Transcript Introduction to Radiation and Radioactivity

Introduction to Radiation and Radioactivity
1
• 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.
Definition of Radiation
2
• Energy
moving in
the form
of waves
or
particles
http://www.ucar.edu/learn/images/spectrum.gif
Ionizing radiation
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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.
http://www.astro.uiuc.edu/~kaler/
sow/emspectrum.jpg
Sources of exposure, US
http://www.doh.wa.gov/ehp/rp/Air/air-images/2%20Radi1.gif
4
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)
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Atomic structure
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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.
http://www.compumike.com/scien
ce/nucleusatom.gif
Atomic weight is an averaged atomic mass.
Atomic nomenclature
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
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Isotopes
Isotopes are atoms of an element that all
have the same number of protons, but have
different numbers of neutrons (N).
An isotope that decays and gives off radiation:
radioisotope.
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Nuclear Stability
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• 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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11
12
Same Z, different # of neutrons
Note that there are several stable isotopes
as well as several types of radioisotopes.
13
14
ccinfo.ims.ac.jp/periodic/
E=
mc2
but…
15
• 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.