1Introduction 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.

2Definition of Radiation

• Energy moving in the form of waves or particles

http://www.ucar.edu/learn/images/spectrum.gif

3Ionizing radiation

http://www.astro.uiuc.edu/~kaler/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.

4Sources of exposure, US

http://www.doh.wa.gov/ehp/rp/Air/air-images/2%20Radi1.gif

5Sources 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)

6Atomic structure

Atom has equal number of protons and electrons.

Elements differ by the number of protons in the nucleus.

Z = number of protonsA = mass number (number of protons + the # of neutrons)

As the mass of an atom increases, the more neutrons are needed.

http://www.compumike.com/science/nucleusatom.gif

Atomic weight is an averaged atomic mass.

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Atomic number = Z the number of protons in the atom. Determines which element it is.

Atomic mass (or Mass number) = Athe total number of protons and neutrons.

A = Z + N (# of neutrons)

Nucleon = either proton or a neutron

Atomic nomenclature

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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.

9Nuclear 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: http://www.arpansa.gov.au/images/basics/nuc_stab.gif

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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/

15E = mc2 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.