Transcript Lesson 13: Nuclear Propulsion Basics

Lesson 3: Nuclear
Basics
Dr. Andrew Ketsdever
Nuclear Reactor
Reactor Schematic
Basic Atomic Structure
• Atoms are fundamental
particles of matter
– Composed of three types of
sub-atomic particles
• Protons
• Neutrons
• Electrons
– The nucleus contains protons
and neutrons
• Most of the atom’s mass
• Small part of the atom’s volume
– Electron Cloud
• Contains electrons
• Most of the atom’s volume
Basic Atomic Structure
• Atomic Number
– Number of protons in the nucleus
• Mass Number
– Number of protons AND neutrons in the
nucleus
• Mass of proton : 1.6726 x 10-27 kg
• Mass of neutron: 1.6749 x 10-27 kg
• Mass of electron: 0.00091x10-27 kg
Basic Atomic Structure
• Isotope
– Same element implies two atoms have the
same atomic number
– Isotopes of a given element have the same
atomic number but a different mass number
• Same number of protons in the nucleus
• Different number of neutrons in the nucleus
Hydrogen
Deuterium
Tritium
Basic Nuclear Physics
• An atom consists of a small, positively charged
nucleus surrounded by a negatively charged
cloud of electrons
• Nucleus
– Positive protons
– Neutral neutrons
– Bond together by the strong nuclear force
• Stronger than the electrostatic force binding electrons to the
nucleus or repelling protons from one another
• Limited in range to a few x 10-15 m
• Because neutrons are electrically neutral, they
are unaffected by Coloumbic or nuclear forces
until they reach within 10-15 m of an atomic
nucleus
– Best particles to use for FISSION
Fission
• Fission is a nuclear process in which a heavy
nucleus splits into two smaller nuclei
– The Fission Products (FP) can be in any combination
(with a given probability) so long as the number of
protons and neutrons in the products sum up to those
in the initial fissioning nucleus
– The free neutrons produced go on to continue the
fissioning cycle (chain reaction, criticality)
– A great amount of energy can be released in fission
because for heavy nuclei, the summed masses of the
lighter product nuclei is less than the mass of the
fissioning nucleus
Fission Reaction Energy
• The binding energy of the nucleus is directly
related to the amount of energy released in a
fission reaction
• The energy associated with the difference in mass
of the products and the fissioning atom is the
binding energy


  Z (mp  me )  ( A  Z )mn  M atom
E  c
2
Radioactivity
• In 1899, Ernest Rutheford discovered
Uranium produced three different kinds of
radiation.
– Separated the radiation by penetrating ability
– Called them a, b, g
• a-Radiation stopped by paper (He nucleus, 24 He )
• b-Radiation stopped by 6mm of Aluminum
(Electrons produced in the nucleus)
• g-Radiation stopped by several mm of Lead
(Photons with wavelength shortward of 124 pm or
energies greater than 10 keV)
Half-Life
• The half life is the
amount of time
necessary for ½ of
a radioactive
material to decay
• Starting with 100g
of Bismuth
– Half life of 5 days
– 50 g of bismuth
after 5 days
– 50 g of thallium
a-Particle Decay
• The emission of an a particle, or 4He
nucleus, is a process called a decay
• Since a particles contain protons and
neutrons, they must come from the
nucleus of an atom
bParticle Decay
•
b particles are negatively charged electrons emitted by
the nucleus
– Since the mass of an electron is a small fraction of an atomic
mass unit, the mass of a nucleus that undergoes b decay is
changed by only a small amount.
– The mass number is unchanged.
• The nucleus contains no electrons. Rather, b decay
occurs when a neutron is changed into a proton within
the nucleus.
– An unseen neutrino, n, accompanies each b decay.
– The number of protons, and thus the atomic number, is
increased by one.
gRadiation Decay
• Gamma rays are a type of electromagnetic radiation that
results from a redistribution of electric charge within a
nucleus.
• A g ray is a high energy photon.
• For complex nuclei there are many different possible
ways in which the neutrons and protons can be arranged
within the nucleus.
– Gamma rays can be emitted when a nucleus undergoes a
transition from one quantum energy configuration to another.
– Neither the mass number nor the atomic number is changed
when a nucleus emits a g ray in the reaction
152Dy*  152Dy + g
Fission
Fission Fragments and the Chain
Reaction
Uranium
Enrichment
Plutonium