Transcript CH 22 Powerpoint Nuclear

Nuclear Chemistry
23.1
Nuclear Reactions vs.
Normal Chemical Changes
• 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.
C.
photographic plates and rocks
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
Radioactivity
• One of the pieces of evidence for the
fact that atoms are made of smaller
particles came from the work of
Marie Curie (1876-1934).
• She discovered radioactivity,
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
Mass Defect
• Some of the mass can be converted into
energy
• Shown by a very famous equation!
E=mc2
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.
5.
causes mutations in cells - changes in the
DNA of cells causing rapid growth and a
change in their function
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
Half-Life
• HALF-LIFE 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.
Kinetics of Radioactive Decay
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
Half-Life
Decay of 20.0 mg of 15O. 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 ===> 25
1
2
===>12.5 ===> 6.25
3
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 = 6.69 hours/half-life
4 half-life’s
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
Stability
of Nuclei
• Out of > 300 stable isotopes:
N
Even
Odd
Even
157
52
Odd
50
5
Z
19
9F
31 P
15
2
1
H, 63Li, 105B, 147N, 18073Ta
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 108 m/sec or 186,000 miles a sec
c.
gamma rays, g, are high energy electromagnetic
waves. Most penetrating
Types of Radiation
• Alpha – a positively charged 4
(+2) helium isotope - we usually 2
He
ignore the charge because it involves electrons,
not protons and neutrons
•Beta – an electron
•Gamma – pure energy;
called a ray rather than a
particle
0
1
e
g
0
0
Other Nuclear Particles
• Neutron
1
0
n
• Positron – a positive
electron
0
1
e
•Proton – usually referred to
as hydrogen-1
•Any other elemental isotope
1
1
H
Penetrating Ability
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
ZX
Element Symbol
proton
1p
1H
or
1
1
neutron
1n
0
electron
0b
0e
or
-1
-1
positron
0b
0e
or
+1
+1
a particle
4He
4a
or
2
2
A
1
1
0
0
4
Z
1
0
-1
+1
2
23.1
3.
radioactive decay sequence
92 ----> a +
90
U
Th
238
234
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
88 ----> a +
Ra
226
86
Rn
222
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
91 ---->
92 + beta particle
Pa
U
234
234
90 ----> Pa91 + b
Th
234
234
On page 724 do problems 33,34,35,40,41,42,43
212Po
decays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.
4
alpha particle - 42He or 2a
212Po
84
4He
2
+ AZX
212 = 4 + A
A = 208
84 = 2 + Z
Z = 82
212Po
84
4He
2
+ 208
82Pb
23.1
Nuclear Stability and Radioactive Decay
Beta decay
+-10b + n
14C
6
14N
7
40K
19
40Ca
20
Decrease # of neutrons by 1
+ -10b + n
1n
0
Increase # of protons by 1
1p
1
+ -10b + n
Positron decay
++10b + n
Increase # of neutrons by 1
++10b + n
Decrease # of protons by 1
11C
6
11B
5
38
19K
38Ar
18
1p
1
1n
0
++10b + n
n and n have A = 0 and Z = 0
23.2
Nuclear Stability and Radioactive Decay
Electron capture decay
+n
37Ar
18
+ -10e
37Cl
17
55Fe
26
+ -10e
55Mn
25
1p
1
Increase # of neutrons by 1
+n
Decrease # of protons by 1
+ -10e
1n
0
+n
Alpha decay
212Po
84
4He
2
+ 208
82Pb
Decrease # of neutrons by 2
Decrease # of protons by 2
Spontaneous fission
252Cf
98
1n
2125
In
+
2
49
0
23.2
What radioactive isotope is produced in the
following bombardment of boron?
10B
5
+ 4He
2
? +
1n
0
What radioactive isotope is produced in the
following bombardment of boron?
10B
5
+ 4He
2
13N
7
+
1n
0
Write Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60.
60Co
27
0e
-1
+
60Ni
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-Müller Counter
23.7
Geiger Counter
• Used to detect radioactive substances
Artificial Nuclear Reactions
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 4He
and 11B.
Reactions using neutrons are called
g reactions because a g ray is usually
emitted.
Radioisotopes used in medicine are often made by
g reactions.
Artificial Nuclear Reactions
Example of a g
reaction is production
of radioactive 31P for use in studies of P
uptake in the body.
31
15P +
1
0n --->
32
15P
+ g
Transuranium Elements
Elements beyond 92 (transuranium) made
starting with an g reaction
1 n
0
92U +
239
92U
--->
239
0 b
Np
+
93
-1
239 Np
93
--->
239
94Pu +
--->
239
+ g
238
92U
0
-1b
Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q
Quality Factor
g-ray = 1
b=1
a = 20
23.8
Effects of Radiation
Nuclear Fission
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., 235U + neutron)
2. Propagation.
236U
fission releases neutrons that
initiate other fissions
3. Termination.
Nuclear Fission
Nuclear Fission
235U
92
+ 01n
90Sr
38
1n + Energy
+ 143
Xe
+
3
0
54
Energy = 3.3 x 10-11J per 235U
= 2.0 x 1013 J per mole 235U
= 235 grams = 0.5 lbs
Combustion of 1 ton of coal = 5 x 107 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
Nuclear Fission & POWER
• 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
Nuclear Fission
Annual Waste Production
35,000 tons SO2
4.5 x 106 tons CO2
3.5 x 106
ft3 ash
1,000 MW coal-fired
power plant
70 ft3
vitrified
waste
1,000 MW nuclear
power plant
23.5
Nuclear Fusion
Fusion
small nuclei combine
2H
1
+
3H
4He
1
2
+ 1n +
0
Occurs in the sun and other stars
Energy
Nuclear Fusion
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
•
24Na,
•
131I,
t½ = 14.8 hr, b emitter, thyroid gland activity
•
123I,
t½ = 13.3 hr, gray emitter, brain imaging
•
18F,
t½ = 1.8 hr, b emitter, positron emission tomography
•
99mTc,
t½ = 14.8 hr, b emitter, blood-flow tracer
t½ = 6 hr, gray emitter, imaging agent
Brain images
with 123I-labeled
compound
23.7
protection from radiation
A.
Shielding
sunscreen, lead apron
B.
distance
- inverse square law
Nagasaki Japan
August 9, 1945
1.
Nuclearreview
You
have
a
review
test
A radioactive atom will lose the greatest amount of mass
when it emits
1. a neutron'
2. a proton
2
3.a beta particle ,
4.an alpha particle
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
3. 5.0 g
2. 2.5 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 90Th234 -> 91Pa234 + 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 88Ra226 emits an alpha particle, the resulting atom is
1. 86 Rn 2 2 2
2. 86 Rn 2 2 4
3. 88 Ra 2 2 2
4. 88 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 H2 + 1 H2
===> 2He4
2. on1 + 13A127
==> 11Na24 + 2He4
3. 13A127 + 2He4
===> 15P30 + 2 He4 + 0 n1
4. 7 N1 4 + 2 He4
===> 1 H1 + 8O17
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. 52Te132
2. 54Xe131
3. 53I130
4. 51 Sb1 27
14. Which element is formed when 82Pb214 emits a beta particle?
1. 84 Po 21 8
2. 80 Hg 2 0 0
3. 83Bi213
4. 83Bi214
15. Radioactive changes differ from ordinary chemical changes
In that radioactive changes
1.are explosive
3.involve changes in the nucleus
2.absorb energy
4.release energy
16. In the reaction
9 + X ----> C12 + n1 the X represents
Be
0
4
6
1.an alpha particle
3.an electron
2.a beta particle
4.a proton
18.
Which nuclear equation represents beta decay?
30 + n1
1. 13A127 + 2He4 -->
15P
o
2 . 92 U2 3 8
-- -> 90 Th2 3 4 + 2 He4
14+
0
3. 6 C1 4
- ->
N
e
7
-1
37
o
37
4. 18Ar + -1 e -->
17Cl
19.
An atom of Ra226 decays to Rn222 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
3.gamma ray
2.beta particle
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 show
This radiation could be
1. _1eo
2. 2 He4
3. 1 H1
4. 0 n1
26. When 90Th234 emits a beta particle ( -1 e0), 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
3.neutron
2.electron
4.proton
29.When two light nuclei combine into a heavier nucleus,
the process is called
1.fission
3.beta decay
2.fusion
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 92U238 --> 90Th234 + X, X represents
1.a beta particle 3. a positron
2.a neutron
4. an alpha particle
Nuclear Fusion
Fusion Reaction
2
2
3
1
1 H + 1H
1 H + 1H
2H
1
+ 13H
6Li
3
+ 12H
4He
2
2
+ 10n
4He
2
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
Balancing Nuclear Equations
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
+ 10n
138
55 Cs
+
96
37 Rb
+ 2 10n
235 + 1 = 138 + 96 + 2x1
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
+ 10n
138
55 Cs
+
96
37 Rb
92 + 0 = 55 + 37 + 2x0
+ 2 10n
23.1
Radiocarbon Dating
14N
7
+ 01n
14C
6
14C
6
14N
7
+ 11H
+ -10b + n
t½ = 5730 years
Uranium-238 Dating
238U
92
206Pb
82
+ 8 24a + 6-10b
t½ = 4.51 x 109 years
23.3