CLRS 321 Nuclear Medicine Physics and Instrumentation 1 Unit I: the Physics of Nuclear Medicine Lecture 1 Matter and ELECTROMAGNETIC RADIATION (Pages 224-227 In Nuclear Medicine And PET/CT) CLRS 321 Nuclear Medicine Physics and Instrumentation 1

Lecture 1 Objectives Describe the structure of the atom, its components, and their properties Describe the nuclear families as well as their characteristics Define “radioactivity” Describe properties of electromagnetic radiation, including its relationship to energy Define “ionizing radiation”

Matter How would you describe matter?

Atoms & Molecules We cannot see atoms because visible light wavelengths are too big. We can use electron beams to bombard atomic atoms and get information to construct pictures like this—an array of silicon atom pairs. What we are seeing are the electron clouds of pairs of silicon atoms. Atoms are mostly space. The nucleus of the atom is deep within the relatively expansive electron cloud and is infinitesimally small. At the atomic level things get very strange, for we are dealing with the fundamentals of existence. “The Atom," Microsoft® Encarta® Online Encyclopedia 2006 http://encarta.msn.com © 1997-2006 Microsoft Corporation. All Rights Reserved

Atoms Atom Smallest division of a type of matter that retains the same electrical and magnetic properties of that matter and has the same mass characteristics Composed of Protons Quarks Neutrons Electrons Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-4, p 42.

Atoms & Molecules Bohr Model of the Atom Photo taken from “A Science Odyssey” by Charles Flowers, page 32 (c 1998 by William Morrow & Co. New York)

Balmer Series Bohr looked at the hydrogen’s spectral emissions (the Balmer Series) and offered an explanation for the specific wavelengths of visible light. Bohr’s model attributed the distinct wavelengths apparent in the Balmer Series to “quantum leaps” between varying energy states of electrons. (UT Astrophysics, Aug. 2006—Sept 8 2006)http://csep10.phys.utk.edu/astr162/lect/light/absorption.html

Atomic Structure (according to Bohr) Small central nucleus surrounded by electron shells. Nucleus occupied by nucleons Positively charged proton Charge = +1.602176565 X 10-19 coulombs Mass =1.672621777 X 10-17 kg Neutron with no charge Mass = 1.674927351 X 10-17kg Shells are filled with electrons in different energy states Electrons Charge = -1.602176565 X 10-19 Mass = 9.10938291 X 10-31 kg Shells labeled K, L, M, N, O, P, Q Increasing position of letter in the alphabet indicates increasing energy state Also subshells! Electrons = Protons (in stable atom)

Energy States of Electrons This picture from the old Sodee text represents the electron energy states as different speed limits around the nucleus of an atom. In order for a car at 70 mph to go down to the 65 mph speed limit, it must lose a “quantum” of 5 mph. For electrons, this quantum is in the form of a specific wavelength of electromagnetic radiation. Paul Early, D. Bruce Sodee, Principles and Practice of Nuclear Medicine, 2nd Ed., (St. Louis: Mosby 1995), pg. 11. (UT Astrophysics, Aug. 2006—Sept 8 2006)http://csep10.phys.utk.edu/astr162/lect/light/absorption.html

Electron Binding Energy A different but related concept is electron binding energy. This is the specific energy that holds an electron in its orbit. The closer the orbital shell is to the nucleus, the greater its binding energy. (Conversely, the electron energy states increase with the distance of the orbital shell to the nucleus.) This diagram from the Sodee Text gives an example of variations in binding energy (in keV) for a series of electron orbital shells. Paul Early, D. Bruce Sodee, Principles and Practice of Nuclear Medicine, 2nd Ed., (St. Louis: Mosby 1995), pg. 11.

Nuclear Notation X = Chemical Symbol A = Atomic Mass Number Neutrons + Protons Z = Atomic Number Number of protons (which defines the element) For efficiency sake, the Z is usually dropped since this is dependent upon the element type (X)

Nuclear Notation Interactive Periodic Table Link From “The Periodic Table.” Library.Thinkquest.org retrieved 27 Aug 2012 from http://library.thinkquest.org/3616/chem/Periodic.htm Interactive Periodic Table Link

Back to Atomic Structure Atomic Nucleus Nucleons Protons and neutrons Surrounded by electron cloud 1st 20 elements of periodic table—neutrons to protons is 1:1 Larger nuclei require more neutrons than protons to increase binding energy and maintain nuclear stability Nuclei not having an appropriate neutron to proton ratio are unstable From “Atomic Nucleus.” Wikipedia.org. Retrieved 27 Aug 2012 from http://en.wikipedia.org/wiki/Atomic_nucleus

Nuclides & Radionuclides Any configuration of protons & neutrons composing an atom There are about 3100 of these configurations or nuclides 270 nuclides are stable comprising 83 elements The remaining are unstable and are termed… radionuclides Note: “nuclide” does not necessarily mean the same thing as “isotope.” Isotope implies a specific relationship between two nuclides.

Nuclear Families Isotope: Same element, different forms. Isotones: Different elements, same number of neutrons Isobars: Different elements, same atomic mass Isomers: Same atom, different energy state (metastable—”m”) Xe-131from “Gamma Ray-Isomeric Transistion,” ecampus at OregonState.edu, available at https://courses.ecampus.oregonstate.edu/ne581/three/index2.htm . Accessed Aug 27, 2017. Isomers

Radioactivity A.k.a. “activity,” refers to the number of unstable nuclei that are transforming to a more stable state for a given unit of time. Standard units are used to quantify radioactivity: Becquerel (Bq)—1 transforming (or disintegrating) nucleus per second Bq is used for the International System of Units (SI) Curie—3.7 X 1010 disintegrations per second Still most used in the USA Based on the dps for 1 g of Radium (Madame Curie)

Converting Radioactivity Units Because NM doses are much larger (mCi—3.7 X 107 dps), we usually convert to mega Becquerels (Mbq—a million [106] Becquerels) 1 mCi = 37 MBq Example: 20 mCi is how many MBq? Example: 185 MBq is how many mCi?

Electromagnetic Radiation Blue: Electric Field (E) Green: Magnetic Field (H) The electromagnetic field travels out (yellow arrows) from the origin at the velocity of light (c) H C Electromagnetic Radiation," Microsoft® Encarta® Online Encyclopedia 2006 http://encarta.msn.com © 1997-2006 Microsoft Corporation. All Rights Reserved

Electromagnetic Radiation (EMR) Relationship of Wavelength & Frequency c =λv and v = c/λ C = Velocity of EMR (3x1010cm/s) λ = Wavelength v = Frequency (cycles/sec or hertz) A photon is the unit of electromagnetic radiation (a quantum) and it’s energy can be determined using Plank’s constant (h) and the wavelength.

Electromagnetic Radiation Relationship of frequency to Energy E = hv or (E is energy in eV) What’s an eV???? h = Planck’s Constant = 4.135 X 10-15 eV-sec (alternatively, 6.626 X 10-34 J-sec or 6.625 X 10-27 erg-sec) C = velocity of electromagnetic radiation = 3 X 108 m/s (in a vacuum) or = 3 X 1018 Angstroms/sec λ = in Angstroms or 10-10 m (or 0.1 nm)

e⋅lec⋅tron-volt   –noun Physics. a unit of energy, equal to the energy acquired by an electron accelerating through a potential difference of one volt and equivalent to 1.602 × 10−19 joules. Abbreviation: eV, ev, Also, electron volt. Origin: 1925–30 Dictionary.com Unabridged Based on the Random House Dictionary, © Random House, Inc. 2009. In the radiological sciences, we usually measure energy in kilo (i.e. 1000) electron Volts, or keV electronvolt. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved August 22, 2009, from Dictionary.com website: http://dictionary.reference.com/browse/electronvolt

Electromagnetic Radiation Relationship of frequency to Energy Therefore, we take the relationship between wavelength and frequency: And substitute it into our relationship between frequency and energy:

Electromagnetic Radiation Electromagnetic Spectrum Lower frequency—longer wavelength—lower energy Higher frequency—shorter wavelength—higher energy-> <-More Wave like More particle like-> Electromagnetic Radiation," Microsoft® Encarta® Online Encyclopedia 2006 http://encarta.msn.com © 1997-2006 Microsoft Corporation. All Rights Reserved

Ionizing Radiation Electromagnetic radiation strong enough to break the binding energy of an electron to its nucleus and strip it from the atom is ionizing radiation. Usually happens above UV wavelengths X-rays Originate from abrupt changes in electron energy states Gamma rays Originate from the release of nuclear binding energy Paul Christian, Donald Bernier, James Langan, Nuclear Medicine and Pet: Technology and Techniques, 5th Ed. (St. Louis: Mosby 2004) p 52. Since nuclear binding energy is usually higher than electron energy states, gamma rays tend to be more energetic than x-rays, but this is not always the case. Electromagnetic Radiation," Microsoft® Encarta® Online Encyclopedia 2006 http://encarta.msn.com © 1997-2006 Microsoft Corporation. All Rights Reserved

Next time… Mass energy equivalents and units (pp. 228-229) Photo courtesy of NASA, from Cassini mission website available at https://www.nasa.gov/mission_pages/cassini/images/index.html . Accessed Aug 27, 2017.