Transcript NuclearNotes06 - Redwood High School

Nuclear Notes:
Structure
and
Radioactivity
Online @ redwood.org/stewart
I. Structure of the Atom
Recognize
Me?
Draw
Me!
II. Periodic Table--p. 346 in GS
Atomic # vs. Atomic Mass
A. Atomic No. = p = number of protons (p) in the nucleus
B. Atomic mass = p + n = the sum of the mass of protons (p),
neutrons (n) (and electrons (e)) but e have no significant mass).
1. # n = atomic mass - atomic no.
2. # n is not always the same!
isotopes - atoms of the same element (same number of protons)
that have different number of neutrons
III. Radioactivity
a.k.a. radiation
A. The emission of particles due to the breakdown of
unstable atomic nuclei (radioisotopes).
B. • Isotopes and large atoms are unstable and will break
apart. Nucleus is decomposing: losing mass/particles,
and/or energy
• New, lighter atoms are formed, releasing radiation in
the process.
• Decomposition continues until enough mass has been lost
making the atom stable again.
Unstable = radioactive
Therefore
End, Part 1
IV. Radiation
Energy that is radiated or
transmitted in the form of
rays,waves, or particles.
IV. Types of Radiation
These 3 types of radiation are all naturally-occurring.
A. Alpha () particle (Helium atom): naturally-occurring.
1.Descriptoin: 2 protons lost,
and…2 neutrons lost

2. this makes a Positive charge
(of +2); Mass of 4
3. So…The atomic # of
decaying atom DECREASES
by 2 and the mass DECREASES by 4
4. Shielded by: paper and dead skin
Symbol



Sum of mass
numbers (p + n)
and sum of atomic
numbers (p)
is the SAME on
both sides of
equation.
Helium
atom!
B. Beta (  ) particle (electron): naturally-occurring.
1. Description: One neutron is converted into a proton and an electron.
2. The electron is lost: negative charge (-1) No measurable mass lost.
3. The atomic # of the decaying atom INCREASES by 1 and the mass does
not change.
4. Shielded by: plastic, glass and aluminum
Symbol





Sum of mass
numbers (p + n) and
sum of atomic
numbers (p)
is the SAME on both
sides of equation.
ENERGY
 
C. Gamma ( ) radiation: naturally-occurring.
1. Description: High energy photon is released. ENERGY given off!
Virtually all nuclear reactions have this (including naturally and nonnaturally occurring reactions)
2. No charge. No measurable mass lost.
3. The atomic number and mass of the decaying atom do not change.
Shielded by: thick lead and concrete. Powerful and dangerous.
Symbol



Sum of mass numbers
(p + n) and sum of
atomic numbers (p)
is the SAME on both
sides of equation.
ENERGY
Where does the
gamma radiation
come from? Mass is
converted into
energy (more on
this later).
Summary of Naturally-occurring Radiation
V. Nuclear Fission
A.
B.
Definition of Fission: the splitting of a large atom into smaller
fragments (particles and/or smaller atoms)
This is the nuclear reaction the world currently uses to
generate any and all usable nuclear energy--not naturally
occurring.
Process
A large atom is struck by a single neutron. Smaller atoms are
created. Energy and neutrons are released
Sum of mass
Uranium: the most common large atom used:
numbers (p +
n) and sum of
Uranium (U) - 235 (atomic number 92)
atomic
numbers (p)
Question: How many neutrons does U-235 have?
is the SAME
on both sides
Answer: 235 - 92 = 143
of equation.
ENERGY

QuickTime™ and a
H.263 decompressor
are needed to see this picture.
VI. Nuclear Fusion
A. Definition of Fusion: the combining of 2 smaller
atoms into a larger atom--not naturally occurring on
earth (but happens on sun and stars).
B. Only possible with isotopes of Hydrogen: Deuterium
and Tritium.
Trit
ENERGY

He
Neutron
Summary of Non-naturally occurring Nuclear Energy

ENERGY
End, Part 2

ENERGY
VII. Where does the kinetic energy
in a nuclear reaction come from?
• The mass of protons
and neutrons varies
depending on what
atom they are in.
The mass of protons
and neutrons before a
nuclear reaction is
GREATER than after
the reaction.
Fusion
Fission
VII. Where does the kinetic energy
in a nuclear reaction come from?
• The mass is TRANSFORMED into kinetic
energy according to Einstein’s famous
equation:
• E = mc2 -- mass IS energy! Energy equals
mass times the speed of light squared.
• The speed of light is 300,000 kilometers per
second, so even a very small mass produces a
LOT of energy !
VIII. Energy Evolved
A. FISSION: 1 gram of U-235 evolves 2x107 Cal/g
(20 million Cal/g)*
* which equals the heat from 30 tons of TNT
1 gram of Uranium = 20,000,000 Cal
Versus
1 gram of oil = 9.8 Cal
B. The energy released in nuclear FUSION is about 7
times greater than the energy released in the fission of
Uranium. 10 grams of Deuterium which can be extracted from 500
liters of water could produce enough fuel for the lifetime electricity
needs of an average person in an industrialized country.
IX. Advantages and Disadvantages of Using Nuclear Fuel
A.
B.
Advantages:
•
Fuels are plentiful.
•
If shielded properly, it is inherently safe since any
malfunction results in a rapid shutdown.
•
No atmospheric pollution leading to acid rain or global
warming.
•
Small amounts of mass yield high amounts of energy.
Disadvantages:
•
What are some disadvantages of using Nuclear Fuel to
generate electricity?
End (Part 3)