1. Nuclear Medicine 4103 Section I Basic Chemistry

2. Structure of The Atom Nucleus: contains Protons (+) and Neutrons (0) Electron (-) orbiting the nucleus in energy shells Neutrino: not a normal part of the nucleus. Result of interactions within the nucleus. Emitted during several methods of atomic decay. Neutral charge – No mass.

3. Electron shells Energy levels surrounding the nucleus that contain electrons. Identified by letters: K, L, M…. Valence electrons: the outer shell electrons - involved in ionic and covalent bonds.

4. Definitions Atomic number: number of Protons Atomic mass (mass number): number of protons and neutrons

5. Principles of atoms Electrical Neutrality: number of electrons must equal the number of protons. Nuclear Stability: Neutrons must increase at a faster rate than the protons. Nuclear instability: any deviation of the neutron to proton ratio for a particular nuclide will result in nuclear instability.

6. Periodic Chart Created in 1869 by Russian chemist Dmitri Mendeleev. He organized chemicals in order by their atomic weight. Columns – Groups – Families: similar chemical properties Horizontal lines – Periods Left side metals, Right side nonmetals – ending with Noble gases Atoms with the largest radius(most orbits) are at the bottom of their groups. Noble gases are very stable.

7. Binding Energy Coulomb’s law states: like charges repel; unlike charges attract. Binding energy keeps electrons in their orbit – instead of being attracted to the nucleus. Protons should repel each other – but Binding energy keeps the nucleons bound to one another. Binding energy is strongest closest to the nucleus.

8. The Nucleus Protons and Neutrons are in a constant state of motion. When energy is supplied to an atom, the motion increases, and the number of collisions increase. Can result in particle emission.

9. Bonds Covalent: sharing of electrons between atoms. The most predominant bond. Sugar, carbon dioxide, and hydrogen chloride. Nonmetal + Nonmetal Ionic: Complete transfer of electron from one atom to another. Sodium Chloride Na+ and Cl- bind together. Metal + Nonmetal Coordinate Covalent Bond: pair of electrons donated by one atom to another in octet formation. Hydrogen: Only with Hydrogen. Weak bond.

10. Radical (Free Radical) Atom with one or more unpaired electrons. These unpaired electrons leave the atom free to bond or interact with other atoms.

11. Solutions & Colloids Solute : Dissolved substance Solvent : Liquid or gas that dissolves the solute. The substance that the solute is dissolved into. Colloid : mixture where one substance is dispersed evenly within another. Not dissolved. Suspension: fluid containing solid particles. Will eventually settle.

12. Nuclear Families Isotope: form of the same element with the same atomic number, but different mass numbers. Demonstrate the same chemical properties. The different weight is due to the different number of neutrons in the nucleus. If the atom is unstable, the radioactive properties will differ. An isotope may be stable or unstable. Isotone: same number of neutrons, no other similarities. Isobar: 2 atoms with same mass number, different atomic number, different chemical properties. Same number of protons and neutrons. No interest in NM. Isomer: One of 2 or more nuclides that has the same mass number and atomic number as the others but exists for measurable times in the excited state. Nuclide: Refers to any nucleus plus it’s orbital electrons. Radionuclide : unstable nuclide

13. X-Rays Vs. Gamma Rays Both are release of energy X-Rays: Energy released as a result of changes in the orbital electrons Gamma Rays: Energy released as a result of changes in the nucleus.

14. Gamma Radiation Energy remaining in the nucleus (following particle emission), raises the nucleus to an excited state. When a nucleus is raised to an excited state of 500 keV, it will return to ground state and release energy known as gamma radiation. Gamma energy that occurs most frequently is called the Primary energy peak.

15. Possible types of Reactions methods of decay to achieve stability Spontaneous Fission Alpha ( α) Decay Beta (β -) Decay Positron (β +) Decay Electron Capture (EC) Isomeric Transition (IT)

16. Spontaneous Fission Heavy nucleus breaks down into 2 fragments (60:40) Emission of 2-3 neutrons (mean energy of 1.5 MeV) Release of 200 MeV of energy (mostly heat) Can happen spontaneously or by bombardment

17. Alpha –Particle Emission An alpha particle (2 protons & 2 Neutrons) is released from the nucleus~ Helium ion Reduction of mass number by 4 Travel only a few centimeters in air Unable to penetrate even thin paper Useless for imaging

18. Beta-Particle Emission Found in nuclides with neutron excess Beta-particle and anti-neutrino released from the nucleus. Range of about 1cm in tissue Not useful for imaging

19. Positron Emission Too many protons in the nucleus The positron travels a short distance and combines with an electron. When this happens, two photons of 511 keV are emitted in opposite directions. This radiation can be imaged Results from conversion of the masses of the positron and electron into energy

20. Electron Capture Alternative to positron decay, when there isn’t enough energy available for positron emission. Inner-orbital electron is captured by a proton in the nucleus Transforms a proton into a neutron May be accompanied by gamma emission Always creates Characteristic radiation. Both can be used in imaging.

21. Isomeric Transition Decay of upper excited state to a lower excited state Energy is given off as gamma rays Number of protons and neutrons is not changed When isomeric states are long-lived, called metastable ( 99m Tc)

22. Definitions Neutrino: particle of no charge or mass emitted with variable energy during positron emission or electron capture Antineutrino: entity almost without mass or charge. Needed to conserve energy in the decay. Emitted during Beta decay.

23. Half-Life Time required to reduce initial activity to ½ t 1/2 Example : t 1/2 of 99m Tc is 6 hours 10 mCi of 99m Tc would be 5 mCi in 6 hours

24. Radioactivity Expressed in units 1 curie (Ci) = 3.7 X 10 10 dps 1 millicurie (mCi) = 3.7 X 10 7 dps 1 microcurie (uCi) = 3.7 X 10 4 dps