Download PHGN 422: Nuclear Physics - Lecture 2: The Nuclear Force

PHGN
422: NUCLEAR PHYSICS
PHGN 422: Nuclear Physics
Lecture 2: The Nuclear Force
Prof. Kyle Leach
August 25, 2015
Slide 1
PHGN
422: NUCLEAR PHYSICS
Last Lecture.....
• TA Office Hours: MWF 1-2pm (Timberline 1 Conference
Area)
• The atomic nucleus is composed of nucleons (protons and
neutrons)
• The nuclear mass A is the sum of the number of protons and
neutrons in a given nucleus (A = N + Z)
• The proper notation for a nuclear system is A X, where X is the
chemical symbol from the periodic table
• Nuclei are organized on the nuclear chart according to the
number of protons and neutrons each system has
Slide 2 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Nuclear Chart
Phil Walker, New Scientist Magazine, October 2011
Slide 3 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
As we think about limits of nuclear existence (bound nuclei), we must
first discuss the nuclear force, and what holds nuclei together.
Slide 4 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
As we think about limits of nuclear existence (bound nuclei), we must
first discuss the nuclear force, and what holds nuclei together.
• What is the nuclear force?
Slide 4 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
As we think about limits of nuclear existence (bound nuclei), we must
first discuss the nuclear force, and what holds nuclei together.
• What is the nuclear force?
• First...what are the fundamental forces anyway?
Slide 4 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
As we think about limits of nuclear existence (bound nuclei), we must
first discuss the nuclear force, and what holds nuclei together.
• What is the nuclear force?
• First...what are the fundamental forces anyway?
Source: xkcd.com
Slide 4 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
Force
Theory
Mediator
Relative Strength
Range (m)
Strong
QCD
gluon (g)
1
∼ 10−15
Electromagnetic
QED
Weak
Electroweak
Gravitational
Gravity
photon (γ)
W
±
α=
1
137
≈ 10−2
−5
and Z bosons
∼ 10
unknown
∼ 10−38
∞
∼ 10−18
∞
More on the fundamental forces can be found at: http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
Slide 5 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
Force
Theory
Mediator
Relative Strength
Range (m)
Strong
QCD
gluon (g)
1
∼ 10−15
Electromagnetic
QED
Weak
Electroweak
Gravitational
Gravity
photon (γ)
W
±
α=
1
137
≈ 10−2
−5
and Z bosons
∼ 10
unknown
∼ 10−38
∞
∼ 10−18
∞
More on the fundamental forces can be found at: http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
We will go through all of these forces as the course evolves (except
the gravitational force). For now, we will focus on the strong nuclear
force....
Slide 5 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Fundamental Forces
Force
Theory
Mediator
Relative Strength
Range (m)
Strong
QCD
gluon (g)
1
∼ 10−15
Electromagnetic
QED
Weak
Electroweak
Gravitational
Gravity
photon (γ)
W
±
α=
1
137
≈ 10−2
−5
and Z bosons
∼ 10
unknown
∼ 10−38
∞
∼ 10−18
∞
More on the fundamental forces can be found at: http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html
We will go through all of these forces as the course evolves (except
the gravitational force). For now, we will focus on the strong nuclear
force....
To tie this back into the bigger picture...let’s take a quick look at what
we think the history of the forces look like.
Slide 5 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Forces and the History of the Universe
Slide 6 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Known Fundamental Forces
Slide 7 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Nuclear Force
Back to the strong interaction....
Now that we have an idea about the relative magnitude of the strong
nuclear force we can investigate it in further detail:
Source: http://www.cpepweb.org
Slide 8 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Nuclear Force
Back to the strong interaction....
Now that we have an idea about the relative magnitude of the strong
nuclear force we can investigate it in further detail:
Source: http://www.cpepweb.org
• We’ll turn to the chalkboard for the fundamental and residual
interactions for the strong force.
Slide 8 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Question:
Why Can’t We Use the Fundamental Interaction to
Describe All Nuclei? (and in fact all matter in nature?)
Slide 9 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Question:
Why Can’t We Use the Fundamental Interaction to
Describe All Nuclei? (and in fact all matter in nature?)
Courtesy: Witold Nazarewicz for the UNEDF collaboration
Slide 9 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Force Between Nucleons
Some forms of nuclear theory are able to use the residual interaction
between nucleons. We’ll start by comparing what we know about the
nucleon-nucleon interaction to atomic physics.
Slide 10 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Force Between Nucleons
Some forms of nuclear theory are able to use the residual interaction
between nucleons. We’ll start by comparing what we know about the
nucleon-nucleon interaction to atomic physics.
Electrons and Atoms
Slide 10 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
Nucleon-Nucleon Interaction
PHGN
422: NUCLEAR PHYSICS
The Force Between Nucleons
Some forms of nuclear theory are able to use the residual interaction
between nucleons. We’ll start by comparing what we know about the
nucleon-nucleon interaction to atomic physics.
Electrons and Atoms
• Coulomb interaction
Slide 10 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
Nucleon-Nucleon Interaction
• Strong interaction
PHGN
422: NUCLEAR PHYSICS
The Force Between Nucleons
Some forms of nuclear theory are able to use the residual interaction
between nucleons. We’ll start by comparing what we know about the
nucleon-nucleon interaction to atomic physics.
Electrons and Atoms
• Coulomb interaction
• Electrons in classical orbits
that have large (relative)
energy spacings
Nucleon-Nucleon Interaction
• Strong interaction
• Nuclear orbits (shells) have
small (relative) energy
spacings†
The Nuclear Shell Model will be discussed in week 5 of the course
Slide 10 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Force Between Nucleons
Some forms of nuclear theory are able to use the residual interaction
between nucleons. We’ll start by comparing what we know about the
nucleon-nucleon interaction to atomic physics.
Electrons and Atoms
• Coulomb interaction
• Electrons in classical orbits
that have large (relative)
energy spacings
• Electron distances are large
(ie. small e-e interaction
probability)
Nucleon-Nucleon Interaction
• Strong interaction
• Nuclear orbits (shells) have
small (relative) energy
spacings†
• Due to the small nuclear size,
a given nucleon will strongly
interact with all
nearest-neighbour nucleons
The Nuclear Shell Model will be discussed in week 5 of the course
Slide 10 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Quantum (Nuclear) Many-Body Problem
Strikes Again....
Conclusion: If we consider only the bare nucleon-nucleon potential,
with so many interactions, we quickly run into the quantum
many-body problem. Although there are some systems today that
can be calculated using the bare nucleon-nucleon interaction, it is
typically limited to very light nuclei (A < 15).
Slide 11 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
The Quantum (Nuclear) Many-Body Problem
Strikes Again....
Conclusion: If we consider only the bare nucleon-nucleon potential,
with so many interactions, we quickly run into the quantum
many-body problem. Although there are some systems today that
can be calculated using the bare nucleon-nucleon interaction, it is
typically limited to very light nuclei (A < 15).
So...how do we get around this? And how have we done it in the
past?
Slide 11 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Experimental Probes of the Nucleus
Well...first we need to find a way to probe the nucleus experimentally
before we can really answer this question. Let’s turn to the
chalkboard again for insight into how we might go about this.
Slide 12 — Prof. Kyle Leach — PHGN 422: Nuclear Physics
PHGN
422: NUCLEAR PHYSICS
Next Week...
Reading Before Next Class
• Supplemental material on electron scattering
• Section 3.1 in Krane
Next Class Topics
• We will finish our current thoughts on probing the nuclear charge
density, and what that can tell us about nuclear matter.
• Following that, we can start to discuss nuclear binding energies,
and the nuclear mass itself.
Slide 13 — Prof. Kyle Leach — PHGN 422: Nuclear Physics