Date post: | 22-Dec-2014 |
Category: |
Education |
Upload: | nofal-umair |
View: | 100 times |
Download: | 2 times |
NUCLEAR CHEMISTRYPresenter
Nofal Umair
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
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.
Discovery Of Radioactivity
Discovered in 1896 by Henry Becquerel. Marie Curie & hubby discovered two new
elements, both of which emitted uranic rays
Polonium & Radium
Types of Radioactive Decay
Rutherford and Curie found that emissions produced by nuclei
Different types: Alpha decay Beta decay Gamma ray emission
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
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
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
Figure 5.3: Ionizing power and penetrating power: an analogy.
© 2003 John Wiley and Sons Publishers
11
Radioactive decay series
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
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
Trans-uranium elements
- Element with atomic numbers above 92- Produced using artificial transmutations,
either by:a. alpha bombardmentb. neutron bombardmentc. bombardment from other nuclei Examples:
a.
b.
4He2Pu239
94 + Cm24296
1n0
+
1n0
U23892 + U239
92
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.
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
Nuclear Fusion
H-bonds utilize fusion (but needs high-temps to react because both positively charged)
As does the sun: 21H + 3
1H 42He + 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.
A flare ejected from the surface of the sun.
© 2003 John Wiley and Sons Publishers
Courtesy NASA
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
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 + 10n 14
6C + 11H
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
Applications
Medicine Chemotherapy Power pacemakers Diagnostic tracers
Agriculture Irradiate food Pesticide
Energy Fission Fusion
Images of human lungs obtained from a γ-ray scan.
© 2003 John Wiley and Sons Publishers
Courtesy CNRI/Phototake
A cancer patient receiving radiation therapy.
© 2003 John Wiley and Sons Publishers
Courtesy Kelley Culpepper/Transparencies, Inc.
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.