1 Atomic Structure Protons 1 1 p ( amu) Neutrons 1 0 n ( amu) Electrons ( amu) Neon Ne ( amu)

2 Nucleus of the Atom The nucleus contains protons and neutrons All atoms of the same element contain the same number of protons Isotopes of an element can have differing numbers of neutrons Isotopes having a nearly equal number of protons and neutrons are most likely to be stable

3 Nuclear Shorthand and Definitions Mass Number: (A) # Protons + #Neutrons Atomic Number: (Z) # Protons (the atomic number defines the element) Isotope: Nuclides of an element with the same atomic number (number of protons) but differing numbers of neutrons

THE ATOM The nucleus structure – protons and neutrons = nucleons – Z protons with a positive electric charge ( C) – neutrons with no charge (neutral) – number of nucleons = mass number A The extranucleus structure – Z electrons (light particles with electric charge) equal to proton charge but negative Particle Symbol Mass Energy Charge (kg) (MeV) Proton p 1.672* Neutron n 1.675* Electron e 0.911*

Identification of an Isotope

6 Question #1 A P 32 atom has 15 protons in the nucleus. How many neutrons does it have? a.15 b.16 c.17 d.18

IONIZATION-EXCITATION Energy

characteristic radiation Auger- electron DEEXCITATION

THE NUCLEUS ENERGY LEVELS The nucleons can occupy different energy levels and the nucleus can be present in a ground state or in an excited state. An excited state can be reached by adding energy to the nucleus. At deexcitation the nucleus will emit the excess of energy by particle emission or by electromagnetic radiation. In this case the electromagnetic radiation is called a gamma ray. The energy of the gamma ray will be the difference in energies between the different energy levels in the nucleus. Occupied levels ~8 MeV 0 MeV ENERGY Particle emission Gamma ray DeexcitationExcitation

Energy particles photons NUCLEAR EXCITATION

alpha-particle beta-particle Gamma radiation NUCLEAR DEEXCITATION

INTERNAL CONVERSION characteristic radiation conversion electron

Radioactive decay IAEA Training Material on Radiation Protection in Nuclear Medicine

STABLE NUCLIDES long ranged electrostatic forces short ranged nuclear forces p p n Line of stability

Stable and unstable nuclides Too many neutrons for stability Too many protons for stability

RADIOACTIVE DECAY Fission The nucleus is divided into two parts, fission fragments. and 3-4 neutrons. Examples: Cf-252 (spontaneous), U-235 (induced)  -decay The nucleus emits an  -particle (He-4). Examples: Ra-226, Rn-222  -decay Too many neutrons results in   -decay. n=>p + +e - +. Example:H-3, C-14, I-131. Too many protons results in   -decay p + =>n+ e + + Examples: O-16, F-18 or electron capture (EC). p + + e - =>n+ Examples: I-125, Tl-201

Multiple & prefixes (Activity) Multiple Prefix Abbreviation 1 - Bq Mega (M) MBq Giga (G) GBq Tera (T) TBq

18 Types of Ionizing Radiation: Alpha, Beta, & Gamma Alpha Particle Beta Particle Large Mass (nuclei) – Helium Atom with a +2 charge Small Mass - Electron (subatomic particle) Gamma Photon and X-Rays No Mass (Electromagnetic Radiation) Radiation) + +

19 Penetrating Power of Radiations Alpha          Beta Gamma and X-rays PaperPlastic Lead

20 Radioactivity Units Activity = Rate of decay of a radioactive sample or the number of atoms that decay per unit time 1 Curie (Ci)= 3.7x10 10 dps or 2.22 x dpm 1 millicurie (mCi) = 3.7 x 10 7 dps or 2.22 x 10 9 dpm 1 microcurie (  Ci) = 3.7 x 10 4 dps or 2.22x10 6 dpm 1 Becquerel (Bq) = 1 disintegration per second Specific Activity: amount of radioactivity in a given mass or volume, e.g. μCi/ml or mCi/mg

21 Half-Life The time required for the amount of radioactive material to decrease by one-half

22 Half-Life: I day half-life ½ ¼ 1/8 1/16 20 mCi 10 mCi 5 mCi 2.5 mCi 1.25 mCi

It is impossible to know at what time a certain radioactive nucleus will decay. It is, however possible to determine the probability l of decay in a certain time. In a sample of N nuclei the number of decays per unit time is then: RADIOACTIVE DECAY

24 Activity Calculations A = A o e - t (λ = ln 2 ÷ T ½ = 0.693/ T ½ ) Phosphorus-32 has a half-life of 14.3 days. How much is left of a one millicurie shipment after 30 days? A = 1 mCi × e -(0.693/14.3 d) x 30 d A = mCi