2. Nuclear Chemistry
Nuclear chemistry is the subfield of chemistry dealing
with radioactivity, nuclear processes and nuclear properties.
We will discuss the following sub-fields
Radiochemistry
Nuclear Power
Nuclear Reactions
Applications
3. Radiochemistry
Emission of subatomic particles or high-energy electromagnetic
radiation by nuclei
Such atoms/isotopes said to be radioactive
It is a spontaneous phenomena.
We refer to these as radionuclide's.
4. Discovery Of Radioactivity
Discovered in 1896 by Henry Becquerel.
Marie Curie & hubby discovered two new elements,
both of which emitted uranic rays
Polonium & Radium
5. Types of Radioactive Decay
Rutherford and Curie found that emissions produced by nuclei
Different types:
Alpha decay
Beta decay
Gamma ray emission
6. 6
Alpha decay
Has largest ionizing power
Ability to ionize molecules & atoms due to largeness of -particle
But has lowest penetrating power
Ability to penetrate matter
Skin, even air, protect against -particle radiation
7. 7
Beta decay
Lower ionizing power than alpha particle
But higher penetration power
Requires sheet of metal or thick piece of wood to arrest
penetration
more damage outside of body, but less in (alpha particle is
opposite)
8. 8
Gamma ray emission
Electromagnetic radiation
High-energy photons
0
0
No charge, no mass
Usually emitted in conjunction with other radiation types
Lowest ionizing power, highest penetrating power requires
several inches lead shielding
12. Predicting the mode of decay
1. High n/p ratio (too many neutrons; lie above band of stability) --
- undergoes beta decay
2. Low n/p ratio (neutron poor; lie below band of stability) ---
positron decay or electron capture
3. Heavy nuclides ( Z > 83) --- alpha decay
13. Nuclear Transmutations
Transforming one element into another
In 1919, Rutherford bombarded N-17 to make O-17
The Joliot-Curie’s bombarded Al-27 to form P-30
In ’30’s, devices needed that could accelerate particles to high
velocities:
1. linear accelerator
2. cyclotron
14. Trans-uranium elements
- Element with atomic numbers above 92
- Produced using artificial transmutations, either by:
a. alpha bombardment
b. neutron bombardment
c. bombardment from other nuclei
Examples:
a.
b.
4He
2
Pu239
94
+ Cm242
96
1n
0
+
1n
0
U238
92
+ U239
92
15. Nuclear Energy
There is a tremendous amount of energy stored in nuclei.
Einstein’s famous equation, E = mc2, relates directly to the
calculation of this energy.
In the types of chemical reactions we have encountered
previously, the amount of mass converted to energy has been
minimal.
However, these energies are many thousands of times greater in
nuclear reactions.
16. Nuclear Fission
Nuclear fission is the type of reaction carried out in nuclear
reactors
Bombardment of the radioactive nuclide with a neutron starts the
process.
Neutrons released in the transmutation strike other nuclei, causing
their decay and the production of more neutrons
17. Nuclear Fusion
H-bonds utilize fusion (but needs high-temps to react because both
positively charged)
As does the sun: 2
1H + 3
1H 4
2He + 1
0n
10 x more energy/gram than fission
Fusion would be a superior method of generating power.
The good news is that the products of the reaction are not
radioactive.
The bad news is that in order to achieve fusion, the material
must be in the plasma state at several million Kelvin's.
19. 19
More facts
20 rem decreased white
blood cell count after
instantaneous exposure
100-400 rem vomiting,
diarrhea, lesions, cancer-risk
increase
500-1000 death w/in 2
months
1000-2000 death w/in 2
weeks
Above 2000 death w/in
hours
20. 20
Radiometric dating: radiocarbon
dating
Devised in 1949 by Libby at University of
Chicago
Age of artifacts, etc., revealed by
presence of C-14
C-14 formed in upper atmosphere via:
14
7N + 1
0n 14
6C + 1
1H
C-14 then decays back to N by -emission:
Taken up by plants via 14CO2 & later
incorporated in animals
Living organisms have same ratio of C-
14:C-12
Once dead, no longer incorporating C-14
ratio decreases
24. Chemistry In Action: Food Irradiation
Dosage Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in
pork. Kills or prevents insects from reproducing in grains, fruits, and
vegetables.
100 – 1000 kilorads
Delays spoilage of meat poultry and fish. Reduces salmonella. Extends
shelf life of some fruit.
1000 to 10,000 kilorads
Sterilizes meat, poultry and fish. Kills insects and microorganisms in
spices and seasoning.