Transcript Photo chapter opener 21 Subatomic particle tracks in a bubble

The Nucleus:
A Chemist’s View
Nuclear Stability and Radioactive
Chapter 19 Lesson 1
Nuclide
• A nuclide is a type of atom characterized by its
proton number, neutron number and its energy
condition.
• Nuclides with identical proton number but
differing neutron number are called isotopes.
• Conditions with a life of less than 10-10s are
called excited conditions of a nuclide.
• At present, more than 2,770 different nuclides
are known, distributed over the 113 currently
known elements, only 279 are stable with
respect to radioactive decay.
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A
Z
X
A : the sum of the neutrons and protons
Z : atomic numbers
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Radioactive Stability
• Nuclides with 84 or more protons are unstable.
• Light nuclides are stable when Z equals A – Z
(neutron/proton ratio is 1).
• For heavier elements the neutron/proton ratio
required for stability is greater than 1 and
increases with Z.
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Radioactive Stability
• Certain combinations of protons and neutrons
seem to confer special stability.
 Even numbers of protons and neutrons are
more often stable than those with odd
numbers.
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Known nuclides
• Light nuclides are
stable when (A-Z)/Z
ratio is 1.
• For heavier elements
for stability, (A-Z)/Z
ratio is greater than 1
and increases with Z.
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• Magic numbers: 2, 8, 20, 28, 50, 82, 126
• Specific numbers of protons or neutrons
produce especially stable nuclides.
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Types of Radioactive Decay
a-particle production
The common modes of decay
238
92
U He(a )
4
2
234
90
Th  He(a )
230
90
4
2
Th
226
88
Ra
Spontaneous fission
(a)The splitting of a heavy nuclide into two
lighter nuclides with similar mass numbers.
(b)Slow rate for most nuclides
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Types of Radioactive Decay
b-particle production
The common modes of decay
Th  Pa  e( b )
234
90
131
53
234
91
0
1
I Xe  e( b )
131
54
0
1
(a)The net effect of b-particle production is to
change a neutron to a proton.
(b)The nuclides lie above the zone of stability.
(c)The ratios of neutron/proton are too high.
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Types of Radioactive Decay
gray production
238
92
U He 
4
2
Th  2 γ
234
90
0
0
(a) high-energy photon
(b) g-ray production accompanies unclear
decays and particle reaction.
(c)The emission of g rays is one way a nucleus
with excess energy can relax to its ground state.
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Types of Radioactive Decay
positron production
22
11
Na  Ne e
22
10
0
1
(a)The net effect of this process is to change a e a
proton to a neutron.
(b)Higher neutron/proton ratio
(c)Nuclides lie below the zone of stability.
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Antiparticle
0
1
e  e 2 γ
0
1
0
0
Matter-antimatter collisions, is called annihilation.
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13
Types of Radioactive Decay
• Electron capture:
Inner-orbital electron
Concept Check
Which of the following produces a b particle?
a)
68
31
b)
62
29
c)
212
87
d)
129
51
Ga +
0
1
Cu 
Fr 
Sb 
e 
0
1
4
2
e+
He +
0
1
e+
68
30
62
28
Zn
electron capture
Ni
positron
208
85
At
alpha particle
Te
beta particle
129
52
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Decay series
• Often a radioactive
nucleus cannot reach a
stable state through a
single decay process.
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The Kinetic of Radioactive
Decay
• First order reaction
dN
N
Rate  
 kN  ln(
)  kt  N  N 0 e  kt
dt
N0
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Half-Life
• Time required for the number of nuclides to
reach half the original value.
t1/ 2
ln  2  0.693
=
=
k
k
Nuclear Particles
Half-Life of Nuclear Decay
Exercise
A first order reaction is 35% complete at the
end of 55 minutes. What is the value of k?
k = 7.8 x 10-3 min-1
Nuclear Transformation
• The change of one element into another.
27
13
249
98
Al + He 
4
2
30
15
1
0
P+ n
263
Cf + 188 O  106
Sg + 4 01 n
The decay of a 10 g sample
of Sr-90
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Change in the amount of Mo
with time
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Nuclear Transformations
• The conversion of one element into another
Observatio n from Rutherford
14
7
N  He  O H
4
2
17
8
1
1
Observatio n from Irene Curie
27
13
Al He  P n
4
2
30
15
1
0
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Experiments for Nuclear
Transformations cyclotron
Particle accelerators
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Diagram of a linear accelerator
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Detection of Radioactivity
Geiger-Muller counter

Ar(g) 
 Ar (g)  e
high energy particle

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