Download 1 Intro to Nuclear Chemistry

Intro to Nuclear Chemistry
Honors Chemistry
http://www.chem.orst.edu/graduate/pics/Reactor.jpg
How does a nuclear reactor work?
http://www.lanl.gov/science/1663/images/reactor.jpg
How does a small mass contained
in this bomb cause……
• Nuclear
Bomb of
1945
known as
“fat man”
http://www.travisairmuseum.org/assets/images/fatman.jpg
…this huge nuclear explosion?
http://library.thinkquest.org/06aug/01200/Graphics/705px-Nuclear_fireball.jpg
Is there radon in your basement?
http://a.abcnews.com/images/Blotter/abc_1radon_ad_070625_ssh.jpg
Notation Review
Some terms
• Nucleons
• Radioactivity
• Radioisotopes
H
H
http://education.jlab.org/glossary/isotope.html
H
Isotopes of Carbon
•
•
•
•
C-11 unstable
C-12, C-13 stable
C-14, C-15, C-16 unstable
Unstable or radioactive isotopes
Discovery of Radioactivity
• Henri Becquerel 1896 accidentally
observed radioactivity of uranium salts
• His associates were Marie and Pierre
Curie.
Marie Curie: born 1867, in Poland
as Maria Sklodowska
• Lived in France
• 1898 discovered the
elements polonium and
radium.
http://www.radiochemistry.org/nuclearmedicine/pioneers/images/mariecurie.jpg
Marie Curie a Pioneer of
Radioactivity
• Winner of 1903
Nobel Prize for
Physics with Henri
Becquerel and her
husband, Pierre
Curie.
• Winner of the sole
1911 Nobel Prize
for Chemistry.
Types of Radiation
• Alpha
a
• Beta
b
• Gamma g
Alpha Decay
Emission of alpha particles a :
•
•
•
•
•
•
Helium nuclei
Two protons and two neutrons
Charge +2
Mass 4 amu
Relatively slow
Can be stopped by a sheet of
paper, clothing.
Alpha Decay
Uranium
Thorium
Alpha Decay
http://education.jlab.org/glossary/alphadecay.gif
Beta Decay
• Beta particles have the same charge and
mass as "normal" electrons.
• High velocity
• Can be stopped by aluminum foil or a
block of wood.
Beta Decay
• Electrons ejected from the nucleus
• Atomic number increases by 1
• Mass remains the same
Beta Decay
Thorium
Protactinium
Beta Decay
Beta decay
• A neutron is “transformed” into a proton.
• n0 → p+ + b-
Gamma Decay
•
•
•
•
Gamma radiation g
Gamma rays are electromagnetic waves.
No mass.
No charge.
– Most Penetrating, can be stopped by 1m thick
concrete or a several cm thick sheet of lead.
Gamma radiation
• 28Ni61  28Ni61 + g
• No change in mass or number
• Change in nuclear stability
More Examples of Radioactive
Decay
Alpha decay:
230  ?
Th
90
230  He4 +
Th
90
2
226
Ra
88
Beta decay:
27  ?
Mg
12
27 
0 +
Mg
e
12
-1
27
Al
13
Which is more penetrating? Why?
Other Particles
•
•
•
•
•
Positron (or beta positive)
11 
0 +
11
C
e
B
6
+1
5
Atomic number decreases
p+ → n0 + b+
14  ?
O
8
• 8O14  +1e0 + 7N14
• Electron Capture (K-capture )
• Large nuclei
• 37Rb81 + -1e0 → 36Kr81
• p+ → n0 + b+
Additional Reactions
• Induced radioactivity
• Fission
• Fusion
STABILITY AND NUCLEAR
REACTIONS
Nuclear Stability
•
Depends on a number of factors
including:
1. Binding energy
2. Size of the nucleus
3. Neutron to proton ratio
Band of Stability
Number of Neutrons, (N)
Number of Protons (Z)
What happens to unstable nuclei?
• They undergo decay
• The type of decay depends on the reason
for the instability
Predicting the Decay
• Guidelines based on observations
Large Nuclei
• Nuclides with atomic number > 83 are
always unstable or radioactive
How do they become more stable?
• Losing mass
• Usually by alpha decay
What type of decay will happen if
the nucleus contains too many
neutrons?
• Beta Decay
Example:
14
6
C 
14
N
7
+
0
e
-1
In N-14 the ratio of neutrons to protons is 1:1
What type of decay occurs if the
nucleus contains too many
protons?
• Positron (beta positive) emission
• K-capture (electron capture)
Band of Stability
Number of Neutrons, (N)
Number of Protons (Z)
Other interesting facts
• Nuclei with even numbers of neutrons and
protons tend to be stable
• Nuclei with odd numbers of both protons
and neutrons are likely to be radioactive
• Only four stable isotopes with odd
numbers of protons and neutrons are
known in nature:
• H-1
• Li-6
• B-10
• N-14
HALF-LIFE
Radioactive Half-Life (t1/2 ):
• The time for half of the radioactive nuclei
in a given sample to undergo decay.
Graph of Amount of Remaining
Nuclei vs Time
A=Aoe-lt
A
Common Radioactive Isotopes
Isotope
Half-Life
Radiation
Emitted
Carbon-14
5,730 years
b, g
Radon-222
3.8 days
a
Uranium-235
7.0 x 108 years
a, g
Uranium-238
4.46 x 109 years
a
Radioactive Half-Life
How many grams of o 2.00 g sample of C14 will remain in an organic sample after
28,650 years?
The half-life C-14 = 5730 years.
time(yrs)
0
5700
11,460
17,190
22, 920
28,650
# cycles Amount remaining(g)
0
2.00
1
1.00
2
0.50
3
0.25
4
0.125
5
0.0625
Time
0
5730
11,460
17,190
22,920
28,650
#cycles
0
1
2
3
4
5
amount
2.00
1.00
0.5
0.25
0.125
0.0625
fraction left
1
½
¼
1/8
1/16
1/32
Half-life Equation
Ar = Ao x 1/2n
n= T/t1/2
T = time elapsed
T1/2 = half-life
Problem 1
• Iron-59 has a half-life of 45 days. How
much of a 4.00g sample will remain after
135 days?
• Answer = 0.500g
Problem 2
• A sample of 3x107 Radon atoms are
trapped in a basement that is sealed. The
half-life of Radon is 3.83 days. How many
radon atoms are left after 31 days?
•
answer:1. x105 atoms
Problem 3
• A piece of charcoal found at an
archeological site originally contained
60.00 g of C-14. Today it contains 3.750 g.
How old is it? T1/2 = 5730. years?
• Answer = 22,920 years
Problem 4
• Strontium-90 is found in nuclear fall-out.
How long will it take for a mole of it (90.0g)
to decay to a safe level of 0.150 g?
T1/2=28.1 yrs
• Answer = 259 yrs