Nuclear Physics 2

ANNOUNCMENTS
CW Test on CW 11, 12
(Special Relativity and Nuclear Physics) on Monday 27 Feb during normal lecture times.
Come to same room as last term CW Tests
No Labs This Week
New Textbooks are now available at Library
(College Physics, Serway, 10th Edition)

Detecting radiation and
nuclear energy
e.g., Geiger Muller tube
Mica window
Low pressure gas
High voltage
Anode/cathode
High E field
Massive ionization
Electron avalanche
Pulse

Atomic mass unit
One atomic mass unit (amu or u) is equal to a mass of
1u =1.661 x 10-27 kg
This small mass can be measured using a mass spectrometer

Example 1:
1u =1.661 x 10-27 kg
Find its equivalence in
Joules of Energy, and
MeV of Energy

Example 2:
Using mass spectrometry, physicists have measured the masses of nuclei, protons and neutrons accurately. An alpha particle has a mass of 4.002603 u, a proton 1.007276 u and a neutron 1.008665 u. How is this possible?

Mass defect
In any type of nuclear transformation,
reactants products
(sum of rest masses of reactants)
(sum of rest masses of products)
MASS DEFECT

Nuclear binding energy
Work must be done to remove any nucleon from a nucleus.
Nuclear binding energy
is …
The nuclear binding energy is the energy equivalent of the mass defect.

Binding energy per nucleon
More convenient to use ‘binding energy per nucleon’.
Mostly between 7 to 9 MeV per nucleon

Energy Difference of
Fusion and Fission
Effect of fusion and fission
Both decrease the average nucleon PE (increasing binding energy per nucleon). PE lost is emitted as gamma rays and KE of particles.

Spontaneous and induced fission
Spontaneous – occurs naturally
Induced – requires a ‘slow’ neutron to react with nucleus
For fission, is only one nuclear transformation possible?

Fission fragments
Many different reactions are possible when U-235 fissions.
How much more probable is it that a fission product has an mass number of 110 than 85?

Example 3
a) A possible fission reaction is shown above. Given that the masses of U, La, Br and n are 235.1 u, 148.0 u, 84.90 u and 1.009 u respectively, how much energy in joules is released in each fission?
b) How many joules would be released if all the atoms in 10.00 kg of U-235 undergo fission?

Some facts about reactors
As of Feb, 2012 worldwide, 31 countries have 435 active reactors producing 368 GW of Energy.
63 new reactors now under construction in 15 countries.
France “most nuclear”; 76.2% of electricity
UK has 19 reactors; USA 104, Kazakhstan 0 (but planning) and China 16 (26 under construction; 90 proposed).
From: http://www.euronuclear.org

The ‘controversial’ business of neutrons
In fission, one slow neutron combines with U-235, causing the emission of two or more neutrons. In turn, these neutrons cause two fissions, etc
We obtain a chain reaction
If uncontrolled in a large amount of U-235, a chain reaction leads to…

Why mushrooms?

Atomic bombs (using fission)

What do you know about the history of nuclear tests within Kazakh territory?
Semipalatinsk Test Site

Nuclear reactors - controlled fission

Fusion
Fusion occurs in the sun: the proton cycle.
Fusion has been used in an uncontrolled way in the hydrogen bomb. A fission detonator was used to create high temperature and enable fusion.
A challenge for this century is to recreate and control fusion. One interesting reaction to use is:
In this case Q is 18.0 MeV

Simulating fusion
JET, the Joint European Torus, using the TOKAMAK (toroidal magnetic chamber)

READING Adams and Allday: 8.26 to 8.32, inclusive.
At the end of this lecture you should
Have met and understood how to use Einstein's equation ΔE=Δmc2
Understand the phrases binding energy and mass defect
Understand how energy can be released from nuclear reactions by fission and fusion
Have a basic knowledge of the 'binding energy per nucleon' curve and be able to interpret it
Know what the terms critical mass, moderator, coolant and chain reaction mean in relation to production of energy from a nuclear reactor
Be aware of the main steps of hydrogen fusion in the sun