1 Introduction to Radiation and Radioactivity Is your notebook radioactive? –Of course. Many of the elements found in everyday items include radioactive isotopes. –Concern is about radioactivity over and above what occurs naturally; a question of amount, not presence. An atom is radioactive when changes occur in the nucleus resulting in the release of energy.

2 Definition of Radiation Energy moving in the form of waves or particles

3 Ionizing radiation sow/emspectrum.jpg Ionizing radiation (e.g. x-rays and gamma rays) have very short wavelengths, thus high energy. They can knock electrons from atoms, producing ions. High energy particles (beta, alpha) can do likewise. Ionized atoms are very reactive, can damage nearby molecules.

4 Sources of exposure, US

5 Sources continued External sources include –Cosmic rays (from the sun and beyond) –Terrestrial other than radon High exposure in stone houses Radioisotopes from earth’s creation Radioisotopes created by cosmic bombardment Internal includes –K-40 from K+ accumulated by cells –C-14 (we are carbon based organisms)

6 Atomic structure Atom has equal number of protons and electrons. Elements differ by the number of protons in the nucleus. Z = number of protons A = mass number (number of protons + the # of neutrons) As the mass of an atom increases, the more neutrons are needed. ce/nucleusatom.gif Atomic weight is an averaged atomic mass.

7 Atomic number = Z the number of protons in the atom. Determines which element it is. Atomic mass (or Mass number) = A the total number of protons and neutrons. A = Z + N (# of neutrons) Nucleon = either proton or a neutron Atomic nomenclature

8 Isotopes are atoms of an element that all have the same number of protons, but have different numbers of neutrons (N). Isotopes An isotope that decays and gives off radiation: radioisotope.

9 Nuclear Stability The larger the atom, the greater the proportion of the nucleus that must be neutrons. –The A/Z ratio is greater than 2 (or the N to P ratio is increasingly greater than 1) Atoms in which the A/Z ratio is outside a certain range undergo radioactive decay –A neutron or proton breaks down, releasing radiation, and restoring the A/Z ratio to a stable number. Slides:

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12 Same Z, different # of neutrons Note that there are several stable isotopes as well as several types of radioisotopes.

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14 ccinfo.ims.ac.jp/periodic/

15 E = mc 2 but… Radioactive material ≠ radiation Matter and energy are interconvertible, but are not the same. –A radioactive material gives off radiation. –You can be contaminated with radioactive material, but not contaminated with radiation. –You can determine how radioactive a material is by how much radiation it gives off.