Chapter 30: Nuclear Energy and Elementary Particles. Homework : Read and understand the lecture note. What is nuclear fission?. Nuclear fission occurs when a heavy nucleus, such as , splits, or fissions, into two smaller nuclei.
Homework : Read and understand the lecture note.
Number of nuclei in
1.0 kg of uranium
Total energy released
Total energy released from
Nkg kg of uranium
The liberated energy is carried by
gamma rays, positrons and neutrinos.
What is the world made of?
Model of Atoms
What is matter made of?
Building Blocks of Matter
Discoveries of too many “elementary” particles and anti-particles lead to more fundamental model the Standard Model. Anti-particle
has the same property as particle except that charge is opposite to that of particle.
Proton p : uud
Neutron n : udd
Pion p+ : ud
Particles made of quarks are called
hadrons and among them they
interact through strong force.
neutrinos n : feel only weak force
charged lepton : feel electromagnetic
e-,m-,t- and weak force
How many kinds of forces are there?
There are four know fundamental forces:
Free neutron decay
Examples of weak interaction
Free neutron decay: n -> p + e- + ne
Muon decay: m- -> e- + ne + nm
What is our dream?
Unification of Forces
Grand Unified Theories (GUTs)
Neutrino mass/oscillation (found)
Nucleon decays (not yet found)
What is neutrino oscillation?
There are three kinds of neutrinos:
If neutrinos have mass, they can change their identities (flavours)
A simple example:
- sin q
+ cos q
neutrinos with definite mass
It depends on
masses, q and
distance it travels
~Earth’s diameter 12,000 km
Neutrino pathlength (km)
Source of atmospheric neutrinos
Earth’s atmosphere is constantly
bombarded by cosmic rays.
Energetic cosmic rays (mostly
protons) interact with atoms in
These interactions produce many
Neutrinos are produced in decays
of pions and muons.
50,000 tons of pure water equipped with 12,000 50 cm photomultipliers
and 2,800 20 cm photomultipliers (PMTs).
Physicists are having fun on a boat in Super-Kamiokande
How does a water Cherenkov detector work?
Water Cherenkov Detector: Kamiokande,IMB,Super-Kamiokande,SNO
Water is cheap and easy to handle!
When the speed of a charged
particle exceeds that of light
IN WATER, electric shock
waves in form of light are
generated similar to sonic boom
sound by super-sonic jet plane .
These light waves form a cone
and are detected as a ring by
a plane equipped by photo-
How do we detect atmospheric muon and electron neutrinos ?
+ n -> p +
+ n -> p +
Most of time invisible
How do we see neutrino oscillation in atmospheric neutrinos?
cos (zenith angle)
Actual probability for measured zenith angle
due to measurement errors
Evidence of neutrino oscillation/mass
low energy nm
low energy ne
high energy ne
high energy nm
First crack in the Standard Model!!!
How does the Sun shine?
Nuclear fusions generate:
1 MeV = 1x106 eV
How does the neutral current confirm neutrino oscillation?
n + e- -> n + e-
-This reaction is available only for ne .
-Available for both water and heavy
How do we see the Sun underground?
Image of Sun by Super-Kamiokande
Seeing the Sun underground
How do we see neutrino oscillation with solar neutrinos?
Super-Kamiokande : 0.465+-0.005+0.016-0.015
nm is not visible to all
How do we know detected neutrinos are from a supernova?
Birth of a supernova witnessed with neutrinos
A few hours before optical observation
Number of photomultipliers fired
Taken by Hubble Telescope