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The Atomic Nucleus
Review…the nucleus
 The nucleus is
 protons and neutrons
composed of particles
called nucleons..__ & __
 Neutrons and protons
have the same mass,
with ___ being slightly
greater.
 Neutrons have nearly
2000 times the mass of
 _____.
 neutrons
 electrons
Review…the atom
 The mass of an atom is
almost equal to the mass
of the _____ alone
 nucleus
 Nucleons are bound
together by an attractive
nuclear force called the
____ force
 The positively charged
protons in the nucleus
hold the negatively
charged electrons in their
____
 strong
 orbits
Review…the atom
 The number of ___ in the
nucleus determines the
chemical properties of
the atom
 The # of protons
determines the # of ____
that orbit the atom
 The # of ___ has no
direct effect on the # of
electrons
 protons
Review…the atom
 The principal role of the
neutrons in the nucleus
is to act as a sort of ____
to hold the nucleus
together
 The electrical force acts
as a ____ force between
protons
 The atom needs a
certain balance of
neutrons and protons for
___
 cement
 repulsive
 stability
The symbol was created in 1946 UCBerkeley to represent “activity
coming out of a atom”
What is Radioactivity?
 Radioactive decay is the process in which an
unstable atomic nucleus loses energy by emitting
radiation in the form of particles or electromagnetic
waves.
 There are numerous types of radioactive decay. The
general idea:
 An unstable nucleus releases energy to become
more stable
Radioactive Decay
Radioactive Decay
 A neutron is very unstable. A lone neutron will
spontaneously decay into a proton + an electron.
 If you have a lot of neutrons, within 11 minutes ½ of
them will have decayed
 Particles that decay are said to be radioactive
 A lone neutron is radioactive
All the elements heavier than Bismuth (At # 83)
Their atoms emit 3 things…alpha, beta
particles and gamma rays
Which is more penetrating?
Radioactive Isotope
 Iodine-131, a beta emitter, is taken as sodium iodide
in drinking water. Almost all of it will find its way to
the thyroid
Isotopes
 They are atoms of the same element that have
different numbers of neutrons.
Radioactive Half-life
Radioactive Half-Life
 The half-life of an element is the time it takes for half
of the material you started with to decay
Remember, it doesn’t matter how much you
start with. After 1 half-life, half of it will have
decayed.
 Each element decays into a new element
 C14 decays into N14 while U238 decays into Pb206
(lead), etc
 The half-life of each element is constant. It’s like a
clock keeping perfect time
Half-life
Half-life
Half-life
Half-life
“How much of this element remains after 4
half-lives?
Just remember that at the end
of one half-life, 50% of the
element will remain. Find
50%
on the vertical axis, Follow
the
blue line over to the red
curve
and drop straight down to
find
the answer:
Carbon Dating
 The radioactivity of once living things decreases at a
predictable rate
Uranium Dating
 The dating of older, non-living things (like rocks) is
accomplished by radioactive minerals, such as
Uranium. Uranium decays very slowly.
 Rocks on Earth have been dated to 3.7 bil yrs old
 Rocks on Moon dated to 4.2 bil yrs old
 The Earth has been dated to 4.6 bil yrs old
Review…whew!
 https://archive.org/details/NASARealWorldMath_
WhatIsRadioactiveDecay_HD
 http://en.wikipedia.org/wiki/Barium_swallow
Radiation Penetrating Power
Three Common Types of Radioactive
Emissions - Penetrability
Alpha particles may be
completely stopped by a
sheet of paper, beta
particles by aluminum
shielding. Gamma rays,
however, can only be
reduced by much more
substantial obstacles, such
as a very thick piece of
lead.
Radiation Penetrating Power
 http://www.passmyexams.co.uk/GCSE/physics/pen
etrating-properties-of-radiation.html
Radiation and You (and me)!
 http://people.chem.duke.edu/~jds/cruise_chem/nu
clear/exposure.html
Is there radon in your home?
Sources of Radioactivity
 Primordial - from before the creation of the Earth
 Cosmogenic - formed as a result of cosmic ray
interactions
 Human produced - enhanced or formed due to
human actions (minor amounts compared to
natural)
Radiation Exposure to Americans
Review
 Name three of the science pioneers in the study of
Radioactivity.?
 Why does a nucleus decay?
 Order these emissions from least to greatest
penetrability: Gamma, Alpha, Beta.
 What is the greatest source of exposure to
radioactivity in our everyday lives?
Nuclear Fusion - Energy released when
two light nuclei combine or fuse
•However, a large amount of energy is
required to start a fusion reaction:
repulsion forces
o Need this energy to overcome ________
of protons.
o Extremely high temperatures can provide start-up
energy.
More energy in fusing hydrogen that fission of uranium