Announcements Practice Final now posted. Today: quiz, more nuclear physics (nuclear power, alpha tunneling example, nuclear spin and angular momentum) If time permits, some clicker questions on nuclear physics. We will get to fission and fusion a bit later. Professor Pui Lam will substitute for me next week while I am at a conference in India.

Electricity generated by nuclear power worldwide Japan used to be at ~30%

Electricity generated by nuclear power worldwide

FAQ: Are there any nuclear power reactors in Hawaii ? Ans: Yes but they are not on land (~O(17)) Power ~O(150) Megawatts Question: What is the typical power of a nuclear power plant ?

QM Tunneling and alpha decay http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/alpdet.html#c1 Let’s work out a numerical example and remember how to calculate tunneling probabilities

QM Tunneling and alpha decay (I) In a simple model for a radioactive nucleus, an alpha particle (m=6.64 x 10-27kg) is trapped by a square barrier that has width 2.0 fm and height 30 MeV. What is the tunneling probability if the kinetic energy of the alpha particle is 1.0 MeV below the top of the barrier ? [Also try 10 MeV below U0] 1 MeV E

Example of QM Tunneling and alpha decay (II) An alpha particle (m=6.64 x 10-27kg) is trapped by a square barrier that has width 2.0 fm and height 30 MeV. What is the tunneling probability if the kinetic energy of the alpha particle is 1.0 MeV below the top of the barrier ? Remember to convert to MKS units for kappa Here G= 0.5 and the tunneling probability T= 0.09 or 9%

Example of QM Tunneling and alpha decay (III) An alpha particle (m=6.64 x 10-27kg) is trapped by a square barrier that has width 2.0 fm and height 30 MeV. What is the tunneling probability if the kinetic energy of the alpha particle is 1.0 MeV below the top of the barrier ? The tunneling probability T= 0.09 or 9% for an alpha 1.0 MeV below the top of the well T=0.014 or 1.4% for a particle 10 MeV below the barrier (energy 20 MeV)

Nuclear spin Like electrons, protons and neutrons are spin ½ particles. Spin and total angular momentum are quantized Question: What is S for a single nucleon ? Question: What is SZ for a single nucleon ?

Nuclear spin The total angular momentum is the sum of the spin and orbital angular momentum of all nucleons.

Nuclear magnetic moments and a mystery There is also a nuclear magneton. Question: How does this compare to the Bohr magneton ? Ans: It is 1836 times smaller than μB because of the ratio of the electron and proton mass (x 1836 heavier). Question: Shouldn’t the proton z component be +- μn ? And shouldn’t the neutron be zero ? What is going on ? Ans: quarks

Important applications of nuclear spin What is this called ? Ans: Nuclear Magnetic Resonance (NMR)

Importance of nuclear spin

Importance of nuclear spin

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 ?

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.

Nuclear Stability Clicker Question Why do stable nuclei with many nucleons (those with a large value of A) have more neutrons than protons? A. An individual nucleon interacts via the nuclear force with only a few of its neighboring nucleons. B. The electric force between protons acts over long distances. C. The nuclear force favors pairing of both neutrons and protons. D. both A. and B. E. all of A., B., and C. Answer: D

Nuclear Stability Clicker Question Why do stable nuclei with many nucleons (those with a large value of A) have more neutrons than protons? A. An individual nucleon interacts via the nuclear force with only a few of its neighboring nucleons. B. The electric force between protons acts over long distances. C. The nuclear force favors pairing of both neutrons and protons. D. both A. and B. E. all of A., B., and C. Answer: D