1. Announcements Today: Superconductivity, Nuclear Physics
No quiz but a few clicker questions towards the end.
Final exam: 6 problems + 2 pages of conceptual/short answer questions (up to Chap 44).
Problem 1: Interference
Problem 2: Heisenberg Uncertainty Principle (Particles and/or Waves)
Problem 3: QM I: Wave Functions
Problem 4: QM II: Atomic Structure
Problem 5: Molecules/Solid State
Problem 6: Nuclear Physics
Problems 7&8: Short answer questions (will include energy/momentum special relativity)

2. Left over: Origin of energy bands and band gaps
Condensed matter physics
Atomic physics

3. Superconductivity

4. Bardeen, Cooper and Schrieffer explained all this in 1956
Superconductivity
Bardeen, Cooper and Schrieffer explained all this in 1956
Temperature
Resistivity
Zero!
The BCS physics in a nutshell:
At low temperatures, the electrons in superconductors bind into pairs that have zero spin – the pairs are “composite bosons.” They love being in the same state and they condense into it.
A boson condensate can flow without scattering, it’s a charged “superfluid.”
Meanwhile a gap (not a band gap) opens up and there are no single-electron states left to accelerate and experience scattering.  Zero Resistance!
This does not happen in a superconductor.
DEMO: Hi Tc levitation
Demo

5. 1972 Nobel Prize in Physics

6. High Tc superconductors
Do not need liquid helium, huge cost savings but brittle and hard to handle.
Liquid nitrogen
But the BCS mechanism does not explain these materials (need magnetic spin interactions between electron pairs)

7. Some Applications of Superconductivity
To date, applications have mostly been specialized. In particular, it is much cheaper to operate high field (high current) electromagnets if the wire is superconducting.
MRI (Magnetic Resonance Imaging)
or NMR (Nuclear Magnetic Resonance)
LHC (Large Hadron Collider)
Accelerator in Geneva, Switzerland

8. Some Applications of Superconductivity
Superconducting Quantum Interference Devices (SQUIDs) are also used to make very sensitive magnetic field measurements (e.g., to make one part in 1012 measurements of magnetic susceptibility).
Can use superconducting junctions for quantum computing,
the next frontier.

9. More Applications of Superconductivity
Shanghai airport magnetic levitation train (431 km/h or 268 mph)
A project is underway to build a similar train from Tokyo to Nagoya.
(Current travel time 1h 40 min)
Superconducting magnets on a train above a track made out of a permanent magnet lock the train into its lateral position. It can move linearly along the track, but not off the track.

10. More Applications of Superconductivity
The holy grail of SC technology is electrical power distribution (7% is lost in the power grid). This is one reason why HiTc superconductors are important, but it’s not yet competitive.
Commercial superconducting power cable

11. Goals for Chapter 43 To understand some key properties of nuclei
To see how nuclear binding energy depends on the number of protons and neutrons
To investigate radioactive decay
To learn about hazards and medical uses of radiation
To analyze nuclear reactions
To investigate nuclear fission
To understand the nuclear reactions in our sun

12. A few important points about nuclear physics
How can we date ancient biological artifacts?
Most of the mass of an atom is found in its tiny nucleus.
Some nuclei are stable, but others spontaneously decay.
Fission and fusion are important nuclear reactions. We (life on earth) would not exist without the fusion in our sun.

13. All nuclei have approximately the same density.
Properties of nuclei
The nucleon number A is the total number of protons and neutrons in the nucleus.
The radius of most nuclei is given by R = R0A1/3 where R0=1.2 x 10-15m=1.2 fm
All nuclei have approximately the same density.
For example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ?

14. Iron nucleus
For example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ? (Note 1 amu = 1.66 x 10-27kg).
But the density of solid iron is about 7000 kg/m3  this is orders of magnitude more. What holds it together ?

15. Iron nucleus cont’d
For example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ? (Note 1 amu = 1.66 x 10-27kg).
But the density of solid iron is about 7000 kg/m3  this is orders of magnitude more. What holds it together ?
Ans: Strong interaction or strong nuclear force
Interesting to note that neutron stars are macroscopic objects with density of nuclei.

16. The nuclear force
The nuclear force binds protons and neutrons together. It is an example of the strong interaction.
Important characteristics of the nuclear force:
It does not depend on charge. Protons and neutrons are bound. It has a short range, of the order of nuclear dimensions.
Because of its short range, a nucleon only interacts with those in its immediate vicinity.
It favors binding of pairs of protons or neutrons with opposite spins and with pairs of pairs (a pair of protons and a pair of neutrons, each pair having opposite spins).

17. Nuclides and isotopes
The atomic number Z is the number of protons in the nucleus. The neutron number N is the number of neutrons in the nucleus. Therefore A = Z + N.
A nuclide is a single nuclear species having specific values for both Z and N.
The isotopes of an element have different numbers of neutrons.
Question: These are three isotopes of hydrogen. How many protons and neutrons do they contain ? What are they called ?

18. Nuclides and isotopes cont’d
Question: These are three isotopes of hydrogen. How many protons and neutrons do they contain ? What are they called ?
Ans: 1proton, 1 proton and 1 neutron, 1 proton and 2 neutrons.
They are called hydrogen, deuterium, and tritium.
Follow-up: What happens if hydrogen is replaced by deuterium in water ?

19. Nuclides and isotopes cont’d
Life and death question:
What are the two isotopes of the element uranium ?
Ans: U235 (92 protons and 143 neutrons) and U238 (92 protons and 146 neutrons). The values are the atomic numbers of the elements.
Question: Which one is useful for atomic energy and bombs ? Which one is more common ?
Ans: 235U with low enrichment for nuclear power plants, high enrichment for bombs. U238 is much more common.

20. Nuclides and isotopes cont’d
Life and death question:
What are the two isotopes of the element uranium ?
President Mahmoud Ahmadinejad of Iran touring centrifuges

22. There is also14C

23. Nuclear Physics clicker question
A nucleus of neon-20 has 10 protons and 10 neutrons.
A nucleus of terbium-160 has 65 protons and 95 neutrons.
Compared to the radius of a neon-20 nucleus, the radius of a terbium-160 nucleus is
A. 9.5 times larger.
B. 8 times larger.
C. 6.5 times larger.
D. 4 times larger.
E. 2 times larger.

24. A43.1
A nucleus of neon-20 has 10 protons and 10 neutrons.
A nucleus of terbium-160 has 65 protons and 95 neutrons.
Compared to the radius of a neon-20 nucleus, the radius of a terbium-160 nucleus is
A. 9.5 times larger.
B. 8 times larger.
C. 6.5 times larger.
D. 4 times larger.
E. 2 times larger.
r=R0A1/3 ratio is (160/20)1/3=(8)1/3

25. Alpha decay
An alpha particle α is a 4He nucleus (question: how many protons and neutrons ?)
The α decay of the 226Ra (radium) nuclide to Radon.
N.B. alpha decay requires quantum mechanical tunneling (original nucleus is bound and inside a potential well)

26. Mystery of beta decay energy spectrum
In a nuclear beta decay, a neutron transforms into a proton and electron (np + e)
Pauli solved the problem
Maybe energy is not conserved

27. Mystery solved
1930: In a letter to the attendees of a physics conference in Tübingen, Germany, Wolfgang Pauli proposes as a "desperate remedy" the existence of a new neutral particle to explain the apparent energy non-conservation in radioactive decays.
During the next few years, scientists elaborate Pauli's theory and conclude that the new particle must be very weakly interacting and extremely light.

28. Beta and gamma decay
There are three types of β decay: β- beta-minus, β+ beta-plus, and electron capture.
A beta-minus β– particle is an electron. (example Co60)(question: what is a β+ ?)
A γ ray is a photon (note the A or Z do not change in this type of decay, go from excited state to a lower energy state).
Question: Is beta plus decay possible for a proton in the hydrogen atom ?

29. Beta decay requirements
Question: Is beta plus decay possible for a proton in the hydrogen atom ?
No. The mass of the original atom must be at least two electron masses larger than that of the final atom.
Beta- decay can occur whenever the mass of the original atom is larger than that of the final atom.
Question: Why are most nuclei stable ? Hint: what kind of interaction is this ?
Electron capture can occur whenever the mass of the original neutral atom is larger than that of the final atom.