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Discovery of Radioactivity http://www.radiation-scott.org/timeline/table.htm• Radioactivity was first observed in ______by
the French scientist Henri Becquerel. He discovered that Uranium salts would “fog up” a photographic plate.
• In 1898, Marie Curie and her husband Pierre coined the term radiation and radioactivity and went on to discover several new elements: ___________ and ________.
• She went on to win 2 Nobel Prizes: 1903 in Physics & 1911 in Chemistry, but she died of ________ caused by radiation exposure in 1934 at the age of 66.
• Her husband died in 1906 after getting hit by a horse and buggy.
Marie Curie
1896
Polonium Radium
cancer
Nuclear Reactions• Nuclear reactions involve the _________ instead of the
___________ as in a regular chemical reaction.• The instability of the nucleus of a radioactive element
causes the # of protons and neutrons to change.• Some of the ______ can be converted into a
tremendous amount of energy shown by a very famous equation:
E=mc2
Energy = (mass)x(speed of light)2 c= 3.0 x 108 m/s
nucleuselectrons
mass
Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.
BE + 19F 9 1p + 10 1n9 1 0
Mass defect (∆m) = 9 x (p mass) + 10 x (n mass) – 19F mass
E = mc2E = mc2
∆m (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984
∆m = 0.1587 amu = 2.636x10-28 kg
BE = 2.636x10-28 kg x (3x108 m/sec)2 = 2.37 x 10-11J
23.2
When this atom forms, a tiny When this atom forms, a tiny amount of matter is converted to amount of matter is converted to energy energy
Energy = mass(kg) x [speed of light ]2
Speed of light = c = 300,000,000 m/sec Speed of light = c = 300,000,000 m/sec
This may look small, but it means that when 19 g of flourine forms there is 14,000,000,000 kJ of energy released. That’s the same as burning 285,000 tons of coal!
2.0141 kg
Nuclear Reactions
1.0078 kg 3.0160 kg
3.0160 – (2.0141 + 1.0078) = 0.0059kg
E=mc2
E= 0.0059 x (3.0 x 108)2 = 5.31 x 1014 Joules
What makes a nucleus stable or unstable?• It depends on the p+
and no ratio.
• Z= Atomic # = p+
• A = Mass # = no + p+
• “Nucleons” are just the particles in the nucleus.
•
• ex) 2 He
AZ
Element symbol
4
Nuclear Reactions: Radiation• Nuclear reactions release 3 main types of radiation:
– (α) Alpha Particles … ________ nucleus (2 p+ and 2 n0)– (β) Beta Particles… high energy ___________– (γ) Gamma Rays… high energy _________________
radiation
helium electronselectromagnetic
How To Write Nuclear Particles--α Particles … helium nucleus (2 p+ and 2 n0)
2 He --β Particles… high energy electrons
-1 e--γ Rays… high energy electromagnetic radiation
0 γ
-- Positrons…positive charged electrons
1 e
-- Neutrons…neutrally charged particles in the nucleus that contributes to the mass of an atom
0 n
4
0
0
0
1
Balancing Nuclear Reactions• In chemical reactions the elements stay the same. • In nuclear reactions, the elements ________ but the
mass #’s and atomic #’s are ___________.
Alpha Emission
Beta Emission
changeconserved
Another type of nuclear reaction is “electron capture” where an atom “_________” one of its own electrons. absorbs
Positrons: They are just like an electron, but they have a (___) charge instead of a negative charge.+
Nuclear Fission• In fission, the nucleus _______ apart.(Fission is
division.)
• Atom bombs and nuclear power plants use fission of U-235 .
splits
Detecting Radiation
When the argon gas is hit by a particle, it ionizes and produces a current…“click”.
Nuclear Power
• Currently about _____ nuclear power plants in the U.S. and about _____worldwide.
• _____ of the world’s energy comes from nuclear.
• There are ___ nuclear power plants in Illinois. The closest one to us is in _________.
103
435
17%
6
Clinton
Nuclear Power Plants• Nuclear power plants use the heat of a controlled nuclear
fission reaction to ______ water that makes steam which turns a _________ and that produces electricity.
boilturbine
Nuclear Power Plant “Disasters”• One possible type of reactor disaster is known as a __________. In such an accident, the fission reaction goes out of control, leading to the emission of great amounts of radiation.
meltdown
• In ______, a much worse disaster struck Russia's Chernobyl nuclear power plant. In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several _______ died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.
1986
dozen
Nuclear Fusion• In Fusion, nuclei combine to form a _________ nucleus.
• When the p+ and n0 bind, this releases tremendous amounts of ________.
• Nuclear fusion occurs in the _____ and other stars.
heavier
energy
sun
Food Irradiation• Food can be irradiated with gamma rays from 60Co or 137Cs.
• Irradiated milk has a shelf life of __________without refrigeration.
• USDA has approved irradiation of _______ and eggs.
3 months
meats
Isotope Half-Life Radiation Emitted
Carbon-14 5,730 years
Radon-222 3.8 days
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
• Radiocarbon Dating--The radioactivity of a sample can be used to determine how _____ it is.• Half-life: The time for ______ of the nuclei to decay.
oldhalf