Review and
Radioactivity
Review
 Atomic # = # P = # e

form electrically neutral atom

If # P does not equal #e then it is called an ION
 Isotope…same p/e…different # of neutrons

ex - C12 or C14 as is mass #
 You can determine valence e- by the group number on
Periodic Table
 Properties of Metals vs. Nonmetals
 Elements with full valence electron shells are STABLE
Radioactivity
 Nucleus contains almost all the mass of an atom (p/n have
all mass)…electrons are negligible (little mass)

EX. Marble sitting in middle of football field
 Nuclear decay/Radioactive decay – When unstable nuclei
decay particles and energy (called nuclear radiation) are
emitted (given off)

This happens spontaneously (naturally)
 Occurs mostly in large elements because large nuclei are
unstable and decay more than small nuclei

attraction forces aren’t as strong to hold particles within
nucleus
Nuclear Decay
 3 types of nuclear radiation
 A. Alpha-particles
 B. beta-particles
 C. gamma-electromagnetic wave
Alpha
 Particle
 Least energy
 Helium nucleus is
 Least penetrating power
emitted (2 p/2 n)
 Charge =+2
 Mass = 4
 LARGEST
- stopped by paper
 Dangerous if swallowed
or inhaled (Radon gas)
 Transmutation occurs
symbol
Beta particle
 Particle
 More energy than alpha
 An electron is emitted
 Goes thru
(given off)
 Charge is -1
 mass is .0005 (very
small)
paper….stopped by foil
 Penetrates skin and
nerve cells
 Transmutation occurs
131
131
I
53
+
e-
Xe
=
54
Gamma Rays
 Waves
 No mass and no charge
 Most powerful and penetrating of all
 Lead and concrete can stop gamma rays
 Passes through body – can cause or cure cancer
 Transmutation does NOT occur
Half-life
 Half-life - The amount of time a radioactive isotope takes
for half the nuclei of a sample to decay
 Steps:
1) Set up your chart (EVERYTIME)!
2) Fill in your ZEROS.
3) Fill in what you already know.
4) Calculate what you don’t know.
a) Amount – divide by 2
b) Time – add another half life
5) Use the chart to answer the question.
Half Life Table
Problems examples
 The half life of calcium is 10 days. How much of a
100 g sample will remain after
1) 20 days?
2) 30 days?
3) 40 days?
4) 50 days?
Another look
 A sample of Phosphorous-18 originally has 30g.
Phosphorous-18 has a half life of 2,000 years. In 2000
years, how many grams would remain undecayed?
1) 4,000 yrs
2) 8,000 yrs
Another look
 At the end of 45 days, 100 g of Carbon-14 has
decayed to 12.5 g. What is the ½ life of Carbon 14?
Gieger counter data
Time in
days
0.0
5.0
10.0
15.0
Counts per
second
1000
2000
3000
4000
What is the half life of the radioisotope?
Type? Transmutation?
FUSION AND FISSION
THE SUN
Nuclear Fusion
 Nuclear fusion is the process by
which multiple nuclei join together
to form a heavier nucleus.
 It is accompanied by the release of
energy
FUSION
NEUTRON
DEUTERIUM
HELIUM
TRITIUM
http://fusioned.gat.com
Fusion Changes Mass to Energy
E=mc2
.993 kg Helium
1kg Hydrogen
NUCLEAR FISSION
A reaction in which a nucleus of a
radioactive element splits by
bombardment from an external source,
with simultaneous release of large
amounts of energy, used for electric
power generation
Nuclear Fission
Neutron induced in U235
Fission is Exothermic
The sum of the masses of
the resulting nuclei is less
than the original mass
0.1% less)
(about
The “missing mass” is converted to
energy according to E=mc2
Review
Nuclear fission:
A large nucleus splits into several
small nuclei when impacted by a
neutron, and energy is released in
this process
ENERGY GENERATION
Nuclear fusion:
Several small nuclei fuse
together and release
energy.
THE SUN