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

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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

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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

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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

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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

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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.