Intro to Nuclear Chemistry/Nuclear Decay

How does a nuclear reactor work? http://www.lanl.gov/science/1663/images/reactor.jpg

How does a small mass contained in this bomb cause…… Nuclear Bomb of 1945 known as “fat man” http://www.travisairmuseum.org/assets/images/fatman.jpg

…this huge nuclear explosion? http://library.thinkquest.org/06aug/01200/Graphics/705px-Nuclear_fireball.jpg

Is there radon in your basement? http://a.abcnews.com/images/Blotter/abc_1radon_ad_070625_ssh.jpg

Notation

Nucleons Protons and Neutrons

The nucleons are bound together by the strong force.

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

H H H http://education.jlab.org/glossary/isotope.html

Isotopes of Carbon

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

Marie Curie: born 1867, in Poland as Maria Sklodowska Lived in France 1898 discovered the elements polonium and radium. http://www.radiochemistry.org/nuclearmedicine/pioneers/images/mariecurie.jpg

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

3 Main Types of Radioactive Decay Alpha a Beta b Gamma g

Nuclear Chemistry Nuclear chemistry involves a change to an atoms nucleus. Nuclear reactions are accompanied by tremendous energy changes as an unstable isotope spontaneously undergoes changes. Some types of nuclear decay include: Alpha decay: An atom emits an alpha particle, thus the nucleus loses 2 protons and 2 neutrons. The atomic number decreases by 2, and the mass number decreases by 4. Beta decay: An atom emits a beta particle in the form of an electron when a neutron is changed into a proton. The atomic number increases by 1 while the mass number remains the same. Gamma decay: Usually accompanies alpha or beta emissions as an energy release. Gamma rays cause no change in atomic or mass number since it is a form of energy only.

Alpha Decay Emission of alpha particles a : 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 http://education.jlab.org/glossary/alphadecay.gif

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

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

Beta Decay

Beta Decay Thorium Protactinium

Gamma Decay Gamma radiation g : 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.

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

Which is more penetrating? Why?

Nuclear Stability Half-Life 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 1:1 14 C  N + e In N-14 the ratio of neutrons to protons is 1:1 6 -1 7

Nuclei with atomic number > 83 are radioactive

Radioactive Half-Life (t1/2 ): 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 b, g Radon-222 3.8 days a Uranium-235 7.0 x 10^8 years a, g Uranium-238 4.46 x 10^9 years a

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=Aoe-lt 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? How many grams are left after two half-lives?

Problem A sample of 3x107 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:1.2x105 atoms