms have nuclei that contain excess energy or an unstable nucleus. To reach stability, the nucleus spontaneously emits particles and energy to transform itself into another atom. This process is called radioactive disintegration or radioactive decay.