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B2 a) Consider the motion of a spin particle of mass m in a potential well of length +00 2L described by the potential ro 0 SX S2L VO elsewhere i) For this particle, determine the energy levels and the corresponding eigenfunctions and specify their degeneracy. [6 marks] ii) The spinį particle is now placed in a weak magnetic field Bu. Bu, 03XL B where u, and u are the unit vectors in the x LSX S2L and z directions respectively. This field gives rise to the perturbation À, = -A:B , where û My is the Bohr magneton and Ŝ is the spin A operator. Use time-independent degenerate perturbation theory to calculate the energy shifts due to the magnetic field to first order in the field. 2μες, [17 marks] b) Consider now two non-interacting spin particles in the unperturbed potential well of length 2L. Calculate the lowest possible energy for the triplet spin state and the spatial part of the corresponding wavefunction. [7 marks)