Nuclear Energy Notes
December 01, 2014
May 8-8:57 AM
Atom Review (Short)
Atom Review (Long)
May 7-9:26 PM
1
Nuclear Energy Notes
December 01, 2014
What holds the nucleus together?
Strong Nuclear Force holds the nucleus together
despite the fact that there are many positive protons together
The neutrons appear to play a role in holding the nuclei
When the strong nuclear force cannot hold the nucleus together the
nucleus is said to be unstable and certain nuclear changes, called
Decay appears to correct a bad neutron-to-proton ratio, N/z, if the ratio
strays too far from an ideal stable value.
May 7-9:38 PM
Radioactive Decay
Decay appears to correct a bad
nucleon-to-proton ratio, n/z, if the ratio
strays too far from an ideal stable
value.
Beta and Gamma decay
May 7-9:38 PM
2
Nuclear Energy Notes
December 01, 2014
Alpha Decay
Parent nuclei emits an alpha particle, a helium nucleus (2 protons
& 2 neutrons) from parent nuclei creating a new daughter nuclei.
Increases the n/z ratio.
May 7-9:39 PM
Beta-Negative Decay
The newly formed (+) proton remains in the nucleus and
increases atomic number by 1 which changes the identity of the
nucleus.
The newly formed electron (beta particle) is emitted from the
nucleus as radiation.
(Z) increases by 1.
May 7-9:39 PM
3
Nuclear Energy Notes
December 01, 2014
Beta-Positive Decay
+
) as it turns into a
neutron.
The atomic number decreases but the atomic weight
remains the same.
May 7-9:40 PM
Electron Capture
An electron close to the nucleus is captured by the
nucleus.
neutron.
This increases the n/z ratio as it creates a new nuclei as it
reduces the atomic number by 1
May 7-9:40 PM
4
Nuclear Energy Notes
December 01, 2014
Gamma Decay
becomes “de-excited” by giving off its energy as
electromagnetic photons or gamma rays.
May 7-9:41 PM
Decay Summary
Type of Decay
Radiation
Demonstration of Radiation
Emitted
Particle
Symbol
Emitted
Particle
Electric
Charge
Penetrating Ability
helium nucleus
+2
can penetrate skin
or paper, but is
slow moving
beta-negative
beta particle
decay
electron
-1
can penetrate a few
sheets of aluminum
foil
beta-positive
decay
positron
+1
can penetrate a few
sheets of aluminum
foil
----
not applicable
alpha decay
electron
capture
alpha particle
beta particle
----
gamma decay gamma rays
no particle
----
photon
0
Do #1 - 3, #5 on page 329
can penetrate a few
centimetres of lead
Practice Sheet
May 7-9:47 PM
5
Nuclear Energy Notes
December 01, 2014
7.3 Half-Life
Decay reactions are spontaneous with no way to
predict when a nucleus will disintegrate.
Radioactive materials decay at different rates.
The average length of time it takes a material to
decay to half its original mass is called the half-life.
The material loses 50% of
its radioactive nuclei
during each “half-life”.
May 13-7:49 PM
The half-life must be determined experimentally by following the
radioactivity A or the mass of a radioisotope over a time period t.
In this class we can only safely simulate radioactivity with something
May 13-8:18 PM
6
Nuclear Energy Notes
December 01, 2014
(a) What percent of an initial sample will remain after 10 s?
Recall the equation relating to half-life...
Multiplying the M/M
ratio by 100% turns the
fraction into a percent
remaining
The M/M ratio is the
fraction remaining
Do questions 1 - 7, page 333
and questions 29 - 34 on the
Nuclear equations worksheet
(previously distributed)
May 13-11:18 PM
Nuclear Fission and Nuclear Power Generation
E=mc
"Energy and matter are different manifestations of
Law of Conservation of Mass-Energy
that the total mass-energy in an isolated system remains
constant.
May 9-9:32 AM
7
Nuclear Energy Notes
December 01, 2014
Mass Defect and Binding Energy
What is the mass defect for Lithium-7?
The actual mass of Lithium-7 is actually 7.01600 u
but the mass of lithium-7 should be the mass of 3 protons, 4 neutrons and 3
electrons
Mass = 3m + 4m + 3m = 3(1.007 276 u) + 4(1.008 665 u) + 3(0.000 549 u) =
7.058 135 u
So the mass defect (the difference between theoretical and actual mass of an
isotope) would be:
Mass defect = 7.058 135 u - 7.016 00 u = 0.042 135 u (1.66 x 10-27 kg/u) = 6.994 4
x 10-29 kg
Finally the binding energy (the energy that would be needed to separate all of the
nucleons in an isotope's nucleus) would be:
E = mc = 6.994 4 x 10-29 kg(3.0 x 10 m/s) = 6.295 0 x 10-12 J /1.602 x 10-13 J/MeV
So the Binding energy is 39 MeV
May 11-10:33 PM
Nuclear Fission
Fission is the splitting of a heavy nucleus, usually
uranium or plutonium, which releases energy and
produces two smaller nuclei and some new fast
neutrons.
captured by the nucleus.
The nucleus becomes unstable with a higher n/z ratio.
Fission results to reduce the n/z ratio.
Newly produced fast neutrons can go on to initiate more
fission if they are moderated.
May 9-9:15 AM
8
Nuclear Energy Notes
December 01, 2014
Nuclear reaction simulated with mousetraps
Chain Reaction
If neutrons formed as a result of a fission can be moderated
(slowed to thermal speeds) by water or by passing through the
fissile material then they may cause another fission in what is
called a chain reaction.
moderated
May 11-10:59 PM
How much energy is released from the following fission reaction?
Isotope/Nucleon
Quantity
Nucleon
Total
U-235
1
235.043 092 4
n
1
MD =
Total Reactants
Kr-92
91.926 152 8
Ba-141
140.914 411 9
E = mc =
n
The mass defect is
Total Products
and the binding energy is
Do practice problem 1, page 338
May 11-2:34 PM
9
Nuclear Energy Notes
December 01, 2014
Nuclear Reactors
reaction to produce heat. The heat is used to heat water to steam
which in turn drives a steam turbine that generates electrical
CANDU Nuclear Power Reactor
Gas Cooled Reactor
>
or helium as a coolant.
May 11-2:35 PM
The Candu Nuclear Reactor
May 11-2:20 PM
10
Nuclear Energy Notes
December 01, 2014
Breeding Plutonium
Real Plutonium
Fast Breeder Reactor
> Extra “fast” neutrons not used to continue the chain reaction are
238U is converted to fissionable 239Pu
absorbed by a blanket of 238
233
May 9-9:15 AM
Little Boy - Cannon
Fat Man - Implosion
Hiroshima
Miscalculation
May 9-9:15 AM
11
Nuclear Energy Notes
December 01, 2014
The nuclear weapons of today are "Hydrogen" fusion weapons.
These require dynamite to fission reaction (A-Bomb) to provide the
activation energy for fusion
Miscalculation
May 4-10:47 PM
Nuclear Fusion
May 12-5:44 AM
12
Nuclear Energy Notes
December 01, 2014
Fusion Reactor - Magnetic Confinement
May 12-5:57 AM
Food Irradiation
> Gamma ray exposure from a Co source kills harmful bacteria which
may have profound implications for feeding hungry nations in
developing countries.
Materials Imaging
Radiography (like X-ray imagery but with neutrons)
Radioactive Dating
Thickness monitoring
May 12-5:59 AM
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