Transcript 9.2 Nuclear reactions

Chapter 9 Nuclear Radiation
9.2
Nuclear Reactions
Copyright © 2009 by Pearson Education, Inc.
1
Alpha Decay
When a radioactive
nucleus emits an
alpha particle, a new
nucleus forms that has
• a mass number that is
decreased by 4.
• an atomic number that
is decreased by 2.
Copyright © 2009 by Pearson Education, Inc.
2
Balancing Nuclear Equations
In a balanced nuclear equation, the sum of the mass
numbers and the sum of the atomic numbers are
equal for the nuclei of the reactants and the products.
MASS NUMBERS
Total =
251
251Cf
=
98
=
98
Total =
251
247Cm +
96
4He
2
98
ATOMIC NUMBERS
3
Changes in Nuclear Particles Due
to Radiation
When radiation occurs,
• particles are emitted from the nucleus.
• mass number may change.
• atomic number may change.
Copyright © 2009 by Pearson Education, Inc.
4
Guide to Balancing a Nuclear Equation
5
Equation for Alpha Emission
Write an equation for the alpha decay of Rn-222.
STEP 1: Write the incomplete equation
222Rn
?s + 4He
86
2
STEP 2: Determine the mass number
222 – 4 = 218
STEP 3: Determine the atomic number 86 – 2 =
STEP 4: Determine the symbol of element
84
84 = Po
STEP 5: Complete the equation
222Rn
86
218Po
84
+
4He
2
84
Po
85
At
86
Rn
4He
2
6
Beta Emission
A beta particle
• is an electron emitted
from the nucleus.
• forms when a neutron
in the nucleus breaks
down.
1n
0e + 1H
0
-1
1
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7
Writing An Equation for a Beta Emitter
STEP 1:
Write an equation for the decay of
42potassium, a beta emitter.
42K
new nucleus + 0e
19
STEP 2:
STEP 3:
STEP 4:
STEP 5
-1
Mass number :
(same)
Atomic number:
19 + 1
Symbol of element: 20
42K
19
42Ca
20
+
= 42
= 20
= Ca
0e
-1
0e
-1
19
K
20
Ca
8
Learning Check
Write the nuclear equation for the beta decay of 60Co.
9
Solution
60Co
60Ni
27
28
+ 0e
1
beta particle
10
Positron Emission
In positron emission,
• a proton is converted to a neutron and a positron.
1p
1n + 0e
1
0
+1
• the mass number of the new nucleus is the same, but
the atomic number decreases by 1.
49Mn
25
49Cr
24
+
0e
+1
11
Gamma Radiation
In gamma radiation,
• energy is emitted from an unstable nucleus,
indicated by m following the mass number.
• the mass number and the atomic number of the
new nucleus are the same.
99mTc
43
99Tc
43
+ 
12
Summary of Types of Radiation
Copyright © 2009 by Pearson Education, Inc.
13
Producing Radioactive Isotopes
Radioactive isotopes are produced
• when a stable nucleus is converted to a radioactive
nucleus by bombarding it with a small particle.
• in a process called transmutation.
Copyright © 2009 by Pearson Education, Inc.
14
Learning Check
What radioactive isotope is produced when a
neutron bombards 59Co?
59Co
27
+
1n
0
? +
4He
2
15
Solution
mass numbers
60
=
60
59Co + 1n
56Mn +
4H e
27
0
27
25
2
=
27
atomic numbers
16