DE Chemistry – King William High School
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Radiation – small particles of energy that are
spontaneously emitted from unstable nuclei
that is radioactive
Radioisotope – an isotope of an element that
emits radiation
Atomic number 93 and higher are man made
and only have radioactive isotopes
Radioactive isotopes are named by writing
the mass number after the name (iodine-131)
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An unstable nucleus becomes more stable by
emitting radiation and forming a lower
energy nucleus
Alpha particle (a) – helium nucleus  42a
Beta particle (b) – a high energy electron 
0 e or 0 b
-1
-1
Positron – an unstable nucleus transforms a
proton into a neutron and a positron (0+1 b)
A positron is an example antimatter
Antimatter – a particle that is the
opposite of another particle
 When a positron and electron collide
their masses are converted to energy in
the form of gamma (g) rays
 Gamma rays – high energy radiation
(00g)
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1
 Proton – hydrogen ( 1H)
1
 Neutron ( 0n)
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Rapidly dividing cells are most susceptible to
radiation (bone marrow, skin, reproductive
organs and intestinal lining…and ALL cells in
growing children)
Cancer cells rapidly divide. That’s why we
treat with radiation…radiation kills carcinoma
at a faster rate than normal, healthy cells
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Read radiation protection on page 137-8!
Notes gamma rays are the most
dangerous because they penetrate
deeply
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Radioactive decay – nucleus spontaneously
breaks down by emitting radiation
Alpha decay – unstable nucleus emits an
alpha particle
238
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EX:
241
92U 
95Am 
234
90Th +
4 He
2
+
4 He
2
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Beta decay – breakdown of a neutron into a
proton and electron
14
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EX:
90 Y
39
6C 

14 N
7
+
+
0 e
-1
0 e
-1
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Gamma decay is rare
Example – technetium (Tc)…the unstable
isotope if given the symbol m (metastable)
99m
99 Tc +
Tc

43
43
0 g
0
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Usually produced in small amounts by
converting stable (nonradioactive) nuclei into
radioactive ones
Transmutation – a stable nucleus is
bombarded by high speed particles
4 He
2
+
10 B
5

bombarding particle + stable nucleus 
13
7N +
1
0n
radioactive isotope + neutron
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Geiger counter – used to detect beta and
gamma radiation
Curie (Ci) – number of disintegrations of a
substance per second
SI unit is the becquerel (Bq)
RAD (radiation absorbed dose) – the amount
of radiation absorbed by a gram of material
(i.e. body tissue)
Read pages 145-147
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Is the amount of time it takes for ½ of a
sample to decay
EX: a 20 mg sample of iodine-131 has a halflife of 8.0 days…how much is left after 32
days?
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Read pages 152-155
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Fission – energy created by splitting the atom
(atomic energy)
235 U + 1 n
92
0
 23692U 
91 Kr
36
+
142 Ba
56
+
The mass of the products is less than the starting
materials…the missing mass has been converted into BIG
amounts of energy. Remember Einstein (E = mc2)
NOTE: 1 g U = 3 tons of coal
3
0n
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Look at visual on page 156
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Two small nuclei combine to form a larger
nucleus
3
1H +
2 H
1

4 He
2
+ 10n + energy
EX: sun/stars constantly have fusion reactions
occurring (producing heat and light)