Transcript Nuclear Fission sim

Nuclear Chemistry
Vocabulary: copy the definitions
• Radiation—the emission of particles or
electromagnetic waves (such as visible light, X-rays,
and microwaves).
• Nuclear radiation—a form of ionizing radiation that is
caused by changes in the nuclei of atoms.
• Radioactivity—the spontaneous emission of particles
and energy from atomic nuclei.
Electromagnetic spectrum
Radioactive Decay
• In chemical reactions, the atomic number does not change;
an atom of aluminum (13 protons) always remains an
aluminum atom.
• However, atoms with unstable nuclei—radioactive atoms—
can spontaneously change their identities. When this
happens, the identity of the radioactive atom usually
changes because the number of protons changes, and it
becomes an atom of a different element. This process is
radioactive decay.
Alpha (α) Decay: Copy for notes
The nucleus of the parent atom decays by emitting
an alpha particle (a helium nucleus with two protons
and two neutrons). The daughter atom’s atomic
number decreases by two; its mass number
decreases by four.
Beta (β) Decay: Copy for notes
In beta decay, a neutron (either by itself or inside a
nucleus) spontaneously changes into a proton by
emitting a high-energy electron (the β particle, up to
0.9c).
Notice the atomic increases by one but the mass stays
the same. Carbon-14 (atomic number is 6) to Nitrogen
(atomic number is 7).
Gamma (γ) Decay: Copy for notes
Gamma decay often follows almost immediately after
α and β decay because the daughter nucleus is in an
energetically excited state that is unstable so it
releases a high-energy photon called a gamma ray to
achieve stability.
Penetration of Ionizing Radiation
Which is the most damaging?
• In general the greater the charge and mass of the type of
radiation, the more damage it does when it hits or
collides, but this also means it travels less distance
through air or other matter before giving up its energy.
• α particles do the most damage because they have the
greatest charge and mass and easily ionize any atom they
come near but they are the easiest to shield against.
• β particles do less damage than α particles, but they are
harder to protect against.
• γ rays cause the least amount of ionization, but they are
the hardest to stop.
Radon Gas
• Radon is the heaviest noble gas and naturally occurs
in Earth’s atmosphere as a decay product of Uranium238 in soils and building materials.
• It has become a health issue as homes have become
more airtight as we strive to conserve energy.
Remedies include sealing cracks in floors and
increasing ventilation.
• When radon is inhaled, it decays to produce heavy
metal ions of polonium, bismuth and lead which
cannot be exhaled so they stay in the body and emit
damaging alpha particles.
Half-Lives of Various Isotopes
Radioactive Isotope
Half-Life
Hydrogen-3
12.3 years
Carbon-14
5730 years
Radon-222
3.82 days
Potassium-40
1.28 billion years
Oxygen-15
122.22 seconds
Uranium-235
703 million years
Plutonium-239
24,100 years
Why do we care about half-lives? Knowing how long a
radioisotope used in a medical test will remain active in the
body lets doctors get information but minimize harm to a
patient. We can plan how to best store hazardous nuclear
waste from nuclear power plants. Scientists can estimate the
ages of bones, metal objects, or rocks.
Nuclear Fission: copy for notes
• Splitting the nucleus of an atom into two smaller
nuclei is nuclear fission.
• The nuclear fission of heavy atoms such as uranium
releases huge amounts of energy, much more (a
million times!) than is released in a chemical reaction.
• This energy comes from converting the small amount
of mass that is lost during fission into energy. (E=mc2,
you know!)
Fission of Uranium-235: Copy for notes
Nuclear Fission sim
Nuclear Fusion: Copy for notes
• Nuclear fusion is the combining or fusing of two
smaller nuclei into the nucleus of a larger atom.
• This process occurs inside of stars and powers
our sun, which burns hydrogen gas and creates
helium and heavier elements.
• Once again, the creation of new elements results
in a small mass difference, and this mass is
converted into energy which the sun radiates into
space and gives us heat and light.
Nuclear Fusion of Hydrogen
Why do fission and fusion produce so much
energy?
• Nuclear fission and fusion are the splitting and
combining of NUCLEI and their bonds, while chemical
reactions involve the bonds of atoms’ ELECTRONS.
• The energy in chemical reactions comes from the
difference between electrons’ bonds in reactants and
in products. Energy is released as heat, when the bonds
of products are stronger than in reactants.
• Both mass and energy are conserved in chemical
reactions.
Why do fission and fusion produce so much
energy?
• In nuclear reactions, energy comes from converting tiny
amounts of mass lost when the bonds between protons
and neutrons are broken and made. These bonds are due
to the strong force.
• The strong force is a thousand times stronger than the
electrical force which holds atoms and ions together in
chemical bonds.
• However, the energy produced by the fission or fusion of
just one atom is too small to be practical.
Chain Reaction
• In order for nuclear reactions to produce practical
amounts of energy, there have to be a LOT of them. How
can we do that?
• Some fissionable materials have the property that, while
they require one neutron to fission, they produce more
than one neutron. This means that, if you have enough
atoms (a CRITICAL MASS), the one neutron you started
with quickly produces more neutrons which cause more
and more atoms to fission, producing even more
neutrons. The reaction continues until you run out of
fissionable material. This is called a CHAIN REACTION.
Fission of Uranium-235
Watch the “Nuclear Fission” sim
Nuclear Power Plants
• Instead of using fossil fuel combustion to boil water to
produce steam to turn turbines to generate electricity,
nuclear power plants use heat released from nuclear
fission reactions to boil the water.
• The essential parts of a nuclear power plant are the fuel
rods, control rods, moderator, generator,
and cooling system.
New Mexico’s Role in Nuclear Science
Los Alamos Research Center, 1943 - present
Founded during World War II as a secret, centralized facility for
scientific research on the Manhattan Project, the project to
develop the first nuclear weapons. After the Cold War, research
emphasis has shifted to include medicine (vaccines for AIDS,
breast cancer) and renewable energy.
White Sands, Alamogordo, NM, July, 1945
First test of a nuclear weapon, ‘Trinity’ was a
plutoniumimplosion device (20 kilotons TNT) detonated above ground.
Considered to be the start of the ‘Atomic Age.’
New Mexico’s Role in Nuclear Science
Sandia National Labs, Kirtland AFB near Albuquerque,
1949-present
Sandia Labs’ “mission [is] to maintain the reliability and
surety of nuclear weapon systems, conduct research
and development in arms control and nonproliferation
technologies, and investigate methods for the disposal
of the United States' nuclear weapons program's
hazardous waste.” (Wikipedia, 4/17/13) Other research
focuses on energy, the environment, critical national
infrastructures, computational biology, mathematics,
materials science, alternative energy, and cognitive
science.
New Mexico’s Role in Nuclear Science
Waste Isolation Pilot Plant (WIPP), near Carlsbad, 1971 present
• Repository for transuranic waste including materials such
as gloves, tools, rags, and assorted machinery which have
come in contact with radioactive substances (mostly
plutonium and uranium) in the production of nuclear fuel
and weapons.
• Designed to store this waste in rooms in stable salt
formations for 10,000 years.
• First waste arrived in 1999; will accept waste for another
25-35 years then be sealed.
New Mexico’s Role in Nuclear Science
National Enrichment Facility, URENCO, Eunice, 2006present (began enriching 2010)
Plant for the enrichment of uranium for use in nuclear
power plants. Natural uranium has only 0.72% U-235
(the fissionable isotope), so this plant processes it into
low-enriched, reactor grade uranium (3-4% U-235).
Waste Control Specialists, Andrews, TX, 2009 – present
(actually 5 mi east of Eunice)
Treatment, storage, & disposal company dealing in
low-level radioactive, hazardous, and mixed wastes.