Nuclear Physics - University of Houston

Download Report

Transcript Nuclear Physics - University of Houston

What’s New in Nu-clear Physics
Ed V Hungerford
University of Houston
According to Pogo:
“Nuclear Physics is not
so new, and not so clear
either.”
06-20,2005
UH Teacher Workshop
The Answers to our questions are
only as good as the questions
themselves
Why did the tree grow in the
notch in the fence ?
06-20,2005
UH Teacher Workshop
75 years ago Nuclear Physics was New
•The neutron had just been discovered
•The Proton and Neutron were considered elementary particles
•The nuclear force was not understood
•Nuclear models were primitive and based on classical
liquids
Today Nuclear Physics in some sense is Mature
•Nucleons are not “elementary” but are composed of other
particles called quarks
•The nuclear force is understood as an exchange of field quanta
called gluons
•The nucleus is a VERY complicated interaction of many hadrons
whose interaction is described by a theory called Quantum
Chromodynamics
06-20,2005
UH Teacher Workshop
The Particles and Symmetries of the
Standard Model
3
Families
06-20,2005
UH Teacher Workshop
There are 4 known interactions in nature
•One of the fundamental driving philosophies of physics is the
assumption that these interactions can be “unified”
•Two of these are manifestations of the same force (electroweak)
•QCD is patterned after the electroweak interaction (gauge theory)
•Gravity still lies outside a quantum theory
•The new discovery of Dark Energy, if it is real, may imply a 5th force
Field
06-20,2005
UH Teacher Workshop
QCD
The Interaction through Fields
Particle A
Particle B
A Field Quanta
The interaction of B with
A occurs through the
absorption of field quanta
at B produced by A
06-20,2005
UH Teacher Workshop
QCD Features
• An interaction that becomes stronger the greater
the distance and the lower the energy between interacting
particles
• A weak interaction at short distances and high energies
• A permanently bound quarks and gluons
• A self interaction between the field quanta (gluons)
• A highly non-linear theory greatly complicating
calculations and making intuitive predictions difficult
• A symmetry of SU(3) expressed by 3 states of quarks
and Gluons (color)
06-20,2005
UH Teacher Workshop
The Quark and Gluon Constituents of the Baryon
Valence Quarks
Gluon Field
Sea Quarks
06-20,2005
UH Teacher Workshop
Quantum ChromoDynamics (QCD) is the
Theory of the Strong Interaction
(Nuclear Force)
Quarks and
Gluons
06-20,2005
Flux Tube
UH Teacher Workshop
Linear Potential vs
distance
How do we probe a Nucleon or a Nucleus
To determine its Quark Content ?
Incident
Hadron
Incident
Electron
06-20,2005
UH Teacher Workshop
Quark Scattering
Emission of a Quark Stretches
the “interaction String”
When the string breaks, Quarkanti-quark pairs are produced
This is called Hadronization of
a Quark Jet
Long Range Nuclear force
Collapses to quark-antiquark
Exchange (Yukawa Interaction)
the “interaction String”
06-20,2005
UH Teacher Workshop
Chiral Symmetry, and Mass
Chiral symmetry is the fundamental symmetry of QCD
Velocity
Right Handed
Velocity
Left Handed
But the particle must not have mass
06-20,2005
UH Teacher Workshop
The QCD Condensate
Particles acquire mass through their interaction with the vacuum, i.e.
the condensate of quarks and gluons in the vacuum
A nucleon in a simple visualization, is a bubble in the vacuum
condensate
Interaction of these quarks with the condensate at the bubble surface
gives an “effective” mass to the system.
Chiral Symmetry is then said to be spontaneously broken
06-20,2005
UH Teacher Workshop
The Vacuum is NOT Empty
This Computer simulation
shows the instantaneous
gluon field that might be
Present in a vacuum. Red
Indicates bending
(winding) in the field lines
perhaps a precursor to quark
condensates
06-20,2005
UH Teacher Workshop
Each of the 4 interactions is has its own
impact on the existence of our Universe
The Strong (nuclear) force is responsible for the creation
and stability nuclear matter
Phase Diagram of Matter
We Live Here
06-20,2005
UH Teacher Workshop
Studying the Vacuum and QCD
Relativistic
Colliding
Nuclei
06-20,2005
Quark Gluon
plasma
UH Teacher Workshop
Hadronization
Connecting the very large to the very small
One of the more recent advances
in physics has been to connect
microscopic theory to macroscopic
(cosmology)
For example, stellar burning and
supernovae produce the nuclei of
which the Universe is composed
We can use this information to
look back in time, as well as discuss
the present features in our
universe
06-20,2005
UH Teacher Workshop
Mesons and baryons are
composed of quarks
Flavor SU(3) Symmetry
Allows Placement of lowest Mesons
And Baryons in Symmetry Octets
06-20,2005
UH Teacher Workshop
The Nuclear Equation of State
Nuclear Matter
Neutron Star
06-20,2005
UH Teacher Workshop
A modern cut-away view of a Neutron Star
06-20,2005
UH Teacher Workshop
Measuring Matter Creation in the Galaxy
06-20,2005
UH Teacher Workshop
Proton number vs Neutron Number Stability
06-20,2005
UH Teacher Workshop
The Present Model of a Supernovae
06-20,2005
UH Teacher Workshop
Inside a Supernova
Extreme temp: photodissociates nuclei
back to protons, neutrons and alphas.
>8 M evolves ~107 yr
3000 km
Core
bounces
3x107 km
Huge thermal
emission of
neutrinos
~5-10 seconds
Neutronisation: p+e-  n+ne
n
n
n
10 km
n
n*
n
n
.
M
n
100 km
Dense
core
n
n
.
M
n
e++e-  g+g ; g+g  nx + nx (all flavours equally)
06-20,2005
UH Teacher Workshop
r ~ few x rnuclear
Supernovae: Facts and Figures

Energy release ~3x1046 J (the
gravitational binding energy of the
core), in about 10 seconds






Equivalent to 1000 times the energy
emitted by the Sun in its entire
lifetime.
Energy density of the core is
equivalent to 1MT TNT per cubic
micron.
99% of energy released is in the
form of neutrinos
~1% is in the KE of the exploding
matter
~0.01% is in light – and that’s
enough to make it as bright as an
entire galaxy.
Probably site of the r-process.
06-20,2005
UH Teacher Workshop
¼ MT test
(Dominic Truckee, 1962)
A Computer model of a Supernovae
06-20,2005
UH Teacher Workshop
A Brief Summary
Nuclear Science has tremendous breadth and complexity
After 75 years we have found some to the “right” questions to ask but
others remain
I have purposely avoided discussion of the more traditional nuclear studies
There are impressive new results and insights into nuclear matter. But these
require detailed exposition and are difficult to develop to grasp without some
prior knowledge.
As a mature, advanced science, there are significant applications in
Including the fields of Medicine, Computing, Industrial Products, Energy,
Finance, etc.
More than 50% of the Phd graduates in Nuclear Physics are employed
in industry, medicine, and national defense.
06-20,2005
UH Teacher Workshop
06-20,2005
UH Teacher Workshop