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NUCLEAR CHEMISTRY
Henri Becquerel 1896 - Discovers
natural radioactivity
FYI: Historical Perspective
FYI: Historical Perspective
Marie Sklodowska, Polish chemist marries Pierre Curie, French physicist
Marie died from leukemia caused by her exposure to radiation
Pierre was killed while crossing the street when he was hit by a vegetable wagon.
FYI: Historical Perspective
Earnest Rutherford 1899 – Discovers alpha,
beta and gamma radiation
Nuclear Reactions
Involve changes in the composition of nuclei Accompanied by the release of tremendous
amounts of energy
Nuclear Fission
The splitting of a heavy nucleus into lighter nuclei
Nuclear Fusion
The combination of light nuclei to produce a heavier nucleus
Nuclides
Different atomic forms of all elements Most small nuclides have equal # of protons
and neutrons Some nuclides have “magic #’s” of protons
and neutrons and are especially stable
The neutron-to-proton ratio determines the stability of the nucleus
For low atomic #’s:– Equal #’s of protons and neutrons
Above atomic #20:– More neutrons than protons
Nuclei whose neutron-to-proton ratio is unstable undergo radioactive decay by emitting 1 or more particles and/or electromagnetic rays:
Nuclei whose neutron-to-proton ratio is unstable undergo radioactive decay by emitting 1 or more particles and/or electromagnetic rays:
Type/
symbol
Identity Mass (amu)
Charge Penetration
Alpha
Beta
Gamma
Proton
Neutron
Heor 42
eor 01-
00
Hor p 11
11
n10
helium nucleus
electron
high energy radiationproton, H nucleus
neutron
4.0026 2+
0.00055 1-
0 0
1.0073 1+
1.0087 0
low
low-med
high
low-med
very high
Comparing penetrating ability…
Alpha Particle Decay
Example 1: Radium-226 transmutates by alpha decay. Write the nuclear equation that represents this process.
RnRa 22286
22688
or
HeRnRa 42
22286
22688
Beta Particle Decay
Example 2: Write the nuclear equation for the beta-decay of boron-12.
+ +
CB 126
125
or
eCB 01
126
125
Gamma Radiation
Example 3: Write the nuclear equation representing gamma radiation given off by the unstable radionuclide cobalt-60.
CoCo 6027
6027
Nuclear Fission & Fusion
FISSION: a heavy nucleus splits into 2 lighter nuclei
some elements undergo fission spontaneously
some elements can be induced to undergo fission when bombarded with other particles (e.g. neutrons)
FUSION: 2 nuclei combine to form a heavier nucleus
the sun is a tremendous fusion reaction; the major fusion reaction in the sun is thought to be:
both fission & fusion release large amounts of energy (fusion more than fission)
energy!nHeHH 10
42
31
21
The Atomic Bomb (FISSION)
when the nucleus of U-235 splits, 2 isotopes are formed, plus neutrons are emitted
these neutrons collide with other U-235 atoms, causing them to undergo fission; they release neutrons, and so on…
The result - CHAIN REACTION!!
FISSION
CHAIN REACTION!!!
The Atomic Bomb (FISSION)
The Atomic Bomb (FISSION)
CRITICAL MASS
The minimum mass of fissionable material that must be used to sustain a chain reaction
One type of bomb…
Little Boy: U-235 (Hiroshima)
Fat Man: Pu-239 (Nagasaki)
subcritical mass of U-235
subcritical mass of U-235
TNT(dynamite)
Nuclear Reactors (controlled FISSION)
Nuclear Reactors (FISSION)
use subcritical masses of fissionable material CORE: contains fuel pins made of U-235;
interspersed among the pins are control rods control rods: absorb neutrons
– pull rods out of core: fission increases– push rods back into the core: fission decreases
Safety feature: if power is lost, rods will automatically fall into the core and shut the reaction down.
Nuclear Reactors (FISSION)
“The energy produced by breaking down the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine.”
Ernest Rutherford
Nuclear Reactors (FISSION)
Nuclear Power Plants
Nuclear Power Plants
Nuclear Power Plants
TO GENERATE ELECTRICITY:
1) Fission heats up water in vessel and heat is carried away.
2) This heat is used to heat up water in a second system, which turns into steam.
3) Steam turns turbine of a generator.
4) Generator makes electricity.
PROS OF NUCLEAR ENERGY:
no air pollution enormous amt. of energy released alternative to using our rapidly decreasing
fossil fuels
CONS OF NUCLEAR ENERGY
containers for waste products may erode or break
thermal pollution (heated water returned to rivers, etc.)
potential theft of fuel (Pu-239) for use in weapons
Controlled Nuclear FUSION
PROS:– A very abundant supply of energy world wide.– Environmentally clean– No creation of weapon materials– No chance of runaway reactions leading to
accidents
CONS:– It doesn’t work; at least not yet…
Nuclear Fusion
"Every time you look up at the sky, every one of those points of light is a reminder that fusion power is extractable from hydrogen and other light elements, and it is an everyday reality throughout the Milky Way Galaxy."
Carl Sagan, Spitzer Lecture, October 1991
Nuclear Fusion
Obstacles…– HOT – plasma at least 100 million C– High density plasma– Containment of plasma– Confinement time
Rates of Decay & Half Life
Radionuclides have different stabilities and decay at different rates.
Integrated Rate Equation
where… A = the amt. of decaying sample remaining at
some time, t Ao= the amt. of sample present at the beginning k = rate constant; different for each radionuclide t = time
303.2kt
AA
log
Integrated Rate Equation
OR…
where… N = # of disintegrations per unit of time; relative activity No= original activity
303.2kt
NN
log
HALF-LIFE= the amount of time required for half of the original sample to decay
Half Life
0
20
40
60
80
100
120
0 5 10 15 20
Time
Am
ou
nt
HALF-LIFE= the amount of time required for half of the original sample to decay
0
50
100
150
200
250
0 5 10 15 20
Amount
Tim
e
Parent
Daughter
HALF-LIFE
Half-life = the amount of time required for half of the original sample to decay
k693.0
k2 ln
t2
1
21t
0.693k
Example: Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. How much of a 3.42 g of cobalt-60 remains after 30.0 years?
5.27 years0.693
k -1yr1315.0
303.2kt
AA
log
303.2
)(30.0yrs)(0.1315yr
A
g42.3log
-1
713.1A
g42.3log
How do you solve for A???
Take the ANTILOG (10x) of both sides.
Example: Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. How much of a 3.42 g of cobalt-60 remains after 30.0 years?
713.110A
g42.3
6.51
g42.3A
A6.51g42.3
g0.0662A
713.1Ag42.3
log1010 OR 713.1antilog
A
g42.3logantilog
Uses of Radionuclides
Radiocarbon dating: the ages of specimens of organic origin can be estimated by measuring the amount of cabon-14 in a sample.
Example: A piece of wood taken from a cave dwelling in New Mexico is found to have a carbon-14 activity (per gram of carbon) only 0.636 times that of wood today. Estimate the age of the wood. (The half-life of carbon-14 is 5730 years.)
.636NN
years57300.693
k -1yr00012094.0
303.2kt
NN
log
303.2
)(t)4yr(0.0001209
.636log
-1
NN
)(t)yr(5.25x10.636
1log 1-5-
Example: A piece of wood taken from a cave dwelling in New Mexico is found to have a carbon-14 activity (per gram of carbon) only 0.636 times that of wood today. Estimate the age of the wood. (The half-life of carbon-14 is 5730 years.)
)(t)yr(5.25x10.636
1log 1-5-
)(t)yr(5.25x1019654.0 -1-5
t=3744 yrs = 3740 yrs
Uses of Radionuclides
***NOTE: Objects older than 50,000 years have too little activity to be dated accurately using carbon dating; instead the following methods are used:
– Potassium-40 decays to argon-40: half-life = 1.3 x 109 years
– Uranium-238 decays to lead-206: half-life = 4.51 x 109 years
Example: A sample of uranium ore is found to contain 4.64 mg of uranium-238 and 1.22 mg of lead-206. Estimate the age of the ore.
Pb g/mol 206
U g/mol 238 x Pb mg 22.1 decayed have 238-U mg 41.1
U mg 6.05 mg 4.64 mg 14.1A
yrs10 x 4.51
0.693k
9 -1-10 yr10 x 1.54
Example: A sample of uranium ore is found to contain 4.64 mg of uranium-238 and 1.22 mg of lead-206. Estimate the age of the ore.
303.2kt
AA
log
yearsbillion 73.1t
303.2
)(t)yr10(1.54
mg64.4
mg05.6log
-1-10
