23.1

•
Nuclear reactions involve the nucleus
•
The nucleus opens, and protons and neutrons are rearranged
•
The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy
• “Normal” Chemical Reactions involve electrons , not protons and neutrons

I.
Nuclear Chemistry
A.
Wilhem Rontgen - discovered x-rays in 1895
B.
Antoine Henri Becquerl - discovered radioactivity
1.
photographic plates and rocks
C.
Marie and Pierre Curie - discovered other radioactive elements
1.
Marie first person to win the Nobel peace prize twice

2.
husband run over by wagon when he was crossing the street
3.
Marie and her children died of radiation poisoning

•
One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of
(1876-1934).
•
She discovered
, the spontaneous disintegration of some elements into smaller pieces.

II.
Radioactivity
A.
Spontaneous break down of an unstable nucleus with the release of particles and rays
B. Mass defect and nuclear stability
1.
the sum of the particles(protons, neutrons and electrons) that make up an atom but does not add up to the mass of an atom
2. the difference between the sum of the masses and the atomic mass is know as the mass defect

•
Some of the mass can be converted into energy
•
Shown by a very famous equation!
E=mc 2
Energy
Mass
Speed of light

C.
Nuclear binding energy
1.
The energy released when a nucleus is formed from nucleons (protons and neutrons)

III Properties of Radioactive elements
1.
They affect photographic film
2.
They produce electric charges in the surrounding air
3. They produce fluorescence with certain compounds a.
fluorescence - makes thing glow

4. Their radiation’s have special physiological effects a. causes mutations in cells - changes in the
DNA of cells causing rapid growth and a change in their function
5.
They undergo radioactive decay a.
Radioactive decay - they emit particles from the nucleus making simpler atoms i.
half-life - the time it takes 1/2 a given amount to decay ii. Half-lives can be from a few seconds to millions of years

is the time that it takes for
1/2 a sample to decompose.
•
The rate of a nuclear transformation depends only on the “reactant” concentration.

For each duration (half-life), one half of the substance decomposes.
For example: Ra-234 has a half-life of 3.6 days
If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5 grams
After 10.8 days > 6.25 grams

Decay of 20.0 mg of 15 O. What remains after 3 half-lives?
After 5 half-lives?

e.g. The half-life of Plutonium -239 is 24110 years.
Of an original mass of 100. g, how much remains after
96440 years first find the number of half-life's
# Half-lifes = 96440 years
24110 Years
= 4 now divide the gram sample in 1/2 four times
100 ===> 50
1
===> 25
2
===>12.5
3
===> 6.25
4

The half-life of thorium -227 is 18.72 days. How many days are required for 3/4 of a given amount to decay
18.72 days 18.72 days
1 ===> 1/2 ===> 1/4
This tells you that you have 1/4 of the original amount left
- therefore - 3/4 of a given amount has decayed you must multiply 18.72 days by 2 == 37.44 days

e.g
Exactly 1/16 of a given amount of protactinium-234 remains after 26.76 hours. What is the half-life of protactinium - 234
First find the number of half-life's
1 ==> 1/2 ===> 1/4 ===> 1/8 ===> 1/16
You must pass threw 4 half life’s
26.76 hours
4 halflife’s
= 6.69 hours/half-life

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 78 hours?

Nuclear Stability
• Certain numbers of neutrons and protons are extra stable
• n or p = 2, 8, 20, 50, 82 and 126
• Like extra stable numbers of electrons in noble gases
(e = 2, 10, 18, 36, 54 and 86)
• Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
• All isotopes of the elements with atomic numbers higher than 83 are radioactive
• All isotopes of Tc and Pm are radioactive
23.2

When the number of protons in a stable nuclei is plotted against the number of neutrons
Band of Stability and
Radioactive Decay

• Out of > 300 stable isotopes:
Z
N Even Odd
Even
157 52
Odd 50 5
19
9
F
31
15
P
2
1
H, 6
3
Li, 10
5
B, 14
7
N, 180
73
Ta

Radioactive decay
1.
types of particles a.
alpha particles, a, contain two protons and two neutrons - can be stopped by a piece of paper - have low penetrating power - may cause burns to the flesh b.
beta particles, b
, high speed electrons, travel at close to the speed of light, c, which is equal to 3 x 10 8 m/sec or 186,000 miles a sec c.
gamma rays, g
, are high energy electromagnetic waves. Most penetrating

• Alpha – a positively charged
(+2) helium isotope we usually ignore the charge because it involves electrons, not protons and neutrons
2
4
He
• Beta – an electron

0
1 e
• Gamma – pure energy; called a ray rather than a particle
0
0 g

• Neutron
• Positron – a positive electron
• Proton – usually referred to as hydrogen-1
• Any other elemental isotope
0
1 n

0
1 e
1
1
H

Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
Z
Element Symbol
A
Z proton
1
1 p or
1
1 H
1 neutron
1
0 n
1
1 0
0
-1 electron e or
-1
0 b
0
-1
0
+1 positron e or
+1
0 b
0
+1
4
2 a particle
He or
4
2 a
4
2
23.1

3.
radioactive decay sequence
238
U 92 ----> a
+
234
Th 90 parent daughter when you have an alpha ejection - you lose 2 protons and 2 neutron
The 92 of uranium is the number of protons and will go to 90 with an alpha ejection - the number of protons in you nucleus determines the element .

therefore - U turns into Th
The 238 of U is the total number of particles in the nucleus = number of protons and neutrons with an alpha ejection - you lose 2 protons and 2 neutrons your mass goes down by 4 or become 234
226
Ra 88 ----> a
+
222
Rn 86

When you have a beta ejection - you have a neutron change to a protons thus causing your number of protons to go up by one. The total number of particles in the nucleus does not change
234
Pa 91 ---->
234
U 92 + beta particle
234
Th 90 ---->
234
Pa 91
+ b

On page 724 do problems 33,34,35,40,41,42,43

212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po.
alpha particle -
4
2
He or
4
2 a
212
84
Po 4
2
He + A
Z
X
212 = 4 + A
84 = 2 + Z
A = 208
Z = 82
212
84
Po 4
2
He + 208
82
Pb
23.1

Nuclear Stability and Radioactive Decay
Beta decay
14
6
C 14 N + 0 b
+ n
7 -1
40
19
K 40 Ca + 0 b
+ n
20 -1
Decrease # of neutrons by 1
Increase # of protons by 1
1
0 n 1 p + 0 b
+ n
1 -1
Positron decay
11
6
C 11 B + 0 b
+ n
5 +1
38
19
K 38 Ar + 0 b
+ n
18 +1
Increase # of neutrons by 1
Decrease # of protons by 1
1
1 p 1 n + 0 b
+ n
0 +1 n and n have A = 0 and Z = 0
23.2

Nuclear Stability and Radioactive Decay
Electron capture decay
37
18
Ar + 0 e 37 Cl + n
-1 17
55
26
Fe + 0 e 55 Mn + n
-1 25
Increase # of neutrons by 1
Decrease # of protons by 1
1
1 p + 0 e 1 n + n
-1 0
Alpha decay
212
84
Po 4
2
He + 208
82
Pb
Decrease # of neutrons by 2
Decrease # of protons by 2
Spontaneous fission
252
98
Cf 2 125
49
In + 2 1
0 n
23.2

What radioactive isotope is produced in the following bombardment of boron?
10 B + 4 He
5 2
? + 1 n
0

What radioactive isotope is produced in the following bombardment of boron?
10 B + 4 He
5 2
13
7
N + 1 n
0

Write the nuclear equation for the beta emitter Co-60.
60 Co
27 -1
0 e + 60 Ni
28

Positron emission -conversion of a proton to a neutron by the emission of a positron
1.
Positron - particle that has the same mass as an electron, but has a positive charge
Gamma radiation - does not change the identity of the element but makes the atom more stable
Transmutation - changing the identity of an element through the release of radioactive particles
Isotopes - atoms of the same element that have different number of neutrons

Geiger-M üller Counter
23.7

• Used to detect radioactive substances

New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron
-- or even a much heavier particle such as 4 He and 11 B.
Reactions using neutrons are called g
because a g ray is usually emitted.
Radioisotopes used in medicine are often made by g reactions.

Example of a g
is production of radioactive 31 P for use in studies of P uptake in the body.
31
15
P + 1
0 n ---> 32
15
P + g

Elements beyond 92 (transuranium) made starting with an g reaction
238
92
U + 1
0 n ---> 239
92
U + g
239
92
U ---> 239
93
Np + 0
-1 b
239
93
Np ---> 239
94
Pu + 0
-1 b

Biological Effects of Radiation
R adiation a bsorbed d ose ( rad )
1 rad = 1 x 10 -5 J/g of material
R oentgen e quivalent for m an ( rem )
1 rem = 1 rad x Q Q uality Factor g
-ray = 1 b
= 1 a
= 20
23.8

Fission is the splitting of atoms
These are usually very large, so that they are not as stable
Fission chain has three general steps:
1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron)
2. Propagation. 236 U fission releases neutrons that initiate other fissions
3. Termination.

Nuclear Fission
235
92
U + 1
0 n 90
38
Sr + 143
54
Xe + 3 1
0 n + Energy
Energy = 3.3 x 10 -11 J per 235 U
= 2.0 x 10 13 J per mole 235 U
= 235 grams = 0.5 lbs
Combustion of 1 ton of coal = 5 x 10 7 J
23.5

Representation of a fission process.

Nuclear Fission
Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.
The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass .
Non-critical
Critical
23.5

•
Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.
• 17% of the world’s energy comes from nuclear.

Diagram of a nuclear power plant

35,000 tons SO
2
4.5 x 10 6 tons CO
2
Nuclear Fission
Annual Waste Production
1,000 MW coal-fired power plant
3.5 x 10 6 ft 3 ash
1,000 MW nuclear power plant
70 ft 3 vitrified waste
23.5

small nuclei combine
2 H + 3 H 4 He + 1 n +
1 1 2 0
Occurs in the sun and other stars
Energy

Fusion
•
Excessive heat can not be contained
• Attempts at “cold” fusion have
FAILED.
• “Hot” fusion is difficult to contain

Radioisotopes in Medicine
• 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
• 24 Na, t
½
= 14.8 hr, b emitter, blood-flow tracer
• 131 I, t
½
= 14.8 hr, b emitter, thyroid gland activity
• 123 I, t
½
= 13.3 hr, g ray emitter, brain imaging
• 18 F, t
½
= 1.8 hr, b  emitter, positron emission tomography
• 99m Tc, t
½
= 6 hr, g ray emitter, imaging agent
Brain images with 123 I-labeled compound
23.7

protection from radiation
A.
Shielding sunscreen, lead apron
B.
distance
inverse square law

Nagasaki Japan
August 9, 1945

Nuclear review
You have a review test
1. A radioactive atom will lose the greatest amount of mass when it emits
1. a neutron' 3.a beta particle ,
2. a proton 4.an alpha particle
2 A sample of iodine-131 contains 10. grams.
Approximately how much iodine-131 will remain after 24 days
(half life -8 days)?
1. 1.25g
2. 2.5 g
3. 5.0 g
4. 10. g
3. What is the moderator in a nuclear reactor?
1. carbon dioxide 3. cadmium
2. boron 4. graphite

4. In the reaction
90
Th 234 ->
91
Pa 234 + X, X represents
1.a neutron 3. an alpha particle
2.a positron 4. a beta particle
5. One of the biggest advantages of a fusion reactor is it
1. produces no radioactive wastes
2. is small in size
3. will never explode
4. has no reaction control problem
6. Which particle has the least mass?
1. alpha particle 2. proton 3. neutron 4. electron

7. A neutron has approximately the same mass as
1. an alpha particle 3. an electron
2. a beta particle 4. a proton
8. When
88
1.
86
Ra 226 emits an alpha particle, the resulting atom is
Rn 2 2 2
Rn 2 2 4 2.
86
3.
88
4.
88
Ra 2 2 2
Ra 2 2 4
9. To make nuclear fission nuclear reactor more efficient, which device is used to slow the speed of neutrons?
1. internal shield 2. external shield 3.control rod 4.moderator
10. If radioactive substance has a half-life of 9 days, what fraction of its original mass would remain after 27 days?
1. 1/8 2. 1/4 3. 1/2 4. 3/4

11.
Which reaction illustrates fusion?
1
. 1
H 2 +
1
2. o n 1 +
13
H 2 ===>
2
He 4
A1 27 ==>
11
Na 24 +
2
He 4
3.
13
4.
7
N
A1 27 +
2
1 4 +
2
He 4 ===>
15
He 4 ===>
1
P 30 +
2
H 1 +
8
O
He 4 +
0
17 n 1
12. Control rods in nuclear reactors are commonly made of boron and cadmium because these two elements have the ability to
1) absorb neutrons
2) emit neutrons
3) decrease the speed of neutrons
4) increase the speed of neutrons
13. If iodine-131 undergoes beta decay, which symbol represents the resulting nucleus?
1.
52
Te 132 2.
54
Xe 131 3.
53
I 130 4.
51
Sb 1 27

14. Which element is formed when
82
1.
84
Po 21 8 2.
80
Hg 2 0 0
Pb 214 emits a beta particle?
3.
83
Bi 213 4.
83
Bi 214
15. Radioactive changes differ from ordinary chemical changes
In that radioactive changes
1.are explosive
2.absorb energy
3.involve changes in the nucleus
4.release energy
16. In the reaction
4
Be 9 + X ---->
6
C 12
1.an alpha particle
+
0 n 1 the X represents
3.an electron
2.a beta particle 4.a proton

18.
Which nuclear equation represents beta decay?
1.
2 .
3.
4.
13
A1 27 +
U 2 3 8
92
6
C 1 4
18
Ar 37 +
2
He 4 -->
-1 e o
-- ->
- ->
-->
15
P 30 + o n 1
90
Th 2 3 4 +
7
N 1 4 +
- 1
37
17
Cl
2 e 0
He 4
19.
An atom of Ra 226 decays to Rn 222 by emitting
1.a proton 3. an alpha particle
2.an electron 4. a beta particle
20.
Heavy water may be used in a nuclear reactor as a
1.moderator 3. shielding
2.fuel 4. control rod
21. When an atom emits a beta particle, the total number of nucleons
1. decreases 2. increases 3. remains the same

22. The radioactive particle or ray with the greatest penetrating power is the
1.alpha particle
2.beta particle
3.gamma ray
4.proton
23.
The major portion of an atom's mass consists of
1) electrons and protons 3) neutrons and positrons
2) electrons and neutrons 4) neutrons and protons
24.
During a chain reaction the number of nuclei reacting per second
1. increases 2. decreases 3. remains the same

25. A radioactive source emits radiation which is deflected as shown in the diagram. .
This radiation could be
1. _
1
2.
2 e o
He 4
3.
1
H 1
4.
n 1
0

26. When
90
Th 234 emits a beta particle (
-1 e 0 ), the element formed is
1. Ra 2. Th 3. Pa 4. U
27. A 40.0 milligram sample of phosphorus -33 decays to
10.0 milligrams in 50.0 days. What is the half-life of phosphorus-33?
1.12.5 days 3.37.5 days
2.25.0 days 4.75.0 days
28. During a fission reaction, which type of particle is captured by a nucleus?
1.deuterium
2.electron
3.neutron
4.proton
29.When two light nuclei combine into a heavier nucleus, the process is called
1.fission
2.fusion
3.beta decay
4.nuclear disintegration

30, An electron has a charge identical to that of
1. a neutron 3. an alpha particle
2.a proton 4. a beta particle
31 . In the reaction
92
U 238 -->
90
Th
1.a beta particle 3. a positron
234
2.a neutron
+ X, X represents
4. an alpha particle

Nuclear Fusion
Fusion Reaction
2
1
H + 2
1
H 3
1
H + 1
1
H
2
1
H + 3
1
H 4
2
He + 1
0 n
6
3
Li + 2
1
H 2 4
2
He
Energy Released
6.3 x 10 -13 J
2.8 x 10 -12 J
3.6 x 10 -12 J
Tokamak magnetic plasma confinement
23.6

1. Conserve mass number (A).
The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.
235
92
U + 1
0 n 138
55
Cs +
96
37
Rb
235 + 1 = 138 + 96 + 2x1
+ 2 1
0 n
2. Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.
235
92
U + 1
0 n 138
55
Cs + 96
37
Rb
92 + 0 = 55 + 37 + 2x0
+ 2 1
0 n
23.1

Radiocarbon Dating
14
7
N + 1
0 n 14
6
C + 1
1
H
14
6
C 14 N + 0 b
+ n
7 -1 t
½
Uranium-238 Dating
238
92
U 206
82
Pb + 8 4
2 a
+ 6 0
-1 b
= 5730 years t
½
= 4.51 x 10 9 years
23.3