Intro to Nuclear Chemistry

How does a nuclear reactor work?

How does a small mass contained in this bomb cause…… Nuclear Bomb of 1945 known as “fat man”

…this huge nuclear explosion?

Is there radon in your basement?

Notation

Nucleons Protons and Neutrons

The nucleons are bound together by the strong force.

Isotopes Atoms of a given element with: same #protons but different # neutrons

H H H

Isotopes of Carbon

Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus. Henri Becquerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film. His associates were Marie and Pierre Curie. Radioactive Isotopes

Marie Curie: born 1867, in Poland as Maria Sklodowska Lived in France 1898 discovered the elements polonium and radium.

Marie Curie a Pioneer of Radioactivity Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie.Pierre Curie Winner of the sole 1911 Nobel Prize for Chemistry.

3 Main Types of Radioactive Decay Alpha  Beta  Gamma   energy only 

Emission of alpha particles  : helium nuclei two protons and two neutrons charge +2e can travel a few inches through air can be stopped by a sheet of paper, clothing. Alpha Decay

Uranium Thorium

Alpha Decay

Beta Decay Beta particles  : electrons ejected from the nucleus when neutrons decay ( n -> p + +  - ) Beta particles have the same charge and mass as "normal" electrons.

Beta Decay Beta particles  : electrons ejected from the nucleus when neutrons decay n -> p + +  - Beta particles have the same charge and mass as "normal" electrons. Can be stopped by aluminum foil or a block of wood.

Beta Decay

Thorium Protactinium

Gamma radiation  electromagnetic energy that is released. Gamma rays are electromagnetic waves. They have no mass. Gamma radiation has no charge. –Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead. Gamma Decay

Examples of Radioactive Decay Alpha Decay Po  Pb + He Beta Decay p  n + e n  p + e C  N + e Gamma Decay Ni  Ni +  (excited nucleus)

Which is more penetrating? Why?

Introduction to Nuclear Energy Nuclear energy –Energy released by nuclear fission or fusion Nuclear fission –Splitting of an atomic nucleus into two smaller fragments, accompanied by the release of a large amount of energy Nuclear fusion –Joining of two lightweight atomic nuclei into a single, heavier nucleus, accompanied by the release of a large amount of energy

Nuclear Fission U-235 is bombarded with neutrons The nucleus absorbs neutrons It becomes unstable and splits into 2 neutrons 2-3 neutrons are emitted and bombard another U-235 atom Chain reaction

Radioactive Isotope Half-lives

How Electricity is Produced

Nuclear Fission Nuclear Fuel Cycle –processes involved in producing the fuel used in nuclear reactors and in disposing of radioactive (nuclear) wastes

Breeder Nuclear Fission A type of nuclear fission in which non- fissionable U-238 is converted into fissionable Pu-239

Pros and Cons of Nuclear Fission Pros –Less of an immediate environmental impact compared to fossil fuels

Pros and Cons of Nuclear Fission Energy Pros (continued) –Carbon-free source of electricity- no greenhouse gases emitted –May be able to generate H-fuel Cons –Generates radioactive waste –Many steps require fossil fuels (mining and disposal) –Expensive

Fusion Fuel= isotopes of hydrogen

Fusion Way of the future?? –Produces no high-level waste –Fuel is hydrogen (plenty of it!) Problems –It takes very high temperatures (millions of degrees) to make atoms fuse –Confining the plasma after it is formed Scientists have yet to be able to create excess energy from fusion –(more out than they put in)

Part II Nuclear Stability Half-Life

Nuclear Stability Depends on the neutron to proton ratio.

Band of Stability Number of Neutrons, (N) Number of Protons (Z)

What happens to an unstable nucleus? They will undergo decay The type of decay depends on the reason for the instability

What type of decay will happen if the nucleus contains too many neutrons? Beta Decay

Example: C  N + e In N-14 the ratio of neutrons to protons is 1:

Nuclei with atomic number > 83 are radioactive

Radioactive Half-Life (t 1/2 ): The time for half of the radioactive nuclei in a given sample to undergo decay.

Common Radioactive Isotopes Isotope Half-Life Radiation Emitted Carbon-14 5,730 years  Radon days  Uranium x 108 years  Uranium x 109 years 

Radioactive Half-Life After one half life there is 1/2 of original sample left. After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

Graph of Amount of Remaining Nuclei vs Time A=A o e - t A

Example You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. How many grams are left after one half- life? Answer:50 g How many grams are left after two half- lives?

Problem A sample of 3x10 7 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:1.2x10 5 atoms