Physics Test 1 PDF

Lesson 1 Energy and the structure of matter Chapter 1&2 Chapter 1 Introduction to the Imaging Sciences Matter and energy Matter Anything that occupies space Building blocks of matter are atoms and molecules Primary characteristic of matter is mass Radiation Energy emitted and transferred through...

Lesson 1 Energy and the structure of matter Chapter 1&2 Chapter 1 Introduction to the Imaging Sciences Matter and energy Matter Anything that occupies space Building blocks of matter are atoms and molecules Primary characteristic of matter is mass Radiation Energy emitted and transferred through matter Ionization A reaction in which radiation interacts with matter Removal of an electron from an atom Ionizing radiation 5 Radiation capable of ionization Physics - science that deals with matter and energy Radiation Physics – the branch of physics that deals with radiation and matter Mass 5 Quantity of matter within a physical object, it is constant within the universe Mass remains unchanged when matter changes from one form to another (block of ice to water to vapor) Weight 5-6 Used to describe the mass of an object in a gravitational field The force exerted by a physical object under the influence of gravity A person weighs 200 lbs. on earth, on the moon which has a gravitational force 1/6 that of the earth, the person would weigh 34lbs. (200/6) The mass of the person remains the same, only the weight changes Energy 7 The ability to do work, work is measured in joules Potential energy 7 Capacity to do work because of the position of an object Roller coaster at the top of an incline, stretched spring on an open screen door Kinetic energy 7 Energy of motion, possessed by all matter in motion Car in motion, turning windmill wheel, falling guillotine blade Chemical energy 7 Energy released in a chemical reaction The violent burst resulting from the lighting of dynamite, Nitroglycerin and Ammonium nitrate in the presence of heat or flame, the chemical reaction increases the internal pressure in the dynamite tubes causing the explosion or energy release Electrical energy 7 Work done when an electron (negative particle) or electronic charge moves through an electric potential (voltage) through a wire Thermal energy 7 Energy of motion at the molecular level, kinetic energy of molecules Thermal energy or heat is measured by temperature The faster the molecules of matter are moving, the more thermal energy the matter contains and the higher the temperature of the substance Nuclear energy Energy contained in the nucleus of an atom, the atomic bomb Electromagnetic energy Type of energy in the x ray beam and used in MRI, includes radiowaves, microwaves or light Just as matter can be transformed from one form to another, so can energy Electrical energy in the x ray unit produces electromagnetic energy in the form of an x ray beam, which is then converted into light (screen) and chemical energy(film) resulting in an image on an x ray film Electromagnetic energy emitted by a source and transferred through space is called electromagnetic radiation UV rays from the sun, heat from a stove Albert Einstein combined the concepts of mass and energy in the theory of relativity, E=mc2 , E=energy, m=mass and c=speed of light Ion pair – the atom that lost an electron and the orbital electron Bushong Chapter 2 Structure of the Atom Atom – the smallest part of an element that has all the properties of that element Element – consists of atoms having the same structure and reacting the same chemically The Greek Atom 16 The earliest recorded reference to the atom around 200 B.C. Composed of four substances – earth, water, wind and fire All matter could be described as combinations of these 4 substances in various proportions These substances were modified by 4 basic essences – wet, dry, hot and cold The term atom described the smallest part of the 4 basic substances Today there are 108 substances or elements, 92 naturally occurring and 16 artificially produced in particle accelerators There are particles smaller than the atom called subatomic particles The Dalton Atom 17 In 1808, John Dalton showed that elements could be classified according to integral values of atomic mass According to Dalton, an element was composed of identical atoms, each acting the same way in chemical reactions The physical combination of one type of atom to another was interpreted as being a hook and eye affair, the size and number of hooks and eyes were different for each element A scholar named Mendeleev, showed that if the elements were arranged in order of increasing atomic mass, repetition of similar chemical properties occurred, his work resulted in the first Periodic Table of Elements, superscript – atomic number, subscript – elemental mass Atomic number – number of protons in the nucleus Atomic (Elemental) mass number – number of protons and neutrons in the nucleus Thomson Atom 17 The atom was described by Thomson as looking like plum pudding, where the plum represented negative electric charges and the pudding was a shapeless mass of uniform positive electrification The number of electrons was thought to equal the quantity of positive electrification because an atom was known to be electrically neutral Ernest Rutherford disproved this and introduced the nuclear model which described the atom as containing a small dense positively charged center surrounded by a negative cloud of electrons Bohr Atom 18 In 1913, Niels Bohr introduced a model that was like a miniature solar system in which the electrons revolved around the nucleus in prescribed orbits or energy levels The Bohr atom contains a small, dense, positively charged nucleus surrounded by negatively charged electrons that revolve in fixed, well-defined orbits around the nucleus. In the neutral atom, the number of electrons is equal to the number of positive charges in the nucleus Fundamental particles 18 The atom used today is the Bohr atom With the invention of the high energy particle accelerators, (cyclotron) or atom smashers, the structure of the nucleus of an atom is slowly being identified The fundamental particles of an atom are the: Electron, proton and neutron Electrons: Have 1 unit of negative electric charge, orbit the nucleus of an atom at about the speed of light in precisely fixed orbits The arrangement of the electrons around the nucleus determine how atoms interact An electron’s mass is 9.1 * 10-31 kg Because atomic particles are very small, their mass is expressed in atomic mass units (amu) One amu =1/12th the mass of a carbon-12 atom The electron mass is.000549amu When preciseness is not necessary, atomic mass numbers, amu, (whole numbers) are used The atomic mass number of an electron is 0 The nucleus of an atom contains nucleons, there are 2 types – protons and neutrons Both protons and neutrons have about 2000 times the mass of an electron The atomic mass number of each is 1 The difference between a proton and neutron is the electric charge Proton has 1 unit of positive charge A neutron carries no charge, it is electrically neutral Atomic structure The atom is mostly empty space The nucleus contains nearly all the space The electron orbits are grouped into shells The arrangement of the electrons in these shells determines how an atom reacts chemically (how it combines with other atoms to form molecules), specifically the number and arrangement of the electrons in the outermost shell determines the chemical reaction The number of protons determine the chemical element Electrons can exist only in certain shells, which represent different electron binding energies or energy levels Going from the electron shell closest to the nucleus to the farthest from the nucleus the shells are given a code: Closest to the nucleus: K, L, M, N, O, P, Q The closer an electron is to the nucleus, the higher its binding energy In their normal state, atoms are electrically neutral, they have a charge of 0 The # of electrons = the # of protons If an atom has an extra electron, or has one removed, it is ionized Atoms can’t be ionized by the addition or subtraction of protons, this would change the element Ionization occurs when the x ray photon transfers its energy to an orbital electron and ejects that electron from the atom Requires approximately 34 eV (electron volts) of energy, the x ray ceases to exist and an ion pair is formed The remaining atom is now a positive ion, since it has one more positive charge than negative charge In all except the lightest atoms, neutrons outnumber the protons Electron arrangement The maximum # electrons that can exist in a shell increases with the distance of the shell from the nucleus Formula for calculating the max. # electrons in each shell: 2n2, n = shell number Shell # Shell symbol # of electrons 1 K 2 2 L 8 3 M 18 4 N 32 5 O 50 6 P 72 7 Q 98 EXAMPLE: Uranium has 92 protons and 146 neutrons Electron distribution: 1 K 2 2 L 8 3 M 18 4 N 32 5 O 21 6 P 9 7 Q 2 What is the reason for the neutrons, they don’t have a charge? Physicists call the shell number the principal quantum number. Every atom can be identified by the principal quantum number There is a relationship between the # of shells and the position on the periodic table of elements O2 has 8 (e-), 2 in the K shell and 6 in the L shell, it is in the 2 nd period and the 6th group on the periodic table The number of the outermost electron shell of an atom is equal to its period in the periodic table The number of the electrons in the outermost shell is equal to its group No outer shell can contain more than 8 electrons The orderly scheme of atomic progression is interrupted in the 4 th period Electrons are added to an inner shell instead of an outer shell These atoms are called transitional elements An electron (e-) does not spontaneously fly off from the nucleus because electrons (e-) are negatively charged and protons (p+) are positively charged Centripetal force Also called “center seeking” force, the force that keeps an electron in orbit This attraction is described as a basic law of electricity that states opposite charges are attracted to each other and like charges repel (e-‘s) revolve around the nucleus in fixed orbits. The electrostatic attraction produces a centripetal force or center seeking force that just matches the force of motion or velocity, centrifugal force, so the electrons maintain their distance from the nucleus When you whirl a ball around at the end of a string, centripetal force applied to the string keeps the ball moving in a circle. Gravity can also do the job, as it does when the Earth holds the Moon in orbit Centrifugal force “Flying out from the center” force In the normal atom, the centripetal force just balances the centrifugal force or flying out from the center force Tends to cause an electron to travel straight and leave the atom The ball exerts and equal and opposite force, called, on the string and on you. If you cut the string attached to your ball, the ball flies away on a tangent -- a straight line in the direction it was moving at the instant the string was cut. It's like taking a corner in your car a little too fast and ending up in the ditch. Electron binding energy (Eb) Strength of attachment of an (e-) to the nucleus The closer an (e-) is to the nucleus, the more binding energy it has K shell electrons have higher binding energies than L shell electrons Not all K-shell (e-) have the same binding energy, the more (e-) in an atom, the more tightly each is bound It takes more energy to ionize a large atom than a small one Atomic nomenclature Chemical symbol Alphabetic abbreviation of an element The chemical properties of an element are determined by the number and arrangement of the electrons around the nucleus In the electrically neutral atom, the number electrons =the number of protons The number of protons is called the atomic number (Z) The atomic number of barium is 56, it has 56 protons in the nucleus of an atom of barium The atomic number of tungsten is 74 (high), has 74 protons in the nucleus The number of protons plus the number of neutrons in the nucleus is called the atomic mass number or mass number (A), always a whole number, the number of nucleons in an atom Shorthand notation for the chemical symbol with sub and superscripts is used to identify atoms Mass number A X (chemical symbol) Atomic number Z The subscript and superscript to the right are values for the number of atoms per molecule and the valence state or energy level of the atom The subscript and superscript to the rleft are values for the atomic number and atomic mass number Concentrate only on the subscript and superscript on the left AX Z Figure 4-6 on page 42 Isotopes Atoms that have the same atomic number but different mass numbers Have the same number of protons but different or varying numbers of neutrons Most elements have more than 1 stable isotope The number of neutrons in a nucleus = A-Z (mass number – atomic number) From the chart on page 33, Barium’s atomic number = 56 (# of protons), 130 Ba has 74 neutrons Isobars Have the same atomic mass number but different atomic numbers Have different numbers of protons and neutrons but the same number nucleons Isotones Have same number of neutrons but different number of protons Have different atomic numbers and mass numbers but a constant value for A-Z Isomers Have the same atomic and mass numbers Arrangement Atomic # Mass # Neutron # Isotope same different different Isobar different same different Isotone different different same Isomer same same same Combination of atoms Molecules Atoms of various elements combining to form a structure Molecules can combine to form larger combinations Hydrogen atoms can combine to form H2 , Oxygen atoms can combine to form O2 Then two molecules of Hydrogen (2H2) can combine with one molecule of oxygen (O2) to form 2 molecules of water 2H2O An atom of Sodium (Na), can combine with an atom of Chlorine (Cl) to form a molecule of NaCl = table salt Compound The new substance formed when two or more atoms of different elements combine The formula NaCl represents one molecule of the compound sodium chloride Atoms combine with each other to form compounds (chemical bonding) in two main ways: Covalent and Ionic Bonding Covalent bonding O2 has 6 electrons in its outermost shell, it has room for 2 more, so in a H 2O molecule the 2 hydrogen atoms share their single electron with the O2. The H electrons orbit both the H and the O binding the atoms together Covalent bonding is characterized by the sharing of electrons Ionic bonding Na has 1 electron in its outermost shell, Cl has room for one more electron in its outermost shell The Na atom gives up its electron to the Cl, when it does it becomes ionized, because it lost an electron and has an imbalance of electrical charges, the Cl atom also becomes ionized because it gained an electron The result is that they are attracted to each other because of the opposite charges When a positive ion and a negative ion are brought close together, strong electrostatic forces between the charges of opposite signs are set up, and the ions are held together The smallest particle of an element is an atom, the smallest particle of a compound is a molecule Radioactivity Some atoms exist in an abnormally excited state characterized by an unstable nucleus To reach stability, the nucleus spontaneously emits particles and energy and transforms itself into another atom This is called radioactive disintegration or decay Only nuclei that undergo radioactive decay are radionuclides Radioisotopes The most important factor that affects nuclear stability is the # of neutrons When there is too many or too few it can disintegrate radioactively This brings the # of neutrons and protons into the proper ratio-stable isotope Radioisotopes Can be artificially produced in a particle accelerator 7 have been artificially produced for barium Some have naturally occurring radioisotopes: Some originated at the time of the formation of the earth Uranium decays into radium which decays into radon Radioactive decay Occurs in 2 ways: 1. beta emission An electron-like particle created in the nucleus is ejected from the nucleus leaving with high kinetic energy, the atom loses a unit of negative electric charge from the nucleus A neutron undergoes conversion into a proton, at the same time The net result is an increase in the atomic number by one, mass number remains the same, an atom changes from one element to another 2. alpha emission An alpha particle consists of 2 protons and 2 neutrons bound together, atomic mass number is 4 Only heavy isotopes are capable of alpha emission, helium nuclei Must be extremely unstable It loses 2 units of positive charge and 4 amu Radioactive half life Radioisotopes disintegrate into stable isotopes of different elements at a continuously decreasing rate and consequently the quantity of radioactive material never reaches 0. The radioactive decay and quantity of material present at any given time is described by the radioactive decay law From this the half life is derived (T ½ ) The half life of a radioisotope is the period of time required for a quantity of radioactivity to be reduced to one half its original value Varies from less than one second to hundreds/thousands of years Used in NM, has application in radiography – half value layer – the thickness of material used to reduce the x ray beam intensity to one half its original intensity Types of Ionizing Radiation 2 categories 1. particulate – alpha and beta particles 2. electromagnetic – x and gamma rays, called photons, have no mass or charge, travel at the speed of light and are considered energy disturbances in space Radiation used in US (sound radiation) and MRI is non ionizing MRI (electromagnetic but photon energy isn’t strong enough to cause ionization) Differences in ionizing radiation Based upon: 1. mass 2. energy 3. charge 4. origin 5. velocity Electromagnetic radiation 1. X rays 2. Gamma rays Often called photons Have no mass or charge, travel at the speed of light, only difference is origin Gamma rays are emitted from the nucleus of a radioisotope, associated with beta and alpha emission X rays are produced outside the nucleus in the electron shells Wavelength Distance between any 2 corresponding points of adjacent waves (peak to peak / trough to trough) Frequency # of peaks to pass a specific point over a time interval Wavelength and frequency of x rays are inversely proportional, because the speed of x rays is constant at the speed of light (3 * 10-8 m/s) Unit of measure of x rays = Angstrom 1 Angstrom = 10-10 meters