## Special topics

### Problem 1:

The time a laser light beam takes to travel from Earth to the Moon and back is most nearly

(A)  2 microseconds.
(B)  2 milliseconds.
(C)  2 seconds.
(D)  2 minutes.
(E)  2 hours.

### Problem 2:

If only volume and surface energies are considered, which of the following expressions best approximates the binding energy of a large nucleus containing A nucleons (a and b are positive constants)?

(A)  aA  - b A-1/3
(B)  aA  - b A-2/5
(C)  aA  - b A-2/3
(D)  aA  + b A-1/3
(E)  aA  - b A2/3

### Problem 3:

In the nuclear reaction α + 40Ar --> p + X, the nucleus X is

(A)  41K.    (B)  42K.    (C)  43K.    (D)  44K.    (E)  41Ar.

### Problem 4:

From the knowledge of the size of atoms and nuclei, which of the following is the most reasonable approximation for the ratio of the density of nuclear matter to the density of water?

(A)  1    (B)  103    (C)  105    (D)  1010   (E)  1014

### Problem 5:

Which of the following decays is possible in vacuum?

(A)  π+ --> μ- + νμ
(B)  π- --> μ+ + e- + e-
(C)  π0 --> e- + p
(D)  p --> n + e+ + νe
(E)  n --> p + e- + νe(bar)

### Problem 6:

Why is β- decay more common than β+ decay among naturally occurring radioactive elements?

(A)  The binding of positrons in nuclei is greater than that of electrons.
(B)  Electrons are more easily excited by γ rays than positrons.
(C)  The binding energy per nucleon is approximately constant for heavy nuclei.
(D)  Positrons cannot exist in ordinary matter.
(E)  Alpha (α) decay leaves nuclei neutron rich.

### Problem 7:

135B --> 73Li + 42He + Q

An unstable Boron nucleus decays at rest into a lithium nucleus and a helium nucleus with total kinetic energy Q as shown.  Which of the following is true?

(A)  Each decay product has half the kinetic energy.
(B)  Each decay product has the same speed.
(C)  The decay products tend to go in the same direction.
(D)  The lithium nucleus has more momentum than the helium nucleus.
(E)  The helium nucleus has more kinetic energy than the lithium nucleus.

### Problem 8:

Which of the following properties of a nucleus can be determined from studies of the hyperfine structure of optical spectra?

(A)  Spin
(B)  Mass defect
(C)  Binding energy
(E)  Atomic number

### Problem 9:

Which of the following is NOT true for the Debye theory of the specific heat of solids?

(A)  The number of vibrational modes is 3N, where N is the number of atoms in the solid.
(B)  The vibrational modes are all assumed to have the same frequency.
(C)  Well above the Debye temperature, the classical equipartition theory holds.
(D)  The specific heat is proportional to T3 at low temperatures.
(E)  The lattice modes are assumed to correspond to sound waves in the solid.

### Problem 10:

Which of the following is not characteristic of any superconductor?

(A)  The resistivity vanishes below the transition temperature.
(B)  A sufficiently large magnetic field can destroy the superconducting state.
(C)  A gap exists in the allowable energy levels of the material.
(D)  A magnetic field is exclude from the superconductor.
(E)  The superconductor is paramagnetic.