5. Quadrupole moments in the shell model. We will calculate an estimate of the quadrupole moment for the special case of a single proton moving in an orbital around a closed shell spherical core. So, the only contribution to the quadrupole moment is from this single proton. We will also assume that the proton moves in an orbital with j = l + 1/2. The space wave function of the proton is Yj,m = R(r)Ym,0p) where Y is the spherical harmonic, and R is the radial part of the wave function. They are normalized, i.e.
I = ∫ |uPuX.&] pue [=Up"'1x""x|
(a) Since m = m + m, what must m and m be if m = j? [2 marks]
(b) Show that the quadrupole moment, when m = j, is given by
To do this, start with the quadrupole moment given by Q = ∫ (3z^2 r)dV. Given that the spherical harmonic
Y0, = √(3/4π) cos θ, write the quadrupole moment operator in terms of Y2o and use the integral, ∫ Y0,Y2o,dΩ = √(5/16π). Also note √(2/3) = 1/√3.
(c) Apply this result to the ground state of Sc, which has j = 3/2. Write the configuration for this ground state and confirm that the condition of j = l + 1/2 holds. Estimate (r^2) using r = 1.2 Å fm. Compare your result to the measured quadrupole moment of -0.145 ± 0.003 b. [2 marks]
(d) Apply this result to the ground state of F, which has j = 2. Compare your result to the measured quadrupole moment of 7.6 ± 0.4 fm^2 (note that this measurement did not determine the sign of the quadrupole moment, only the magnitude). [2 marks]